Combined effects of gamma irradiation and solvent-driven extraction on saponin and functional properties of okara

Soy saponins are amphiphilic triterpenoid glycosides valued for their surface activity and wide-ranging functionality and bioactivity. Okara, a by-product of soymilk production, is a potential source of saponins, but its recovery is limited by strong interactions with the insoluble matrix. This study investigated the effects of gamma irradiation (GI- 0.5 kGy) applied as a seed-level pretreatment, combined with 70 % aqueous organic solvent (methanol, ethanol and acetone) extraction of varying polarity on total saponin recovery from okara. The purified extracts were then analysed for total saponin content (TSC) and evaluated for emulsifying capacity (EC) and foaming capacity (FC) as indicators of surface-active functionality. The results showed that irradiation significantly increased total saponin recovery across all solvent, with the highest increase observed with methanol (18.17 mg/g DW), representing a ~27 % rise compared with the corresponding non-irradiated control. Irradiated extracts also exhibit enhanced emulsifying (1.31–1.35-fold) and foaming capacities (1.39–1.42-fold). Multivariate analysis revealed strong positive correlations between saponin content and functional properties and clearly distinguished irradiated from non-irradiated samples, with methanol showing the strongest combined effect with irradiation. To the best of our knowledge, this study provides the first evidence that GI combined with polarity-optimised solvent extraction substantially enhances saponin yield and surface-active functionality in okara. Overall, these findings highlight okara as a value-added sustainable source of saponins with potential applications as natural surfactants and phytonutrients in food-related applications.