Lab 6 Dairy Products & Alternatives

Question 1

Lipids

Answer 1

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

Question 2

Lactose

Answer 2

Disaccharide dominant in milk, firm from glucose and galactose. Lactose crystals are responsible for the sandy texture of some ice creams.

Question 3

Whey

Answer 3

Liquid that realism from the curd of clotted milk; contains lactose, some proteins, water-soluble vitamin, and some minerals

Question 4

Casein

Answer 4

Collective name for the milk protein fraction which precipitated at pH 4.6

Question 5

Curd

Answer 5

Milk precipitate that contains casein

Question 6

Rennin

Answer 6

Proteolytic enzyme from the stomach lining of calves that eliminated the protective function of k-casein in micelles and results in curd formation.

Question 7

Carbohydrates

Answer 7

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.

Question 8

Proteins

Answer 8

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.

Question 9

Casein precipitation mechanisms:

Answer 9

Milk acidification and use of rennin

Question 10

Milk acidification

Answer 10

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

Question 11

Use of rennin

Answer 11

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.

Question 12

Main whey proteins

Answer 12

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.

Question 13

Turbidity of milk

Answer 13

Casein micelles, although smaller than fat globules effectively block light transmission.

Question 14

Pasteurization

Answer 14

Heat treatment of milk adequate to kill microorganism that cause illness in humans.

Question 15

Hold method pasteurization

Answer 15

Milk is heated to 65C and held for 30 minutes before it is cooled.

Question 16

High temperature short time (HTST) pasteurization

Answer 16

Milk is heated to 72C and held for 15 seconds before it is cooled.

Causes less cooked flavor

Question 17

Ultra high temperature (UHT) pasteurization

Answer 17

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.

Question 18

Homogenization

Answer 18

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.

Question 19

Evaporation

Answer 19

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.

Question 20

Drying

Answer 20

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.

Question 21

Cultured milk/ fermentation

Answer 21

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.

Question 22

Foaming

Answer 22

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.

Question 23

Whipping cream

Answer 23

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.

Question 24

Foam 2

Answer 24

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.

Question 25

Milk

Answer 25

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.

Question 26

Cream

Answer 26

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%.

Question 27

Fermented milks

Answer 27

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.

Question 28

Yogurt

Answer 28

Fermented milk product in gel form. Microorganism used to ferment milk to yogurts are Streptococcus thermophilus and Lactobacillus delbrueckii subsp. Bulgaricus.

Question 29

Ice cream

Answer 29

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.

Question 30

Ice cream 2

Answer 30

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.

Question 31

Cheese

Answer 31

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%

Question 32

Curd

Answer 32

Coagulated mess which is separate from the whey. The degree of removal of whey determines hardness or softness of cheese.

Question 33

Curing process

Answer 33

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.

Question 34

Ripening or aging of cheese

Answer 34

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.

Question 35

Melting properties of cheese

Answer 35

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.

Question 36

Non-melting cheese

Answer 36

Ricotta, goats cheese, Indian paneer, and Latin queso blanco.

Question 37

Reduced fat cheeses

Answer 37

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.

Question 38

Processed cheese

Answer 38

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.

Question 39

Non-dairy substitutes

Answer 39

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.

Question 40

Soy milk

Answer 40

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.