Effect of Low Temperature Microfiltration on the Composition, Micellar Structure, and Coagulation Properties of Bovine Milk
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Abstract:
β-Casein (β-CN) dissociates from milk during low-temperature treatment. Skim milk was subjected to low-temperature microfiltration to obtain milk samples with β-CN removal ratios of 10, 20, or 30%. High-performance liquid chromatography (HPLC), field emission scanning electron microscopy, rheometry, and laser scanning confocal microscopy were used to study the changes in protein composition, CN micellar structure, and coagulation properties of these milk samples. The results showed no significant differences between skim milk and the milk sample treated with low-temperature microfiltration in fat content, total calcium content, and pH value, but significant differences were found in total protein content. Among proteins, no difference was found in κ-CN and αs2-CN concentrations, and significant differences were found for αs1-CN concentrations. However, although no difference was found in αs1-CN concentration among the samples treated by low-temperature microfiltration, highly significant differences were found in the concentrations of β-CN and whey protein, and these were significantly decreased with increasing processing time. Both skim milk and treated milk samples could form a compact and porous gel structure, and the trend in the rheological changes of the coagulations induced by glucono-delta-lactone (GDL) and GDL combined with chymosin were similar. However, with increasing β-CN removal ratio, the maximum G′ characterizing the hardness of curds gradually decreased, the curd structure gradually became loose, and more pores with a larger size appeared.
