ABN 220 Introduction to Food Science and Technology PDF

ABN 220 Introduction to Food Science and Technology 1 2  Ibadan Distance Learning Centre Series ABN 220 Introduction to Food Science and Technology By Okubanjo A. O. (Ph.D), Omojola A.B. (Ph.D),...

ABN 220 Introduction to Food Science and Technology 1 2  Ibadan Distance Learning Centre Series ABN 220 Introduction to Food Science and Technology By Okubanjo A. O. (Ph.D), Omojola A.B. (Ph.D), Ogunsola O.O (M. Sc) Department of Animal Science University of Ibadan All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without permission of the copyright owner. First published 2002 ISBN General Editor: Prof. Abiola Odejide Series Editor: Mr. C.O. Adejuwon Typeset @ Distance Learning Centre, University of Ibadan Printed by 3 Content Lecture One: Scope of Food Science and Technology 1 Lecture Two: Food and Its Functions … … … 10 Lecture Three: Food Distribution and Marketing … … 14 Lecture Four: Composition and Structure of Nigerian and West African Foods … … … … … … 19 Lecture Five: Principles of Food Processing and Preservation (Part I) … … … … … 29 Lecture Six: Principles of Food Processing and Preservation (Part II) … … … … … … 38 Lecture Seven: Deterioration and Spoilage of Foods … 45 Lecture Eight: Food Poisoning and its Prevention. … 51 Lecture Nine: Contamination of Foods from Natural Sources … … 56 Lecture Ten: Sensory Qualities of Foods – Texture and Flavour 62 Lecture Eleven: Sensory Qualities of Foods - Colour 68 Lecture Twelve: Determinant of Food Consumption Pattern 74 4 Lecture One Scope of Food Science and Technology Introduction In prehistoric times, man was basically a farmer, tilling the ground and obtaining his food from nature’s bounty. His fruits and vegetables he got off trees and wild plants and his meat through his hunting prowess. His environment, soil, climate, topography of his place of abode and other factors beyond his control governed his everyday activities. The growth of big towns and cities and in recent times, megalopolis implied large concentration of people who neither till the ground nor practise any form of animal husbandry but yet require mega-tonnes of food of various classes for their daily activities. Food must therefore be sourced from distant places requiring conscious intervention of man in the natural processes for production, harvesting, processing, preservation and distribution of the foods. Nations which succeeded in harnessing all these technological efforts in effectively controlling the forces of nature have access to varieties of abundant nutritious and wholesome foods as is evident in most of the western world. Where these efforts were not initiated or have failed, famine, nutritional diseases, pestilences, underdevelopment and the like are the vogue as in several countries of Africa, Asia and South America. Objectives At the end of this lecture, students should be able to: 1. Explain meaning of food science and technology. 2. Discuss the range of activities and challenges facing the food scientist. Pre-Test 1. Give a concise definition of Food Science and Technology. 2. Discuss the interrelationship of several scientific disciplines embodied in the field of food science and Technology. 5 CONTENT Food Science and Technology Defined Food Science and Technology is the totality of organised scientific and engineering knowledge applicable to the abundant production, storage, processing, preservation, modification, diversification and utilisation of food that is wholesome and safe for human consumption. It is evident from this definition that the activities of food scientists are multifarious bordering on all facets of the physical and biological sciences. The following discussions touch on some of the well known areas in the field. They are neither exhaustive nor self exclusive and many more will become apparent to the student in his everyday living activities. Food Preservation With the increase in available quantity of food for human consumption has come the need to introduce varieties into food and protect food from spoilage from the point of production through to sales and consumption. Most often it is necessary to preserve foods. One of such methods is drying and it includes sun drying, freeze drying and hot air drying which is perhaps one of the oldest methods of food preservation. Curing with salt, nitrite and nitrate with or without smoking, has been in use for a long time in meat preservation. A gamut of food products arise from fermentation of raw materials by mould, yeast and bacterial colonies with formation in them of organic acids and alcohols which cause detoxification and destruction of anti-nutritive factors and natural toxins. Wine and beverages, SOY OGI, IRU and GARI fall into this group. Other preservation methods include canning of a wide range of foods, freezing and refrigeration, use of chemical preservatives including antimicrobials, aseptic and modified atmosphere packaging, irradiation, use of high pressure, application of heat as in cooking or use of microwave oven and low temperature non-thermal process as with pulsed electrical field (PEF). Food Chemistry/Biochemistry The physical and mental well being of man depends on the nutritional quality of the food he eats. The food chemist determines the nutritional and qualitative composition of each food, the bioavailability, and utilization of nutrients in such foods in relation to human health as a prelude to setting nutrient standards and blending suitable nutritional supplements for such foods. Nutrient stability during cooking, processing, storage and distribution are also of interest. Some endoenzymes in foods continue to function physiologically after harvest and in storage bringing about autolysis, spoilage, colour reactions and other undesirable changes. Yet, other endoenzymes or added enzymes are consciously encouraged to bring about desirable end products. It is the work of food scientists to harness these 6 changes productively in producing good quality foods such as in evaluating the colour and flavour changes and chemical reactions accompanying the ripening process. A rapidly expanding field is that of flavour chemistry for improvement of food tastes through development of new flavours in some foods or synthesizing artificial flavours resembling or enhancing real or natural flavours e.g. saccharin, aspartame and other sweeteners, monosodium glutamate in maggi cube and other flavour enhancers all of which can be cheaply and easily mass produced. Some food constituents also chemically react with other chemical constituents of processing machineries, cooking utensils, packaging materials and holding vessels resulting in off colour and sometimes toxicity. Food – drug interactions, presence of allergens in foods and nutritional impact of genetically engineered foods on human health are all equally of concern to the food scientist. Food Engineering This is of immense importance in the design and monitoring of all food processing operations from the farm to the final consumer. It deals with the functional layout of the processing factory, equipment design and material testing appropriate for the particular food being processed as well as the work flow and processing conditions for production of safe high quality foods and management of wastes. It determines the optimal use of resources such as raw material, energy and water and evaluates the rheological properties of foods. It is also involved in translating laboratory scale processes to industrial scale production of foods and in designing functional food packaging systems that will keep foods fresh and wholesome. Examples of application of food engineering are evident in the design of efficient and appropriate machineries for cassava and yam processing, rice and maize milling, beer brewing and others. Food Microbiology Various microbes, yeast and mould, virus, bacteria, helminth eggs and protozoan parasites are to be found variously in raw and poorly processed foods including drinkable water. They destroy crops in the field and spoil them in storage, during handling along the processing and marketing chain and at destination points thereby reducing their commercial value. More importantly of concern in public health are those food borne pathogens that are potentially harmful in causing food poisoning and infection. Among them are coliforms, fecal streptococci, salmonella, staphylococcus, clostridium perfrigens, clostridium botulinum and a host of others. Viral Bovine Spongiform Encephalopathy (BSE) (Mad cow disease) and African swine fever) are presently of topical issues. The goal of the food microbiologist is to find ways of totally eliminating the pathogens through “hurdle intervention” at all stages of food handling and processing. 7  And yet not all microbes are harmful, for others have been of immense functionality in the manufacture of many food products. All alcoholic drinks are products of yeast fermentation. Yogurt, dry and semi-dry sausages are fermented products using bacterial cultures. Iru, gari ogi, fufu and many others are similarly naturally fermented products. Mycoproteins from fungi have also been made into functional and nutritious meat alternatives. Food Quality Assurance Quality control processes are necessary to provide food items at least a profitable cost to meet consumer quest for overall satisfaction. To meet this objective, stringent specifications are set for raw material quality, ingredient supplies, processing schedule, packaging materials and shelf life for uniformity of finished products. Involved also are the training of quality control personnel, appropriate testing for desired quality attributes along the processing chain using appropriate methodologies, proper keeping of quality control records and prompt re-evaluation and re-adjustment of processing schedule to minimize product rejects and process failure. Maintenance of a successful quality control programme therefore requires a good link between the overall managers of the food industry, the raw material procurement division, the production unit, the warehousing and sales division on the one hand and the quality control section on the other. Food Additives A host of substances are added to foods for specific purposes and as such become part of those foods. These substances, while edible are very rarely eaten by themselves. Among these are nutritional supplements like vitamins and minerals which are designed to upgrade the nutrient content of some foods, food grade colours to improve the appearance of an existing food colour or introduce a new one, anti-caking agents added to salt and some other foods to make them free flowing, anti-oxidants like BHA and BHT to retard rancidity in foods, flavour enhancers like maggi cube, and others containing monosodium glutamate to boost food flavour. Others serve preservative action in certain foods either by inhibiting or killing microorganisms, (antibiotics) destroying endogenous enzyme activities in foods, while others serve as texturizers. Food Warehousing and Food Merchandising Post harvest losses of farm produce in the tropics range from 20-50% from the farm gate to point of consumption due to insects, rodents, mould and other natural or human factors. Proper warehousing with proper protective measures mitigates this problem. It also helps to eliminate seasonal gluts and shortages through efficient processing and storage systems to even