The protective effect of sodium dodecylsulphate on the thermal precipitation of conalbumin. A study on thermal aggregation and denaturation

The thermal precipitation and denaturation of conalbumin was studied separately at different pH values, low concentrations of an anionic detergent and salt concentrations relevant to food products. Sodium dodecylsulphate (SDS) was used as a model detergent and was found to lower the limit for thermal precipitation from pH 10–11 to pH 6–8 leaving a neutral pH region open for heat processing without any decrease in solubility. This protection against precipitation took place at the expense of a reduced thermal stability of conalbumin. Analysis at linearly increasing temperatures was shown to be a productive method to study the coupling between the thermal precipitation and denaturation processes. This coupling was examined at two heating rates, 10 and 1.25°C/min, respectively. Two types of precipitation behaviour were identified, a rapidly and a slowly sedimenting one. At the lower heating rate and under conditions where rapidly sedimenting precipitates were formed there was a close correlation between precipitation and denaturation. The precipitation was, however, always completed prior to denaturation. When approaching conditions where no precipitation took place, which also implied a successive transition towards slowly sedimenting precipitates, the precipitation process became delayed compared to denaturation. Precipitation could thus be registered at temperatures far above those of complete denaturation. The precipitates formed showed a considerable variation in particle size and water holding capacity.