超高温乳加工过程中纤溶酶活性变化规律的研究

Study on the changing rule of plasmin activity in processing of ultra high temperature milk

中文关键词:  UHT乳  纤溶酶  酶联免疫吸附法

英文关键词:ultra high temperature milk  plasmin  enzyme-linked immunosorbent assay

中文摘要:

      目的 探究超高温(ultra high temperature, UHT)乳生产过程中可能影响纤溶酶活性的关键因素。方法 采用酶联免疫吸附法(enzyme-linked immunosorbent assay, ELISA), 测定并分析从原料乳到UHT成品乳生产过程中多种因素对纤溶酶活性造成的影响。具体研究的影响因素包括牛患乳房炎程度、乳中体细胞数、接种疫苗、改变饲喂条件、离心处理、巴氏杀菌预热条件、微滤处理及UHT预热条件。结果 在原料乳阶段, 牛乳中纤溶酶活性高低与牛乳房炎的严重程度及乳中体细胞数呈现显著正相关, 而与牛是否接种疫苗或是否改变饲料种类无显著相关性。在生产加工阶段, 离心除菌会使得乳中纤溶酶活性略有上升; 55 ℃相比于其他温度的巴氏杀菌预热处理能最有效地抑制纤溶酶活性上升; 微滤可降低约10%的纤溶酶活性; 不同UHT预热处理均会导致酶活性上升, 其中90 ℃处理5 s的条件下, 酶活性上升幅度较小, 仅为1.52%。结论 牧场端需对患乳房炎的奶牛进行重点控制, 并关注体细胞数异常的牛乳。工艺端可采用合适的巴氏杀菌预热条件及UHT预热条件以抑制乳中纤溶酶活性上升, 可引入微滤工艺以降低纤溶酶活性。本研究为抑制UHT乳中纤溶酶活性及该酶对成品乳造成不良影响的相关研究提供科学依据。

英文摘要:

      Objective To investigate the key factors that may influence plasmin activity during the production of ultra high temperature (UHT) milk. Methods An enzyme-linked immunosorbent assay (ELISA) was employed to assess and analyze the effects of various factors on plasmin activity throughout the UHT milk production process. The specific factors examined included the degree of mastitis in cows, somatic cell count in milk, vaccination status, changes in feeding conditions, centrifugation processes, pasteurization preheating conditions, microfiltration techniques, and UHT preheating conditions. Results At the raw milk stage, a significant positive correlation was observed between plasmin activity levels in bovine milk and both the severity of bovine mastitis and somatic cell counts. However, no significant correlation was found regarding vaccination status or changes in feed type. During UHT milk production, centrifugal sterilization resulted in a slight increase in plasmin activity; pasteurization preheating at 55 ℃ proved most effective at inhibiting this increase. Microfiltration reduced plasmin activity by approximately 10%. Additionally, varying UHT preheating conditions led to an overall increase in enzyme activity; however, under treatment at 90 ℃ for 5 seconds, a condition yielding only a minimal increase of 1.52%, the rise remained relatively low. Conclusion For pasture, it is essential to focus on managing cows with mastitis and monitoring those milk with abnormal somatic cell counts. At the processing stage, implementing appropriate preheating conditions for pasteurization and UHT can effectively inhibit increases in plasmin activity within milk. Furthermore, incorporating microfiltration can serve as an additional strategy to reduce such enzymatic activities. This study provides a scientific foundation for further research aimed at controlling elevations of plasmin activity in UHT milk.