out supplies throughout the year within and beyond geographical regions without loss of quality. Thus in time of plenty, banana, plantain, orange harvested at the half ripe stages could be stored over a long 8 period and the ripening process controlled until time for marketing. Food warehousing is an important aspect of a nation’s food security against emergency situations during famine as in Somalia, and under natural and man-made disasters. Foods sometimes require transporting over long distances to service expanded and diversified markets requiring modifying control of natural physiological processes, temperature and humidity regimes to control spoilage, dehydration, chilling injuries during passage thereby increasing storage and shelf life. Processed foods in colourful eye catching packages are brought closer to the final consumer through vigorous marketing campaigns. Such campaign could be spread through radio, television, tabloid and internet advertising at prime time to create awareness on a global scale to increase the sales of each product. New Foods Development Limited only by the ingenuity of the food scientist, many new foods are now available in the market with more on the drawing board. They are the result of co- operative efforts of the farm producer, the food chemist, or analyst, the food engineer, the production crew, the quality control team, the packaging manufacturer, food advertising and food marketing team. Varieties are introduced into foods that are common as in the production of snacks and convenience foods like suya and kilishi from meat, kokoro from gari or maize fortified with soya bean protein, vitamins and minerals, breakfast cereals and gurudi from coconut. New foods are also developed to improve diets of people suffering from various forms of protein-calorie malnutrition and to meet the needs of diverse ethnic and cross cultural groups and specific market tastes. Thus with rising income and more food taken away from home, traditional dishes will be made more available in ready to cook and ready-to-eat cuisines and fast foods. Specific foods are also directed at specific groups of people; the very young and the very old, women, students, pregnant and lactating mothers, diabetics requiring low sugar diet, hypertensive patients requiring cholesterol fighting foods, people with lactose intolerance and others with specific health problems. Some industrial processes convert unconventional raw materials and waste products into foods for human consumption e.g. cellulose into edible carbohydrates as in edible cellulosic casing, edible sugars and sweeteners. Food gum or methylcellulose has egg white functionality. Mycoproteins and phytoproteins have also been processed into meat analogs and other foods that are rich in protein and fibre. Other new foods of note include foods with exotic colours and flavours as in fruit drinks, vegetarian diets, encapsulated products, confectionary and energy foods, fish burgers and chicken nugget. Nutraceuticals A rapidly developing facets of food science is the production of a whole range of functional health food products, the so called nutraceuticals. They include botanicals, pre and probiotics which are claimed to be able to improve health when 9 taken in appropriate amount. The origin of many nutraceuticals are plants and animals that are not domesticated but live in the wild. They are used in form of pills, capsules, powders or liquids and as constituents of beverages, nutrition bars, snack foods and herbal medicines. They are believed to have some marginal nutritive value but more importantly, that they promote health by preventing certain diseases and inflammations especially, cardiovascular diseases, atherosclerosis, hypertension, cancer, diabetes, some nervous and nutritional disorders with some enhancement of the body’s immune system. An example is garlic powder, which contain 5-allylcysteine, a known inhibitor of cholesterol synthesis. It has also been found to show anti-microbial, antithrombotic and anti tumor activities. Honey has also been known to have many therapeutic effects on body functions. Food Laws and Regulations The government of each country sets up regulatory bodies which are backed by laws and statutes which set out regulations relating to food production and processing, factory inspection, monitoring of substandard food products, food adulteration and potential hazards in foods. These laws also govern food labeling including ingredient and nutritional contents, manufacture and expiry dates, batch number of the product, declaration as to weight and volume and import-export status. In Nigeria, these regulatory functions are performed by the Standard Organisation of Nigeria (SON), and the National Agency for Food and Drug Administration and Control (NAFDAC). Food Toxicology Fertilizers used for dressing the soil and treating lawns and industrial chemicals often find their way into streams, lakes and other body of water where they pollute aquatic life including our sea foods. Man also uses insecticides, fungicides, germicides, antibiotics and other chemicals to enhance good crop yield as well as protect and preserve his foods both on the field and in storage. Some of these are carried over as toxic residues e.g. methyl-mercury in fish. Mycotoxins, phytotoxins and other toxic plant constituents, such as allergens, mold metabolites and various environmental contaminants that also serve as toxicants in our foods. Dioxin if found in the fat of contaminated meat, fish, egg or dairy products can on consumption by man cause reproductive failure, heart disease, diabetes and cancer. Aspergillosis is associated with the toxin produced by the mold Aspergillus niger in moldy grains. Gammalin wrongly used in fish capture has been known to kill consumers of such fish. The food toxicologists through the Federal Environmental Protection Agency (FEPA) monitor these hazards and ensure their complete elimination from the food chain. 10 Water Security We obtain water for domestic and industrial uses through rainfall, streams, rivers, fresh water lakes, deep wells and boreholes, or even the ocean. Such water to be used in food processing must be safe to drink and therefore free of unacceptable odor, color, taste, clarity, chemical constituents and pathogenic microbes. It should be economically available in large quantities. Purification of water requires such treatments as sedimentation electrofloatation, flocculation, dissolved air floatation, filtration, chlorination, ultraviolet light irradiation or boiling among others. Such industrial and municipal water is delivered through the public water main. Water used in making soft drinks, beer, other beverages and foods are purer than tap water to prevent undesirable interaction between residual impurities in the water and the active ingredients. In recent years, water for drinking purposes have come in polyvinyl sachets and plastic bottles and are sealed, pure and portable. Such water packs must be certified by the controlling regulatory body, National Agency for Food, Drugs and Administration Control (NAFDAC) as shown by the NAFDAC number. ‘Enhanced water’ may be fortified with minerals, vitamins and some natural flavours while ‘Super oxygenated’ water contains fifteen times more oxygen than natural water and is good for athletes and others engaged in work or sport requiring energy use. Sewage Pollution and Industrial Waste Management The food processing operations involve various activities such as washing, sorting, peeling, slaughtering, cleaning, sanitizing and the like depending on each specific food. The solid wastes and waste effluent water from meat, milk, fruit juice, egg, starch and other food processing factories become sources of serious pollution when discharged in large volumes with attendant undesirable environmental impact. Controlled management of these wastes through creation of sewage lagoons, solid and liquid waste recycling and conversion into useful by-products would ensure proper environmental friendliness, water conservation, energy saving and added profitability to the food industry without compromising safety. The Federal Environmental Protection Agency (FEPA) is the regulatory body charged with ensuring that both sewage effluents and solid wastes do not become sources of pollution in the environment. Food biotechnology is another recent but fast growing development involving cloning, gene transfer and genetic modification of some of our food resources. Some of the achievements attributed to genetic engineering of foods include the removal of allergy causing factor in such crops as groundnut and soya bean; production of livestock whose meat is resistant to bacterial growth and spoilage thereby providing disease resistance, reduced transmission of zoonotic micro- organisms and longer shelf life. Others include selective improvement of the status of specific nutrients like PUFA in some foods or downgrading the status of less desirable ones like cholesterol. 11 Food Science Education, Research and Development A virile food industry requires a staunch support base inspired by excellence in Food Science education, research and development. In Nigeria, the National University Council through its accreditations and minimum academic standards and the Nigerian Institute of Food Science and Technologists through its out-come based guidelines to Food Science Departments ensures that graduates of food science acquire the skills necessary for a rewarding career in food science. Food Science Education in all areas previously discussed and many more ensures the training of qualified personnel for career services at the secondary and tertiary institutions, research institutes, government agencies and parastatals, hospitals, and various food industries. The career opportunities are almost limitless. Summary In this chapter, aspects of the scope of food science have been discussed. These included food preservation, food chemistry, food engineering, food microbiology, food quality control, food additives, food warehousing and merchandising, new food development nutraceuticals, food laws and regulations, food toxicology, water security, sewage pollution and industrial waste management and food biotechnology. They are neither exhaustive nor mutually exclusive and other activities in relation to food science will continue to manifest as the student advances. Post-Test Which of these areas of food science have received minimal attention in Nigeria? 1. Food engineering. 2. Food microbiology. 3. Food quality control. 4. New food development. 5. Food toxicology. 6. Food biotechnology. References Fereidoon, S. (2002). Nutraceuticals and functional foods: Research addresses bioactive components. Food Tech. 56(5): 23. Jay, J.M. (1992). Modern Food Microbiology. Chapman and Hall, New York. Okubanjo A.O. (1990). Meat for Nigeria’s Millions. Faculty Lecture series No 3. Faculty of Agriculture and Forestry, University of Ibadan. Rodger G. (2001) Mycoprotein – A meat alternative new to the U.S. Food Tech. 55(7), 36-41. 12 Lecture Two Food and Its Functions Introduction A hungry man is an angry man therefore the consumption of food is important to man as it plays an important role in his physical and intellectual development. Food supplies nutrients that are used for growth, maintenance and repair of body cells. The food needs of man are therefore classified into six groups of nutrients, namely, carbohydrates, fats, proteins, minerals, vitamins and water. A single food does not contain all the above nutrients. Foods are therefore classified based on the nutrients they contain. Objectives At the end of this chapter, you are expected to be able to: 1. Explain why we should avoid eating too many foods of the same class. 