ELECTROPHORETIC CHARACTERIZATION OF THE PROTEIN PRODUCTS FORMED DURING HEAT-TREATMENT OF WHEY-PROTEIN CONCENTRATE SOLUTIONS

Whey protein concentrate (WPC) solutions containing 10, 30, 60 and 120 g dry powder/kg were heated at 75 degrees C and whey protein aggregat ion was studied by following the changes in the distribution of beta-l actoglobulin, alpha-lactalbumin and bovine serum albumin, using one di mensional and two dimensional PAGE. The one dimensional PAGE results s howed that a minimal quantity of large aggregates was formed when 10 g WPC/kg solutions were heated at 75 degrees C for up to 16 min whereas appreciable quantities were formed when 30, 60 and 120 g WPC/kg solut ions were similarly treated. The two dimensional PAGE analysis showed that some disulphide-linked beta-lactoglobulin dimers were present in heated 10 g WPC/kg solution, but very little was present in heated 120 g WPC/kg solution. By contrast, SDS was able to dissociate monomeric protein from high molecular mass aggregates in heated WPC solution of 120 g/kg but not in 10 g WPC/kg solution heated for 30 min. The rates of loss of native-like and SDS-monomeric beta-lactoglobulin, alpha-lac talbumin and bovine serum albumin during heating increased as the WPC concentration was increased from 10 to 120 g/kg. In 120 g WPC/kg solut ion heated at 75 degrees C, the amounts of SDS-monomeric beta-lactoglo bulin in each sample were greater than the quantities of nativelike pr otein. However, in WPC solutions of 10, 30 and 60 g/kg, the difference s between the amounts of native-like and SDS-monomeric proteins were s light. The loss of the native-like or SDS-monomeric proteins was consi stent with a first or second order reaction. In each case, the apparen t reaction rate constant appeared to be concentration-dependent, sugge sting a change of aggregation mechanism in the more concentrated solut ions. Overall, these results indicate that in addition to disulphide-l inked aggregates, hydrophobic aggregates involving beta-lactoglobulin, alpha-lactalbumin and bovine serum albumin were formed in heated WPC solution at high protein concentration, as suggested by model studies using binary mixtures of these proteins.