Yak milk whey protein denaturation and casein micelle disaggregation/aggregation at different pH and temperature

At the natural pH of yak milk (pH 6.6), a low level (<30%) of K-casein (K-CN) was found in the serum phase after heating at 95 degrees C for 30 min, indicating that as much as 70% of the beta-lactoglobulin (beta-Lg) and K-CH complexes is associated with the micelle colloidal particles. The beta-Lg and K-CN levels increased from 13.2% and 2.6% at pH 6.0 to 35.2% and 60.1% at pH 7.0, respectively, when yak milk was heated at 95 degrees C for 30 min. At pH 6.0-6.4, the denatured whey proteins were associated with the caseins in the colloidal phase, resulting in milk gelation upon heating. The distribution of beta-Lg and K-CN complexes increased in the serum phase, demonstrated by the increasing levels of both beta-Lg and K-CN with increasing pH; at high pH (6.6-7.0), large proportions of beta-Lg and a-lactalbumin were lost, presumably forming complexes in the colloidal phase. (C) 2017 Elsevier Ltd. All rights reserved.