Dairy Chemistry And Biochemistry

MILK PROTEINS^199

selective, 12-48h

Probably Moderate, selective Extensive, selective Extensive, non-

none 19 days in rots, mice 12- 48h

Figure 4.30 Transfer of maternal immunoglobulins to the foetus and neonate of representative
mammalian species. Group I species transfer Ig in utero before birth. Group I1 species transfer
Ig both in utero before birth and via colostrum after birth. Group 111 species transfer Ig only
via colostrum after birth. The size of the immunoglobulin notation (IgA, IgM, IgG, IgG,)
indicates the relative percentage composition of the immunoglobulins in colostrum. Species in
group I1 may have IgG as the predominant Ig in colostrum. Significant IgG, also may be
present in the colostrum of some Group I11 species. The relative absorption of immuno-
globulins in the gut of the neonate is also shown. (From Larson, 1992.)

4.11 Minor milk proteins

Milk contains numerous minor proteins, including perhaps 60 indigenous
enzymes, some of which, e.g. lipase, proteinase, phosphatases and lac-
toperoxidase, are technologically important (Chapter 8). Most of the minor
proteins have biological functions and probably play very significant roles
(section 4.16).

4.12 Non-protein nitrogen

Nitrogen soluble in 12% TCA is referred to as non-protein nitrogen (NPN),
of which milk contains 250-300mgl-', i.e. 5-6% of total milk nitrogen.
The NPN is a very heterogeneous fraction (Table 4.7).