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

Abstract

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 10-1 1 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.

Polyols (Glycerol and Ethylene glycol) mediated amorphous aggregate inhibition and secondary structure restoration of metalloproteinase-conalbumin (ovotransferrin)

“…1A and D) with slight low turbidity and scattering indicate that protein denatures and the onset of aggregation occurs just before the denaturation. The same pattern was also observed at neutral pH (close to isoelectric point) as denaturation occurs in the pI range of CA 6.0-6.8 [53]. The reduction in turbidity and Rayleigh scattering is due to the interaction of polyols with CA which nearly quash the impact of heat treatment.…”

Application of differential scanning calorimetry in food research and food quality assurance

“…Thermal stability of several proteins of interest to the food industry were investigated indeed by DSC as affected by various environmental factors. Studies on egg proteins such as ovalbumin [8,9], conalbumin [10] and lyzozyme [11], milk proteins such as beta-lactoglobulin [12][13][14], ot-lactalbumin [15,16] and casein, as well as muscle proteins such as myosin and actin [17,18] and plant proteins such as vicilin from faba beans [8] and rapeseed storage protein [19], and globulins isolated from various cereal grains [20] can be mentioned.…”

“…The introduction of DSC improved greatly also the understanding of proteindetergent interactions, using an anionic detergent such as sodium dodecyl sulfate [3,10] and helped to clarify the utility of naturally occurring substances such as fatty acids to either stabilize or denature a protein.…”

Unexpected differences in the behavior of ovotransferrin at the air–water interface at pH 6.5 and 8.0

“…The analysis of the gelation properties of apo-ovotransferrin by DSC has allowed characterizing its thermal denaturation around 65°C at pH 7.0: it is the most heat-sensitive protein of egg white [7][8][9]. Its foaming properties seem intermediate between those of ovalbumin and lysozyme [10,11].…”