MILK LIPIDS Table 3.4 Total fat and phospholipid content of some milk products Total lipid Phospholipids Phospholipid Product (%,w/) % w/w. of total lipid Whole milk Cream 03-04 0.16-0.29 002-008 Skim milk Buttermilk 003-0.18 the presence of proportionately larger amounts of membrane material in ese products. Cholesterol(Appendix 3C)is the principal sterol in milk(>95% of total sterols); the level (-0.3%, w/w, of total lipids) is low compared with many other foods. Most of the cholesterol is in the free form with less than 10% holesteryl esters. Several other sterols, including steroid hormones, oc at trace levels Several hydrocarbons occur in milk in trace amounts. Of these, caro tenoids are the most significant. In quantitative terms, carotenes occur at only trace levels in milk (typically -200 ugl) but they contribute 10-50% of the vitamin A activity in milk(Table 3.5)and are responsible for the yellow colour of milk fat. The carotenoid content of milk varies with breed (milk from Channel Island breeds contains 2-3 times as much carotene as milk from other breeds) and very markedly with season (Figure 3. 4 ). The latter reflects differences in the carotenoid content of the diet(since they are totally derived from the diet); fresh pasture, especially if is rich in clover and alfalfa, is much richer in carotenoids than hay of silage(due to oxidation on conservation) or cereal-based concentrates. The higher the carotenoid content of the diet, the more yellow will be the colour of milk and milk fat, e.g. butter from cows on pasture is yellower than that Table 3.5 Vitamin A activity and B-carotene in milk of different breeds of cows Channel Island breeds Non-Channel island breeds Winte Retinol (ul 1 Contribution (%)of β carotene to vitamin a ctivity Modified from Cremin and Power(1985).MILK LIPIDS 73 Table 3.4 Total fat and phospholipid content of some milk products Total lipid Phospholipids Phospholipid as Product (%. WIV) (%, WIV) YO, w/w, of total lipids Whole milk 3-5 Cream 10-50 Butter 81-82 Butter oil - 100 Skim milk 0.03-0.1 Buttermilk 2 0.02-0.04 0.6- 1 .O 0.07-0. I8 0.3-0.4 0.14-0.25 0.16-0.29 0.02-0.08 0.02-0.08 0.01-0.06 17-30 0.03 -0.18 10 the presence of proportionately larger amounts of membrane material in these products. Cholesterol (Appendix 3C) is the principal sterol in milk (> 95% of total sterols); the level (-O.3%, w/w, of total lipids) is low compared with many other foods. Most of the cholesterol is in the free form, with less than 10% as cholesteryl esters. Several other sterols, including steroid hormones, occur at trace levels. Several hydrocarbons occur in milk in trace amounts. Of these, caro￾tenoids are the most significant. In quantitative terms, carotenes occur at only trace levels in milk (typically -2OOpg1-') but they contribute 10-50% of the vitamin A activity in milk (Table 3.5) and are responsible for the yellow colour of milk fat. The carotenoid content of milk varies with breed (milk from Channel Island breeds contains 2-3 times as much p-carotene as milk from other breeds) and very markedly with season (Figure 3.4). The latter reflects differences in the carotenoid content of the diet (since they are totally derived from the diet); fresh pasture, especially if it is rich in clover and alfalfa, is much richer in carotenoids than hay or silage (due to oxidation on conservation) or cereal-based concentrates. The higher the carotenoid content of the diet, the more yellow will be the colour of milk and milk fat, e.g. butter from cows on pasture is yellower than that Table 3.5 Vitamin A activity and P-carotene in milk of different breeds of cows ~ ~ ~ ~~ ~~~~~ Channel Island breeds Non-Channel Island breeds Summer Winter Summer Winter Retinol (pl 1- ') 649 265 619 412 j-Carotene (pl I-') 1143 266 315 105 Retinollb-carotene ratio 0.6 11.0 2.0 4.0 Contribution (%) of 46.8 33.4 20.3 11.4 p-carotene to vitamin A activity Modified from Cremin and Power (1985)