2. Classify food into different groups. Pre-Test 1. What do you understand by the word ‘food’? 2. Why is food classification important? 3. Discuss briefly the functions of food. CONTENT Food and Its Functions The science of nutrition is defined as the study of nourishing the body adequately. Three main purposes are thereby attained. These are: 1. Growth 2. Maintenance 3. Repairs of damaged body and worn out tissues. Except for water (H2O) and oxygen (O2), food supplies the raw materials that are needed for growth, maintenance and repairs. 13  In general, foods must contain substances that function in providing fuel. That is, foods are substances that on oxidation in the body release energy that is needed for the various activities of the individual. Foods must also build/maintain body tissues and lastly, food must regulate body processes. An individual food could perform all the three functions, it could perform only one of the three. But the diet as a whole must serve the three functions in order that the individuals should remain healthy. Any chemical substance in food that functions in one or in the three ways is called Nutrient. There are six kinds of nutrient that are needed by the body. These are the carbohydrates, proteins, fats vitamins, minerals, and water. The carbohydrates, protein, and fats are often referred to as Fuel Nutrients. The fuel nutrients supply energy in the form that is suitable for work and heat. The fuel nutrients are Organic Substances that are combustible and these can be used interchangeably as the source of energy. The mineral, and water are called the Inorganic Nutrients. The protein, minerals and water are all found in the composition of the body tissues and they also function for the repair of the tissue. The vitamins are diverse organic substances that are present in very small quantities in the food. Vitamins are essential for the normal growth and for maintenance of health. The vitamins and minerals are body regulators and they promote oxidative processes and the normal functioning of nerves and muscles. Water also serves in regulating body functions by holding substances in solution. Water is also a component of the digestive juices and of blood, tissues and it regulates the temperature of the body. The excretion of waste product also occurs with the aid of water. Food Groups Foods are grouped together in the order of their general functions and foods in a particular group can readily substitute for other members of the group. Avoid eating too many food that are of the same class of food and also ensure that not one group is inadequately represented in the food that you consume. Food Classification There are 3 different ways of classifying food. 1. The Ten Food Groups: (i) Grain products (ii) Potatoes (iii) Meat, poultry, fish and eggs (iv) Dry beans, peas and nuts (v) Milk, cheese and ice cream 14  (vi) Green and yellow vegetables (vii) Citrus fruits and tomatoes (viii) Other fruits and vegetables (ix) Butter and other fats (x) Sugars, syrups and sweets. 2. The Basic Seven (i) Bread, flours and cereals (ii) Meat, poultry, fish and eggs (iii) Dry beans, peas and nuts (iv) Milk, cheese and ice cream (v) Leafy greens and yellow vegetables (vi) Citrus fruits and tomatoes (vii) Butter and fortified magarines. 3. The Four Main Groups (i) Bread and cereals that consist of the inexpensive energy and protein sources. In this group we have the whole cereal grains that contain not only iron but also some vitamins. (ii) Meat, poultry, fish, eggs, legumes and nuts. This group contains foods that are rich in protein, minerals and vitamins. (iii) Milk and milk products; consist of foods that are the sources of proteins, calcium and other minerals and vitamins. (iv) Vegetable groups: These are foods that are mainly the sources of vitamins and minerals. Uses The 10 basic group of food is used in planting crops to meet the food needs of a country. It covers all classes of foods. The basic 7 is used for planning diet. The numbers of servings from each group is specified for ease of utilization. The 4 main group is used primarily by the home economists. It forms the foundation of a good meal and it is simplified for general use. 15 Summary The main functions of food include growth maintenance and repair of body tissues. Food contains substances that are referred to as NUTRIENTS. There are six basic nutrients found in food and these include carbohydrate, protein, fats vitamins, minerals, and water. Foods are classified into 3 main groups: the ten food group, the basic seven and the four main groups. Post Test 1. Discuss briefly why it is important to eat different classes of food. 2. Give a precise classification of food from a home economist’s view. Answer to Post Test 1. No single food contains all the nutrients. Foods in a particular group can readily substitute for other members of the group. One should avoid eating too many foods of the same class in order that the body may adequately be nourished. 2. The four main group is used primarily by the home economists since it forms the foundation of a good meal and it is simplified for general use (please see the four main group in the text) References Ihekoronye A.I and P. O. Ngoddy (1985.) Integrated Food Science and Technology for the Tropics. Macmillan/International College Edition. Christian J.L. and Greger J.L. (1985). Nutrition for Living. The Benjamin/Cummings Publishing Co. Inc. California. 16 Lecture Three Food Distribution and Marketing Introduction In this lecture, we shall be discussing how food is distributed and marketed and the classification of food. Effective distribution and marketing of food is vital so that the food products gets to the consumer quickly and also to keep them informed about the kinds of products that exist. Objectives At the end of this lecture, students are expected to be able to: Discuss food distribution and food trade in both rural and urban areas. Pre – Test 1. How is the quality and quantity of food eaten in the rural areas different from that of Urban areas? 2. What is mal-nutrition? CONTENT Food distribution in Nigeria depends largely on the types of food that are produced. The populace relies on four major types of factors. These are the agricultural lands, seas, lakes and rivers for the food we obtain: the fish from water and crops and livestocks from agricultural lands. There are some others that rely on the forest e.g game and the wildlife. These foods that are classified either as plant origin or as animal origin can be broken down into distinct groups. These are plants and animal products. Under each of these headings are various products 17 1(a) Plants (i) Cereal: These include maize, sorghum, millet, wheat and rice. (ii) Pulses: These include, cowpea, lima beans, and soyabean (iii) Fruits: Banana, plantain, guava, pineapple, pawpaw, avocado pea, citrus fruits (oranges, lemon, tangerine, tangerlo, lime, grape). (iv) Melon and Squashes: Melon, water melon, squash. (b) Vegetables (i) Leafy vegetables: Bitter leaf, waterleaf, lettuce, etc. (ii) Root vegetables: Carrot and radish (iii) Seed vegetables: Green peas, green beans, okro, pepper (iv) Others: Onion, tomatoes, cucumber. (c) (i) Tuber: Yam, cassava, sweet potatoes, cocoyam (ii) Nuts: Groundnut, cashew nut, and walnut. (iii) Sugars: sugarcane, sugar beet and date (iv) Oil Seeds: Cotton seed, olive, palm kernel, soyabean, coconut. (v) Beverages: Cocoa, coffee, tea. 2. Animal Products (a) Milk, butter and cheese (b) Meat and entrails (c) Eggs (d) Fish (e) Shellfish – crabs, crayfish, lobsters, shrimps. 3. Manufactured Products (Modified Plants and Animals) The manufactured products are all obtained from the processing industries, they include; (i) Canned foods (ii) Frozen foods 18  (iii) Dehydrated foods (iv) Salted and cured foods (v) Dairy products: ice cream, yoghurt. (vi) Meat products: Sausages, ham, etc. (vii) Sea foods: fish, fillets (viii) Oleomagarines (ix) Fermented food. Food Distribution in the Urban and Rural Areas Urban Areas It is important to note that in the urban area, income is a major determinant of the quality and the quantity of food that is consumed. The financial commitment also affects the disposable amount that is used for food. This commitment includes transportation, house rent, clothing, school fees and other related expenses. The other things that affect the quality and quantity of food are the prices of the foodstuff and the type of food consumed. Roots, tubers and the grains form a bulk of the foods that are consumed by the low income group. Some of the low-income groups also consume maize, millet, sorghum and rice. Legumes are consumed in low quantity and the major legumes consist of groundnut and melon seed. Meat and meat products are expensive and are consumed in low quantity. The total food consumption both in quality and quantity are inadequate. For the urban affluent, they eat more of grains and grain products. They consume wheat and wheat products in the form of bread, cakes, pastries, sausage rolls, spaghetti and wheat puff. They also consume rice and rice products. A number of them consume maize products especially in form of corn flakes. There are also some roots and tubers in their food. The root and tubers come mainly in the form of pounded yam. They eat very little of cassava produce, their meal is rich in meat, fish and snail and the presence of milk and milk products in their diet is a common feature. There are eggs and beverages in their diet. The beverages include wine and beer, carbonated drinks and fruit juices. On the whole, the urban affluent tends to be over nourished and the consequences include obesity and other health problems. Rural Areas In the rural areas, the economic situation is mostly subsistence and there is low income generally. There are two main types of the rural dwellers. They are either pastoral or agricultural. A number of people combine both activities. 