Chemistry Reference
In-Depth Information
-tocopherol between 0.2 and 0.7 mg/l in bovine milk (Renner et al., 1989;
Jensen, 1995).
-Tocopherol has also been found and trace amounts of some
other vitamers. Barrefors et al. (1995) reported
-tocopherol levels of
7.4-10.0 mg/g lipid for different herds and also observed the presence of
low levels of
-tocopherol and
-tocotrienol. Colostrum contains about
1.9 mg/l of
-tocopherol and the level decreased in approximately 4 days to
the level in fresh milk (0.3 mg/l) (Hidiroglou, 1989).
-Tocopherol is also
present in small amounts in colostrum. The transfer of vitamin E into colos-
trum does not appear to occur through a passive mechanism following the
transfer of lipid (Debier et al., 2005). A mechanism involving low-density
lipoproteins (LDL) may be responsible for the high vitamin E concentration
in colostrum compared to mature milk (Schweigert, 1990). Also, tissue deliv-
ery of
-tocopherol into milk may be promoted by the action of lipoprotein
lipase on triglyceride-rich lipoproteins (Martinez et al., 2002). The quantita-
tive secretion of
-tocopherol (also
-carotene) from plasma into cows' milk
appears to follow Michaelis-Menten kinetics for active transport across
membranes (Jensen et al., 1999). According to these authors the daily secre-
tion of
-tocopherol and
-carotene is limited in quantity and is independent
of the yield of milk and fat content. The concentration of vitamin E in milk
appears to be dependent principally on the amount consumed by the cow.
Indyk et al. (1993) observed that the vitamin E content of cow's milk exhibits
a significant seasonal pattern that is largely independent of fat content, with
pasture maturity and quality the dominant factors. However, this seasonal
effect was not observed in an Irish study, probably because farm management
practices include supplementation of the diets of spring-calved cows with
silage or concentrates from mid-September onwards (O'Brien et al., 1999).
The vitamin E concentration in human milk is also much higher in
colostrum than in mature milk. Boersma et al. (1991) observed that human
colostrum contained 22
14 mg/l as
-tocopherol equivalents compared with
transitional milk (14
8) and mature milk (8
5). Barbas and Herrera (1998)
also observed significantly higher levels of vitamin E in human colostrum
(14.4
2.3 mg/l) compared with 3.1
0.5 mg/l in mature milk. The vitamin E/
linoleic acid ratio in human colostrum is higher (89.8
14.7 mg/g) compared
with 25.9
3.49 mg/g in mature milk. Vitamin E does not consistently cross the
placental barrier (Quigley and Drewey, 1998), and as a consequence, plasma
vitamin E concentration in pre-suckled newborn infants (Sinha and
Chiswick, 1993) and calves (Nonnecke et al., 1999) is very low. Colostrum
ingestion is therefore important to provide mammalian neonates with an
adequate source of vitamin E to protect against oxidative stress and enhance
the immune response. Following birth, colostrum intake induces a sharp
increase in the circulating and tissue levels of vitamin E in the young
(Hidiroglou et al., 1993)
