Thermal stability of skim milk whey protein solution blends

Dried protein fractions consisting predominantly of alpha-lactalbumin, beta-lactoglobulin or a whey protein concentrate (WPC) were dissolved in skim milk ultrafiltration permeate at 3.44% (w/w) protein. Each solution, denoted as alpha-FS, beta-FS or WPCS, was blended with skim milk at ratios of 100/0-60/40 (g skim milk g(-1) whey protein solution), to increase the ratio of whey to casein protein without changing the concentration of total protein. The blends were adjusted to pH values in the range 6.6-7.1 and heat stability determined by measuring the heat coagulation time at 140 degrees C. At initial pH 6.6-6.7, blends of skim milk and alpha-FS were slightly more heat stable than normal skim milk; gel electrophoresis indicated that thermal association between alpha-la and casein may have augmented heat stability. From pH 6.8-7.1, the blends were considerably less heat stable than normal skim milk, possibly due to the formation of soluble complexes between alpha-la and kappa-casein and accompanying heat-sensitive, kappa-casein-depleted casein micelles. In most cases, enrichment of skim milk with beta-lg, by blending with beta-FS or WPCS, caused a drastic reduction in heat stability; this was attributed to the low heat stability of beta-lg. An exception to this trend was the high heat stability of a 70/30 blend of skim milk and beta-FS or skim milk and WPCS; electrophoresis indicated that the heat stable entity was a complex between beta-lg and casein. (C) 1998 Canadian Institute of Food Science and Technology. Published by Elsevier Science Ltd.