19 Pastoral Originally the pastoral groups are well nourished as their diets are rich in animal proteins and a number of them drink nothing but milk. With time and increase in the number of herd, over-gazing, soil erosion, and desertification occurred. The loss of pasture was followed by a reduction in the number of livestock and there was the increase in trans human activity. Consequently, conflicts arose between the pastoral and the agricultural groups. Poor Food Distribution and Its Consequences The food and nutrition strategies are designed to ensure satisfactory levels of nutrition among a given population. The nutritional levels are poor because of the food quantity and quality that are not in adequate supply on one hand while on the other hand there is over eating. The food distributed globally is not well balanced as industrial nations obtain more food than they need hence most developing nations experience periodic food shortages. These developing nations have to import foods especially grains. A term that is used to depict the level of food adequacy is malnutrition. Mal-nutrition is a term that covers a range of different pathological conditions. Mal-nutrition could be shortage of energy, of protein or of the individual vitamins and minerals. But generally, mal-nutrition is due to multiple deficiencies. The predominant characteristics are: (i) A lack of energy (ii) A shortage of high quality protein (iii) The deficiencies of specific vitamins such as vitamin A. (iv) The deficiencies of specific trace mineral such as Iodine. There are four types of mal-nutrition. (i) The energy mal-nutrition – This is called marasmus. (ii) The protein mal-nutrition – This is referred to as kwashiorkor. (iii) The mineral deficiency in which minerals like I,Fe and Cu are deficient in the feed. (iv) The vitamin deficiency in which vitamins like vitamin A, or any other may become deficient. Food Distribution and Marketing Generally, people talk about the protein calorie mal-nutrition (PCM) or protein energy mal-nutrition (PEM). The two terms are used as energy and protein mal- nutrition and tend to occur simultaneously in many cases e.g. in adults, a balance of hypocalorific diet induces a progressive loss of weight whereas in children the diet produces a slow growth and the tissue maturity is attained at a prolonged rate i.e. at the age that is later than normal. This type of mal-nutrition is called relative mal- 20 nutrition. Relative mal-nutrition occurs when there is poverty and the whole population may have stunted growth that is referred to as nutritional dwarfism. In this case the average weight and the height will be below their genetic potential. Denutrition (marasmus) leads finally to the progressive disappearance of proteinous fat and thus wasting away of active tissue as the subject emaciates. Marasmic denutrition is prevalent in babies that are sucking and in children that are given very diluted powdered milk. Between 10-20% of the death in infants that are under one year old could be attributed to marasmic denutrition in some localities. Food Trade The trade in foods becomes necessary as a result of over production in one country and underpopulation in another country. Food trade is designed to even out as much as possible the food situation in any one country. There are several products that are traded. The tropical root tuber especially cassava had been identified as a desirable raw material for compounding livestock feeds. In the international trade, cassava is marketed as dried roots or as meal, chips, pellets, flour and also in the form of starch. In Germany, Denmark, Australia and Japan, most of the cassava that is imported goes into the food industry whereas in India and Netherlands, the cassava is used for industrial purposes. Grains It becomes necessary to distinguish between the grain legumes and the cereal grains. Both of these grains are used for food and they form items of trade either on a local level or as international items of trade. In Nigeria, the trade in grain legumes is essentially of local nature i.e. very little of the grain legumes is exported and it is neither imported. A major grain distribution centre is in the North. Cowpea is mainly produced in the northern states and the dried grains are transported to the South. The food grain legumes contain a range of 22 – 25% crude protein and Nigeria produces at least 950,000 tonnes per annum. The food legumes are the natural supplements to the staple diet of the cereal, grains, the root and the tubers. Beans serve as a major complement to the food of most Nigerians, than other grains. Summary This lecture has discussed the classification of food of either plant or animal origin and how such food is distributed into both the rural and urban areas. Poor food distribution and its consequences are also discussed. Post – Test 1. What are the consequences of poor food distribution? 2. Why is food trade essential for any nation? 21 Answer to Post Test Poor food distributions will result in; 1. Poor nutritional levels because the quantity and quality of food are in inadequate supply. 2. Developing nations will get poorer while developed nations will get more industrialized. 3. Health hazards will result e.g. mal-nutrition of various grades will become prominent (Marasimus, kwashiorkor e.t.c. To even out as much as possible the food situation in any one country. To make available food that are not grown as a particular nations. 22 Lecture Four Composition and Structure of Nigerian and West African Foods Introduction In this lecture, we shall be discussing the composition and structure of some foods typical to Nigeria and West Africa. Objective At the end of this lecture, students are expected to be able to discuss the composition, and other typical characteristics of some Nigerian and West African foods. Pre – Test What are the similarities and differences in the composition of the following food items: (i) Yam (ii) Cassava (iii) Maize CONTENT Yam Yam belongs to the genus Dioscorea. It contains about 600 species, but the main variety that will be discussed is: Dioscorea rotundata. The yam tuber is economically the most important of the plant. The weight of a yam tuber may vary from 50kg – 200g. The tubers are bitter to taste due to the poisonous alkaloid that is called dioscorine. The toxic substance that is present in yam are made harmless by soaking yam in water or by boiling. Yams are present naturally in only 3 areas of the world. These are (i) West Africa (ii) The Caribbean Island 23  (iii) South-East Asia The global production is about 30 million tonnes per annum. --- By far, the largest average and of course the greatest amount of yam production takes place in West Africa. Over 95% of the world production of yam occurs in West Africa. Within the region of West Africa, yam production is confined to the region that stretches from Cote de voire, down to Cameroon. In this region, the major yam producing countries in order of importance are Nigeria, Cote de voire, Ghana, Togo and Benin Republic. Nigeria accounts for 70% of the world production of yam. The Caribbean Island is the second most important yam producer apart from West Africa. The other countries where yam is significantly produced include Brazil, Venezuela, Papua New Guinea, China and Philippines. Composition of Yam Yam varies in composition. The variation is dependent on the cultural practices, climate and the edaphic factors. The conditions under which yam is grown therefore varies all over the world. The maturity of the yam as well as the method and the length of storage all affect the composition of the yam. In general, yam consists of: Moisture 53-73% Carbohydrate 23% Fat 0.12% Crude protein 1.09 – 1.99% Crude fibre 0.35 – 0.79% Ash 0.63 – 2.56% Yam is made up essentially of water as well as carbohydrates (CHO). The CHO consist of starch and there is a negligible amount of sugars. The sugar that is present in yam is less than 1 per cent. The main constituent of yam starch is amylopectin. The amylopectin exists in the form of starch grains within the cells. The protein content of yam is low and the proteins are low in sulphur containing amino acid mainly methionine and cystine. Apart from being a good source of CHO, yam contains a significant amount of Vitamin C as well as iron, calcium and nicotinic acid. The calorie present in yam is one thousand calorie, gm/gm (1000 Cal., gm/gm) Composition Per kg of Yam Calories 1000 Cal, gm/gm Protein 20g Calcium 150mg Iron 10mg 24  Thiamine 1mg Riboflavin 0.3mg Nicotinic acid 4mg Vit. C. 50mg. Storage of Yam There is a conservative estimate that 15% of the yam that is produced annually do not get to the market due to post harvest losses. The losses are due to the lack of appropriate storage. In addition, a variety of diseases and pests as well as sprouting also account for losses. It is estimated that a million tonnes of yam tubers are lost annually during storage in West Africa. The sources of storage losses include rotting of yam, pests, respiration as well as sprouting. Sprouting causes a reduction in the food resources by translocating the carbohydrates from the tubers into the sprouts for metabolic processes. Sprouting also increases the respiration rate, thereby increasing the rate of loss of dry matter. There is also the acceleration of moisture loss through the permeable surface of the sprouts. As a result, the yam becomes progressively soft to the touch from the bottom upwards, thereby resulting in the rotting of the yam. Sprouting of the yam can be delayed by a non-lethal dose of gamma radiation. The rotting in the yam tuber causes the greatest loss of dry matter during storage. Rotting is due mainly to the effect of fungi and bacteria. In particular the Servatia spp have been implicated. To prevent rotting of yams during storage, wounding of the tubers have to be prevented. The curing of yam tubers at about 25oC with a low humidity of between 55-62% for a period of 5 days before storage prevents to a certain degree the yam from rotting. There is also substantial loss of yams due to rodents and insects. Respiration Respiration is a serious source of the storage loss in yam. Since harvested tubers are living things, they continue to respire and the substrate for the respiration is the dry matter, which is stored in the tubers. Up to 10% of the dry matter may be lost in the yams that are stored for a period of 5 months as a result of respiration. The effective way to reduce the respiratory loss is to keep the temperature low but not below 16oC. Yams are stored for two major reasons. (i) To preserve the yams as planting materials for the next years crop. (ii) To preserve the yams for future use as food. In general the storage of yams for consumption should not last longer than 6 months. 25 Yam Processing Yam could be boiled, fried or roasted. Pounded yam could also be made by peeling the tubers, removing the inedible parts, cutting the yams into pieces and by boiling the yams until it is soft. The boiled pieces are then pounded using a wooden mortar and pestle, until the cellular and to some extent, the starch granule become soft and a stiff glutinous dough is obtained. The discorea rotundata is the most viscous of all yams. It also has a high gel strength and these properties make the discorea yam the preferred species for the making of pounded yam because a stiff dough can readily be obtained. Apart from pounded yam, the yam flour which is a composite flour for baking can be made from yam. At least 50% of the yam flour goes into the mixture for baking purposes. The instant yam flakes are also produced from yam. Non-Food Uses of Yam A number of yam species contain small amounts of sapogenins as well as alkaloids. In particular, the alkaloid Discorine (C13H19O2N) are more abundant. There are various species of saponins and sapogenins and these occur in varying quantities in the various species of yams. The saponins are usually hydrolysed to form the sapogenins and the major sapogenin that is found in the yam is the diosgenin. All the important sapogenins in yams are steriod in nature and they are all related to the steriod that is called cortisone. They are used as raw materials for the manufacture of corticosteriod drugs in the pharmaceutical industries. The corticosteriods are used as anti- inflamatory agents, as metabolic stimulants and as general stress reaction protectives. There is the commercial production of Diosgenin especially in Mexico where Dioscorea mexicana, Discorea rotundata and Discorea composita are all grown mainly for medicinal purposes. The alkaloids that are present in yams include