Dairy Chemistry And Biochemistry

232 DAIRY CHEMISTRY AND BIOCHEMISTRY

about 99% of the faecal microflora of breast-fed infants. These bacteria also
represent a high proportion of the microflora of bottle-fed infants but
several other genera, e.g. Bacteroides, Clostridium and coliforms, also occur
at high numbers. Furthermore, the predominant species of Bifidobacterium
in breast-fed infants is B. bifidum, with lesser numbers of B. longum; the
faecal microflora of bottle-fed infants is dominated by B. longum, with lower
numbers of B. bifidum, B. infantis, B. adolescentis and B. breve.
The preponderance of B. biJdum in the faeces of breast-fed infants is due
to the presence of stimulatory factors in human milk. The most important
of these are N-acetylglucosamine-containing saccharides, referred to as
bifidus factor I, which is present at high levels in human milk and colostrum
and bovine colostrum but at very low concentrations in the milk of cows,
goats and sheep. Human milk also contains several non-dialysable bifidus-
promoting factors which are glycoproteins, referred to as bifidus factor 11.
Many of the glycoproteins have been isolated and characterized (see Fox
and Flynn, 1992).
Bifidobacterium spp. are also stimulated by lactulose, a derivative of
lactose (Chapter 2) which is not related to bifidus factors I and 11.

4.16.7 Milk protein hydrolysates

Several methods have been described for the production, characterization
and evaluation of milk protein hydrolysates tailored for specific applications
in the health-care, pharmaceutical, baby food and consumer product areas
(see Fox and Mulvihill, 1992, for references).
Several peptides with specific properties may be prepared from milk
proteins, either in vivo or in vitro; some may have commercial potential and
can be produced on a relatively large scale by preparative ion-exchange
chromatography.

Macropeptides from rc-casein. These peptides represent the C-terminal
region of rc-casein (residues 106-169) which is released by rennet during the
manufacture of cheese or rennet casein (Chapter 10). The (g1yco)macropep-
tides are released into the whey which contains 1.2-1.5gl-l, and from
which they can be readily recovered, e.g. by anion exchange using Spherosil
QMA resin. The peptides contain no Phe, Tyr, Trp or Cys; the absence of
aromatic amino acids makes the macropeptides suitable for the nutrition of
patients suffering from phenylketonuria.

Phosphopeptides. It is claimed that phosphopeptides prepared from casein
hydrolysates stimulate the absorption of Ca in the intestine, but views on
this are not unanimous. Such peptides are resistant to proteolysis due to the
high density of negative charges; they have been detected in the small
intestine of the rat and may pass intact through the intestinal wall. Since