Water mobility during renneting and acid coagulation of casein solutions: a differentiated low‐resolution nuclear magnetic resonance analysis

Abstract

Changes in water mobility during renneting and fermentation (acidification) of casein micelle solutions measured by nuclear magnetic resonance (NMR) are presented. Casein solutions (native and ultra‐high temperature or UHT‐treated) were renneted and fermented directly in the NMR instrument to detect changes in water mobility due to the induced structural changes online. The data were analysed using a newly developed method capable of differentiating several fractions of water in terms of their mobility according to the T 2 relaxation times in four distinct ranges, that is, immobile, weakly mobile, mobile and very mobile. Whereas obvious changes in the water mobility take place during acidification, no changes in the water mobility during renneting were observed. This is explained by proposing a model building on different mechanisms of coagulation between acidification and renneting.