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ABSTRACT
Although many studies have reported negative effects on cheese properties resulting from the use of buttermilk in cheese milk, the cause of these effects has not been determined. In this study, buttermilk was manufactured from raw cream and pasteurized cream, as well as from a cream derived from pasteurized whole milk. Skim milks with the same heat treatments were also manufactured to be used as controls. Compositional analysis of the buttermilks revealed a pH 4.6-insoluble protein content approximately 10% lower than that of the skim milk counterparts. Milk fat globule membrane (MFGM) proteins remained soluble at pH 4.6 in raw cream buttermilk; however, when heat was applied to cream or whole milk before butter making, MFGM proteins precipitated with the caseins. Rennet gel characterization showed that MFGM material in the buttermilks decreased the firmness and increased the set-to-cut time of rennet gels, but this effect was amplified when pasteurized cream buttermilk was added to cheese milk. The microstructure of gels was studied, and it was observed that gel appearance was very different when pasteurized cream buttermilk was used, as opposed to raw cream buttermilk. Model cheeses manufactured with buttermilks tended to have a higher moisture content than cheeses made with skim milks, explaining the higher yields obtained with buttermilk. Superior retention of MFGM particles was observed in model cheeses made from pasteurized cream buttermilk compared with raw cream buttermilk. The results from this study show that pasteurization of cream and of whole milk modifies the surface of MFGM particles, and this may explain why buttermilk has poor coagulation properties and therefore yields rennet gels with texture defects.
Key words: buttermilk, rennet gel, milk fat globule membrane, cheese
INTRODUCTION
In 2005, butter production totaled 6.1 × 10^sup 8^ kg and 8.4 × 10^sup 7^ kg in the United States (USDA, 2006) and Canada (Statistics Canada, 2007), respectively. Most plants produce butter from 40% milk fat containing pasteurized cream. Churning of 40% milk fat cream yields almost equal amounts of butter and buttermilk. Buttermilk contains most of the aqueous soluble components, including a portion of the shredded milk fat globule membranes (MFGM). Considering the rather large volumes of buttermilk produced, this low-value by-product is either condensed or spray-dried to ensure longer shelf life. Because...