محاضرات تكنولوجيا الاغذية والالبان 12.pptx

Food Technology and dairy products Food Technologist Aref Alsakkaf Introduction to food technology Basic considerations in food technology Definition of Food Technology Food Technology is the theoretical concepts and practical applications that are considering all...

Food Technology and dairy products Food Technologist Aref Alsakkaf Introduction to food technology Basic considerations in food technology Definition of Food Technology Food Technology is the theoretical concepts and practical applications that are considering all food considerations in the areas of production, storage, marketing, distribution and consumption in its final stages. Food Technology applies The principles and concepts of engineering to problems of food handling and processing Studies the interrelationships between the properties of materials and the changing methods of handling , manufacturing them.  Introduction to food technology The Importance and Source of Food The raw materials of present day foods generally originate from two major sources: the plant and animal kingdoms.  The Importance and Source of Food Plant Products A. Grains (cereals) wheat, corn (maize), sorghum , barley, oats, rice, B. B. Pulses beans (red kidney) peas, lentils, broad beans, vetch (fitches) C. C. Fruits 1. Tropical fruits banana, , pineapple, papaya, guava, mango, avocado, D. 2. Subtropical fruits (a) Citrus fruits orange, lemon, , grapefruit,(b) Other, olives, E. Vegetables 1. Leaf(y) vegetables 2.. Others cauliflower and broccoli The Importance and Source of Food Animal kingdoms MILK Cows, buffaloes ,sheep , goat, and camels are great source of milk. Milk is also called as an ideal food Eggs Chickens, ducks, geese and quails are raised for eggs and meat. It's a rich source of protein and vitamin, phosphorus, calcium and iron  The Importance and Source of Food Meat Meat is of two types –red meat and white meat. Cow ,goat , sheep. has a lot of fat and is called red meat. White meat contains less fat and is obtained from chicken and fish. Meat is rich in proteins , vitamins, zinc, phosphorus and iron  Introduction to food technology Components of food technology FOOD ANALYSIS AND CHEMISTRY FOOD QUALITY FACTORS FOOD MICROBIOLOGY,MYCOLOGY, TOXICOLOGY FOOD PROCESSING AND ENGINEERING NUTRITIVE ASPECTS OF FOOD CONSTITUENTS , EFFECT OF PROCESSING AND HANDLING. Food properties The functional properties of food are the physical and chemical changes that occur during food storage ,preparation and presentation 1 caramelisation Mono-disaccharides turn brown Occur in browning of biscuits 2 dextrinisation Is non-enzymatic browning and chemical change Toasting bread 3 Gelatinisation Custard  Functional properties 4 Crystallization Occur only at very concentration levels 4 Toffee , caramel denaturation and coagulation 5 Cooked meat  Functional properties 6 solutions Salt and water 7 shortening fats helps stop gluten forming 8 foam Gas mixed into a liquid like in ice cream. 9 Emulsions liquids that will not mix together Example oil and water we use lecithin to mix  The major manufactured food products ▫ 1. Sugars: cane, beet, maple, corn. ▫ 2. Starches: corn, potato, cassava (manioc), arrowroot, sago, wheat. ▫ 3. Flour, bread, and cereals. ▫ 4. Sweet baked goods. ▫ 5. Confectionery products. ▫ 6. Canned foods. ▫ 7. Frozen foods. ▫ 8. Dried (dehydrated) foods. ▫ 9. Pickled and marinated foods. ▫ 10. Salted and cured foods  The major manufactured food products 11. Dairy products: market milk (homogenized0, cheese, butter, cultured milks, ice cream, dry nonfat solids, milk concentrates. 12. Meat products: sausages, hams, luncheon meats, meat extract, pastes. 13. Seafood products: fillets, fish sticks, breaded shrimp, sausages, pastes. 14. Oleomargarine and other food fats and oils: soybean, corn, sunflower, cotton seed, olive. 15. Jams and jellies 16. Fermented foods: pickles, sauerkraut, fish sauces. 17. Fermented beverages: wine, beer. 18. Soft drinks: carbonated and still drinks. 19. Mixes: baking, soup. 20. Soybean products. The major manufactured food products.Corn products.21 Yeast: food yeast, bakers’ yeast,.22.brewers’ yeast.Fish flour.23.Protein hydrolyzates.4 2 Imitation foods (spun proteins,.25 fruit drinks, synthetic cream, etc.)  