Exploring new methods of processing milk

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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.