Dairy Ingredients for Food Processing

Chemical, Physical, and Functional Characteristics of Dairy Ingredients 41

ester that hydrolyzes aromatic residues, the

B - type that hydrolyzes alphaphilic esters

rapidly and aromatic esters slowly, and the

C - type that hydrolyzes alkaline esters.

Several enzymes in milk have antibacte-

rial functions including lysozyme, lactofer-

rin, and lactoperoxidase. The enzymes with

major functions in milk and milk processing

are discussed below.

Lysozyme

Lysozyme consists of 148 amino acids and it

is a relatively small, single polypeptide

protein. It is found in low concentrations in

bovine milk (0 to 2 mg/L). This enzyme ’ s

level rises signifi cantly during infection with

mastitis.

Lactoperoxidase

The lactoperoxidase enzyme consists of 712

amino acids and has antimicrobial activity.

Its optimum activity is at pH 6.0, but it is

stable over pH 5.0 to 10.0. Higher concentra-

tions of this enzyme are present in bovine

milk compared to human milk. It chelates to

metals including iron.

Oxidoreductases

Milk contains oxidoreductases such as xan-

thine oxidase, sulfhydryl oxidase, and super-

oxide dismutase. Xanthine oxidase is a

Trace elements from various sources are
found in milk, possibly from the feed, con-
tamination after milking, and during milk
processing. Zinc the highest concentration in
milk (3 mg/kg). Other elements include sili-
cone, fl uoride, manganese, and iodine.
Manganese is an important element for lactic
acid bacteria metabolism, particularly citrate
fermentation. Other minor components in
milk include organic acids in the milk serum,
nitrogenous compounds, gases (O 2 , CO 2 ),
hormones such as prolactin, and steroids.

Milk Enzymes

There are several enzymes in bovine milk.
They occur in various states including free in
solution, as associated or integral parts of
membrane fractions of the fat globule mem-
brane or membrane vesicles (in skim milk),
and associated with casein micelles or micro-
somal particles. Approximately 60 indige-
nous enzymes are excreted from secretory
cells in the mammary gland including lipo-
protein lipase, plasmin, phosphatases, lactate
dehydrogenase, catalase, lactoperoxidase,
and xanthine oxidase. Several have important
functions in dairy processing and quality
control including lipoprotein lipase, plasmin,
and alkaline phosphatase.
Esterases also occur in milk. Three types
have been determined: the A - type carboxylic

Table 2.4. Vitamin composition of various milks.

Vitamins/100 g Whole milk Skim milk Sheep milk Human milk

Thiamine (B 1 )(mg) 0.045 0.038 0.15

Ribofl avin(B 2 )(mg) 0.175 0.17 0.62 0.38

Niacin (B 3 )(mg) 0.09

Pyridoxine (B 6 )(mg) 0.05 0.05 0.14

Pathothenic acid (mg) 0.35 0.28 0.35 0.21

Biotin ( μ g) 3.5 5.0 9.0 0.58

Folic acid ( μ g) 5.5 300 8.0

Vitamin B 12 ( μ g) 0.45 0.4 0.05

Vitamin C (mg) 2 4.3 6.5

Vitamin A ( μ g) 40 2.4 0.43 71

Vitamin D ( μ g) 0.03 trace 0.073

Vitamin E ( μ g) 100 trace 278

Vitamin K ( μ g) 5 0.01 0.296

Adapted from Kailasapathy (2008) and Souci (2008)