Heat induced gelation of acid milk: balance between weak and covalent bonds

Abstract

Gelation of acidified milk at pH[ges ]5, after heat treatments is a well known phenomenon, due to the precipitation of whey proteins, and especially β-lactoglobulin onto κ-casein (Sawyer, 1969). High heat treatments cause denaturation of whey proteins which associate with κ-casein through disulphide interchange reactions (Hill, 1989). Since their charge is reduced, the denatured proteins associated with casein micelles become susceptible to aggregation when milk is then acidified, which promotes enhanced protein–protein interactions (Lucey et al. 1997). The gelation phenomenon involves disulphide bonds (Hashizume & Sato, 1988; Goddard, 1996) which are responsible for the gel firmness (Goddard, 1996). However, other interactions between proteins can occur, such as hydrogen and hydrophobic bonds, especially at the initial stage of interactions (Haque et al. 1987; Haque & Kinsella, 1988; Jang & Swaisgood, 1990). It is therefore relevant to investigate a possible contribution of weak linkages to the gel structure and firmness.