不同乳糖酶酶学特性比较及在无乳糖原料奶生产中的应用

以3 种乳糖酶为研究对象，研究其酶学特性，并应用于无乳糖原料奶的生产。采用聚丙烯酰胺凝胶电泳法分析乳糖酶的成分及分子质量；邻硝基苯酚β-D-半乳糖苷法测定乳糖酶活力；用电子鼻检测原料奶储存过程中气味的变化。结果表明：酶A的等电点为4.0和5.0，酶B为5.0，酶C为3.0；酶A在40 ℃和pH 6.5时酶活最高，酶B在35 ℃和pH 6.5时酶活最大，酶C在45 ℃和pH 5.0时活力最高。电子鼻检测结果表明，在4～10 ℃储存12 h，原料奶气味无显著性差异。在4～6 ℃条件下，添加6 000 U/g乳糖酶A在5～6 h内可将原料奶中乳糖水解至0.5%以下；添加6 000 U/g乳糖酶B在8～9 h将原料奶中乳糖水解至0.5%以下。因此，乳糖酶A和酶B为中性乳糖酶，乳糖酶C为酸性乳糖酶；生产无乳糖原料奶采用中性乳糖酶A较好。

Comparison of Enzymatic Characteristics of Lactases from Different Sources and Their Application in Lactose-Free Raw Milk Processing

The objective of this work was to research the enzymatic characteristics of three lactases derived from different sources, and their application in the production of lactose-free raw milk. The composition and molecular mass of the lactases were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Lactase activity was detected using o-nitrophenol β-D-galactoside (ONPG). An electronic nose was used for detecting changes in the odor of raw milk during storage. The results showed that the isoelectric points of lactase A was 4.0 and 5.0, the isoelectric point of lactase B was 5.0, and the isoelectric point of lactase C was 3.0. Lactase A had the highest enzymatic activity at 40 ℃ and pH 6.5, B had the highest enzyme activity at 35 ℃ and pH 6.5, and C had the highest activity at 45 ℃ and pH 5.0. The results of electronic nose showed that there was no significant difference in the odor of raw milk stored at 4–10 ℃ for 12 h. In addition, after hydrolysis with 6 000 U/g of lactase A for 5–6 h or lactase B for 8–9 h at 4–6 ℃, the lactose content in raw milk was reduced to less than 0.5%. Therefore, lactases A and B were neutral lactases while lactase C was an acid lactase, and the use of neutral lactase A was more suitable to produce lactose-free raw milk.