the Dioscorine especially in the Dioscorea hispida as well as dihydro dioscorine that is found in Dioscorea dumentorium. Dioscorine is toxic as it causes paralysis of the Central Nervous System (CNS) while the saponines are haemolytic. Cassava Cassava is a product that is grown mainly in the equatorial region and the region is bounded by latitude 30oN and 30oS of the equator. Cassava is restricted to zones that are less than 200m above the sea level. There is an annual rainfall of between 200 – 2000mm. Within these region, cassava is an important staple food for about 900 million people. The annual per capital intake of cassava is greatest in Africa. The average consumption is 120 kg per year. In the central Africa republic, Congo 26 and Gabon and in the Democratic republic of Congo, the annual rate of consumption of cassava exceeds 300kg per person per year. In Latin America, the average consumption is around 40kg per person per year. The fresh peeled cassava is eaten as a vegetable after boiling or roasting. In some West African countries cassava is boiled and pounded with boiled plantain to form an elastic dough. The dough is eaten with vegetables and meat soups. The peeled cassavas are often sliced, dried and ground into flour. This is called kokonite in Ghana. The main form in which cassava is eaten in the whole of West Africa is as a roasted granular product that is prepared from peeled, grated and fermented cassava roots called “Gari”. However, in South America and Latin America, a product that is called the farinka demadioca is very popular. The farinka demandioca is similar to gari but it is considerably less fermented during its preparation. There is another African product from cassava called Chickwangwe. Chickwangwe is prepared by soaking the cassava in water for a period of 2-7 days until it softens after which the root is peeled and the product is mashed. The fibres are removed and the paste that remains is firm and elastic. This firm and elastic product is wrapped in palm leaves or banana leaves. It is found in the East African countries. In the Philippines, cassava is made into the landtang (cassava rice). There are other products obtained from cassava. These include biscuits, cakes and beer. Generally, animal feeds are also obtained from cassava. Animal Feeds Obtained from Cassava In animal feeds, cassava is used as a source of energy. Cassava pellets as well as chips are used for animal consumption. For the production of chips, the fresh roots are washed peeled and cut into slices with the slices usually 3-6cm in length. The slices are then dried on large concrete surfaces in the open spaces. The pellets are made from the chips. The dried chips are ground into cylindrical pellets that are about 2cm long and up to 1cm in diameter. The cassava chips and pellets are exported mainly from Thailand, Malaysia and Indonesia. These products are exported to the European community and the United States of America where they are used mainly for feeding animals. Industrial Products from Cassava Cassava is an important raw material for the non food industries. It contains a low amylose content and there is a high amylopectin present in cassava. This gives the necessary viscocity and cassava is therefore used in areas where high adhesive properties are required. It is therefore useful in the paper and textile industries. The cassava starch is also used in glues. A very important industrial product that is made from cassava is ethyl alcohol (ethanol). Ethanol is used for fuel in automobiles in Brazil and Mexico. 27 The Composition of Cassava Cassava has a high moisture content. Content Peeled tubers Dry tubers Total matter % % Moisture 66.2 33.8 Starch 27.2 81.5 Sucrose 1.0 3.0 Glucose 0.4 1.1 Fructose 0.3 0.8 Protein 0.4 1.3 Fats 0.2 0.4 Minerals 0.8 2.5 Dietary fibre 1.5 4.3 About 35mg of 100g (35mg/100g) of ascorbic acid is found in cassava and this level of ascorbic acid is significant considering the amount of cassava that an individual consumes. Unfortunately, a large proportion of the ascorbic acid is lost during the processing of cassava. The protein content is low (0.4%) and those who rely heavily on cassava are prone to kwashiokor. The main amino acid that are present in cassava are the arginine, histidine, isoleucine, leucine and Lysine. The sulphur containing amino acids that are present in cassava are deficient and in addition the cassava roots contain prussic acid. The level of the prussic acid is in the range of 10-490mg/kg of the fresh cassava tuber. Toxicity and Detoxification Cassava contains two major cyanogenic glucosides. These are: (i) The linamarin (ii) The lotaustraline Both of these compounds can be hydrolysed to produce the hydrocyanic acid, which is also called prussic acid. The HEN (HCN) is poisonous especially when it comes in contact with the enzyme Linamarase. The enzyme linamarase is released when the cells of the root are ruptured. The presence of the cyanogenic glucoside in most cassava cultivas necessitates a certain degree of detoxification of the cassava before it is consumed. The prussic acid is very lethal if more than about 0.1g of the prussic acid is contained in the food that is eaten at any one time. In general, three methods of detoxifications are employed. 28  (i) Microbial detoxification, through fermentation (ii) Decomposition of the glucosides especially by heating above 150oC. (iii) Rupture of the cells to allow intimate interaction between linamarase and glycosides. There is then the volatilization of the resulting hydrolytic products. It is important to note that all forms of cassava processing only decrease the level of the cyanogenic glycosides in the final product. In other words, it is difficult to produce a cassava product that is absolutely free of prussic acid. Maize Maize is also called corn. It plays an important role in the diets of millions of people. This is so for several reasons among which are: (i) High capacity to produce a large amount of dry matter. (ii) The ease of its cultivation (iii) The versatile food mass and its usage (iv) Its storage characteristics. On account of these properties, maize is grown throughout the world. Most of the maize that is grown in the Western Hemisphere is fed to animals whereas in Asia, Africa and Latin America, a large proportion of the maize that is produced is for human consumption. The three leading producers of maize are the U.S.A; China and India. There are various cultivars of maize that are produced in the world and the most important maize varieties are the flint corn, floury soft corn, dent corn and the pop corn. Other varieties of minor importance include the sweet corn, waxy corn and the starchy sweet corn. The Use of Maize as Human Food It has been estimated that bout 200 million people make use of maize as food and the maize comes in the form of thin round unleavened cake. They make use of maize in the form of porridge. In Africa South of the Sahara, porridge is the most wide spread form in which maize is consumed. In Western countries, maize is consumed usually as cornflakes. In West Africa, especially in Ghana, “kenkey” is very popular. There is also the maize porridge or the maize gruel. In East Africa the maize meal or maize dough is used for cakes and other foods. In Cameroon Koga is prepared by mixing ground maize, palm oil, salt and pepper. The mixture is rolled and it is steamed in plantain leaves. In Nigeria, maize could be boiled and eaten with or without coconut. Maize could also be roasted and eaten. In all of these cases, maize is usually consumed for its carbohydrate content. In many countries, alcoholic drinks could also be prepared from maize. In South Africa, a non-alcoholic drink that is called MAHEWU is prepared from maize. The maize starch is used as a thickening agent especially for soups. The maize starch is used as 29 a gel-forming agent especially in confectionery. It is also used as a moisture retention agent in cake icing. The oil from maize is very good. It is highly digestible and corn oil is a good source of the essential fatty acids. Maize as Animal Feed The bulk of maize that is produced in the industrialized countries are fed to livestock. In the U.S.A, between 75-90% of the maize that is produced is fed to livestock. Maize starch is produced from the wet milling and maize oil is also obtained. The residue then forms the basis for several animal feeds. These include the maize soluble also known as the steep liquor or condensed fermented maize extractives and: (i) Pericap and other fibrous materials that may contain some of the un- recovered endosperm. (ii) Gluten – the proteinous part of the endosperm (iii) Germ residue – Remnants after oil refining (iv) Mother liquor: It is obtained from the crystallization of dextrose All these feed products are obtained during the distillation process. They are mainly mixtures of fibre, gluten, germ, unfermented endosperm and the yeast cells. The yeast cells are separated from the soluble. The maize gluten is traditionally fed to the ruminant animals whereas the condensed fermented maize extracts serve as growth factor for the chickens. The maize gluten meal is used to feed poultry because of its high xanthophyll content. The xanthophylls colour the egg yolk, the body fat, shank and the beak of the birds. Maize as a source of food for human and animal consumption has some limitations. It is primarily an energy source with poor quality and quantities of protein. It is also relatively low in vitamin content. Pigs, the poultry, human beings require high qualities of protein, while on the other hand cattle, sheep and goat can utilize maize very profitably. Composition of Maize The composition of maize varies with the cultural practice types of seeds that are produced and it also depends on weather conditions. Constituents Composition (% dry weight) Carbohydrate 80 Protein 10 Oil 4.5 Fibre 3.5 Minerals 2.0 30  On account of the high carbohydrate content, maize is regarded as a starchy product. The protein of maize contain Albumin (7% of the total protein), Globulin (10% of the total protein), Zein (39% of the total protein) and Glutelin (35% of the total protein). The albumin, glubulin and glutelin are the major proteins that are present in germ while zein and other glutelins are concealed in the endosperm. The protein of maize are deficient in both glycine and tryptophan. Starch is predominant in maize and the ratio of amylose to amylopectin is 27.73. In other words, there is a large proportion of amylopectin that is present in maize. Maize Oil The maize oil varies considerably in its physical and chemical properties. The variation depends on the method of cultivation and the genetic background of the maize kernel. The oil also varies with the method of recovery and also with the method of estimation. Maize oil like other vegetable oils has a variable composition. It melts within a certain temperature range and the melting point is dependent on the crystal structure of the glycosides. The crude oil contains up to 3% of the free fatty acid. The level of the free fatty acid depends on the level of refining to which the maize oil has been subjected. Free Fatty Acid of the Maize Oil Myristic acid 0.5% Palmitic acid 9.7% Stearic acid 3.6% Hexadecanoic acid 0.2% Oleic acid 30.4% Linoleic acid 55.6% The bulk of the unsaponifiable matter of the maize oil and fats consist essentially of sterines. The sterines are in the form of free fatty acids. They are esterified with fatty acids and they exist as glycolipids. The sterine content of the crude maize oil is in the range of 0.58 and 1.0%. The Cornflakes Cornflakes are hydrothermally treated maize products with worldwide popularity. They are high in nutrient content and they also combine these high nutrient values with low caloric content. They are highly digestible. In its manufacture of flaking is undertaken. Flaking is a process that consists of cooking fragments of the cereal kernel grit to a mass with a certain consistency. The mass is then pressed after cooking. The rollers that are used then form the flakes and there is the roasting of the flakes at an appropriate temperature. 