Raw material selection Definition of Quality Degree of excellence and include such things as taste, appearance, and nutritional content. The composite of characteristics that have significance and make for acceptability  The Importance of Raw Material Selection A poor raw material cannot be converted into a good finished product. In food processing; General rule:- the effective methods must be carefully applied to conserve the original qualities of the raw materials - cannot improve the raw material  Appearance Factors Include such things as; Size Approximated by weight after rough grading Ex. Determining the weight of dozen eggs Shape Have more than visual importance The grades of certain types of pickles include the degree of curvature  Appearance Factors Color and Gloss Color is commonly an index of ripeness and spoilage: Potatoes darken in color as they are fried Blenching of dried tomato powder on storage Consistency May be considered a textural quality attribute Measured by viscosity of food: – Higher viscosity – higher consistency –  Texture Factors Texture Factors Texture Refers to those qualities of food that we can feel either with the fingers, the tongue, the palate or the teeth. A departure from an expected texture is a “quality defect”. Expected texture – Chewing gum to be chewy – Crackers and potato chips to be crisp – Steak to be compressible and sharable between the teeth  Flavor factors Flavor factors Flavor A combination of both taste and smell Largely subjective Hard to measure because of difference of opinion: People differ in – Their sensitivity to detect different tastes and odors – Their preference – Their cultures  Food preservation by use of low temperature Low temperature preservation principle reducing the microbial activity by subjecting to low temperature condition All metabolic activities of microorganism are catalyzed by enzymes Enzyme reactions are dependent on temperature the low temperature slows down enzyme activity , thereby brings about reduction in microbial activity. The reduced microbial activity prologs shelf life of food. Methods of low temperature preservation Low temperature preservation is generally attained by employing three different temperature conditions. They are : Chilling temperature : keeping foods at 10_ 15 “c ( slightly above refrigerated temperature ) Refrigerator temperature : keeping foods at 0_7”c Freezer temperature : storage of foods below – 18”c Chill storage of food Chill storage temperature of food is reduced close to freezing point of water ( 0”c ) delays both biochemical and bacteriological processes, thus prolongs shelf life Deteriorative changes are retarded as long as low temperature is maintained. This ensures preserving natural nutritional properties of food factors influencing of chilled food Quality of chilled food depends upon factors as : Raw material quality Method and duration of chilling Efficiency of storage method Chilling can be achieved by use of ice ( crushed / flake ice ) and use of homogenous coolant ( cold air or cold liquid ), and refrigerated temperature Use of cold liquid may be in the form of chilled freshwater for light chilling brine to attain temperature of 0-1”c  Bacteria associated with low temperature Gram negative bacteria are more common than gram positive Growth at temperature below 0”c mainly yeasts and molds than bacteria because of low water activity. The lowest recorder temperature for growth of microorganism in food is -34 “c , by yeast. Common bacterial genera associated with chilling temperature condition of foods are : Acinetobacter, Aeromonas , Enterococcus, Pseudomonas, Vibrio, Enterobacter, Achromobacter,Flavobacterium,Micrococcus etc.  B preservation by freezing Freezing- lowering of temperature of food to -20°C and storage at same temperature At this temperature the water in food as well as in microorganism is converted to ice crystals which affect fluidity of cell This ensures prolonged shelflife as microbial activity is completely stopped at this temperature condition.  