Food Microbiology & General Principles of Food Hygiene PDF

Food Microbiology & General principles of Food Hygiene Best Study-Material for FSSAI CBT 2 and interactions between microorganisms, food and us the community. It covers food bome disease, food hygiene, foodsspoilage, fermented foods and beverages, use of microorgan...

Food Microbiology & General principles of Food Hygiene Best Study-Material for FSSAI CBT 2 and interactions between microorganisms, food and us the community. It covers food bome disease, food hygiene, foodsspoilage, fermented foods and beverages, use of microorganisms to produce food ingredients and processing aids, microbiological aspects of quality control, conventional and novel methods for the microbiological analysis qf foods and aspects of food legislation. Food microbiology therefore, is a vast field of - study in itself. Let us look at the origin of this field of study, next. 1.3 HISTORY OF FOOD MICROBIOLOGY The microorganisms were first observed using primitive microscopes as early as the late 1600s. The science of microbiology is barely 150 years old. A dramatic development and broadening of the subject of microbiology has taken place since World War 11. It is extremely difficult to pinpoint the precise beginnings of man's awareness of the presence and role of microorganisms in foods, evidence available at this time indicates that this knowledge preceded the establishment of microbiology as a science. The era prior to this may be further divided into what has been called as man's 'food gathering period' and the 'food producing period'. The food-gathering period may be from origin of man to 10,000 years ago. During this period, man was presumably carnivorous in his eating habits, with plant foods coming into his diet later in this period. The food producing period dates from 10,000 years ago to present time. Between 3000 BC and 1200 BC, the Jews employed salt in the preservation of various foods. The use of curds iflvolving fermentation of milk was known in India since the Vedic period. The epic Mahabharath dating 5000 BC contains references to milk products like curd and butter. It is presumed that man first encountered problems of spoilage and food poisoning early in the period with the advent of prepared foods. The problem of disease transmission by food and faster spoilage due to improper storage both made theii appearance. The first man to suggest the role of microorganism, in spoiling food was A. Kiremer. In 1658, he examined decaying bodies, meat, milk or other solutions and saw what he referred to as "worms" invisible to the naked eye. Subsequently, L. Pasteur (1837) was the first man to appreciate and understand the presence and role of microorganisms in food. In 1860, he employed heat to destroy undesirable organisms present in wine and beer. So then, starting from 150 years ago till date, food microbiology, as a discipline, has evolved to accommodate various modem developments. We learnt that microorganisms can cause food spoilage and disease, though not all microorganisms are harmhl. Some organisms play a beneficial role in nutrition and well being of humans. This aspect has been studied and great advancements have been made in this area. Some of the recent developments in food microbiology are discussed next: a) Probiotics: The word 'Probiotic' is a Greek word and it means "for life7'. It refers to microorganisms and their 'culture products, which contribute lo the intestinal microbial balance, thus benefiting the host by protecting against disease or improvising its nutrition. It is well known that probiotics, like lactobacillus, assist in the digestion of lactose, inactivate toxins, bind cancer causing chemicals, modulate the gut flora and reduce cholesterol absorption in the gut. We will read about probiotics in greater details in the Advance Nutrition Course in Unit 11. nd The use of biotechnology and understanding the nature of DNA has led to what we call as 'genetic modiJication'. It is a technique of changing by inactivating, deleting or inserting genes to produce a desired characteristic. In this technique,. selected individual genes are transferred from one organism (microbes, plant or animal) to'another organism. When genes are transferred from one species to another, transgenic organisms are produced. Foods produced by genetically modified technique are called ~ e n e t i c a l Mod$ed l~ or GM Foods. The term 'Recombinant technology' or 'Biotechnology' is often used to describe genetic modification process. What is the genetic modification process? Let us next briefly review the process. Initially, the gene that carries the desirable characteristic is identified. Then a gene from a second strain carrying the desired trait is inserted, which produces a genetically modified variety which is identical to the original variety with