31 The Flow Chart for the Production of Cornflakes Maize grit Cleaning Cooking Drying Tempering Flaking Roasting Cooling Cornflakes. Cornflakes are produced exclusively from grit. Grits are obtained from the endosperm of the maize kernel. Grits are cooked for 2-21/2 hours at a temperature of 120oC. The mass that results are then mixed with corn syrup, sugar, salt and some vitamins. The grits are then passed into a drier in which pre heated air is blown to reduce the moisture content to about 15%. The grits are then held in the tempering tanks for a period of 6-8 hours. The tempering is undertaken to permit the residual moisture to become equally distributed. The equal distribution of the moisture is important to ensure uniform toughness for the flaking process. The tempered grits are then pressed into flakes. In the process of flaking, the rollers that revolve at a speed of 180-200 revolution per minute are cooled by the internal circulation of water. The cooling prevents the flakes from sticking to the rollers. The flakes from the rollers are passed on to the toasting oven for a period of 3-5 minutes at a temperature that varies between 200 –250oC. The flakes then emerge with less than 3% moisture content, after which they are cooled to room temperature before they are packed for distribution. During the process of converting grits into cornflakes there are 3 important steps that occur. (i) The starch granules are ruptured by the application of heat. The starch forms a gel of soluble starch dextrin. (ii) Two major reactions occur viz. (a) the particles undergo a browning reaction. This browning reaction is due to the interaction of protein and sugars. (iii) The dextronization and caramelisation of sugars occur as a result of the high temperature in the oven. The flakes become crisp as a result of the reduction of its moisture content. Generally, a 100g of Cornflakes contain approximately 7.5g of protein, 0.7g of fat and 85g of carbohydrate. The bulk density of Cornflakes is about 120-140g/litre. Summary This lectured has discussed the composition and classification and structure of Nigerian and West African foods like yam, maize and cassava. Post – Test What are the similarities and differences in the composition of the following food items: (i) Yam (ii) Cassava and (iii) Maize 32 Answers to Post Test The all have high carbohydrate content. However, maize is high in protein and oil but low in moisture while yam and cassava are very low in protein and fat but high in moisture. 33 Lecture Five Contamination of Foods from Natural Sources Introduction Viable microorganisms could be found in all possible milieu. They are actively involved in the natural processes of recycling carbon, nitrogen and sulphur. Surfaces of all parts of plants and animals and the gastrointestinal tracts of animals are inundated with bacteria, yeast and moulds. Animals also give off microbes in their various excretions. However, the healthy inner tissues of these plants and animals are relatively sterile since they contain very few or no living microbes. Most of the natural microorganisms on the surface of raw ingredients used in food preparation as well as contaminations from various other sources may be inactive or harmless. More importantly however, there are present some microorganisms which serve as agents for food spoilage, food poisoning and infections. Objectives At the end of this lecture, students should be able to identify and discuss: Contaminations arising from the air, water, soil, plants and their fruits, animals, sewage and food processors and vendors. Pre-Test 1. List and expatiate on the various sources of food microbial contaminants. 2. How would you purify air and water? 3. Of what importance is the Presumptive Coliform Test? 4. How does the internal flesh of an animal get contaminated? 34 CONTENT Sources of Contamination Air The air by itself does not contain any natural microorganism of its own, neither does it support their growth and multiplication. But microbes are blown into and dispersed by air on suspended solids like dust and lint, as droplets when we cough or sneeze, in sprays from water falls, streams, lakes or ocean, as dusts from powdery foods and feeds to name a few. Types of micro-organisms present in the air are therefore characteristic of the environmental source or location and their number would vary subject to rate of air movement, humidity, chemical activity of gaseous oxygen, intensity of radiant energy, microbial quality of suspended dust and spray or falling rain. Microorganisms which do not require much water live longest in the air. Mould spores present dominance in air because they are small in size with light weight, a large number of spores are formed and scattered at a time, they are not readily damaged by desication and radiant energy. They also do not readily sediment in humid air as they are not readily wetted. Molds that are important in food spoilage include mucor, aspergillus and penicillium. Bacteria are dispersed on dust particles or on moisture droplets or by skin flakes continuously being shed by animals including man. Spores of bacteria are not found in dust free air. Gram-positive cocci and rod shaped vegetative cells are more numerous than gram-negative bacteria which die rapidly in air. Most encountered species are micrococci, corynebacterium, bacillus and streptomyces. Methods for Purifying Air (a) Filteration with cotton wool, fibre glass, asbestos or activated carbon. (b) Washing by rain or snow. (c) Sterilization with ultraviolet rays of the sun and use of ultraviolet lamps (d) Sedimentation (e) Bubble gas through some chemical solutions or spray aerosols such as triethylene and propylene glycols, formaldehyde or hypochlorites. (f) Electrostatic precipitation of dust particles and microbes. Water In addition to normal microorganisms associated with water in streams, rivers, lakes, lagoon and oceans, these bodies of water may be further contaminated from the soil, by animal and human activities and from sewage and other waste products. These organisms may be drunk with water or picked up by fishes and shellfish which when eaten cause diseases like typhoid fever, cholera, and hepatitis in man. The most 35 encountered species of microbes are Pseudomonas, Chromobacterium, Escherichia coli (choliform group), Aerobacter and Streptococcus. Water to be used for drinking and to process foods must meet the following criteria: (a) Freedom from sewage contamination (b) Acceptable taste, odor, colour, clarity, chemical properties and bacteria count (c) Availability in sufficient volume and uniform composition The extent to which water is contaminated by sewage and other food wastes containing organic water is measured by its Biochemical or Biological Oxygen Demand (BOD). This is the quantity of oxygen needed by aerobic microorganisms and reducing compounds to oxidize the organic compounds present at a given time and temperature usually 5 days at 20C. The presence of sewage contamination is tested for by the presumptive test for the coliform bacteria E. coli. It gives an indication of the possible presence of intestinal pathogens. Water can be Purified By (a) Filteration through sand and filters as in municipal water works or naturally through layers of soil as in ground water or bore holes (b) Natural sedimentation in reservoirs and lakes or artificially following flocculation with chemicals like alum and lime. (c) Chlorination with liquid chlorine or calcium and sodium hypochlorites (d) Natural ultraviolet irradiation from the sun or from U.V. lamps as in pure water sterilization (e) Heating as in boiling of water. Soil The soil contains the most diverse types of microorganisms. It provides strains used for industrial production of amino acids, vitamins, enzymes, antibiotics and various other pharmaceuticals. Soil microbes are also involved in carbon, nitrogen and sulphur recycling which are important in plant growth and by the same principles accelerate food spoilage. Most important species of microbes are present in the soil. The soil is itself further contaminated with microbes from faeces of animals, urine, decayed dead animals and plants and sewage used as fertilizers. Often encountered are strains of Bacillus, Clostridium, Pseudomonas and Corynebacterium, Alcaligenes and Escherichia. Soil microbes contaminate the surfaces of animals and plants that come in contact with the soil. Soil dust is raised by strong air currents, passing vehicles, matching students and soldiers or carried after rain on to running 36 water and then on to foods e.g. Lafun and elubo spread to dry by the way side or slightly muddy water used to wash vegetables, fruits, meat and poultry. Most of the microbes are washed off the surfaces of foods during post harvest handling and processing. Foods of Plant Origin A variety of microbes are found on the surfaces of plants and their products arising from contamination from the soil on which they grow, wash down effects of the rain and inadvertent contamination from burst sewage pipes, urine from man and his livestock and the like. Plant products like contaminated flour, spices and the like cross contaminate other foods with which they are mixed. The type and number of microbes present vary with the type of plant or fruit and the ability of the microbes to stick to their surfaces. Most encountered species are Corynebacterium, Pseudomonas, Alcaligenes, Flavobacterium Achromobacterium, Bacillus and Coliforms. Also important are the lactic acid bacteria including Lactobacillus brevis and L. plantarium, Leuconostock messenteroides, Streptococcus faecium and S. feacalis and molds like Aspergillus. These are responsible for spoilage of fruits, vegetables, cereals, oilseeds, root crops and others. Animals The internal flesh of animals are relatively very sterile. However, the exterior including the skins, hides, hoofs, hair, feather and feet of poultry, carry typical flora associated with the beddings, manure, feed, water and air in the vicinity. The nose and throat of animals carry microbes which though normally harmless occasionally cause disease under stressful conditions. Some of these microbes are important spoilage organisms or may be pathogenic causing diseases. The gastro-intestinal tract of animals including man, through fecal wastes contaminate foods with such pathogen as Salmonella, Enterobacteriaceae and the protozoan. Other species are the coliforms, the lactics or lactic acid forming bateria, the propionics, Bacilli and Clostridia among others. Sewage Sewage arises from domestic activities (night soil) or as industrial waste products from food processing factories. It may be discharged into lagoons and streams from which contaminated water may be taken to wash fruits, vegetables, meat etc. as can be seen in some slaughter slabs and markets. Man and his animals defeacate on crop lands and burst sewage pipes which often serve as source of microbial contamination of crops growing in the vicinity. Raw foods so contaminated may be infected with human pathogens especially those causing gastro intestinal disorders. 