Wiking Lars, Bertram Hanne C, Björck Lennart, Nielsen Jacob H
Dept of Food Science, Danish Institute of Agricultural Sciences, Research Centre Foulum, P.O. Box 50, DK-8830 Tjele, Denmark.
J Dairy Res. 2005 Nov;72(4):476-81. doi: 10.1017/S002202990500141X.
Cooling strategies for pumping of raw milk were evaluated. Milk was pumped for 450 s at 31 degrees C, or pumped after cooling to 4 degrees C and subsequently subjected to various incubation times. Two types of milk were used; i.e. milk from cows fed a diet high in saturated fat supplements resulting in significantly larger milk fat globules than the other type of milk which comes from cows fed a low-fat diet that stimulates high de novo fat synthesis. The content of liquid fat was determined by low-field 1H NMR, which showed that milk from cows given the saturated fat diet also contained less liquid fat at both 4 degrees and 31 degrees C than the other type of milk. This can be ascribed to the differences in the fatty acid composition of the milk as a result of the fatty acid composition of the diets. After pumping of the milk at 31 degrees C, measurement of fat globule size distribution revealed a significant coalescence of milk fat globules in the milk obtained from the saturated fat diet due to pumping. Pumping at 4 degrees C or pumping the other type of milk did not result in coalescence of milk fat globules. Formation of free fatty acids increased significantly in both types of milk by pumping at 31 degrees C. Cooling the milk to 4 degrees C immediately before pumping inhibited an increased content of free fatty acids. However, when the milk was incubated at 4 degrees C for 60 min after cooling and then subjected to pumping, a significant increase in the formation of free fatty acids was observed in both types of milk. It is suggested that this increase in free fatty acids is caused by transition of polymorphic crystal forms or higher level of attached lipoprotein lipases to the milk fat globule before pumping.
对生鲜乳泵送的冷却策略进行了评估。将乳在31℃下泵送450秒，或者冷却至4℃后泵送，随后进行不同的孵育时间。使用了两种类型的乳；即来自喂食富含饱和脂肪补充剂日粮奶牛的乳，其乳脂肪球明显大于另一种来自喂食低脂日粮奶牛的乳，后者刺激大量的从头脂肪合成。通过低场1H NMR测定液态脂肪含量，结果表明，在4℃和31℃下，喂食饱和脂肪日粮奶牛的乳中液态脂肪含量也低于另一种类型的乳。这可归因于日粮脂肪酸组成导致的乳脂肪酸组成差异。在31℃下泵送乳后，脂肪球大小分布测量显示，由于泵送，来自饱和脂肪日粮的乳中乳脂肪球出现显著聚结。在4℃下泵送或泵送另一种类型的乳不会导致乳脂肪球聚结。在31℃下泵送，两种类型的乳中游离脂肪酸的形成均显著增加。泵送前立即将乳冷却至4℃可抑制游离脂肪酸含量增加。然而，当乳冷却后在4℃下孵育60分钟，然后进行泵送时，两种类型的乳中游离脂肪酸的形成均显著增加。提示这种游离脂肪酸的增加是由泵送前多晶型晶体形式的转变或附着在乳脂肪球上的脂蛋白脂肪酶水平升高引起的。
