Powder It is a manufactured product produced by removal of water from whole, skim milk, , milk, and to lesser extend . Dried dairy products have even greater amounts of water removed to usually less than 4%. Purposes of drying milk Drying of milk is to preserve it; where, milk powder has a far longer than liquid milk and does not need to be refrigerated, due to its low moisture content. Another purpose is to reduce its bulk for economy of transportation. So it is easy to supply the places where the fersh milk out of reach of many. Composition of some types of milk powder:

Constituents

Milk powder Prepared from

Whole milk

Skim milk

Whey SweetCream

Fat 26 1 1 5 Milk Powder

62

Lactose 38 51 72-47 46 19.5 27 0.6 26 Other proteins 5.3 6.6 8.5 8 Ash 6.3 8.5 8 8 Lactic acid — — 0.2-2 — Water 2.5 3 3 3 Manufacture of milk powder: There are tow methods of manufacture Spray methods or Roller methods. The steps of manufacture for both methods are summarized as follow: 1- Milk preparation: used for manufacture of milk powder must be of high quality, and pass by a series of physical, chemical, and bacteriological tests to ensure its quality. 2- Clarification, Separation and Standardization: Milk used in the production of milk powders is first clarified, standardized and separated into skim milk and cream using a centrifugal cream separator. Surplus cream is used to make butter or anhydrous milk fat. 3- Homogenization: It applied in case of whole milk powder, to prevent cream line formation and to decrease the free fat content in the reconstituted milk. 4- Preheating: The standardized milk is heated to temperatures of at 72 ْ C for 15 seconds. Preheating causes a controlled denaturation of the whey proteins in the milk and it destroys bacteria, inactivates enzymes, generates natural antioxidants and imparts heat stability. 5-Evaporation: In the evaporator the preheated milk is concentrated in stages or "effects" from around 9.0% total solids content for skim milk and 13% for whole milk, up to 45-52% total solids. This is achieved by boiling the milk under a vacuum at temperatures below 72C. More than 85% of the water in the milk may be removed in the evaporator. The milk is then evaporated prior to drying for the following reasons: less occluded air and longer shelf life for the powder viscosity increase leads to larger powder particles less energy required to remove part of water by evaporation; more economical 6- Drying process: Two methods are used for drying process either Spray or Roller methods. a) Spray drying: Spray drying is the most used method for producing milk powders. Milk is first concentrated in an evaporator to about 50% milk solids to increase the capasity of the dryer and to fasten drying as well as giving a fine texture to the produced milk powder. The resulting concentrated milk is sprayed into a heated drying chamber in a flow of hot air up to 130 C through nozzle where the water almost instantly evaporates, leaving fine particles of powdered milk solids. b) Roller drying: Alternatively, the milk can be dried by drum drying. Milk is applied as a thin film to the surface of a heated drum (130150 C), and the dried milk solids are then scraped off by mean of sharp knife ( scraping knife) in the form of a thin sheet, which is easily broken into flakes as it falls, then it ground into a powder using special brushes. Powdered milk made this way tends to have a cooked flavor, due to caramelization caused by greater heat exposure. 7- Packaging and storage: After drying, the powder must be packaged in containers able to provide protection from moisture, air, light, etc. There are two methods for packing either vacuum method or atmospheric method a)- Vacuum method The dried milk is packed into suitable containers, then the containers are introduced into a vacuum chamber to evacuate the air which is replaced by an inert gas as H2, N2, or Co2, then the containers are sealed. b)- Atmospheric method used only for roller dried milk with low fat content where the product is packed in sacs or barrels leaving no air inside the can. Whole milk powder can then be stored for long periods (up to about 6 months) of time at ambient temperatures. Comparison between roller and spray dried milk powder Characters Roller dried milk spray dried milk Shape of particles Solid mass irregular in shape and size Regular, spherical or oval particles, vary in size 66

