DAIRY TECHNOLOGY LECTURE.pdf

DAIRY PRODUCTS TECHNOLOGY milk and milk‐derived food products Milk is the first food of young mammals produced by the mammary glands of female mammals. It is a mixture of fat and high‐quality protein in water and contains some carbohydrate (lactose), vitamins, and minerals. Milk and mil...

DAIRY PRODUCTS TECHNOLOGY milk and milk‐derived food products Milk is the first food of young mammals produced by the mammary glands of female mammals. It is a mixture of fat and high‐quality protein in water and contains some carbohydrate (lactose), vitamins, and minerals. Milk and milk products may be obtained from different species, such as goats and sheep. While fluid milk contains a very large percentage of water, it may be concentrated to form evaporated milk and cheeses. Throughout the world, it is used in a variety of ways, such as a beverage, cheese, yogurt, or in soups and sauces. 600 x Structure of a casein micelle. (A) The exact structure of casein micelles remains unknown, but they are thought to be made of many smaller “submicelles” held together by a calcium phosphate. (B) Short negatively charged regions of casein proteins (“protruding chains”) are exposed all over the surface of the micelle. (C) An electron micrograph of a single casein micelle; scale bar represents 100nm. A second protein fraction of milk is the whey or serum. It makes up approximately 20% of milk protein and includes the lactalbumins and lactoglobulins. Whey proteins are more hydrated than casein and are denatured and precipitated by heat rather than by acid. 23 GENEREL MILK PROCESSING 28 30 Separation Centrifuges can be used to separate the cream from the skim milk. The centrifuge consists of up to 120 discs stacked together at a 45 to 60 degree angle and separated by a 0.4 to 2.0 mm gap or separation channel. Milk is introduced at the outer edge of the disc stack. The stack of discs has vertically aligned distribution holes into which the milk is introduced. Under the influence of centrifugal force the fat globules (cream), which are less dense than the skim milk, move inwards through the separation channels toward the axis of rotation. The skim milk will move outwards and leaves through a separate outlet Standardization The streams of skim and cream after separation must be recombined to a specified fat content. This can be done by adjusting the throttling valve of the cream outlet; if the valve is completely closed, all milk will be discharged through the skim milk outlet. As the valve is progressively opened, larger amounts of cream with diminishing fat contents are discharged from the cream outlet. With direct standardization thecream and skim are automatically remixed at the separator to provide the desired fat content Pasteurization The process of pasteurization was named after Louis Pasteur who discovered that spoilage organisms could be inactivated in wine by applying heat at temperatures below its boiling point. The process was later applied to milk and remains the most important operation in the processing of milk. Definition: The heating of every particle of milk or milk product to a specific temperature for a specified period of time without allowing recontamination of that milk or milk product during the heat treatment process. Purpose There are two distinct purposes for the process of milk pasteurization: 1-Public Health Aspect - to make milk and milk products safe for human consumption by destroying all bacteria that may be harmful to health (pathogens) 2-Keeping Quality Aspect - to improve the keeping quality of milk and milk products. Pasteurization can destroy some undesirable enzymes and many spoilage bacteria. Shelf life can be 7, 10, 14 or up to 16 days. Typical Pasteurization Regulations Milk: 63° C for not less than 30 min., 72° C for not less than 16 sec., or equivalent destruction of pathogens and the enzyme phosphatase as permitted by Milk is deemed pasteurized if it tests negative for alkaline phosphatase. Frozen dairy dessert mix (ice cream or ice milk, egg nog): at least 69° C for not less than 30 min; at least 80° C for not less than 25 sec; other time temperature combinations must be approved (e.g. 83° C/16 sec). Milk based products- with 10% mf or higher, or added sugar (cream, chocolate milk, etc) 66° C/30 min, 75° C/16 sec Methods of Pasteurization There are two basic methods, batch or continuous. Batch method The batch method uses a vat pasteurizer which consists of a jacketed vat surrounded by either circulating water, steam or heating coils of water or steam. The hatched area in the graph above represents the area under the time temperature curve that is taken into consideration for thermal lethality calculations. UHT Processing While pasteurization conditions effectively eliminate potential pathogenic microorganisms, it is not sufficient to inactivate the thermoresistant spores in milk. The term sterilization refers to the complete elimination of all microorganisms. The food industry uses the more realistic term "commercial sterilization"; a product is not necessarily free of all microorganisms, but those that survive the sterilization process are unlikely to grow during storage and cause product spoilage. The UHT process The major steps in a UHT process are as follows: Preheating, with or without a holding time Homogenisation (for indirect systems) Heating to sterilisation temperature Holding at sterilisation temperature Initial cooling Homogenisation (alternative position for direct or indirect systems) Final cooling Aseptic packaging UHT PROCESSING Ultra‐high temperature processing, (less often) ultra‐heat treatment (both abbreviated UHT), or ultra‐pasteurization is the sterilization of food by heating it for an extremely short period, around 1–2 seconds, at a temperature exceeding 135°C (275°F), which is the temperature required to kill spores in milk. The most common UHT product is milk, but the process is also used for fruit juices, cream, soy milk, yogurt, wine, soups, and stews. UHT milk was invented in the 1960s, and became generally available for consumption in the 1970s. High heat during the UHT process can cause Maillard browning and change the taste and smell of dairy products. UHT milk has a typical shelf life of six to nine months, until opened. It can be contrasted with HTST pasteurization (high temperature/short time), in which the milk is heated to 72°C (161.6°F) for at least 15 seconds. UHT Methods There are two principal methods of UHT treatment: 1. Direct Heating 2. Indirect Heating Direct heating systems There are two methods of direct heating; 1. injection 2. infusion Injection: High pressure steam is injected into pre-heated liquid by a steam injector leading to a rapid rise in temperature. After holding, the product is flash-cooled in a vacuum to remove water equivalent to amount of condensed steam used. This method allows fast heating and cooling, and volatile removal, but is only suitable for some products. It is energy intensive and because the product comes in contact with hot equipment, there is potential for flavour damage. Infusion: Food in a free falling film is pumped into a chamber of high pressure steam. The time of the fall matches the desired holding time. The product, therefore, falls onto a cooled surface, followed by flash cooling in vacuum chamber. This method has several advantages: l instantaneous heating and rapid cooling l no localized overheating or burn-on l suitable for low and higher viscosity products Indirect heating systems The heating medium and product are not in direct contact, but separated by equipment contact surfaces. Several types of heat exchangers are applicable: plate tubular scraped surface Membrane Processing of milk Membrane processing is a technique that permits concentration and separation without the use of heat. Particles are separated on the basis of their molecular size and shape with the use of pressure and specially designed semi-permeable membranes. There are some fairly new developments in terms of commercial reality and is gaining readily in its applications: - proteins can be separated in whey for the production of whey protein concentrate (WPC) - milk can be concentrated prior to cheesemaking at the farm level Concentrated and Dried Dairy Products Fluid milk contains approximately 88% water. Concentrated milk products are obtained through partial water removal. Dried dairy products have even greater amounts of water removed to usually less than 4%. The benefits of both these processes include an increased shelf-life, convenience, product flexibility, decreased transportation costs, and storage. Concentrated Dairy Products l Evaporated Skim or Whole Milk l Sweetened Condensed Milk l Condensed Buttermilk l Condensed Whey Dried Dairy Products l Milk Powder l Whey Powder l Whey Protein Concentrates Milk Powder Milk used in the production of milk powders is first clarified, standardized and then given a heat treatment. This heat treatment is usually more severe than that required for pasteurization. Besides destroying all the pathogenic and most of the spoilage microorganisms, it also inactivates the enzyme lipase which could cause lipolysis during storage. 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 Whey Powder Whey is the by-product in the manufacturing of cheese and casein. Disposing of this whey has long been a problem. For environmental reasons it is no longer discharged into lakes and rivers; for economical reasons it is not feasible to use it as animal feed or fertilizer. Converting whey into powder has led to a number products that it can be incorporated into. Whey powder is essentially produced by the same method as other milk powders. Reverse osmosis can be used to partially concentrate the whey prior to vacuum evaporation. Before the whey concentrate is spray dried, Lactose crystallization is induced to decrease the hygroscopicity. This is accomplished by quick cooling in flash coolers after evaporation. Crystallization continues in agitated