Improving emulsifying properties of okara-derived insoluble soybean fiber (ISF): contribution of steam-cooking processing and various fractions of ISF

Abstract

In response to the low utilization and poor emulsifying properties of insoluble soybean fiber (ISF) derived from okara, this work aimed to improve the structural-physicochemical properties of ISF by steam-cooking process through adjusting the pH, temperature and duration. The effects of soluble and insoluble fractions of ISF on its emulsifying properties were investigated. Increased temperature to 120 °C and prolonged durations of steam-cooking at pH 3 disintegrated the ISF matrix and reduced the aggregation, while notable aggregation was observed at pH 11 and 120 °C. The heightened steam-cooking intensity led to stronger hydrogen bonding within ISF, accompanied by the increase in crystallinity index from 26.7%–30.8% to 40.1%–44.2%. Additionally, there was a notable enhancement in gel-like properties, as evidenced by the elastic modulus of ISF suspensions increasing from 0.3–247.2 Pa to 1048.0–1355.0 Pa. The steam-cooking positively influenced the surface wettability and emulsifying properties of ISF, particularly evident by the near-neutral contact angle of ISF steam-cooked at 120 °C, resulting in emulsions with finer droplets. The microstructure and apparent viscosity of the emulsions were primarily influenced by the insoluble fractions, despite the higher capability of soluble fractions to reduce interfacial tension. The insoluble fractions prevented droplet aggregation by facilitating the formation of droplet clusters. Overall, steam-cooking improved the emulsifying properties of ISF by modulating composition and physicochemical properties, providing promising applications for ISF as food ingredients in emulsions and gels.