37  The most encountered species of microbes are coliform bacteria, salmonella, enterococci and other intestinal bacteria. Diseases, caused by sewage contamination of water and foods include typhoid, cholera, diarrheoa, dysentery and hepatitis. Natural water contaminated with sewage will affect shell fishes like crabs, lobsters, shrimps and oysters, fish and other sea foods. Sewage supports growth of phytoplanktons on which zooplanktons depend. Both serve as feed to aquatic organisms. Some of these planktons when eaten by some shellfishes render them highly toxic with shell fish poison causing paralysis of the extremities and ultimate death by respiratory failure. The extent of sewage contamination of foods and water can be determined by estimating the Biochemical Oxygen Demand (BOD) and the presumptive coliform test. Food Handlers and Processors Food contamination can take place before food is harvested, during handling and processing, from various equipments coming in contact with foods, from packaging materials, from personnel and caterers with low personal hygiene in restaurants, institutions, religious and other civic camps. Microbes most associated with food handlers are staphylococcus, salmonella, and shigella. The preventive measure is to avoid contamination from infected food handlers or carriers, personnel with respiratory diseases, gastro-intestinal problems or boil. Hands, equipments and utensils should be properly washed and scrubbed with germicidal detergents and personal hygiene of workers should be paramount. Summary In this lecture, we have discussed the various ways a food substance may become contaminated. We also mentioned some of the microbes that may be so transmitted. Since these microbes are ever present around us, the students may wish to identify other examples of microbial contamination occurring daily around them. Post-Test 1. Why is the air usually inundated with mould spores? 2. What are the properties of safe drinkable water? 3. How do animals contaminate foods? 4. Which diseases are associated with sewage contamination of foods? Answers to Post-Test 1. Small in size Light weight Not easily wetted 38  Resistant to desiccation Not easily destroyed by radiant energy Large number of spores formed Spores easily scattered by wind 2. Free of sewage contamination Available in sufficient volume Of uniform composition Acceptable taste, odour, colour Acceptable chemical properties Low bacterial count. 3. Through their: Hides and skin Hoofs and hair Feather and feet of poultry Beddings and litter Nose and throat Feed, water and air 4. Typhoid, Cholera, Dysentery Diarrhea Hepatitis. References Frazier, W. C. 1977. Food Microbiology. McGraw-Hill Books Co. New York: Jay, J. M. 1992. Modern Food Microbiology. 4th ed. Van Nostrand Reinhold. New York: 39 Lecture Six Deterioration and Spoilage of Foods Introduction All foods are perishable to various degrees. Based on ease of spoilage, a food is said to be perishable, semi perishable or stable. Deterioration of food begins almost as soon after a crop is harvested, milk and eggs are collected or an animal is slaughtered. It continues to downgrade the aesthetic, nutritive and quality values of the food until the food reaches the table. A food is assumed to be properly spoilt when such food is no longer fit for human consumption. Spoilage of food can result from activities of bacteria, yeast and moulds, insects, enzymes naturally present in foods (autolysis) and purely chemical reactions. However, of most concern is spoilage arising from bacteria, yeast and mold activities. This would be the subject of this lecture. Objectives At the end of this lecture, students should be able to: 1. Explain the characteristic growth curve for microbes. 2. Identify the application of the growth curve to the food preservation processes. 3. Appreciate those factors which enhance microbial growth. 4. Describe spoilage symptoms in specific classes of food. Pre-Test 1. What do you understand by the microbial growth curve? 2. Define generation interval. 3. List and explain the factors which enhance growth and multiplication of microbes. 4. Define water activity. 5. How do foods get spoilt by microbes? 6. What are spoilage indicators in different foods? 40 CONTENT Microorganisms are naturally present on food surfaces even though the undisturbed interior may be sterile. They are also present in air, around the raw foods, the soil on which they were grown or fall on during harvesting, the water used to wash the food, on the hands and utensils used in handling and processing the food. These microorganisms’ bacterial, yeast and mould invariably cause food spoilage unless something is done to stop or slow down their activities in foods through food processing and preservation. To understand food spoilage, we must first understand the growth characteristics of microbes. The Microbial Growth Curve Microbes are present in foods as vegetative cells or spores. To grow, the spores must first germinate into vegetative form. A single vegetative cell divides first into two. Each daughter cell again divides into two making four daughter cells. The process continues until millions of daughter cells are formed. If we plot the log of the total number of cells formed against the time taken to form them, a logarithmic growth curve similar to Figure I is obtained. The curve shows the various phases of growth in the microbial population. Fig. I THE MICROBIAL GROWTH CURVE Time in hrs. A-B Lag phase B-C Positive acceleration phase C-D Log pr exponential phase D-E Negative acceleration phase E-F Maximal stationery phase F-G Accelerated death phase G-H Death phase 41 Lag Phase: No apparent growth. Microbe adjusts to its new environment and repairs earlier injuries Positive Acceleration Phase: Increase in number through cell division at increasing rate Exponential or Logarithmic Phase: very rapid but constant increase in growth rate. Microbes fully adjusted to abundant supply of nutrients. Negative Acceleration Phase: Number continues to increase at decreasing rate as available nutrients start to decline and toxic waste starts to accumulate. Maximal Stationary Phase: Rate of cell division equals rate of cell death i.e. births rate equals death rate. Accelerated Death Phase: More cells die rapidly as the environment becomes very hostile. Death Phase: Cell numbers reduce to very low level. Generation or Doubling Interval This is the time taken for one newly formed cell to divide into two new daughter cells. It is shortest during the log phase and longest during the lag phase. Application to Food Preservation Processes In food preservation, it is desirable to lengthen the lag phase and the positive acceleration phase. We can do this by: (i) Keeping initial load of microbes as low as possible, (ii) Avoid contamination or recontamination with microbes in their log phase by personnel, unclean equipments, containers and utensils and by introducing. (iii) Introduction of hurdles of one or more unfavourable environmental conditions e.g. low moisture, low temperature, acid pH, use of inhibitors. (iv) Causing physical damage to microbes with heat or irradiation or pressure. Factors which Affect Microbial Growth in Foods a. pH: Most microbes grow well at neutral pH and few grow below pH of 4. Moulds survive and grow at pH of 2 to 8.5 but more in the acid range. Yeast grows best at pH 4 to 4.5. Bacteria grow best at neutral pH although some are favoured by acid or alkaline pH. Each microbe has a minimum and a maximum pH at which they grow. There is a succession of different species of microbes as pH changes. 42  b. Temperature: Microbes grow well and cause food spoilage over a large range of temperature (-5C to 70C). Each microbe also has its own specific minimum, optimum and maximum growth temperature. Psychrophiles grow best at 0 to 10C, mesophiles at 20 to 45C and thermophiles at above 45C. c. Moisture Content: Microbes require various amounts of available moisture in the food for growth. Such water is defined in terms of water activity, aw or the ratio of water vapour pressure of food substrate (P) to the vapour pressure of water (Po) at the same temperature. Water Activity aw = P/Po It is related to Relative Humidity as follows: RH = 100 x aw. Table 1 Shows the Minimum aw for Microbial Growth Table I: Minimum aw for Microbial Growth in Foods Microbial Group Minimum aw Most gram negative bacteria 0.97 Most gram positive bacteria 0.90 Most yeast 0.88 Most filamentous fungi 0.80 Xalophilic bacteria 0.75 Xerophilic bacteria 0.61 Fresh vegetables, meat, fish and milk with high aw are more likely to be spoilt by bacteria than bread and other bakery products with low aw. d. Relative Humidity relates to the amount of water vapour in the environment. It affects growth of microbes on the food surface. With high relative humidity, a dry food absorbs moisture from the air while at low relative humidity, a moist food loses water. This vapour exchange modifies the water activity of the food. e. Nutrients Microbes require water, sources of energy and protein, vitamins and other growth factors as well as minerals in forms that may sometimes be specific for the microbes. f. Oxidation – Reduction Potential: Some microbes grow in the presence of oxygen (aerobes), in its absence (anaerobes), or under both conditions (facultative microbes). Moulds are aerobic, most yeasts grow aerobically while different species of bacteria grow under the three conditions. 43 Spoilage Effect of Microbes in Foods Foods contain complex organic compounds as carbohydrates, proteins, and lipids. These are digested by various microbial enzymes to simpler chemical products. The undesirable products are manifested as food spoilage and may include toxins which cause food poisoning and objectionable taste, odour, colour or texture in the food. Some end products may however be desirable as are observed in industrial food fermentation as part of food preservation processes. Putrifaction involving terrible odour occurs when protein, peptides or amino acids are broken down anaerobically in high protein foods. Carbohydrates are decomposed to simple sugars and to CO2 and water by aerobes. Anaerobically, various types of fermentation can occur with formation of alcohols like ethanol, butanol and propanol, acids like acetic, lactic, butyric and propionic acids and gases like carbon dioxide and hydrogen which cause swelling in spoilt canned foods. Lipids are broken down to various fatty acids and glycerol which may all be subject to rancidity. Examples of Microbial Spoilage in Foods Meats: Bacterial greening and iridescence, taints, souring, putrifaction and other off odour and taste, surface sliminess, rancidity, stickiness, gassy or bloated cans and vacuum packages. Fish: Fishy and other off odours, green or grayish gills, soft flesh, dull sunken eyes, sliminess. Eggs: Fungal whiskers, blue green and black mould spots in egg white, black, white, green or pink bacterial rot. Milk: Souring, gas (H2 + CO2) formation, curdling and coagulation, ropiness, swelling of canned milk, various flavour defects, discolouration. Cereals: Souring, moldiness with red, white, green black or yellow colouration, ropiness. Vegetables and Fruits: various types of rots by bacteria, yeast and mould, undesirable colour, odour, watery or soft texture, mildew, sliminess, shriveling, mushiness, ropiness, souring. Fruit Juices: Cloudiness, ropiness, sour, acid or bitter taste, foul smell, gassy or swollen cans, yeasty flavour and odour. Summary In this lecture, you were introduced to the concepts of microbial growth curve and the generation or doubling interval. Factors, which affect microbial growth in foods, were discussed. Indicators of spoilage in some classes of foods were also given. 