Solubility degree Low (80-85%) High (95-99%) Bacterial content Not more than 5000/gm Higher about 20,000/gm Shelf life (Long) 6-14 months Short (4-10 months) Uses Manufacturing purposes Infant feeding Uses of milk powder: ● Powdered milk is frequently used in the manufacture of , confectionery such as and caramel, and in recipes for baked goods where adding liquid milk would render the product too thin. ● Powdered milk is also widely used in various sweets such as manufacture. ● In meat industry (susage). ●In animal feeding ( calves) Properties of milk powder 1- Color Normally it is of white color, but it may be yellow due to carotene content, or light brown due to high temperature in roller drying method. 2- Hygroscopic properties All dried milk products have the ability of taking up moisture from air unless sealed in air tight containers. 3- Solubility of milk powder it is the degree of dispersing the milk powder in water. The degree of solubility is depinding on methods of manufacture, where better solubility is obtained in case of milk prepared by spray method than that prepared by roller method. As well there are many factors render casein insoluble and thus it render milk powder insoluble and also can not pass through filter paper. Theses include: 1. High milk acidity 2. High moisture content 3. Increase drying temperature 4. Aging of milk powder 4- keeping quality Milk powder produced by roller method has a longer keeping quality than that produced by spray method. Reconstitution of milk powder 1 part milk powder + 7 parts of water ( The temperature of water used is 20ْ C for spray milk powder & 85ْ C in roller milk powder ). Defects of milk powder 1- Flavour defects aym abnormal flavour in the raw milk used for manufacture may appear in the produced milk powder. So raw milk must be examined and must be of good keeping quality. a)- Oxidizied flavour (Tallowness) It appears in full cream milk powder due to oxidation of fat. Spray milk powder oxidized more rapidly than roller milk powder, due to presence of air inside the particles. b)- Fishy flavour (Fishness) It is due to hydrolysis and oxidation of lecithin into trimethylamin in milk powder containgn high moisture content (above 3.5%). c)- Stale flavour (Old or musty flavour) Occur mostly in skim milk powder due to: ■ High storage temperature ■ Increase moisture contented)- Rancidity Occure in whole milk powder due to the action of lipase enzyme on milk fat either from raw milk or due to lipolytic microorganisms befor preheating process. 2- Texture defect (Agglomeration) It found in milk powder containgn high moisture content (above 5%) where the powder agglomerated toghether forming hard lump. 3- Colours defect Dark brown specks is a common defect in case of roller method as a result of high temperature of the drum. Prevention and control measures to prevent defects in milk powder 1- Milk powder should be of low moisture content les than 3% 2-Efficient preheating process 3- Efficent canning and sealing process 4- Milk powder should be storde in good place and low temperature Instant milk powder After adding water the powder should be reconstituted completely and readily to a homogeneous mixture. Complete reconstitution means that no undissolved pieces or flakes are left and that neither butter grains nor oil droplets appear on top of the solution. In the ideal situation the powder will disperse rapidly when scattered on cold water within few second; this is called instant powder. Special processing steps are needed to achieve this property. Instant milk powder is produced by partially rehydrating the dried milk powder particles causing them to become sticky and agglomerate. The water is then removed by drying resulting in an increased amount of air incorporated between the powder particles. Microbiology of milk powder in dried milk products the low available water acts as the inhibitory factor with respect to any bacterial spores or vegetative cells that have survived the drying process. Preheating of milk destroy the pathogenic microorganisms and minimize the number of nonpathogenic microorganisms. The bacteria present in milk powder depends on: 1- Raw milk especially Thermoduric bacteria that survive pasteurization temperature. 2- Growth of microorganism during processing e.g: Streptococcus durans, and Bacillus stearothermophilus var calidolactis. 3- Accidental contamination can occure by Staphylococcus aureus and E. coli. Process flow diagram for manufacture of milk powder Raw milk produced under normal conditions develops acidity. It has long been recognized that highly acid milk does not putrefy. Therefore, allowing milk to develop acidity naturally preserves the other milk constituents. Bacteria in milk are responsible for acid development. They produce acid by the anaerobic breakdown of milk carbohydrate () to lactic acid and other organic acids. The conversion of carbohydrate to organic acids or alcohols is called fermentation. Nutritive value of fermented milk * Easy digested than ordinary milk due to desirable bacterial activity * It used as a therapeutic as in case of stomach and intestinal disorders, this is due to production of lactic acid as a results of lactose fermentation by lactic acid bacteria. Theses create unfavorable condition for putrefactive bacteria that decompose protein. So it prevents auto-oxidation. * : Lactose-intolerant users can digest yoghurt much better than plain milk. The lowered lactose content of yoghurt plays a part. In addition, other factors must exist that cause easier digestion of lactose. Fermented Alternatively, the depletion of the stomach contents into the duodenum may be retarded when fermented milks are consumed; thereby, the contact time of lactose hydrolyzing enzymes with the substrate would be extended, resulting in a better digestion of lactose. * Acid medium created by consumption of fermented milk help in phosphorus and calcium absorption. * The pathogenic microorganisms cannot survive in presence of acid. Where the consumption of fermented milks causes a smaller increase of the pH of the stomach contents and thereby diminishes the risk of passage of pathogens. This is of particular importance for people suffering from a weakened secretion of gastric juice, e.g., many elderly people and babies. Types of fermented milk 1) Cultured Butter milk 2) Acidophilus milk 3) Fermented skim milk 4) Kumiss 5) 6) Bulgaricus milk 7) Yoghurt (Zabadi) 1) Cultured Butter milk This product was originally the fermented by product of butter manufacture, but today it is more common to produce cultured butter milks from skim or whole milk. The culture most frequently used is S. lactis, S. cremoris. Milk is usually heated to 95°C and cooled to 20-25°C before the addition of the starter culture. Starter is added at 1-2% and the fermentation is allowed to proceed for 16-20 hours, to an acidity of 0.9% lactic acid. This product is frequently used as an ingredient in the baking industry, in addition to being packaged for sale in the retail trade. 2) Acidophilus milk Acidophilus milk is traditional milk fermented with Lactobacillus acidophilus, which has been thought to have therapeutic benefits in the gastrointestinal tract. Skim or whole milk may be used. The milk is heated to high temperature 95°C for 1 hour, to reduce the microbial load and favour the slow growing Lactobacillus acidophilus culture. Milk is inoculated at a level of 2-5% and incubated at 37°C until coagulated. Some acidophilus milk has acidity as high as 1% lactic acid, but for therapeutic purposes 0.60.7% is more common.

