Unraveling the Impact of <i>Aspergillus sojae</i>—A Food-Grade Fungus—On Phytoalexins, Phenolic Acids, and the Antioxidant and Antidiabetic Activity of Different Legumes

Abstract

Legumes are a rich source of polyphenolic compounds known for their ability to promote health. Under stress conditions, legumes have been shown to produce higher levels of secondary metabolites, as a defensive mechanism. Hence, the present study aimed to induce legume seeds (e.g., soybean, chickpea, green pea, and red kidney bean) by inoculating them with Aspergillus sojae (A. sojae) and to evaluate the extracts for phytoalexins, phenolics, and antioxidant, antiobesity, and antidiabetic potentials. The UPLC-DAD findings of A. sojae-induced legumes showed medicarpin and maackiain in chickpea, pisatin in green pea, glyceollin I-III in soybean, and kievitone and phaseollin in red kidney bean. All induced legumes exhibited a higher total polyphenol content compared to the non-induced ones. Among induced legumes, soybean exhibited a higher (4.85 mg GAE/g) polyphenol content. The UPLC-ESI-QTOF-MS/MS findings established that legumes contained substantial levels of protocatechuic acid, vanillic acid, ferulic acid, chlorogenic acid, coumaric acid, 4-hydroxybenzoic acid, and caffeic acid. The results of antioxidant assays revealed a significantly higher level of activity in induced red kidney bean and soybean, whereas the level of activity in non-induced legumes was markedly lower. Moreover, induced red kidney bean effectively inhibited α-glucosidase (87.2%) and α-amylase (63.90%) at 5 mg/mL. Additionally, the maximum lipase inhibitory effects were displayed by induced soybean (72.54%) at 20 mg/mL.

Keywords

• phytoalexins
• <i>Aspergillus sojae</i>
• UPLC
• α-glucosidase
• lipase
• UPLC-ESI-QTOF-MS/MS