Question

(a) State the composition of the major components in milk (e.g. % protein etc.). (2 marks) (b) Describe the sizes of the various major particles in homogenized milk. (2 marks) (c) Describe the major fatty acids in milk fat. (2 marks) (d) Describe the major types of proteins in milk. (2 marks) (e) Name and describe the characteristics and origins of toxins from mushrooms and related health symptoms. (5 marks) (f) Define dietary fibre according to FSANZ. (3 marks) (g) Describe the beneficial effects of dietary fibre for human health. (4 marks)

Answer 1

a)

Milk composition varies between breeds; fat has the highest variation, protein varies slightly and lactose is stable. Table  shows the milk composition variation across different breeds.

Breed averages for percentages of milk fat, total protein and total solids

Breed	Percentage
	Total fat	Total proteina	Total solids
Ayrshire	3.88	3.31	12.69
Brown Swiss	3.98	3.52	12.64
Guernsey	4.46	3.47	13.76
Holstein	3.64	3.16	12.24
Jersey	4.64	3.73	14.04
Milking Shorthorn	3.59	3.26	12.46V

In general, the gross composition of cow's milk is

87.7% water,

4.9% lactose (carbohydrate),

3.4% fat, 3.3% protein,

and 0.7% minerals (referred to as ash).

Milk composition varies depending on the species (cow, goat, sheep), breed (Holstein, Jersey), the animal's feed, and the stage of lactation.

b)

The main goal of homogenization is to break up the large fat globules and create a stable emulsion that has an increased shelf life, a better taste, and improved mouth feel. The LA-300 is an excellent tool to monitor this process. It is able to show the large end of the distribution shift from 10 µm to about 2 µm without a problem. Also, in the low fat milk it is able to see the size distribution of the proteins.

c)

the major fatty acids found in milk are:

Long chain

• C14 - myristic 11%
• C16 - palmitic 26%
• C18 - stearic 10%
• C18:1 - oleic 20%

Short chain (11%)

• C4 - butyric*
• C6 - caproic
• C8 - caprylic
• C10 - capric

* butyric fatty acid is specific for milk fat of ruminant animals and is responsible for the rancid flavour when it is cleaved from glycerol by lipase action.

saturated fatty acids (no double bonds), such as myristic, palmitic, and stearic make up two thirds of milk fatty acids. Oleic acid is the most abundant unsaturated fatty acid in milk with one double bond. While the cis form of geometric isomer is the most common found in nature, approximately 5% of all unsaturated bonds are in the trans position as a result of rumen hydrogenation.

H-C-OH H00C- CH=CH-CH, Saturated (Butyric acid) Fatty Acid H-C-OH H-C - OH Н. Glycerol н HHH | - C-C=C-C- 0 H-C-0-C-R HHH Trans double bond O R-CO-C-H 0 - C-C=C-C- H-C-0-C-RP н Triglyceride HHHH Cis double bond Unsaturated

Triglycerides account for 98.3% of milkfat. The distribution of fatty acids on the triglyceride chain, while there are hundreds of different combinations, is not random. The fatty acid pattern is important when determining the physical properties of the lipids.

• C4 - 97% in SN3
• C6 - 84% in SN3
• C18 - 58% in SN1

The small amounts of mono- , diglycerides, and free fatty acids in fresh milk may be a product of early lipolysis or simply incomplete synthesis. Other classes of lipids include phospholipids (0.8%) which are mainly associated with the fat globule membrane, and cholesterol (0.3%) which is mostly located in the fat globule core.

d)

• There are 2 major categories of milk protein that are broadly defined by their chemical composition and physical properties.
• The casein family
• The serum proteins
• The casein family contains phosphorus and will coagulate or precipitate at pH 4.6. The serum proteins do not contain phosphorus, and these proteins remain in solution in milk at pH 4.6. The principle of coagulation, or curd formation, at reduced pH is the basis for cheese curd formation. In cow's milk, approximately 82% of milk protein is casein and the remaining 18% is serum, or whey protein.