Influence of chemical composition and structural properties on the surface behavior and foam properties of tofu-whey concentrates in acid medium

Abstract

This article focuses on the impact of chemical composition and structural properties of tofu-whey concentrates on their surface behavior at the air/water interface and foaming properties in acid medium. Liquid tofu-whey (pH 5.6 ± 0.1) was concentrated at three combinations of temperature and pressure (50 °C-8.0 kPa, 65 °C-16.0 kPa and 80 °C-24.0 kPa), with further dialysis (4 °C, 48 h) and freeze-drying, giving the samples TWC50, TWC65 and TWC80, respectively. The increase of temperature during the concentration step promoted the enrichment of the concentrates in crude protein and calcium, without appreciable changes in the yield, the carbohydrate content and the polypeptide composition. For TWC80, the increase the degree of glycosylation and the intensity of the hydrophobic effect promoted the decrease of molecular flexibility and the formation of compact aggregates mediated by disulfide bridges as was evidenced by tricine-SDS-PAGE, TGA and FTIR assays. These structural differences have a pronounced impact of the pH-dependence of turbidity and solubility of protein and polysaccharides. At pH 4.0 all concentrates evidenced a ζ-potential close to zero, which enhanced their foam ability (overrun >1500%). Nevertheless, at this pH, TWC80 showed both the highest carbohydrate-to-protein mass ratio in the soluble fraction (>1.8) and foam stability (FS). Thus, the improvement of FS at pH 4.0 would be associated to the effective adsorption of compact rich-in-protein aggregates at the air/water interface and the higher content of soluble polysaccharides in the bulk phase. These findings are relevant for the application of tofu-whey concentrates in acidic dispersed systems, such as foams and aerated food emulsions.