44 Post Test 1. Define generation interval; when is it the longest? 2. What factors are important for the growth of microbes? 3. Do all foods spoil at the same rate? Answer to Post Test 1. The time taken for a newly formed cell to divide into two new daughter cells. It is longest during the lag phase. 2. pH Temperature Moisture content Relative humidity Nutrient Oxidation – Reduction Potential 3. All foods do not spoil at the same rate. Their chemical compositions defer and therefore their ability to support the activities of microbes defer as different spoilage organisms require different optimal factors for growth, multiplication or toxin development. References Frazier, W. C. 1977. Food Microbiology New York: McGraw-Hill Books Co. Ihekoronye, A. I. And Ngoddy, P. O. 1985. Integrated Food Science and Technology for the Tropics. London: Macmillan Publishers, Ikeme, A. I. 1990. Meat Science and Technology, A Comprehensive Approach. Onitsha: Africana – Fep Publishers. Ltd. Nigeria. Jay J. M. 1992. Modern Food Microbiology. New York: Van Nostrand Reinhold. 45 Lecture Seven Principles of Food Processing and Preservation: Part I Introduction In the second lecture, foods and their various functions were discussed. In this lecture and the next, the basic principles employed in the processing and preservation of foods will be expatiated. This is important because a large part of the food which are actually harvested do not get to the consumers’ table because of physical abuse as well as chemical and microbiological spoilage. Chemical spoilage arises from continued physiological activities in the raw food in the presence of endoenzymes or presence of toxic chemical constituents. Microbiological spoilage is the result of activities of bacteria, yeast and mold, some viruses and parasites. Objectives At the end of this lecture, students are expected to be able: 1. To identify the various food preservation methods 2. To introduce the idea of barriers or hurdles and the principles governing them. 3. To have an understanding of the roles of asepsis, removal of micro- organisms, anaerobic conditions, heat and low temperatures in food preservation. Pre-Test 1. List the various methods used in preserving foods 2. What principles are involved in the preservation processes? 3. Discuss some of the various preservation methods listed. 46 CONTENT Food Preservation Methods These include the following: (i) Asepsis (ii) Removal of micro organisms (iii) Maintenance of anaerobic conditions (iv) Preservation by heat (v) Use of low temperature (vi) Drying (vii) Use of chemical preservatives (viii) Irradiation (ix) Mechanical destruction of micro-organisms (x) Combination of two or more of above methods. Principles Involved in the Preservation Processes The primary objective of preservation processes is to create one or more barriers or hurdles, which are inimical to the activities of microbes or endoenzymes present in the food. These hurdles are governed by the following basic principles. 1. Prevention or Delay of Microbial Spoilage (a) By keeping out micro-organisms as in asepsis (b) By removal of micro-organisms as in filtration (c) By hindering the growth and activity of micro-organisms as with low temperature, drying, anaerobic conditions and chemicals (d) By killing the micro-organisms. 2. Prevention or Delay of Autolysis or Self Decomposition of Foods (a) By destruction or inactivation of food enzymes as by blanching (b) By prevention or delay of purely chemical reactions as in the use of antioxidants to prevent oxidation. 3. Prevention of Damages by Insects, Animals and Chemicals Most often, methods used in controlling micro-organisms are sufficient for destroying or delaying enzymatic activities. In some however, auto- oxidation or chemical deterioration may continue if proper precaution is not taken. Preservation by Asepsis (a) Under normal conditions the surfaces of most raw food materials are heavily contaminated from natural sources. 47  (b) Such raw foods possess natural barriers e.g. skin of fruits and vegetables, shell of eggs, hide or skins of animals, which through various mechanisms prevent these microbes from reaching the internal tissues. These therefore remain fairly sterile unless these natural barriers are damaged. (c) This natural prevention of contamination of the interior of raw food is a form of asepsis (d) The same goal is achieved when a food that has been previously pasteurized or sterilized is dispensed into a sterilized container like cans or pouches among others and sealed under conditions that prevent microbial recontamination. (e) Aseptic packaging has wide application with fluids like milk, fruit juices, beer and homogenous soups which can undergo High Temperature Short Time continuous pasteurization (f) Some advantages are that natural flavor of such foods are retained. Glass or metal containers can be replaced with flexible multi-layered packaging which are cheaper. However, it may not completely prevent diffusion of oxygen through the packaging material (g) Aseptically packaged fruit juices retain its quality for more than 6 months at room temperature. Removal of Microorganisms We most often wash our raw foods like fruits and vegetables with clean water before eating and meat also before cooking. We also peel the skin, or remove spoilt portions of tubers and other foods followed by washing prior to cooking as a way of removing microbial contamination from natural sources. In the food industry, filtration through special filters helps in removing microorganisms from fermented beer and wine. Flocculation, filtration and sedimentation are integral processes in purification of water. Anaerobic Conditions Maintenance of anaerobic condition is a must in many packaged foods such as those in metal or glass cans, plastic and composite pouches and others. Anaerobic condition is achieved by completely filling the container prior to sealing it aseptically either by sealing it under vacuum (vacuum packaging) or replacing the air in the container with nitrogen gas or carbon dioxide. Anaerobic condition ensures that micro-organisms, which survive processing in foods, cannot germinate or grow in the absence of oxygen even though moisture is present. 48 Preservation by Heat Preservation by heat includes all methods that utilize temperatures higher than the ambience for food preservation. Microorganisms in foods are destroyed through the coagulation of their proteins. Enzymes in foods are similarly inactivated thereby preventing further metabolism from proceeding in the food. Different foods require different heat treatments depending on the characteristic nature of the food. The kind of organism present in the food whatever its state whether in spore or vegetative form and the environment during heating are also of important consideration. Spores or vegetative cells may be killed in part or almost completely at a given temperature as they differ in their resistance to heat treatment. Some have low resistance to heat and are killed rapidly as temperature begins to rise. Most have medium resistance while a small number will grow at temperatures that are destructive to most bacteria. Heat loving bacteria are called thermophilic bacteria or thermophiles. They survive and grow within a minimum temperature of 45C and maximum temperature of 70C but are at their best between 50 and 60C. If they can survive but will not grow at high temperatures, they are said to be thermoduric. Heat Treatment Methods 1. Pasteurization (a) This is a preservation method that kills part but not all the micro- organisms that are present in food. (b) The temperature achieved during pasteurization is 60-80C. (c) The source of heat is by steam, hot water, dry heat or through electrical energy. (d) Pasteurized foods must be cooled rapidly thereafter. (e) Pasteurization is applied mostly to fluid foods especially milk. A food is pasteurized (a) When a more rigorous heat treatment would be harmful to the product quality such as destruction of vitamins and other valuable nutrients or affect the flavor. (b) When spoilage organisms are not heat resistant. (c) To eliminate all pathogenic bacteria, yeast and moulds including all vegetative cells as in milk, beer and fruit juices. (d) To kill competing microbes leaving behind desirable ones as with starter cultures in cheese manufacture. (e) When surviving spoilage organisms will be subjected to additional preservative method like chilling of milk. 49 Pasteurization methods (a) High Temperature Short Time (HTST) methods: milk is heated as follows 72C for 15 sec 89C for 1.0 sec 94C for 0.1sec or 100C for 0.01 sec. (b) Low Temperature Long Time (LTLT) methods: milk is heated at 63C for 30 min. 2. Sterilization (a) Food is heated to temperature above 100C using steam under pressure or live steam in steam – pressure sterilizers or retorts. (b) Temperature increases from 100C at atmospheric pressure to 121.5C at 1.01kg/sqcm steam pressure (c) The few surviving organisms are non-pathogenic and cannot develop within the product at normal condition of storage (d) Products have long shelf life and are room stable. 3. Canning (a) Process developed initially by Nicolas Appert in France in 1810. This is the preservation of foods in sealed containers. (b) Process carried out in tin cans or tin coated steel, glass and aluminum containers, plastic pouches and other composite materials. (c) Tin coated steel containers may be lined internally specific to milk, meat, beer, fruit juices, etc to slow down discolouration of food or corrosion. (d) Complete sterilization is desired but not always possible (e) Eliminates all pathogenic and spoilage bacteria but surviving bacteria are harmless and do not grow at normal storage temperature (f) Such cans are commercially sterile, practically sterile or bacterially inactive. (g) Temperature required is less in high acid foods than in low or neutral foods. Foods liable to damage at high temperature may be acidified and heated at lower temperature. (h) Some fluid foods may be sterilized in bulk, filled into sterilized containers with sterilized lids and sealed aseptically. 50  (i) Cans can be heated in retorts by direct gas flame or with live steam, by heating in fluidized bed of granular solids or with hydrostatic sterilizer. (j) Cans must be cooled rapidly inside the retort or by immersion in or by spraying with cold water. 4. Blanching or Scalding (a) Blanching is a low heat pre-treatment of foods by immersion in hot water or use of steam followed by other preservation methods. (b) Initial vegetative microbial loads on foods may be reduced by as much as 99%. (c) It inactivates endoenzymes which otherwise would cause autolysis and other undesirable changes in foods during subsequent