tanks for 4 to 24 h. A fluidized bed may be used to produce large agglomerated particles with free-flowing, non-hygroscopic, no caking characteristics Cheese Traditionally, cheese was made as a way of preserving the nutrients of milk. In a simple definition, cheese is the fresh or ripened product obtained after coagulation and whey separation of milk, cream or partly skimmed milk, buttermilk or a mixture of these products. It is essentially the product of selective concentration of milk. Thousands of varieties of cheeses have evolved that are characteristic of various regions of the world. Some common cheesemaking steps are: Treatment of Milk Additives Inoculation and Milk Ripening Coagulation enzyme acid heat-acid Curd Treatment Cheese Ripening Treatment of Milk for Cheesemaking Like most dairy products, cheesemilk must first be clarified, separated and standardized. The milk may then be subjected to a sub-pasteurization treatment of 63-65° C for 15 to 16 sec. This thermization treatment results in a reduction of high initial bacteria counts before storage. It must be followed by proper pasteurization. While HTST pasteurization (72° C for 16 sec) is often used, an alternative heat treatment of 60° C for 16 sec may also be used. This less severe heat treatment is thought to result in a better final flavour cheese by preserving some of the natural flora. If used, the cheese must be stored for 60 days prior to sale, which is similar to the regulations for raw milk cheese. Homogenization is not usually done for most cheesemilk. It disrupts the fat globules and increases the fat surface area where casein particles adsorb. This results in a soft, weak curd at renneting and increased hydrolytic rancidity. Inoculation and Milk Ripening The basis of cheesemaking relies on the fermentation of lactose by lactic acid bacteria (LAB). LAB produce lactic acid which lowers the pH and in turn assists coagulation, promotes syneresis, helps prevent spoilage and pathogenic bacteria from growing, contributes to cheese texture, flavour and keeping quality. LAB also produce growth factors which encourages the growth of non-starter organisms, and provides lipases and proteases necessary for flavour development during curing. Further information on LAB and starter cultures can be found in the microbiology section. After innoculation with the starter culture, the milk is held for 45 to 60 min at 25 to 30° C to ensure the bacteria are active, growing and have developed acidity. This stage is called ripening the milk and is done prior to renneting. Milk Coagulation Coagulation is essentially the formation of a gel by destabilizing the casein micelles causing them to aggregate and form a network which partially immobilizes the water and traps the fat globules in the newly formed matrix. This may be accomplished with: * enzymes *acid treatment *heat-acid treatment Enzymes Chymosin, or rennet, is most often used for enzyme coagulation. Acid Treatment Lowering the pH of the milk results in casein micelle destabilization or aggregation. Acid curd is more fragile than rennet curd due to the loss of calcium. Acid coagulation can be achieved naturally with the starter culture, or artificially with the addition of gluconodeltalactone. Acid coagulated fresh cheeses may include Cottage cheese, Quark, and Cream cheese. Heat‐Acid Treatment Heat causes denaturation of the whey proteins. The denatured proteins then interact with the caseins. With the addition of acid, the caseins precipitate with the whey proteins. In rennet coagulation, only 76‐78% of the protein is recovered, while in heat‐acid coagulation, 90% of protein can be recovered. Examples of cheeses made by this method include Paneer, Ricotta and Queso Blanco. Curd Treatment After the milk has gel has been allowed to reach the desired firmness, it is carefully cut into small pieces with knife blades or wires. This shortens the distance and increases the available area for whey to bereleased. The curd pieces immediately begin to shrink and expel the greenish liquid called whey. This syneresis process is further driven by a cooking stage. The increase in temperature causes the protein matrix to shrink due to increased hydrophobic interactions, and also increases the rate of fermentation of lactose to lactic acid. The increased acidity also contributes to shrinkage of the curd particles. The final moisture content is dependent on the time and temperature of the cook stage. This is important to monitor carefully because the final moisture content of the curd determines the residual amount of fermentable lactose and thus the final pH of the cheese after curing. When the curds have reached the desired moisture and acidity they are separated from the whey. The whey may be removed from the top or drained by gravity. The curd-whey mixture may also be placed in moulds for draining. Some cheese varieties, such as Colby, Gouda, and Brine Brick include a curd washing which increases the moisture content, reduces the lactose content