Winter milk

In milk approximately 90% of the yellow color is because of the presence of -carotene, a fat-soluble carotenoid extracted from feed by cows. Summer milk is more yellow than winter milk because cows grazing on lush green pastures in the spring and summer months consume much higher levels of carotenoids than do cows ham-fed on hay and grain in the fall and winter. Various breeds of cows and even individual animals differ in the efficiency with which they extract -carotene from feed and in the degree to which they convert it into colorless vitamin A. The differences in the color of milk are more obvious in products made from milk fat, since here the yellow color is concentrated. Thus, unless standardized through the addition of colorant, products like butter and cheese show a wide variation in shade and in many cases appear unsatisfactory to the consumer. 

The concentration of vitamin A and carotenoids in milk is strongly influenced by the carotenoid content of the feed. Milk from animals fed on pasture contains higher levels of carotenes than that from animals fed on concentrate feeds. There is also a large seasonal variation in vitamin A concentration summer milk contains an average of 62 fig retinol and 31 fig carotene per 100 g while the values for winter milk are 41 and 11 fig per... 

In cow s milk, nearly all of the vitamin E is a-tocopherol and the level can vary with the cow s feed and the season of the year (Lampert 1975). For example, summer milk can contain five times more vitamin E (1.1 mg a-tocopherol per quart) than winter milk (0.2 mg/quart) (Hertig and Drury 1969 McLaughlin and Weihrauch 1979). It is suggested that vitamin E, due to its antioxidant properties, may have some effect in retarding the development of oxidized flavor in milk (Lampert 1975). 

The principal factor that influences the a-tocopherol content of milk is the feed of the cow, as influenced by the season of the year. Kanno et al. (1968) reported that summer milk produced on green pasture feed averaged 33.8 pg a-tocopherol/g fat, while winter milk produced on dry-lot feeding averaged 21.6 pg a-tocopherol/g fat. Similar findings have been reported by King et al. (1967) and Seerless and Armstrong (1970). 

COW (milk from Jersey and Guernsey cows contains more riboflavin than Holstein milk). Summer milk generally contains slighly higher levels of riboflavin than winter milk. Interspecies variations in concentration are also apparent. Raw sheep s milk contains about 0.32 mg per 100 g while the mean value for pasteurized goats milk (0.13 mg per 100 g) is lower human milk contains 0.03 mg per 100 g. Dairy products also contain significant amounts... 

The higher iodine concentration of winter milk is explained by the use of cow fodder fortified with iodine (Dahl et at, 2003b), and these findings are in accordance with a number of studies from other countries (Varo et al., 1982 Pennington, 1990 Lee et al., 1994 Phillips, 1997 Ministry of Agriculture, Fisheries and Food, 1997, 1999, 2000 Larsen et al., 1999 Rasmussen et al., 2000). The iodine content of animal feed is controlled by legislation in Norway. The fortification of cow fodder with 2 mg-l/kg... 

The seasonal variation in milk fat composition is demonstrated in Table 3.153, winter milk fat being more saturated than summer milk fat. The trans fatty acid content is not frequently recorded. Literature values vary between 2 and 11% with higher values in the summer. The determined values are very method-dependent and values in the range 4-8% are probably realistic (Deman and Deman, 1983). The main trans monounsaturated acid is tran -vaccenic acid (18 1 n-1) (Hay and Morrison, 1970 Lund and Jensen, 1983). 

To optimize this crystallization and finally obtain an oil/fat ratio optimal for the churning process, a defined temperature regime must be applied (see below). This regime depends strongly on the composition of the milk fat, which is subject to seasonal variations the iodine value of winter milk fat is about 30 and that of summer milk fat about 40. 

The D vitamins are limited in distribution. They rarely occur in plants except in sun-dried roughages and the dead leaves of growing plants. In the animal kingdom vitamin D3 occurs in small amoimts in certain tissues and is abundant only in some fishes. Halibut-liver and cod-Uver oils are rich somces of vitamin D3. Egg yolk is also a good source, but cow s milk is normally a poor somce, although summer milk tends to be richer than winter milk. Colostrum usually contains six to ten times the amoimt present in ordinary milk. 

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