Freezing is achieved by -Quick freezing: where temperature is Iowered to -20°C within 30 min - Slow freezing: where temperature is lowered to -20°C within 3*72 hours Quick freezing is more advantageous than slow freezing During freezing water in food is converted to ice crystals of variable size. Freezing also brings about changes in properties of food such as pH, titratable acidity, ionic strength, viscosity, osmotic pressure, freezing point, O/R potential etc Comparison of effect of freezing methods on microorganisms Slow freezing Quick freezing Large ice crystals formed Small ice crystals formed Break down of metabolic rapport Suppresses microbial metabolism and causes cell damage Longer exposure to injurious factors Brief exposure to adverse conditions Gradual adaptation No adaptation to low temperature No thermal shock effec Causes thernmal shock to microbes Accumulation of concentrated No protective effect  Shelf life of frozen foods Frozen foods storage-lose original flavor and texture after thawing Freezer life for frozen foods is determined ,based on texture, flavor, tenderness color and nutritional quality upon thawing and cooking Freezer life of frozen stored food does not depend on microbiology of frozen foods  Effect of freezing on microorganisms Freezing causes sudden mortality immediately on freezing, varying with microbial species The surviving microorganisms die when stored in frozen condition Decline in microbial number is rapid at temperature below freezing point (-2°C) than at lower temperature, and is slow below- 20°C Cocci are more resistant than Gram negative bacteria  Removal of microorganisms (a) Filtration The only successful method for complete removal by using a pre- sterilized filters e.g. in fruit juices, soft drinks and water (b) Centrifugation Not very effective because not all microorganisms are removed, examples: Treatment of drinking water- remove heat resistant bacteria from milk  Removal of microorganisms (c) Washing Especially helpful in removing soil microorganisms from fresh fruits and vegetables that may be resistant to heat process during canning.- water not contaminator (d) Trimming Trim away spoiled portions of a food Food preservation in high temperatures Temperature and time used in heat processing will depend on : (a) The effect of heat on the food (b) Other preservative methods employed Treatment. Classification of heat treatments used on foods (a) Pasteurization (below 100°C) (b) Heat at 100°C  Pasteurization Pasteurization is important when: a) Heat treatment will not harm the quality of product (b) Main spoilage microbes are not very heat resistant e.g. yeast in fruit juices (c) Kill pathogens (d) Any Surviving organisms will be treated with other preservative methods. (e) Competing organisms are to be killed, allowing a desired fermentation  b) Heating at about 100° Sufficient to kill all microbes but not spores, Many acid foods are successfully preserved at100 C. Methods Boiled Immersion Baking Simmering Roasting Frying Blanching Exposure to flowing steam  C) Heating above 100C 121 °C. 1 atm. Commercial sterility: include heating foods at high temperature for short time e.g. ultra heat treatment..All commercially sterile foods should be stored in cool, dry, place to prevent any viable thermophilic spores from germinating and cause, spoilage to the foods. Ultra Heat Treatment: Treatment of milk by heating at 150C by steam injection followed by 'Flash evaporation' of the condensed steam.  Objective of heating foods (a) To destroy pathogens and spoilage microorganisms (b) To destroy toxin present in foods (c) To destroy the vegetative cells and spores of yeast, bacteria and moulds (d) To destroy undesirable enzymes this can affect the quality of foods. (e) To control the growth of surviving microorganisms (f ) To retain the acceptance and nutritional quality of foods (g) To reduce competition  Canning process.Preservation of foods in sealed containers followed by application of heat treatment. Canning (also known as hermetically sealed containers) is done in tin cans, glass containers, aluminum and plastic pouches  Types of spoilage in canned food depends on the type of :microorganisms involved 1. Thermophilic bacteria and spores These bacteria can cause 3 types of spoilage especially when cans are kept at > 43C. (a) "Flat-sour" spoilage (b) Thermophilic Anaerobe Spoilage (c) Sulphide stinker spoilage  Mesophilic bacteria.2 (a) Bacillus spp. (b) Clostridium spp. e.g.: C. sporogenes. 