【作者】 张爱霞；

【导师】 张佳程； 生庆海； 陈德倡；

【作者基本信息】 河北农业大学 ， 农产品加工及贮藏工程， 2003， 硕士

【摘要】 UHT乳是指乳经135～150℃高温杀菌而生产的一种长货架期液态乳。而且UHT乳有营养丰富、保存期长、便于携带和饮用，因此倍受消费者青睐。 乳的凝胶现象是UHT乳产品中较常见的质量问题，对其明确原因目前国内外还无定论。通过本研究发现，UHT处理不能完全钝化乳中的酶，因此在产品贮存过程中，乳蛋白酶、脂肪酶能够水解乳中的蛋白质和脂肪，最终使产品发生一定程度的水解，并表现为乳的粘度、酸度增大，使产品具有形成凝胶的倾向，但是在贮存的前150d并未发现凝胶的形成，所以在UHT乳出现凝胶方面有待于进一步深入研究。 脂肪上浮是UHT乳贮存中存在的普遍现象，影响因素也很多，如原料乳脂肪含量的差异、原料乳与产品的长期高温贮存、均质参数的选择等。本试验分析了乳中的酶与乳的理化成分对乳脂肪上浮的影响。乳中存在的蛋白水解酶对产品的脂肪上浮具有重要影响，表现在产品贮存中，随着蛋白水解度的增大发生脂肪上浮越严重。而且原料乳的理化成分，尤其表现为脂肪与蛋白含量的不同比对产品的脂肪上浮影响也很大。当乳中脂肪含量越高时，产品发生脂肪上浮程度越严重。而当乳中含有的脂肪相对于蛋白含量较低(在1.1左右)时，可以通过添加适量的乳化剂来减缓乳脂肪的上浮，但是并不能完全消除脂肪上浮现象。此外加工过程中的均质工艺对乳的质量也产生一定影响，就目前的产品分析来看，采用二级均质效果较好，均质压力为20MP和5MP，可以使脂肪球大小一致并均匀分布。更多还原

【Abstract】 UHT(Ultra High Temperature) processed milk is a long shelf life liquid milk product, which is sterilized in 135～150℃. Consumers prefer UHT milk by its nourishment enrich, long shelf life, easy to carry and drink.Coagulation is a common phenomenon in UHT milk. And the real reason is not sure in the world. The research indicated that not all milk enzymes were destroyed by UHT processing. Proteolysis and lipolysis enzymes hydrolyzed milk protein and fat, led to increase of milk viscosity and acidity, tendenced to coagulation, but didnot emerge coagulation during storage for 150 days.Fat separation is another general phenomenon during UHT milk storage. There are several factors have an effect on it, such as the quantity of milk fat, storage in a high temperature and enzymes. The study showed that the more degree of milk protein hydrolized, the more severity of fat separation. The value of milk fat to protein affected the fat separation. The higher of the compare of milk fat and protein, the more severity of fat separation. When milk fat is relatively lower to milk protein, the fat separation can be weaken by mixing some emulsifier properly, but cannot eliminate this phenomenon. High pressure processing made milk fat globe smaller and well-distributed ,and it is good for milk quality during storage.更多还原