Effect of high-pressure homogenization on soy hulls and okara with or without soy hulls: Characterization and functionalities

Abstract

The production of soy milk and tofu may or may not involve a hulling step, generating two distinct by-products: okara from dehulled soybeans (okara㊀SH) and non-dehulled soybeans (okara㊉SH), which retain soy hulls (SH). The main objective of this study was to investigate the compositional and functional differences between these by-products and the effects of high-pressure homogenization (HPH) on their physicochemical, structural, and functional properties. Okara㊀SH, okara㊉SH, and SH were analyzed before and after HPH (1000 bar, 1 pass). Results showed that SH significantly impacted okara㊉SH composition, reducing protein content by 9 % (20.73 ± 0.02 %) while increasing cellulose by 46 % (15.44 ± 1.41 %) compared to okara㊀SH (22.61 ± 0.39 % protein, 9.88 ± 0.09 % cellulose). SH also influenced functional properties, lowering swelling capacity by 46 % (7.02 ± 0.69 to 3.80 ± 0.47 mL/g) and glucose adsorption capacity by 34 % (2.40 ± 0.18 to 1.58 ± 0.07 mmol/g) in okara㊉SH. HPH was beneficial for all samples; however, a positive effect of SH was observed for certain properties, such as oil-holding capacity (OHC). HPH significantly improved OHC, with increases of 467 % in SH (from 2.20 ± 0.02 g/g to 12.47 ± 0.68 g/g), 435 % in okara㊉SH (from 2.50 ± 0.05 g/g to 13.38 ± 0.51 g/g), and 425 % in okara㊀SH (from 2.78 ± 0.02 g/g to 14.60 ± 0.40 g/g). Moreover, water-holding capacity and solubility also improved post-HPH, suggesting enhanced application potential. Structural analysis confirmed HPH-induced modifications, including particle size reduction and matrix disintegration. These findings highlight HPH as a promising method for improving the functionality of soy by-products, particularly for food applications requiring enhanced water and oil retention properties.