Structural and functional enhancement of okara (soybean residue) proteins using microwave- and ultrasound-assisted enzymatic hydrolysis

초록

Okara (soybean residue), a nutrient-rich soybean byproduct, remains underutilized due to low protein extraction efficiency and limited information on protein structure-function relationships. This study investigated the effects of alkali, microwave, and ultrasound pretreatments, combined with enzymatic hydrolysis, on the structural and functional properties of okara-derived peptides. Structural analyses (FTIR, circular dichroism, fluorescence spectroscopy, surface hydrophobicity, and scanning electron microscopy) revealed that the microwave and ultrasound pretreatments effectively disrupted protein aggregation, enhancing enzymatic accessibility and modifying secondary structures. Ultrasound-treated samples exhibited the highest degree of hydrolysis (52.07 %) and in vitro digestibility (56.64 %), with favorable particle characteristics and surface charge. Functionally, ultrasound-extracted peptides showed the best antioxidant capacity (ABTS IC50: 1.33 mg/mL) and enzyme inhibitory activities (alpha-glucosidase IC50: 19.57 mg/mL, alpha-amylase IC50: 13.28 mg/mL, ACE IC50: 0.19 mg/mL), attributed to enhanced peptide release and exposure of bioactive residues. Compared to alkali extraction, microwave and ultrasound pretreatments significantly improved the functionality of okara peptides. This study provides an efficient sustainable approach for valorizing soybean residue into functional ingredients with potential applications in health-promoting foods.

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