Impact of environmental stresses on the stability of acidic oil-in-water emulsions prepared with tofu whey concentrates.

The emulsifying properties of tofu-whey concentrates (TWCs) at pH 3.0, 4.0, and 5.0, and the stability of the resultant oil-in-water emulsions against freeze-thawing (24 h, -20 °C) and controlled or mechanical stress (orbital stirring at 275 rpm, 40 min) were addressed. TWCs were prepared from tofu-whey by heating at 50 °C (8.0 kPa) or 80 °C (24.0 kPa), dialysis (4 °C, 48 h), and freeze-drying, giving the samples TWC50 and TWC80, respectively. The particle size and interfacial properties at the oil/water interface were measured. Emulsions were prepared by mixing the TWC aqueous dispersions (1.0% protein w/w) and refined sunflower oil (25.0% w/w) by high-speed and ultrasound homogenization. The preparation of TWCs at higher temperatures (80 °C) promoted the formation of species of larger particle size, a slight decrease of interfacial activity, and the adsorption of more rigid biopolymer structures associated with an increase of film viscoelasticity in interfacial rheology measurements. The emulsifying properties of both concentrates were enhanced with decreasing pH (5.0-3.0), through a significant decrease of particle size (D4,3) and flocculation degree (FD), but only those prepared with TWC80 exhibited higher stability to freeze-thawing and mechanical stress at pH 3.0. This could be ascribed to a combination of low initial D4,3 and FD values, high protein load, and the presence of rigid species that impart high viscoelasticity to the oil/water interface. These results would be of great importance for the utilization of TWCs as food emulsifiers in acidic systems to impart high stability to environmental stresses.

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

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 ±â€¯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.