Lab 6 Dairy Products & Alternatives Flashcards
Lipids
98% of milk fat are triglycerides with an array of fatty acids ranging from 4 to 26 carbon atoms. The most common are palmitic (16 carbons) and oleic acid (18 carbons). The triglycerides containing here diverse fatty acids are dispersed in milk in the form of tiny fat globules as an oil-in-water emulsion
Lactose
Disaccharide dominant in milk, firm from glucose and galactose. Lactose crystals are responsible for the sandy texture of some ice creams.
Whey
Liquid that realism from the curd of clotted milk; contains lactose, some proteins, water-soluble vitamin, and some minerals
Casein
Collective name for the milk protein fraction which precipitated at pH 4.6
Curd
Milk precipitate that contains casein
Rennin
Proteolytic enzyme from the stomach lining of calves that eliminated the protective function of k-casein in micelles and results in curd formation.
Carbohydrates
One cup of milk contains 11 to 12 grams of lactose. Lactose is a disaccharide formed from galactose and glucose which provides 40% of the energy of milk. It also gives a distinctly sweet taste to milk and contribute to the browning (Maillard reaction) of heated milk products. Lactose is particularly difficult to dissolve and keep in solution. It can form crystals which cause the grittiness in ice cream.
Proteins
Whey and casein proteins. 80% of proteins are caseins. Caseins and whey proteins differ in their physiological and biological properties. The pH of milk is adjusted to 4.6 (the approximate isoelectric point of caseins), caseins precipitated to form a soft curd? Which can be separated from the remaining liquid called whey. The whey protein are found in the railing whey, which is a watery mixture that also contains lactose, some minerals, and watery-soluble vitamins.
Casein precipitation mechanisms:
Milk acidification and use of rennin
Milk acidification
Acid moved pH of milk closer to the isoelectric point of one type of casein (k-casein), which is the protein that is preventing the micelles from precipitating. The negative electrician charged that normally are on the surface of casein micelles are counteracted by the plus charges of the hydrogen ions of the acid, the repulsive forces no longer keep the micelles apart
Use of rennin
Rennin, a proteolytic enzyme found in calves stomach, hydrolysis the hydrophilic portion of k-casein on the surface of the casein micelles. In the presence of calcium, the newly formed compound para-k-casein, becomes insoluble. Consequently, the micelles can then aggregate to form a gel.
Main whey proteins
Alpha-lactalbumin and beta-lactoglobulin. They are the main whey proteins and are not coagulated by rennin. They consist of 70-80% of total whey proteins.
Turbidity of milk
Casein micelles, although smaller than fat globules effectively block light transmission.
Pasteurization
Heat treatment of milk adequate to kill microorganism that cause illness in humans.
Hold method pasteurization
Milk is heated to 65C and held for 30 minutes before it is cooled.
High temperature short time (HTST) pasteurization
Milk is heated to 72C and held for 15 seconds before it is cooled.
Causes less cooked flavor
Ultra high temperature (UHT) pasteurization
Milk is heated to 138-145C for at least 2 seconds before it is cooled and packages and sealed in sterile container.
Advantageous over hold method and HTST because it is possible to shore milk in sterile container at room temperature. However, UHT imparts cooked flavour on the milk.
Homogenization
Milk is homogenized to prevent fat globules clustering and rising to the top. Homogenized milk characteristics include: no separation of fat globules from the milk, more viscous, less stable to heat, more sensitive to light-oxidation, foams more readily, curds formed from homogenized milk are softer.
Evaporation
Water is just under 90% of milk and can be reduced by evaporation. Various canned milk products are evaporated to double the concentration of protein and fat and then sterilizing the product at 116C for 15 min.
Drying
Milk is fried to store for extended period of time without refrigeration and/or to reduce the problems of transporting fluid milks, which are subject both to spoilage and to high shipping costs. It is condensed by removing 2/3 of the water and then spray dried to less than 5% moisture level. When dried, the milk powder consists of lactose, fat in globules or free, and protein in the form of casein micelles and precipitated whey proteins. Most non-far dry milk is fortified with vitamin A and D.
Cultured milk/ fermentation
Various micro organisms are used commercially to ferment lactose in milk and milk products. The goal is the production of lactic acid by one or more type of microorganisms. The thickening associated with fermented products is the result of the association of casein micelles, often accompanied by beta-lactoglobulin. When a comparatively large amount of beta-lactoglobulin is bound to the casein micelles, a fairly stable gel is formed and synersis is minimal.
Buttermilk is somewhat thickened as a result of fermentation, whereas yogurt is acidified to the point where a gel forms as a result of fermentation and controlled heat. Whey can be fermented to produce such comparatively sweet cheeses as Myosost and Gjetost.
Foaming
Foams made from milk and cream are used in a lot of food products to introduce air and creating a light, fluffy consistency. Milk can’t form stable foams until there is sufficient concentration of protein. Reconstituting skim milk powder to 3X the concentration of whole milk (10.5% protein) results in pretty stable foam,
Cream foam is stabilized by fat unlike protein foams in milk and egg whites.
Whipping cream
Has minimum fat content of 30% produces very stable foam due to amount of fat present and to the state in which the fat is present in the cream. During beating, particles of air are surrounded by membranes containing fat globules and stabilized by a film of a particularly coagulated protein. The fat globules in the films of milk protein and the liquid between the bubbles tend to clump and thus provide the foam with rigidity and permanence.
