液态奶杀菌技术的发展

液态奶杀菌技术的发展。液态奶是各种微生物的优良培养基。在其生产过程

中，原料乳、半成品、成品都容易被微生物污染，液态奶中常见的微生物包括细菌、乳酸菌、霉菌三大类[62]。细菌包括埃希氏菌属（Eshrichia）、沙门氏菌属（Salmonella）、志贺氏菌属（Shigella）、克雷伯氏菌属（Klebsiella）、肠杆菌素（Enterobacter）、萨雷氏菌属（Serratia）、变形菌属（Proteus）等共30多种[63]。其中有许多菌属能引起伤寒热和痢疾，有的能引起菌血症、脑膜炎，有的能引起生殖道、呼吸道和伤口感染。乳酸菌包括乳链球菌、乳酸球菌、肠球菌、乳酸杆菌等，有的则用于奶油、干酪的发酵剂，但对于液态奶来说过多的乳酸菌会使得奶品变味、粘稠，使得保质期缩短。霉菌中有毛霉、曲霉、青霉根霉等大多数有害，少数如娄地青霉等则作为凝乳霉应用于工业生产[62-65]。杀菌的目的一是确保产品安全，杀死有害细菌或对其代谢毒素灭活；二是延长保质期。传统的方法有巴氏消毒和超高温（UHT）杀菌，其目的首先是杀死引起人类疾病的所有微生物，其特点是微生物杀灭效果好，实施容易，但破坏了鲜乳的口感。新型杀菌技术则有微波杀菌和电场杀菌（PEF），其中微波杀菌也是利用微波至热原理与传统杀菌效果没多大区别。电场杀菌则是利用脉冲高压放电产生高强度电流在短时间内杀死微生物，其机理是在细胞膜建立起电子交换，当电压超过临界值时导致细胞膜紊乱，引起细菌死亡，也有的细菌因电击穿导致死亡。电场杀菌的优点是杀菌后可以避免食品因加热导致能量损失、也不会引起食物感官和理化指标的

变化。

液态奶中微生物检测技术的发展。课题关心的是液态奶在储运和在货架上摆放后是否变质超过相关标准规定的问题，引起变质的主要原因是生产过程中杀菌不彻底、储运不当导致微生物滋生。所以这里只单论奶品中微生物的检测方法发展情况。微生物检测常用的方法是接种、分离纯化和培养及生化反应，虽然新的微生物诊断技术已广泛应用于食品微生物的鉴别，但还是以这些方法为基础，辅以现代传感技术来进行检测。现代生物技术在奶品检验中的应用有：快速酶促反应及细菌代谢产物的检测；免疫学方法检测抗原或抗体，如抗血清凝集技术、乳胶凝集技术、荧光抗体检测技术、采用抗体致敏的SPA检测（即协同凝集试验）、酶联免疫测试技术等；分子生物学技术检测病原性微生物，如核酸探针可以检测因无法培养、不能作生化鉴定、不可观察的微生物产物以及缺乏诊断抗原等方面的检测（如肠毒素），还可以检测同食源性感染有关的病毒（如肝炎病毒）等。

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