Physical stress induces metabolic changes in kidney bean: GABA, polyphenol spectrum, and antioxidant capacity

Germination is a cost-effective way to enrich bioactives in legumes, yet the effects of novel physical stresses during germination remain underexplored. This study investigated the effects of germination under stress conditions (including ultrasound (US), ultraviolet irradiation (UV), cold plasma (CP), and hypoxic (vacuum, VC) treatments) on the nutritional content and antioxidant capacity of kidney beans. The research focuses specifically on the enrichment and accumulation mechanisms of γ-aminobutyric acid (GABA) and polyphenols. Metabolomics combined with analyses of key metabolic enzyme activities revealed that all 4 physical treatments effectively promoted the conversion of glutamate to GABA. Specifically, US and VC treatments enhanced the polyamine-mediated GABA synthesis pathway, while the VC treatment additionally suppressed GABA degradation. Regarding polyphenol enrichment, UV treatment promoted the accumulation of phenolic acids and flavonoid glycosides by enhancing the downstream metabolism of caffeic acid and dihydroquercetin. Meanwhile, VC treatment promoted the enrichment of isoflavones by activating the kiveton metabolic pathway. Furthermore, 17 polyphenols showed a significant positive correlation with in vitro antioxidant capacity. Among them, licoisoflavone A, calendoflavobioside, lupiwighteone, and glycyrrhizaisoflavone B emerged as the core differential markers distinguishing the physical stress-treated groups from the control. The increased levels of these compounds significantly contributed to the enhanced antioxidant activity observed in the physically treated germinated beans. This study provides novel insights for the high-value application of legumes.