3. Non-spore forming bacteria E.g. Streptococcus, micrococcus etc. which will produce acid and gas. 4. Moulds and Yeasts can be killed by mild heat Drying and smoking A. Drying Methods which lower the water content of food to a point where the activities of enzymes and food spoilage and food poisoning microorganisms are destroyed inhibited. The lower the water activity of food, the greater is the inhibition. If Aw is between 0.75 -0.70, the spoilage is delayed. If Aw is 0.65, the spoilage is most unlikely to ocur up to 2 years. Molds and yeasts are more important in spoilage dried foods since bacteria require higher water content for growth. e. g. Streptom yces rouxii Aw 0.65 Aspergillus glaucus Aw 0.60  B. Smoking Heating foods using smoke from various types of wood to preserve foods. The smoke produces heat which kills some microorganismns on the surface Heat also reduces the Aw. It also has an antimicrobial compounds e.g. formaldehyde which can inhibit the growth of some microorganisms. The presence of aromatic compounds will also give a distinctive flavor and around to the food. This will make the foods taste better and more tender e.g. smoked fish. Woodsmoke is more effective against vegetative cells than against bacterial spores. food technology in meat, poultry,and fish The edible flesh of animals, poultry and fish eatenby humans Important part of the human diet Meat remains popular in the diet Origin of meat Structure of meat Muscle fibre Fatty tissue bone  food technology in meat, poultry ,and fish collagen A long stiff protein that is made up of three separate molecules composed of amino acid These are twisted chains The more collagen the tougher the piece of meat. Elastin A protein found in connective tissue, similar to collagen proteins Organic compounds made up of amino acids essential for the body  Extractive Chemical elements of meat that dissolve when cooking. The distribution of fat throughout a piece of Meat Quality of meat Factors contributing to the tenderness of meat include Age of animal younger are more tender as they have done less exercise Part of the animal used greater muscle used the tougher the piece of meat  Extractive Fat content Areas of large amounts of fat tend to be tougher than an even distrubtion. Sex Older non castrated males have a stronger flavour compared to desexed males and females  Extractive Treatment of animal before slaughter Stress= negative impact on meat and impacts on the aging process Treatment of carcass after slaughter Meat must be hung straight after slaughter allowing the enzymes to soften muscle tissue  Selecting meat for optimal quality The following should be considered when purchasing and storing meat Appearance Meat should look moist, not dry and be bright in color Aroma Should smell fresh Do not purchase meat that has a strong or unpleasant aroma  Selecting meat for optimal quality Texture Fresh meat should look and feel moist Not slimy or sticky Storage Raw meat should be covered, kept away from other foods and either refrigerated or frozen. Do not buy meat that has been handled incorrectly or is room temperature  Physical Properties Physical characteristics of all meat should include specific color Beef red Veal pale pink Lamb bright pink Mutton dark red Chemical Properties Meat is an excellent source of Protein Iron But is also high in saturated fats  ?.Why we cook meat 1.to kill bacteria 2. improving the flavour 3.making it easier to chew. 4.When meat is cooked the muscl fibres Denature 5.Permanent structural change of the protein molecules. 6.Occurs by the application of heat. 7.Mechanical actions 8. Additions of enzymes.  ?.Why we cook meat Coagulation Permanent change in the protein from a liquid to a thick mass as a result of heat or acid. Millard reaction Dry heat is applied to protein and the browning in color is the result.  Characteristics of Poultry Meat Muscle to bone ratio in the case of poultry is 1.8 thus the carcass yield is less as compared to other warm blooded animals Chicken meat is pinkish white in breast and wings and in other parts pink to light red. In general poultry meat is described as white meat while meat from other animals is called red meats. Total fat in chicken/broiler is 7.4g per 100 g portion of lean meat, of which is 27.53% saturated, 35.90% Mono-unsaturated and 22.81% Polyunsaturated fatty acids. The total conjugated linoleic acid (CLA) content of chicken and fresh ground turkey is 0.9 and 2.5 mg/g of fat respectively. On the other hand, typical composition chicken is moisture 73.7 %, protein 20-23% and fat 1.0%.  