the improved desirable characteristics. The first GM plants were created in 1983. Since then a variety of crop plants such as maize, soybean, rice, rapeseed (mustard), tomato, cotton, potato etc have been modified by this technique. What are the benefits of genetic modification? Among the many benefits of genetic modification, reduction in the use of pesticides or herbicides, higher yields, better quality food, foods with greater shelf life, nutritional improvement and enhancement in processing qualities are some of the important benefits of genetic modification. Let us understand this concept better by looking at the benefits of genetically modifying a few of the food items: a) Tomatoes: It was discovered in the Nottingham University in the UK that it. is possible to slow down the softening process of tomatoes by genetically modifying the tomato plant. This helped to increase the shelf-life of tomato, keeping it fit to eat for longer and reducing waste during processing. b) Maize: The European corn was made pest-resistant by inserting a gene from the naturally occurring soil bacterium Bacillus thuringiensis. The gene produces a protein that acts as an insecticide, but is harmless to other creatures. c) Golden rice: The natural varieties of rice do not provide vitamin A. Vitamin A deficiency, as you may already know, could lead to blindness, decreased immunity to diseases and deaths of more than a million children. So, the scientists in Switzerland genetically enhanced rice to be rich in p-carotene (a precursor of vitamin A, to be converted to vitamin A in the body) by re-engineering the genes that imparts yellow colour to daffodils. Interesting isn't it! d) Vaccines: In US, foods such as potatoes, tomatoes and bananas that can cany vaccine for the infectious liver disease - Hepatitis B, have been successfully produced on a small scale. Feasibility studies are being conducted to investigate whether these modified crops would help to deliver the vaccines to people living in developing countries. If the positive outcomes are indicated in these studies, it would help to save lives of many millions. In India, so far 3 hybrids of cotton containing Bt gene produced by ~ah~coifvlonsanto has been approved for commercialization by the Genetic Engineering Approval Committee (GEAC) in 2002. One variety of cotton, again containing Bt gene produced by rasi seed was allowed seed production for one hybrid. Other GM crops undergoing field trials include: Mustard containing barnase-bar star gene, produced by the company Proagro and another variety produced by Jawahar La1 Nehru University, Delhi. Rice and brinjal with Bt gene and tomato by the Indian Agricultural Research ~nstitute,New Delhi. Potato containing lysine protein gene from amaranth plant by Jawahar La1 Nehru University, New Delhi. Check Your Progress Exercise 1 1) State whether the following statements are true or false. Correct the false statement. a) All microbes are harmful, since they spoil foods and cause food-borne diseases. b) Man was primarily carnivorous during the food-gathering period. c) A. Kiremer was the first one to discover microorganisms in food. 2) What is food microbiology? What areas does it cover?............................................................................................................................................................................................................................................................................................................................................... 3) Define the'following terms: a) Probiotics.............................................................................................................................................................................................................. b) Biotechnology.............................................................................................................................................................................................................. c) Genetic modification.............................................................................................................................................................................................................. y and prepared and consumed for thousands of years and are strongly linked to cultme and tradition, especially in the rural households and village communities. The development of fermentation technologies is lost in the mists of history. Anthropologists have suggested that it was the production of alcohol that motivated primitive people to settle down and become agriculturists. Some even think that the consumptiqn of fermented foods is pre-human. The first fermented foods consumed probably were fermented fruits. ~unter-gathererswould have consumed fresh fruits but at times of scazcity would have eaten rotten