Formation of whey protein/κ-casein complexes in heated milk:: Preferential reaction of whey protein with κ-casein in the casein micelles

Studies of the formation of soluble kappa-casein/whey protein (WP) complexes in heated (90 degrees C 10 min(-1)) milk and related mixtures of proteins have been made. The use of milk samples containing different genetic variants, and having different compositions, allowed the effects of changing the natural protein balance on the formation of particles to be investigated. In addition, studies were made of the effects of addition of WP or of purified kappa-casein to the milk samples. The addition of WP caused an increase in the amount and the size of the complexes, but addition of kappa-casein to the milk had little or no effect on the complex formation, nor did it seem that the added kappa-casein could react with the WP in the milk. Conversely, in systems where the casein micelles were absent, the purified kappa-casein reacted well with WP, suggesting that in milk heated at its normal pH the WP react preferentially with the kappa-casein on the casein micelles. (c) 2007 Elsevier Ltd. All rights reserved.