Preparation of Carcasses for Cooking Chicken is available either chilled or frozen state. Chilled Poultry should be kept uncooked, loosely wrapped and unfrozen in the refrigerator. It is good practice to wash the residues from the surface of the carcass before using  food technology in fish Fishes classified on the basis of their fat content as lean (less than 2 per cent fat), medium (2 to 5 percent ) and fat (more than5 per cent SEAFOOD-NUTRITIONAL BENEFITS High quality protein. High in omega-3 fatty acids Low in saturated fat Contributes to a healthy heart Contributes to proper growth and development of children. Source of vitamins and minerals  HEALTH BENEFITS- STRONG EVIDENCE Coronary heart disease. High blood pressure. Irregular heart beat Diabetes. Rheumatoid arthritis HIGH QUALITY PROTEIN Protein needed for growth and maintenance. Seafood contains all 9 essential amino acids. Protein is highly digestible  OMEGA-3 FATTY ACIDS Three types: Eicosapentaenoic acid (EPA). Docosahexaenoic acid (DHA) Alpha-linolenic acid (ALA) VITAMINS Source of B complex vitamins. Niacin, B12 and B6, Thiamin. MINERALS Excellent source of minerals Calcium, Iron Zine, Coppe, Potassium, lodine, Phosphorus, Selenium, Magnesium  Biscuit Production Process the main points and steps of the biscuit.manufacturing process Pre-Mixing: Making biscuits begins with.1 mixing all the ingredients in the correct consistency. Here, the pre-mixing stage includes dumping ingredients into the mixer.in the right order, quantity, and temperature Mixing : the dough starts to form, and the.2 liquid ingredients are introduced along with sugar to arrive at the desired consistency mixture. For short dough biscuits, less mixing.is performed for crispiness and fluffiness 3. Moulding : A biscuit's shape is determined in this step, which includes round, finger-shaped, square, oblong, flower, love, and more. This step is crucial since it divides the dough into desired weights and finishes as per the design. The moulding process starts with a knife between a forcing roller and a die. The knife control acts in four directions: down, up, forward, and back. The roller also comes with a press control on both sides.  Milling Operation 3. Purifying It consists of a long-oscillating sieve inclined downward,through which air current is passed in the direction of floor to ceiling. The number of purifiers may be up to 12 for a system with 4 break rolls. 4. Reduction These reduce the endosperm middling to flour size  Milling Operations 5. Scratching A scratch system is some times used as a standby to maintain proper release of endosperm from bran (standby to break and reduction system). 6. Entoleter acts like a detacher and increases the yield of flour. The machine consists of a disc with concentric rings rotating at high speed. If any living matter (insects, fungi) is present, it gets killed because of the centrifugal force. This machine avoids the use of chemicals to control the organisms..  Milling Operations 7.Air classification The product is separated in air classifiers in to their constituent fractions varying in protein content. Air classification is relatively inexpensive and has certain advantages. *Manufacture of more uniform flours from different wheat. Increase of protein content in break flours and decrease of protein in cake and cookie flours. * Controlled particle size and chemical composition. Productiorof special flours fo spectal uses. 8. Conveying system Development of pneumatic conveying was an important advantage for the milling industry. Vacuum is applied using pumps or fans. Besides transportation an intake through roller mills keeps rolls and flour cool during grinding. This milling process is applied for hard wheat.  Fruits and Vegetables Technology General properties What is Fruit? Fruit as a dessert item, is the mature ovaries of plants with their seeds. What are Vegetables? Those plant items that are generally eaten with the main course of a meal are considered to be vegetables. Groups of Fruits and Vegetables They They commonly are grouped into several major divisions, depending principally upon botanical structure, chemical composition and climatic requirements.  Chemical composition of fruits and vegetables.Water. 