不同贮藏温度对UHT乳品质的影响

Effects of Storage Temperature on Physico-chemical Characteristics of UHT Milk

UHT乳作为一种经超高温瞬时灭菌、无菌灌装生产的长货架期液态乳,具有品质优良,饮用方便等优点.但是在贮藏过程中,UHT乳经常会因残留酶或微生物作用而产生蛋白质凝块、沉淀或脂肪上浮等缺陷,从而影响UHT乳的品质.本研究通过UHT中试生产线无菌灌装制备PET瓶装UHT乳,将其分别置于7,25,37℃下保温观察,定期测定色泽、酪蛋白胶体粒径、蛋白质水解度及理化指标等变化.结果表明,贮藏过程中UHT乳发生的主要反应为蛋白质水解、脂质氧化和美拉德反应,UHT乳的pH值、游离钙离子含量和酪蛋白胶体粒径呈下降趋势,b*值、蛋白水解度、脂质氧化程度呈上升趋势.120 d保温试验结束后,除37℃贮藏下的UHT乳色泽从第90 d开始发生明显变化外,各UHT乳样品并未产生明显的脂肪上浮和蛋白沉淀等现象.

As a long shelf life liquid milk, ultra high temperature sterilized （UHT） milk has become an important part of people＇s diet with high quality and convenience. However, the physico-chemical chan- ges often lead to aggregation or sedimentation of milk which affect the quality of UHT milk during storage. In this study, close attention was paid to the reactions occurred in UHT milk during 120 d of storage at 7, 25 and 37 ~C. The UHT milk was produced by the pilot equipment and packed in PET bottle. The overall milk physico-chemical changes revealed the development of the Maillard reaction and proteolysis and lipid oxidation reaction. These reactions resulted in the reduction of pH value, colloidal casein particle size and the ionized calcium content, but the increase of the b＊ value, the degree of milk protein hydrolysis and the level of lipid oxidation reaction for UHT milk during storage. After the end of the storage test, the color of UHT milk at 37 % changed significantly. However, fat floating and protein precipitation did not appear in all UHT milk samples.