and fermented fruits. Repeated consumption would have led to the development of the taste for fermented fruits. There is a reliable information that fermented drinks were being produced over 7,000 years ago in Babylon (now Iraq), 5,000 years ago in Egypt, 4,000 years ago in Mexico and 3,500 years ago in Sudan. Bread-making probably originated in Egypt over 3,500 years ago. Several triangular loaves of bread have been found in ancient tombs. Fermentation of milk started in many places with an evidence of fermented products in use in Babylon over 5,000 years ago. There is also evidence of fermented meat prodqts being produced for King Nebuchadnezer of Babylon. China is thought to be the birth-place of fermented vegetables and 'the use of Aspergillus and Rhizopus moulds to make food. The book called "Shu-Ching" written in the Chou dynasty in China (1 121-256 BC) refers to the use of "chu"- a fermented grain product. Having looked at the history of fermentation, let us review and see what is fermentation? Fermentation is the slow decomposition process of organic substances induced by microorganisms, or by complex nitrogenous substances (enzymes) of plant or animal origin. It can be described as a biochemical change, which is brought about by the anaerobic or partially anaerobic oxidation of carbohydrates by either microorganisms or enzymes. You know that microorganisms are naturally found in foods, since there is no environment where some type of microbes cannot live. These microbes either living or dead and their cellular byproducts all have specific uses in some foods. These include such products as fermented food products. Fermented foods use microbes to convert the ogginal food into a fermented product by the use of specific microbes. These microorganisms use the original product for growth and reproduction, and in the process, they excrete byproducts into the environment surrounding themselves and the food. These byproducts plus the part of the original product that is not consumed is the fermented food. Fermented foods include fermented dairy, meat, fish, cereals, fruits, vegetable products etc. They may be fermented separately or in conjunction with each other to produce the desirable end product. From our discussion, so far, it is evident that, fermentation involves the introduction of the desirable microbes into the original product. Some of the common microbes used in food fermentation are highlighted herewith. Lactococcus lactis - used in dairy fermentation. Steptococcus thermophilus - used in dairy fermentation. Leuconostoc sp. - used in wine making, dairy fermentation. Pediococcus sp. - meat fermentation, vegetable fermentation, ripening of some cheeses. Lactobacillus sp. -meat fermentation, vegetable fermentation, dairy fermentation, sourdough bread. a' Bifidobacterium sp. - added to dairy products to promote intestinal health. Propionibacterium sp. - Swiss cheese.  Yeasts - bread, beer, wine, liquors. Microbiology of Foods Moulds - ripening cheeses, soy sauce. Lactobacillus delbruekii, subspecies bulgaricus and streptococcus thermophilus - making of yogurt. Although fermentation of foods has been in use for thousands of years, it is likely that the microbial and enzymatic processes responsible for the transformations were largely unknown. It is only recently that there has been a development in the understanding of these processes and their adaptation for commercialization. Let us now get to know about a few of the fermented food preparation used commercially. We shall begin our study on fermentation products with the baked preparations. 1.5.1 Fermented Baked Preparations In baked products such as bread and bun, the yeast Saccharomyces cerevisiae which is popularly known as "baker's yeast", helps by raising the dough giving it the texture and also adding flavours. The different ingredients added gives distinctly different tastes to each of the products. The naan, which is popular in India, is made from maida (refined wheat flour) to which salt, yeast or curd is added. It is kneaded vigorously for 15 minutes adding vegetable oil for softening. It is allowed to ferment for 30 minutes - 1 hour. It is then baked rapidly for 5 to 10 minutes. Intense heat causes centre of the dough to expand rapidly and create a central pouch. Saccharomyces cerevisiae is mainly responsible for leavening by carbon dioxide 1.5.2 Fermented Vegetable Foods We all consume vegetables either in raw or cooked form as salad preparations, soup, dry vegetables and curry or as stuffing in a variety of snacks. But, do you know, we can even consume these by making fermented products. Can you think of any such food item? Yes, of course, it is pickles which all of us relish sometimes or the other. Let us learn about these fermented vegetable products and see which microorganisms are involved in their preparation. i) Sauerkraut Sauerkraut is a fermented fresh cabbage product. It is popular in USA and Europe. The main organism which is involved in the fermentation of this pickle is lactic acid bacteria, Leuconostoc mesenteroides followed by Lactobacillus plantarum. ii) Cucumber pickle Cucumber pickle is a fermentation product of fresh cucumbers. Several lactic acid bacteria are involved in the preparation of this pickle. Lactobacillusplantarum is the most important organism required for the fermentation of cucumber pickle. l.5.3 Fermented Soyabean Products Do you enjoy Chinese food? Jf you have tried making it at home, you would have realized that soya sauce is a basic ingredient in Chinese cooking. In fact two of the most commonly consumed soya products are tempeh and soya sauce. We will briefly focus on the preparation of these products. Tempeh is a highly popular soyabean preparation in Indonesia. The chief organism in this preparation is the species belonging to mould Rhizopus oligospor-,- Th- ology and inoculated with tempeh fungus by the addition of a portion of previous batch and allowed to ferment for about 24-48 hours at a temperature 30-40°C, until there is a good mycelium growth. This is then sliced and prepared as per the taste, such as roasting or frying. The taste of the tempeh is considered to be bland, but it is highly nutritious. ii) Soya sauce Soya sauce is a very popular preparation of Japan which has received wide acceptance in many countries. This is prepared by inoculating an Aspergillus species, mostly Aspergillus olyzae in a mixture of soaked and steamed soya bean with roasted wheat in the ratio of 2:l. The mixture is allowed to be incubated for 3 to 5 days. Subsequently, it is subjected to various processing with Lactobacillus bacteria and the yeast Saccharomyces rouxii. After 3 months, the final product is filtered, pasteurized and bottled for use. We will learn more about the fermented soya products in the Principles of Food Science Course, Unit 11. 1.5.4 Fermented Dairy Products A large number of fermented dairy products are available in our markets. These are prepared at our homes as well. How are they made and what are the microorganisms involved in their preparation? The fermented dairy products assume greater importznce in the human diets in India, as invariably, the diets mostly include milk byproducts especially the cheese, butter, yogurt, dahi etc. A variety of bacterial yeasts and moulds are involved with the fermentation of dairy products. We will begin our discussion with cheese. i) Cheese There are several varieties of cheese manufactured all over the world. All types of cheese are the byproducts of lactic fermentation of milk. There are several varieties of cheese which are classified as hard, semi-hard and soft cheese. These are prepared with culturing of the milk either with bacterial or mould species. Among the several varieties, the popular ones are cheddar cheese and swiss cheese which are known as 'hard cheese' whereas roquefort cheese (blue cheese) is a semi-soft cheese and the soft variety is the camembert cheese. The cheddar cheese originated from England and was adopted in USA, the colour of which ranges from white to orange- yellow, depending upon the colour added. The curing is done with the help of Streptococcus and Lactobacillus. The cheese is without the gas holes (the eyes), which characterizes the Swiss cheese. The Swiss cheese is cultured with the help of a mixed culture, L. bulgaricus, Streptococcus thermophilus and Propionibacterium shermanii which imparts the characteristic eye formation. The roquefort cheese is prepared by the inoculation of curd with Penicillium roqueforti and the camembert cheese is produced by the fermentation with Penicillium camemberti. ii) Dahi and Yogurt Dahi or curd is the Indian variety, a version of yogurt and is widely used in the daily menu of an average Indian. Several organisms are involved in the preparation of dahi which contains lactic acid. Yogurt is the preparation with the action of two organisms, Streptococcus thermophilus and Lactobacilius bulgaricus. The ideal ratio of these two organisms is 1:1 for best results. In common usage, dahi refers to 'the domestically prepared fermented milk using a starter of the previous day' while yogurt refers to the 'industrially produced fermented milk using a particular bacteria as the starter.'  Microbiology of Foods' The microorganisms which are involved in the preparation of butter are Streptococcus lactis and Streptococcus cremoris which convert the lactose in the milk to lactic aciu. Then the organisms like Streptococcus diacetilactis, Leuconostoc dextranicum and Leuconostoc citrovorum are involved in imparting the aromatic flavours to the 10°C and culturing for 15-16 hours with bacteria. Check Your Prog~essExercise 2 1) Fill in the blanks: a) Saccha