货架期内品质劣变UHT乳的理化特性及风味品质特性研究

Study on the physicochemical characteristics and flavor quality of UHT milk with quality deterioration during shelf life

以货架期内品质劣变和正常品质的超高温(UHT)灭菌乳为研究对象,通过测定营养成分、pH值、酒精阳性乳、Zeta-电位、电导率、酶活性、色差值来进行对比分析。同时采用气相色谱-质谱(Gas chromatography-mass spectrometry,GC-MS)解析品质劣变和正常UHT乳风味品质的变化规律。结果表明,相较于正常成品乳,多数品质劣变乳的pH值、Zeta电位绝对值降低,电导率增加;多个品质劣变乳为酒精阳性乳,同时品质劣变乳中发现少量的凝块和沉淀,其色度值-a值显著降低,b值显著增加。相较于正常UHT乳,WY工厂的品质劣变乳的蛋白酶活性显著增加,QY工厂脂肪酶活性显著增加,推测导致两工厂品质劣变现象出现的原因并不完全相同。GCMS结果表明,品质劣变乳中影响风味的酯类和酮类化合物明显减少,缺失了很多产生良好风味的挥发性物质,同时增加了一些具有不愉快气味的物质。

Through the measurement of nutrients, pH value, alcohol-positive milk, zeta potential, conductivity, enzyme activity, and color difference values, the UHT sterilized milk with degraded quality and normal quality were compared. Gas chromatography-mass spectrometry(GC-MS)was also used to analyze the changes in flavor quality of the deteriorated and normal UHT milk. The results showed that the pH value and zeta potential of most of the deteriorated UHT milk decreased in absolute value and the conductivity increased in comparison with the normal milk;several of the deteriorated samples were judged as alcohol-positive milk, and a few number of clots and precipitates were found in the deteriorated milk.Compared with the normal UHT milk, the protease activity of the quality deteriorated milk from the WY factory increased significantly and the lipase activity from the QY factory increased significantly, so it is speculated that the causes of the quality deterioration in the two factories are not identical. The dates of GC-MS revealed that there was a significant decrease of esters and ketones affecting flavor in the quality deteriorated milk,many volatile substances that produced good flavor were missing, and some substances with unpleasant smell were added.