1.Mineral substances.2 Carbohydrates.3 Fat.4 Organic acids.5 Nitrogen-containing substances.6 Vitamins.7 Enzyme.8 Pectin.9  PHYSICO-CHEMICAL PROPERTIES OF MILK Physical state Refractive index Specific heat Acidity & pH Electrical conductivity Density & specific gravity Dxidation-reduction potential ……Cont Colour Bailing point Flavour Freezing point Viscosity Surface tension  Importance of properties Helps in detection of adulteration. Helps in determining quality of milk. Helps in processing ot milk & milk products. Helps in evaluating physical changes in milk & milk products during processing  Physical state of milk In milk water is present as continuous phase in which other Constituents are either dissolved or Suspended. Lactose and Portion of mineral salts form Solution. O Pratein and Remainder of minerals form Colloida. Fat forms Emulsion  Acidity and pH of milk (a) Natural or apparent acidity (b) Developed acidity or real acidity Titratable acidity = DA O.13 to U.14 % Cow milk 0.14 to 0.15 % Buffalo milk  ……Cont Casein, acid phosphate, citrates, whey proteins, CO2 etc of milk givesNA Produced Lactic acid fram Lactose by LAB gives- DA TA is measured in terms of present % Lactic acid pH of fresh milk 6.4 to 6.6-Cow milk to 6.8- Buffalo milk 6.7  Density and specific gravity D = Mass (Weight)/ Volume Specific gravity of milk Specific gravity of milk is lowered by addition of water and cream and increased by addition of skim milk or removal of fat. Color of milk Color ranges fram yellowish creamy white (cow milk) to creamy white (butfalo milk). Flavor of milk Flavor is composed of small (odor) and taste. Flavor of milk is a blend of the sweet taste of lactose and salty taste of minerals. Viscosity Viscosity is the resistance to flow Milk: 1.5-2.0 cp at 20°C Surface tension Surtace tension affected by fat content i.e. addition of fat. Milk: 50 dynes /cm at 20 °C Refractive Index Refractive Index is the measure of change in direction of light beam in a medium. Milk 1.344 to 1.348 Specific Heat specific heat milk 0.938 cal at 15 °C Electrical conductivity milk (sp.conductance) 4.2 to 6.9 Oxi- Red potential Milk +0.2 to 0.3 ev Boiling point Milk 100.17°C Freezing point milk 0.525 °C to 0.565 °C  isoelectric point of milk That pH value is known as the isoelectric point (IEP) of the protein and is generally the pH at which the protein is least soluble. For casein, the IEP is approximately 4.6 and it is the pH value at which acid casein is precipitated. In milk, which has a pH of about 6.6, the casein micelles have a net negative charge and are quite stable. During the addition of acid to milk, the negative charges on the outer surface of the micelle are neutralized (the phosphate groups are protonated), and the neutral protein precipitates TYPES OF MICROORGANISMS IN MILK Bacteria Yeasts Moulds Bacteriophagess Biochemical activities Temperature response Ability to cause infection and disease.  Heat treatment Thermisation Thermisation is the mildest heat treatment given to milk. It is used to extend the keeping quality of raw milk when it is known that raw milk may be held chilled for some time, prior to being further processed. The aim is to reduce the growth of psychrotrophic bacteria, which may release heat-resistant proteases and lipases into the milk. These enzymes will not be totally inactivated during pasteurisation and may give rise to off-flavours if the milk is used for cheese or milk powders. Conditions used for thermisation are 57– 68◦C for 15 s, followed by refrigeration. Thermised raw milk can be stored at a maximum of 8◦C for up to 3 days (IDF, 1984). The milk should also be phosphatase-positive in order to distinguish it from pasteurised milk, which is phosphatase-negative. It is usually followed later by pasteurisation or a more severe heat treatment  Pasteurisation Pasteurisation is a heat treatment aimed at reducing the number of any harmful micro- organisms in milk and liquid milk products, if present, to a level at which they do not constitute a significant health hazard. In addition, it results in prolonging the keepa- bility of milk or the liquid milk product and in only minimal chemical, physical and organoleptic changes. Pasteurisation conditions are designed to effectively destroy the organisms (Mycobacterium tuberculosis and Coxiella burnetti).  