3) Fermented skim milk It is by product, which results from manufacture of cream by gravity method (natural fermentation). 4) Kumiss It is traditionally prepared from mare's milk which contains high lactose content that favour alcoholic fermentation. Kumiss contains 3% alcohol and 1% lactic acid. It can be prepared from cow's milk after addition of 5% sugar and yields kumiss of 1% alcohol. Starters used are lactose fermenting yeasts and lactic acid bacteria (S. lactis and Lactobacillus bulgaricus). 5) Kefir Fermented milk prepared from whole or skim milk after homogenization, pasteurization and addition of starters called Kefir grains which consists of a mixture of: ● Strept casei. ● Lactobacillus bulgaricus ● Lactose fermenting yeasts (Saccharomyces kefir) Kefir grains: are irregular granules in which bacteria and yeasts grow, when they are incubated into milk the microorganisms on the granules bring about the fermentation. The combination between bacteria and yeasts enhance alcoholic fermentation with production of (alcohol 1% and lactic acid 1%). It classified into light, medium and strong kefir according to the time of incubation and amount of alcohol and acid production. 6) Bulgaricus milk As acidophilus milk in its preparation, and Lactobacillus bulgaricus used as a starter. 7) Yoghurt (Zabadi) Yoghurt is fermented milk prepared from whole milk, partially , skim milk or cream may be used. Although milk of various animals has been used for production in various parts of the world, most of the industrialized yogurt production uses cow's or buffaloes milk. In order to ensure the development of the yoghurt culture the following criteria for the raw milk must be met: low bacteria count free from antibiotics, sanitizing chemicals, mastitis milk, , and rancid milk no contamination by bacteriophages Composition of yoghurt: Fat 2-3.5% Protein 4% Lactose 5% Acidity 0.85-0.95% PH 4.4-4.5 Manufacture of yoghurt - The milk is clarified and separated into cream and skim milk, then standardized to achieve the desired fat content. - The milk is then pasteurized using a continuous plate heat exchanger for 30 min at 85° C or 10 min at 95° C. These heat treatments, which are much more severe than fluid milk pasteurization, are necessary to achieve the following: Produce a conducive environment for the starter culture Denature and coagulate whey proteins to enhance the viscosity and texture Minimize total bacterial count and destroy pathogenic microorganisms - Milk then cooled to an optimum growth temperature at 40°C. - The yogurt starter culture is added (2-3%) of mixed culture of Streptococcus thermophilus and Lactobacillus bulgaricus (1:1) are added to the jacketed fermentation tank and evenly distributed, then filled in containers (bottles or ) - A temperature of 43°C is maintained for 4-6 h till coagulation occurs. - The coagulated product is cooled to 5°C, depending on the product. Fruit and flavor may be incorporated at this time, and then packaged. - The product is now cooled and stored at refrigeration temperatures (5°C) to slow down the physical, chemical and microbiological degradation.

Manufacture of Zabadi The same as for yoghurt but the starter used is old zabady prepared a day before mixed with the boiled milk and left till coagulation occur. Defects of yoghurt 1- Excessive amount of whey: it is due to insufficient evaporation of milk resulting from low temperature of heating or short time during heating. 2- Excessive acidity: due to * Excessive starter * Long incubation period * Insufficient cooling * Storage at high temperature 3- Off taste due to * Excessive acidity * Insufficient heating * Undesirable bacteria (proteolytic, and coliforms) * Contaminated starter Yogurt Products There are two types of plain yogurt: Stirred style yogurt Set style yogurt The above description is essentially the manufacturing procedures for stirred style. In set style, the yogurt is packaged immediately after inoculation with the starter and is incubated in the packages. Other yogurt products include: ● Fruit-on-the-bottom style: Fruit mixture is layered at the bottom followed by inoculated yogurt, incubation occurs in the sealed cups ● Soft-serve and Hard Pack ● Continental, French, and Swiss: Stirred style yogurt with fruit preparation Yogurt Beverages Drinking yogurt is essentially stirred yogurt which has total solids content not exceeding 11% and which has undergone homogenization to further reduce the viscosity; Flavoring and coloring are invariably added. Heat treatment may be applied to extend the storage life. High Temperature Short Time (HTST) pasteurization with aseptic processing will give a shelf life of several weeks at 2- 4°C, which UHT processes with aseptic packaging will give a shelf life of several weeks at room temperature. Microbiology of yoghurt Presence of microorganisms depending on ● Raw milk contamination ● Contaminated starters ●Post manufacture contamination Yoghurt has been reported to transmitte diseases of human origin as well as enterotoxins of Staph. aureus.