生鲜乳中耐热脂肪酶特性及其对UHT乳品质影响机理的研究

UHT milk (UHT) accounts for about 70% market share of liquid milk in china, and heat-resistant lipase generated by Psychrophtiles in raw milk can tolerate UHT and residual activity often leads to decomposition milk fat of UHT and lead to declining or serious deterioration of milk quality. This project involved study on constitute of enzyme production bacteria in raw milk and its advantage Bacteria enzyme kinetics analysis; interaction mechanism of heat-resistant lipase raw milk and endogenous lipoprotein lipase (LPL); characteristics and structural analysis of heat-resistant lipase enzyme; enzyme inactivation and refolding kinetics and its mechanism; law and its mechanisms of UHT milk fat hydrolysis deterioration generated through thermostable enzyme. Finally ，we can obtain the structure of enzyme producing bacteria and enzyme type in raw milk, the structure, characteristics, and modified kinetic mechanism of heat-resistant lipase, make clear the mechanism of UHT enzymatic metamorphic heat-resistant lipase and for the development of effective enzyme inactivation technology, establish the raw milk quality grading standards suitable for UHT milk products.All of them may play an important theoretical guidance and technical reference to predict the shelf life of UHT milk, and to safeguard the interests of enterprises and consumers health

超高温瞬时灭菌乳（UHT）约占我国液态乳70%市场份额，原料乳中嗜冷菌产生的耐热脂肪酶可耐受超高温杀菌而残留酶活，并缓慢分解乳脂肪导致UHT乳品质下降或严重变质。本项目将通过对原料乳产酶菌相及其优势菌产酶动力学分析；耐热脂肪酶对生鲜乳内源性脂蛋白酯酶（LPL）的互作机制；耐热脂肪酶的酶学特性与结构解析；酶的灭活和复性的动力学分析及其机制研究；耐热酶对UHT乳脂肪水解变质规律及其机制研究等。以期掌握原料乳产酶菌相及酶的种类，探明耐热脂肪酶的结构、特性及变性动力学机制，明确耐热脂肪酶对UHT酶促变质机制，为制定有效的灭酶技术方案，制定适于UHT乳产品的生鲜乳质量分级标准，科学预测UHT乳货架期，维护企业利益和消费者健康发挥重要的理论指导和技术参考。

超高温瞬时灭菌乳（UHT）约占我国液态乳70%市场份额，原料乳中嗜冷菌产生的耐热脂肪酶可耐受超高温杀菌而残留酶活，并缓慢分解乳脂肪导致UHT乳品质下降或严重变质。本项目研究了耐热脂肪酶的酶学特性与结构解析、酶的灭活和复性的动力学分析及其机制研究、耐热酶对UHT乳脂肪水解变质规律及其机制等内容。结果表明，对分离自原料乳中的荧光假单胞菌耐热脂肪酶进行了研究，建立了一种高效表达系统，实现了大量、高活性地表达耐热性脂肪酶；对耐热性脂肪酶进行了分离纯化，建立了耐热酶微量检测技术；明确了耐热性脂肪酶的酶学特性，在核酸、氨基酸水平上阐明了其一级结构，同时模拟出了其一二级结构；建立了脂肪酶热动力学方程，为后续更好的灭酶提供理论基础；建立了通过原料奶耐热酶活性、体细胞数、嗜冷菌数等指标预测预报UHT乳安全货架期的数学模型，分析了原料乳中嗜冷菌数、脂肪酶活、产品风味、品质稳定性之间的相关关系；阐明了耐热性脂肪酶对UHT 乳脂肪水解的酶促变质机理。项目实施的对改善现有UHT 乳加工工艺、提高UHT 乳的货架稳定性、保持其品质的新鲜度和纯正风味具有重要的理论指导意义。本项目的研究成果对制定适于UHT乳产品的生鲜乳质量分级标准，科学预测UHT乳货架期，维护企业利益和消费者健康发挥重要的应用指导和技术参考。