Pasteurisation of milk and cream results in a negative alkaline phosphatase reaction immediately after the treatment. For milk, the minimum pasteurisation conditions are those having bactericidal effects equivalent to heating every particle of the milk to 72◦C for 15 s (continuous flow pasteurisation) or 63◦C for 30 min (batch pasteurisation). Other equivalent conditions can be obtained by plotting a line joining these points on a log time versus temperature graph. Factors affecting the quality of pasteurised milk The main control points for ensuring good quality pasteurised milk products are raw milk quality, - processing conditions: temperature and holding time, - post-processing contamination (PPC) and - storage temper.  Sterilisation Sterilisation of milk to enable it to be kept at room temperature for several months became a commercial proposition in 1894. Milk can either be sterilised in bottles or other sealed con- tainers, or by continuous UHT processing followed by aseptic packaging (see below). Very good accounts of the procedures for producing in-container sterilised milk and problems associated with it have been provided by Cronshaw (1947) and Davis (1955). From a safety standpoint, the primary objective is the production of commercially sterile products with an extended shelf life. The main concern is inactivation of the most heat- resistant pathogenic spore, namely Clostridium botulinum. Since milk is a low-acid food (pH > 4.5), the main criterion is to achieve 12 decimal reductions of Cl. botulinum. This occurs when a product is heated at 121◦C for 3 min, at its slowest heating point (Anony- mous, 1991). The microbial severity of an in-container sterilisation process is traditionally expressed in terms of its Fo value. This takes into account the contributions of the heating, holding and cooling periods to the total lethality and is expressed in terms of minutes at 121◦C. It provides a useful means of comparing processes.  In-container sterilisation Foods have been sterilised in sealed containers, such as cans, for over 200 years. Milk was originally sterilised in glass bottles sealed with a crown cork, but more recently, plastic bottles have been used. Milk sterilisation really developed after 1930 with the advent of the crown cork, which helped with the mechanisation of the bottle-filling process, and the reuse of bottles. In general, the basic principles have remained the same. The main aim is to inactivate heat-resistant spores, thereby producing a product whichis ‘commercially sterile’, with an extended shelf life. Practical drawbacks of in-container sterilisation processes are that the product heats and cools relatively slowly, and that tem- peratures are limited by the internal pressure generated. However, many dairy products are still produced this way worldwide, including sterilised milk, evaporated milk and canned desserts such as custard and rice pudding  Ultra High Temperature Methods of UHT processing There are two major types of direct heating UHT systems known as steam injection (steaminto milk) and steam infusion (milk into steam)In the former, superheated steam is ‘injected’ into a stream of milk, while in the latter, milk is sprayed into or allowed to fall as a thin film or fine streams, through a chamber of superheated steam. A major feature of these two systems is the almost instantaneous rise in the temperature of the milk from preheat to sterilisation temperature through the transfer of the latent heat of vaporisationof the steam to the milk. indirect heating In indirect heating using PTEs or THEs, the heating medium is either steam or superheated water. When water is used, it flows in the reverse direction to that of the milk. The reverse flow minimises the temperature differential between the two liquids and, in turn, minimises the amount of burn-on. Hot water is a significantly better heating medium than steam with respect to burn-on and flavour of the product as it enables a smaller temperature differential  Factors affecting the quality of UHT milk. Raw milk quality is affected by: (a) growth of psychrotrophic bacteria and (b) heat- resistant spore-forming bacteria.  Dairy Processing Storage for Grade A raw milk for pasteurization, ultrapasteurization or aseptic processing (PMO) - Temperature: 45°F or less within 2 h after milking - Bacterial counts: