Incorporation of Radiolabeled Whey Proteins into Casein Micelles by Heat Processing

Abstract

Skim milk was heated at 70, 95, and 140.degree. C to simulate the processes of pasteurization, forewarming, and UHT sterilization, and the specific interactions between .alpha.-lactalbumin or .beta.-lactoglobulin and the caseins studied using tracer amounts of added 14C-labeled whey protein. Radioactivities of the whey and of the washed casein pellets from renneted skim milk were measured and the extent of the interaction estimated. Upon heating skim milk at 70.degree. C for 45 s, less than 2% .beta.-lactoglobulin and less than .3% .alpha.-lactalbumin were incorporated into the curd. Heating at 95.degree. C for .5 to 20 min resulted in 58 to 85% of the .beta.-lactoglobulin and 8 to 55% of the .alpha.-lactalbumin becoming associated with the curd. Heating at 140.degree. C for 2 and 4 s caused 43 and 54% of the .beta.-lactoglobulin and 9 and 12% of the .alpha.-lactalbumin, respectively, to be bound to the curd fraction. The radiolabeling technique is very sensitive and useful for tracing low levels of interaction between whey proteins and casein in heated milk systems.