Increasing the emulsifying capacity of whey proteins at acidic pH values through covalent modification with allyl isothiocyanate

Abstract

The emulsifying capacity of whey protein isolate (WPI) is reduced at acidic pH values, where the protein is fully protonated. A covalent modification (disulphide cleavage and amide group binding) of whey proteins with the electrophilic plant derived compound allyl isothiocyanate (AITC) was previously found to increase their hydrophobicity and backbone flexibility especially at acidic conditions. This could be a promising means to alter the physicochemical properties of WPI proteins in favour of a higher emulsifying capacity at acidic pH values.In a first step, the stability of the AITC modification during high-pressure homogenisation was assessed at pH 2–7. Following this, emulsions (o/w) with rapeseed oil were prepared and the oil droplet size and the zeta potential were measured as a function of pH value and oil concentration. The creaming stability was analyzed during storage and under accelerated conditions using an analytical photo-centrifuge.The AITC-modification remained stable during high-pressure treatment. A significantly enhanced emulsifying capacity of the modified WPI at pH 2 was observed. The creaming stability at pH 2 and 4 increased significantly. The effects were less pronounced at pH 6 or 7.