Chemistry Reference
In-Depth Information
levels of the fat-soluble vitamins and
-carotene in milk are highly dependent
on the amount consumed in the feed (Jensen et al., 1999). Vitamin A and
-
carotene concentrations of milk follow a seasonal trend with higher values
obtained during the outdoor grazing period (O'Brien et al.,1999). Higher
concentrations of vitamin A and
-carotene are present in retail milk during
both the outdoor grazing (June-October) and indoor feeding (December to
March) periods compared to manufacturing milk, which reflected the higher
feed concentrate input in retail milk production (O'Brien et al., 1999). Sea-
sonal variation has also been observed by Hulshof et al. (2006), who observed
that winter milk contains 20% less retinol and
-carotene than summer milk.
Higher amounts of retinyl esters are found in colostrum (233-369 mg/100 ml)
than in mature milk (33-57 mg/100 ml) (Debier et al., 2005). The age of the
cow also appears to exert an effect on the concentration of vitamin A in
colostrum and milk. In cows, primiparous females exhibit significantly higher
vitamin A concentrations in plasma, colostrum and milk than multiparous
females (Kumagai et al., 2001).
Kim et al. (1990) reported that the retinol concentration (mean
SD) in
human milk is 57
25 mg/100 g, and carotenoid concentrations (mg/100 g) are
4.6
1.6 for
-carotene, 3.2
0.9 for
-carotene, 3.8
2.1 for lycopene and
11.5
3.4 for lutein. Meneses and Trugo (2005) determined the concentrations
of retinol,
-carotene and non-pro-vitamin A (lutein
þ
zeaxanthin) carote-
noids in mature human milk. Nutrient concentrations (mm/l, mean
SE) in
milk were as follows: retinol, 1.4
0.1;
-carotene, 0.018
0.002; lutein
þ
zeaxanthin, 0.006
0.001. Similar retinol levels have been described for the
milk of well-nourished lactating women (Roy et al., 1997; Canfield et al.,
1998; Rice et al., 1999). The milk of multiparous women contained higher
levels of retinol than milk of primiparous women. Colostrum samples from
human donors showed considerable variation in total carotenoid concentra-
tion (34-757 mg/100 ml) (Patton et al., 1990). Multiparous mothers had higher
mean colostrum carotene concentrations than did primiparae, 218
194 vs
114
132 mg/100 ml, respectively.
Loss of vitamin A activity of retinoids and carotenoids in foods occurs
mainly through reactions involving the unsaturated isoprenoid side chain,
by either autoxidation or geometric isomerization. The 9-cis and 13-cis
isomers, resulting from all-trans-retinol isomerization reactions, have been
found in many types of food, including cheese, UHT milk and butter, at
different concentrations, depending on the processing and/or storage con-
ditions (Woolard and Indyk, 1986; Fellman et al., 1991). Pasteurized milk
heated at temperatures ranging from 72 to 768C for 15 s had an average 13-
cis:all-trans ratio of 6:100 (Panifili et al., 1998). Milk subjected to a more
severe heat treatment had a higher degree of isomerization (UHT milk,
15.7%; sterilized milk, 33.5%), consistent with increased thermal conversion
