Havemose M S, Weisbjerg M R, Bredie W L P, Poulsen H D, Nielsen J H
Danish Institute of Agricultural Sciences, Department of Food Science, Research Centre Foulum, P.O. Box 50, 8830 Tjele, Denmark.
J Dairy Sci. 2006 Jun;89(6):1970-80. doi: 10.3168/jds.S0022-0302(06)72264-0.
Differences in the oxidative stability of milk from cows fed grass-clover silage or hay were examined in relation to fatty acid composition and contents of antioxidants and copper in the milk. The oxidation processes were induced by exposing the milk to fluorescent light. Protein oxidation was measured as an accumulation of dityrosine, whereas lipid oxidation was measured as an accumulation of lipid hydroperoxides as the primary oxidation product, and as the secondary oxidation products, pentanal, hexanal, and heptanal. No differences were found in the protein oxidation of the 2 types of milk measured as accumulation of dityrosine, but there was an increased accumulation of lipid hydroperoxides and hexanal in milk from cows fed grass-clover silage, compared with milk from cows fed hay. The higher degree of lipid oxidation in milk from cows fed grass-clover silage could not be explained from the concentration of alpha-tocopherol, carotenoids, uric acid, and copper in the milk. However, it was thought to be highly influenced by the significantly higher concentration of linolenic acid present in milk from cows fed grass-clover silage. A larger part of alpha-tocopherol and beta-carotene was transferred from the feed to the milk when cows were fed grass-clover silage than when cows were fed hay as roughage. The significantly higher concentration of polyunsaturated fatty acids in milk from cows fed grass-clover silage may be important for the better transfer of alpha-tocopherol from the feed to the milk. Other circumstances, as the different conditions in the rumen may also play a role, due to the different types of roughages and their digestibility, or be related to the mechanisms during milk production for the higher yielding cows fed grass-clover silage.
研究了以草-三叶草青贮料或干草为食的奶牛所产牛奶的氧化稳定性差异，涉及牛奶中的脂肪酸组成、抗氧化剂含量和铜含量。通过将牛奶暴露于荧光下诱导氧化过程。蛋白质氧化以二酪氨酸的积累来衡量，而脂质氧化以脂质氢过氧化物作为主要氧化产物以及戊醛、己醛和庚醛作为次要氧化产物的积累来衡量。以二酪氨酸积累衡量的两种牛奶的蛋白质氧化未发现差异，但与以干草为食的奶牛所产牛奶相比，以草-三叶草青贮料为食的奶牛所产牛奶中脂质氢过氧化物和己醛的积累有所增加。以草-三叶草青贮料为食的奶牛所产牛奶中较高程度的脂质氧化无法从牛奶中α-生育酚、类胡萝卜素、尿酸和铜的浓度来解释。然而，认为这受到以草-三叶草青贮料为食的奶牛所产牛奶中显著更高的亚麻酸浓度的高度影响。当奶牛以草-三叶草青贮料为粗饲料时，与以干草为粗饲料时相比，α-生育酚和β-胡萝卜素从饲料转移到牛奶中的比例更大。以草-三叶草青贮料为食的奶牛所产牛奶中多不饱和脂肪酸的显著更高浓度可能对α-生育酚从饲料更好地转移到牛奶中很重要。其他情况，如瘤胃中的不同条件也可能起作用，这是由于粗饲料类型及其消化率不同，或者与以草-三叶草青贮料为食的高产奶牛产奶过程中的机制有关。
