Dairy Chemistry And Biochemistry

230 DAIRY CHEMISTRY AND BIOCHEMISTRY

Lf have been reviewed by Lonnerdal and Iyer (1995) and Hutchens and

Lonnerdal (1996).

Lactotransferrins have been isolated from the milks of several species,

including human and bovine, and some have been well characterized,

including determination of their amino acid sequence. Some of the isolation

procedures have industrial-scale potential; the preparations obtained from

such procedures usually contain both Lf and LPO.

4.16.3 Immunoglobulins

The occurrence, significance and interspecies aspects of immunglobulin in

milk were described in section 4.10. Classically, Ig is prepared by salting-out,

usually with ammonium sulphate [(NH4)*S04]. This method is effective but

expensive and current commercial products are usually prepared by ultra-

filtration of colostrum or milk from hyperimmunized cows. Some recently

developed methods for the isolation of Ig, sometimes with Lf, use mono-

clonal antibodies, metal chelate or gel filtration chromatographies (see Fox

and Mulvihill, 1992).

Ig-rich preparations are commercially available for the nutrition of calves

and other neonatal animals. Although human infants do not absorb Ig from

the intestine, Igs still play an important defensive role by reducing the

incidence of intestinal infection. While breast feeding is best for healthy

full-term infants, it is frequently impossible to breast-feed pre-term or

very-low-birth-weight infants, who may be fed on banked human milk. Such

infants have high protein and energy requirements which may not be met

by human milk and consequently special formulae have been developed. A

‘milk immunological concentrate’, prepared by diafiltration of acid whey

from colostrum and early lactation milk from immunized cows, for use in

such formulae has been described; the product contains approximately 75%

protein, 50% of which is Ig, mainly IgG, and not IgA, which is predominant

in human milk.

The development of Ig in cows agains human pathogens, e.g. rotavirus,

an important cause of illness in children, is considered to be an attractive

approach in human medicine. The Ig could be administered in milk or as a

concentrate prepared from milk.

4.16.4 Vitamin-binding proteins

Milk contains specific binding proteins for retinol (vitamin A), vitamin D,
riboflavin (vitamin BJ, folate and cyanocobalamin (vitamin BIZ). Such
proteins may improve the absorption of these vitamins by protecting and
transferring them to receptor proteins in the intestine, or they may have
antibacterial activity by rendering vitamins required by intestinal bacteria
unavailable. The activity of these proteins is reduced or destroyed by heat
treatments.