and final acidity, decreases firmness, and increases openness of texture. Curd handling from this point on is very specific for each cheese variety. Salting may be achieved through brine as with Gouda, surface salt as with Feta, or vat salt as with Cheddar. To acheive the characteritics of Cheddar, a cheddaring stage (curd manipulation), milling (cut into shreds), and pressing at high pressure are crucial. Cheese Ripening Except for fresh cheese, the curd is ripened, or matured, at various temperatures and times until the characteristic flavour, body and texture profile is achieved. During ripening, degradation of lactose, proteins and fat are carried out by ripening agents. The ripening agents in cheese are: bacteria and enzymes of the milk lactic culture rennet lipases added moulds or yeasts environmental contaminants Thus the microbiological content of the curd, the biochemical composition of the curd, as well as temperature and humidity affect the final product. This final stage varies from weeks to years according to the cheese variety. Cheddar  Ice Cream Formulations l Milkfat: >10% - 16% l Milk solids-not-fat: 9% - 12% l Sucrose: 10% - 14% l Corn syrup solids: 4% - 5% l Stabilizers: 0% - 0.4% l Emulsifiers: 0% - 0.25% l Water: 55% - 64% Butterfat Butterfat is important to ice cream for the following reasons: * increases the richness of flavour in ice cream * produces a characteristic smooth texture by lubricating the palate * helps to give body to the ice cream * aids in good melting properties * aids in lubricating the freezer barrel during manufacturing (Non-fat mixes are extremely hard on the freezing equipment) The limitations of excessive use of butterfat in a mix include: * cost * hindered whipping ability * decreased consumption due to excessive richness l high caloric value Milk Solids-not-fat The serum solids or milk solids-not-fat (MSNF) contain the lactose, caseins, whey proteins, minerals, and ash content of the product from which they were derived. They are an important ingredient for the following reasons: * improve the texture of ice cream * help to give body and chew resistance to the finished product * are capable of allowing a higher overrun without the characteristic snowy or flaky textures associated with high overrun * may be a cheap source of total solids The best sources of serum solids for high quality products are: * concentrated skimmed milk * sweetened condensed whole or skimmed milk * superheated condensed skimmed milk * frozen condensed skimmed milk * spray process low heat skimmilk powder Stabilizers The stabilizers are a group of compounds, usually polysaccharides, that are responsible for adding viscosity to the unfrozen portion of the water and thus holding this water so that it cannot migrate within the product. This results in an ice cream that is firmer to the chew. Without the stabilizers, the ice cream would become coarse and icy very quickly due to the migration of this free water and the growth of existing ice crystals. The stabilizers in use today include: Carboxymethyl cellulose (CMC): derived from the bulky components, or pulp cellulose, of plant material Locust Bean Gum: soluble fibre of plant material derived from the beans of exotic trees grown mostly in Africa (Note: locust bean gum is a synonym for carob bean gum, the beans of which were used centuries ago for weighing precious metals, a system still in use today, the word carob and Karat having similar derivation) Guar Gum: from the guar bush, a member of the legume family grown in India for centuries and now grown to a limited extent in Texas Carrageenan: an extract of Irish Moss or red algae, originally harvested from the coast of Ireland, near the village of Carragheen sodium alginate, an extract of another seaweed, brown kelp  Emulsifiers The original ice cream emulsifier was egg yolk, which was used in most of the original recipes. Today, two emulsifiers predominate most ice cream formulations: mono- and di-glycerides: derived from the partial hydrolysis of fats or oils of animal or vegetable origin Polysorbate 80: a sorbitan ester consisting of a glucose molecule bound to a fatty acid, oleic acid Other possible sources of emulsifiers include buttermilk, and glycerol esters. All of these compounds are either fats or carbohydrates, important components in most of the foods we eat and need. Together, the stabilizers and emulsifiers make up less than one half percent by weight of our ice cream Ice cream is both an emulsion and a foam. The milkfat exists in tiny globules that have been formed by the homogenizer. There are many proteins which act as emulsifiers and give the fat emulsion its needed stability. The emulsifiers are added to ice cream to actually reduce the stability of this fat emulsion by replacing proteins on the fat surface. When the mix is subjected to the whipping action of the barrel freezer, the fat emulsion begins to partially break down and the fat globules begin to flocculate or destabilize. The air bubbles which