Foam 2
Temperature will affect the stability of the foam because the clumping of the fat globules will occur only when the fat is in a semi-solid state. The fat is quite girl and gives s rigidity to the cell wall when chilled. When the cream is held at room temperature, the fat globules melt and coalesce, thus preventing the formation of a rigid film. Over-beating causes reversal to the water-in-oil emulsion, resulting in butter.
Milk
Milk and milk produce are available to consumers and food manufacturer in several different forms. In the fluid form, milk can be categorized on the basis of fat content.
Cream
Contains a high fat portion separated from whole milk during creaming process. Light creams, cereal, coffee, and table creams, fat content ranges 10% to 18% and for heavy creams such as whipping creams the fat content is 30-40%. Minimum fat concentration for stable foams is 30%.
Fermented milks
Include cultures buttermilk, sweet acidophilus milk, kefir, and Lactaid. Sweet acidophilus milk is inoculated with Lactobacillus acidophilus, but it is not allowed to ferment and therefore is sweet rather than acidic. Lactose-containing milk, such as Lactaid has reduced Lactose content and is effective for people with lactose intolerance. The enzyme lactase digests a considerable portion of lactose into glucose and galactose.
Yogurt
Fermented milk product in gel form. Microorganism used to ferment milk to yogurts are Streptococcus thermophilus and Lactobacillus delbrueckii subsp. Bulgaricus.
Ice cream
Frozen mixture of cream, with added milk solids and flavourings into which a large amount of air has been stirred. The high fat content of ice creams is responsible for the smooth texture and richness of flavour. The sweeteners (sugar or various corn sweeteners) lower the melting and freezing points in ice creams, a physical phenomenon they digs in production of a smooth product. Gelatine or such gums as guar gum, alginates, or carrageenan are useful stabilizers in ice creams because of their ability to bind water and increase viscosity of the ice cream mixture prior to freezing. Monoglycerides are added as emulsifying agents.
Ice cream 2
Rapid freezing is important in making ice cream because it is partly responsible for very fine ice crystals by establishing s more uniform temperature throughout the freezing mixture. When the ice cream mixture is chiller and begins to freeze, agitation results in the incorporation of air in the foam if the product. This causes an increase in the volume of the mixture or overrun. A desirable level of overrun in commercial ice creams generally is over 70%. Two common defects found in ice cream products are iciness and sandiness, please refer to Appendix 1B for description.
Cheese
Require forming of curd and removing of considerable amount of water (whey). Acid precipitation is used to make cottage cheese and cream cheese. For making most other cheeses, rennin is used to convert k-casein into para-k-casein. Para-k-casein then participates in curd formation by uniting with calcium, an in forms an insoluble material. The gel formed is cut to release the whey. Gentle heating (35C for hard cheeses and 32-33C for soft cheeses) and squeezing, cause the curd to draw tighter so that the whey can be drained, leaving the highly concentrated protein and fat-containing curd. Usually the moisture content of cheese is around 37-40%
Curd
Coagulated mess which is separate from the whey. The degree of removal of whey determines hardness or softness of cheese.
Curing process
Action of enzymes, mould of bacteria used to being characteristic changes to cheese. Ripening alters texture & flavour as well as cooking qualities eg. Increase solubility or protein and increases ease of blending.
Ripening or aging of cheese
During maturation, bacteria and enzymes act on the fat, protein and carbohydrate in the cheese to produce the body, texture and flavour characteristics of mature cheddar and other cheeses. The result of protein and fat degradation transforms the rubbery, elastic mass of curd to a cheese with firm close texture. The release volatile components of the curd gives aroma to cheese and associated flavours. Aging period for mild, medium, and old (or sharp) cheese is approximately 3, 6, and 12 months, respectively.
Melting properties of cheese
Largely due to its age and the moisture and fat levels. Casein proteins bonded together break down in the presence of heat. These protein molecules separate and flow, which gives the appearance of melting. Younger cheeses have high moisture content and proteins flow at lower temperature. Aged cheese have lower moisture and melts at higher temperatures, have stronger protein network. If protein is coagulated by excess heat, protein film breaks and fat separates. During aging cheese solubility increases due to progressive hydrolysis of protein and fat. So ripened cheese with high fat content blends more readily than mild cheese and so it is suitable for cooking.
Non-melting cheese
Ricotta, goats cheese, Indian paneer, and Latin queso blanco.
Reduced fat cheeses
Produced using various approaches. Straightforward way is remove fat, which can be down up to a critical level. The issue is that fat performs several functions in cheese, including contributing significantly to mouthfeel, firmness, and adhesiveness, as well as flavour. Another way is to replace fat with various gums to help achieve desired textural characteristics of the product. Imitation cheese can be made from soy protein.
Processed cheese
Made by hearing natural cheeses (mix young and old cheese) and adding an emulsifying agent (disodium hydrogen phosphate or sodium citrate). The process reduced the size of protein molecules, increases the solubility and the water-binding capacity. It also kills microorganism, which reduces the potential for spoilage during storage.
Non-dairy substitutes
Whipped toppings or non-dairy substitutes usually contain vegetable oil, sugar, flavouring, water and various stabilizers and emulsifiers. Whipped toppings are available in powdered, fluid, frozen fluid, and are ready to serve forms (frozen prepared and pressured containers). Non-dairy creamers or whiteners are also available.
Soy milk
Non-dairy product made from finely ground defatted soybeans. Protein content is 3.2% is collars blue to cow’s milk with added calcium. Other non-dairy milk alternatives include almond and cashew milk, rice milk, and recently coconut milk and hemp milk.
