Mineral modulation of thermal aggregation and gelation of whey proteins:: from β-lactoglobulin model system to whey protein isolate

Solutions of 100 g . kg(-1) of beta-lactoglobulin (beta-Lg), beta-Lg + alpha-lactalbumin (alpha-La), beta-Lg + alpha-La + bovine serum albumin (BSA) or whey protein isolate (WPI) were heated at 75 degreesC, pH 6.8 in water and in the presence of either 100 mmol . L-1 NaCl or 10 mmol . L-1 CaCl2. The subsequent polymerisation-aggregation processes in solution before gelation and the physical properties of the formed gels were determined. The disappearance of native-like proteins, formation of beta-Lg covalent dimer and the nature of the interactions involved in the formed aggregates were addressed. Whatever the protein system, both NaCl and CaCl2 increased gel strength and decreased gelation time. At gelling time, relatively small aggregates, formed by the contribution of the total initial amount of proteins, were observed in samples without added salts. In contrast, with NaCl or CaCl2, only part of the initial amount of proteins was aggregated before gel time. Very large aggregates were formed in the presence of calcium. Under these two mineral conditions, as well as in samples without added salt, covalent disulphide bonds were seen to be the major forces involved in the aggregation process at gel time.