Exploring new methods of processing milk

世界各地加工原料奶的标准方式包括巴氏杀菌法(以杀灭所有人类病原体)和均质化(以减小脂肪球大小以防止奶油起泡)。在加拿大，省级法律要求所有牛奶都要经过巴氏杀菌，因为原料奶可能含有危险的微生物，如副结核分枝杆菌、增生性单核细胞增多性乳杆菌和大肠杆菌。尽管存在这种危险，但越来越多的消费者希望饮用生奶，因为他们觉得目前的加工方法改变了牛奶的感官和营养品质。巴氏杀菌确实会破坏酶和免疫球蛋白，其中几种蛋白质已知对健康有好处。高温还促进乳清蛋白β-乳球蛋白和kappa-酪蛋白之间的相互作用，kappa-酪蛋白抑制了凝乳酶活性，并改变了奶酪和酸奶的质地。在陈化过程中，复合体的形成也会阻碍蛋白质多肽的产生，从而改变最终奶酪的感官品质。鉴赏家知道，用原料奶生产的奶酪在口感和质地上往往比用巴氏杀菌牛奶生产的奶酪更好。均化步骤还会改变原料奶中存在的脱脂乳膜(SMM)的结构，从而改变其口感。这个项目将专门研究热处理和均质如何改变牛奶的结构。申请人最近发表的工作首次表明酪蛋白胶束具有类似纤维的结构(J.乳品科学。90：75-(2007))，并提出了一种新的胶束稳定机理，该机理与酪蛋白原纤维模型一致。因此，这项研究将首先探索酪蛋白胶束原纤维结构如何在温度升高和存在β-乳球蛋白的情况下发生变化。接下来，申请人将研究几种简单的分离技术(膜过滤、沉淀、浮选)，这些技术可用于原料奶，以在进一步加工之前去除各种有价值但不稳定的成分。然后，这些组分可以被用作有价值的食品成分，或者在人类病原体被摧毁后重新引入牛奶中，以生产更健康、更有功能的乳制品。

The standard manner by which raw milk is processed throughout the world involves pasteurization (to destroy all human pathogens) and homogenization (to reduce fat globule size to prevent creaming). In Canada, provincial laws require that all milk be pasteurized, because raw milk can harbour dangerous microbes such as M. paratuberculosis, L. monocytogenes and E. coli. Despite this danger, a growing number of consumers wish to drink raw milk because they feel that current processing methods alter the sensory and nutritional qualities of the milk. Pasteurization does destroy enzymes and immunoglobulins and several of these proteins are known to have health benefits. High temperatures also facilitate interactions between the whey protein beta-lactoglobulin and kappa-casein, which inhibits rennet activity and alters the texture of cheeses and yoghurt. Complex formation also hinders the production of protein peptides during aging, thereby altering the sensory qualities of the final cheese. Connoisseurs know that cheeses produced from raw milk are often superior in taste and texture to those coming from pasteurized milk. The homogenization step also alters the structure of the skim milk membranes (SMM) present in raw milk, thereby changing its mouth feel. This project will specifically look at how heat treatment and homogenization alters milk structure. The applicant has recently published work that was the first to show that casein micelles have a fibril-like structure (J. Dairy Sci. 90:75-89 (2007)) and has proposed a new micelle stabilization mechanism that is consistent with this casein fibril model. Consequently, this study will first explore how casein micelle fibril structure is altered by elevated temperatures alone and in the presence of beta-lactoglobulin. Next, the applicant will examine several simple separation techniques (membrane filtration, precipitation, flotation) that can be used on raw milk to remove the various valuable yet unstable components before further processing. These fractions could then be used as valuable food ingredients or reintroduced into the milk after human pathogens have been destroyed to produce healthier and more functional dairy products.