Effect of Soybean-to-Water Ratio and pH on Pressurized Soymilk Properties

ABSTRACT:  The influence of soybean-to-water ratio (1:6 and 1:8) and pH (6 and 7) on characteristics of soymilk treated by high pressure processing (HPP, 500 and 600 MPa, 10 min, 25 °C) or thermal treatment (95 °C for 30 min) was investigated. Changes in the soymilk appearance were observed only for the 1:6, pH 6 soymilk that underwent a sol formation after HPP treatment and was apparently more viscous after thermal treatment. These changes were reflected in the viscosity values of these soymilks, which were increased by a factor of 4.3 and 3.6, after HPP and thermal treatment, respectively. After HPP treatment at pH 7 at both 1:6 and 1:8 ratios, the viscosity of the soymilks was unchanged compared to the controls. HPP treatment significantly increased the emulsion stability for all soymilks tested except for the 1:6, pH 7 soymilk. Peptide profiles of thermal- and pressure-treated samples were not affected; however, aggregates were observed in the soluble protein fraction after thermal and pressure treatment. Surface free and total free sulfhydryl content, surface hydrophobicity, and solubility of the proteins were decreased after HPP and thermal treatment regardless the soybean-to-water ratios and pH values of the soymilk.