are being beaten into the mix are stabilized by this partially coalesced fat. If emulsifiers were not added, the fat globules would have so much ability to resist this coalescing, due to the proteins being adsorbed to the fat globule, that the air bubbles would not be properly stabilized and the ice cream would not have the same smooth texture (due to this fat structure) that it has. Butter Manufacture Butter is essentially the fat of the milk. It is usually made from sweet cream and is salted. However, it can also be made from acidulated or bacteriologically soured cream and saltless (sweet) butters are also available. Yogurt (also spelled yogourt or yoghurt) is a semi-solid fermented milk product which originated centuries ago in Bulgaria (????) It's popularity has grown and is now consumed in most parts of the world. Although the consistency, flavour and aroma may vary from one region to another, the basic ingredients and manufacturing are essentially consistent: Ingredients Although milk of various animals has been used for yogurt production in various parts of the world, most of the industrialized yogurt production uses cow's milk. Whole milk, partially skimmed milk, skim milk or cream may be used. In order to ensure the development of the yogurt culture the following criteria for the raw milk must be met: l low bacteria count l free from antibiotics, sanitizing chemicals, mastisis milk, colostrum, and rancid milk l no contamination by bacteriophages Other yogurt ingredients may include some or all of the following: Other Dairy Products: concentrated skim milk, nonfat dry milk, whey, lactose. These products are often used to increase the nonfat solids content Sweeteners: glucose or sucrose, high-intensity sweeteners (e.g. aspartame) Stabilizers: gelatin, carboxymethyl cellulose, locust bean Guar, alginates, carrageenans, whey protein concentrate Flavours Fruit Preparations: including natural and artificial flavouring, colour Starter Culture The starter culture for most yogurt production in North America is a symbiotic blend of Streptococcus salivarius subsp. thermophilus (ST) and Lactobacillus delbrueckii subsp. bulgaricus (LB). Although they can grow independantly, the rate of acid production is much higher when used together than either of the two organisms grown individually. ST grows faster and produces both acid and carbon dioxide. The formate and carbon dioxide produced stimulates LB growth. On the other hand, the proteolytic activity of LB produces stimulatory peptides and amino acids for use by ST. These microorganisms are ultimately responsible for the formation of typical yogurt flavour and texture. The yogurt mixture coagulates during fermentation due to the drop in pH. The streptococci are responsible for the initial pH drop of the yoğurt mix to approximately 5.0. The lactobacilli are responsible for a further decrease to pH 4.0. The following fermentation products contibute to flavour: l lactic acid l acetaldehyde l acetic acid l diacetyl 1. Adjust Milk Composition & Blend Ingredients Milk composition may be adjusted to achieve the desired fat and solids content. Often dry milk is added to increase the amount of whey protein to provide a desirable texture. Ingredients such as stabilizers are added at this time. 2. Pasteurize Milk The milk mixture is pasteurized at 185°F (85°C) for 30 minutes or at 203°F (95°C) for 10 minutes. A high heat treatment is used to denature the whey (serum) proteins. This allows the proteins to form a more stable gel, which prevents separation of the water during storage. The high heat treatment also further reduces the number of spoilage organisms in the milk to provide a better environment for the starter cultures to grow. Yogurt is pasteurized before the starter cultures are added to ensure that the cultures remain active in the yogurt after fermentation to act as probiotics; if the yogurt is pasteurized after fermentation the cultures will be inactivated. 3. Homogenize The blend is homogenized (2000 to 2500 psi) to mix all ingredients thoroughly and improve yogurt consistency. 78 4. Cool Milk The milk is cooled to 108°F (42°C) to bring the yogurt to the ideal growth temperature for the starter culture. 5. Inoculate with Starter Cultures The starter cultures are mixed into the cooled milk. 6. Hold The milk is held at 108°F (42°C) until a pH 4.5 is reached. This allows the fermentation to progress to form a soft gel and the characteristic flavor of yogurt. This process can take several hours. 7. Cool The yogurt is cooled to 7°C to stop the fermentation process. 8. Add Fruit & Flavors Fruit and flavors are added at different steps depending on the type of yogurt. For set style yogurt the fruit is added in the bottom of the cup and then the inoculated yogurt is poured on top and the yogurt is fermented in the cup. For swiss style yogurt the fruit is blended with the fermented, cooled yogurt prior to packaging. 9. Package The yogurt is pumped from the fermentation vat and packaged as desired. 79