Food Biochemistry and Food Processing (2 edition)

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496 Part 4: Milk

Protein (g/100 g milk)

0

2

4

16

18

20

Lipids (g /100 g milk)

0

1

2

3

4

Stage of lactation (d)

0 30 60 90 120 150 180

Lactose (g / 100 g milk)

0

2

4

6

8

(A)

(B)

(C)

Figure 26.1.Influence of lactation stage on the concentration of (A)

protein, (B) lipids, or (C) lactose in equine milk. (Data from Ullrey

et al. (1966,•), Mariani et al. (2001,◦) Smolders et al. (1990,
)

and Zicker and L ̈onnerdal (1994,∇).)

advancing lactation (Fig. 26.1B), whereas that the lipid content

in bovine milk shows a distinct minimum after approximately

3 months of lactation (Walstra et al. 2006a). The fat content of

asinine milk increases from approximately 0.5% to 1.5% from

days 15 to 105 but decreases sharply thereafter (Guo et al. 2007,

Salimei et al. 2004). Piccione et al. (2008) reported a decrease

in fat in the milk of Ragusana donkeys throughout lactation and

observed a daily rhythmicity, similar to that found in bovine and

human milk, for the levels of fat, lactose and protein in asinine

milk, with fat and lactose peaking at night and protein reaching

a maximum level during the daytime.

Effect of Equid Breed on Milk Composition

Data in the literature are not conclusive as to whether or not

the breed of mare has an effect on the concentration of protein

in milk. Kulisa (1977), Doreau et al. (1990), Csapo-Kiss et al. ́

(1995) and Csapo et al. (1995) reported no effect of breed on the ́

concentration of proteins or lipids in equine milk throughout lac-

tation. On the other hand, Boulot (1987) and Formaggioni et al.

(2003) have reported significant differences in protein content

between breeds. Civardi et al. (2002), who compared Arabian,

Haflinger, Trotter and Norico breeds, found that Norico milk

had significantly lowerα-lactalbumin (α-La), highest lysozyme

(Lyz) andβ-lactoglobulin (β-Lg) and highest thermal resistance

of the breeds studied. Pelizzola et al. (2006), who compared the

milk of Haflinger, Quarter horse, Sella/Salto and Rapid Heavy

Draft, found that Quarter horse milk had significantly higher

concentrations of the main constituents and higher concentra-

tions of linoleic andα-linolenic fatty acids (ALA) than in the

milk of the other species.

Asinine milk shows variability in fat content among breeds

and is reported to be as low as 0.4% for Martina Franca mares,

0.6% in Ragusana mares and as high as 1.7% in Jiangyue don-

keys (for these donkeys an increase from 0.5% to 1.7% was

recorded in the fat content of the milk over 180 days of lac-

tation) (Guo et al. 2007). Milk yield is significantly lower for

Jiangyue donkeys than for Martina Franca and Ragusana breeds

and the protein pattern of Jangyue milk is significantly different

from the other breeds (Guo et al. 2007)

PROTEINS

While the protein content of mature equid milk is lower than

that of bovine milk, there is a strong qualitative resemblance, the

principal classes of proteins, that is caseins and whey proteins

are similar in both milks. However, while the caseins are the

predominant class of proteins in bovine milk (∼80% of total

milk protein), equid milk contains less casein and more whey

proteins. The distribution of casein and whey proteins in equid

milk is shown in Table 26.2, with comparative data for bovine

and human milk.

Caseins

About 80% of the proteins in bovine milk are caseins that are

primarily a source of amino acids, calcium, phosphate and bioac-

tive peptides for neonates (Shekar et al. 2006). The low-casein

concentration in mature equine milk (∼55% of total protein) has

many implications that will be discussed later. The traditional

method for separating caseins from whey proteins is isoelectric

precipitation of the caseins at pH approximately 4.6. The ca-

sein fraction of most milks consists of four gene products:αs1-,