Unraveling the impact of aspergillus sojae—a food-grade fungus—On phytoalexins, phenolic acids, and the antioxidant and antidiabetic activity of different legumes

Authors: RANA, SHALIKA - Oak Ridge Institute For Science And Education (ORISE); BROUSSARD, WILLIAM - Oak Ridge Institute For Science And Education (ORISE); ELLIOT, STEVEN - Tulane University; BUROW, MATTHEW - Tulane University; Boue, Stephen

Submitted to: Foods
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/1/2024
Publication Date: 11/5/2024
Citation: Rana, S., Broussard, W., Elliot, S., Burow, M.E., Boue, S.M. 2024. Unraveling the Impact of Aspergillus sojae—A Food-Grade Fungus—On Phytoalexins, Phenolic Acids, and the Antioxidant and Antidiabetic Activity of Different Legumes. Foods. https://doi.org/10.3390/foods13223533.
DOI: https://doi.org/10.3390/foods13223533

Interpretive Summary: This study investigated the health-promoting benefits of legumes, specifically focusing on their response to stress conditions induced by inoculation with the food-grade fungus Aspergillus sojae. If was found that legumes can enhance their production of beneficial compounds, particularly polyphenolic compounds, as a defensive response. It was determined that inoculated legumes, such as soybean, chickpea, green pea, and red kidney bean, exhibited increased levels of phytoalexins, total polyphenols, and total flavonoids compared to non-inoculated counterparts. Notably, the inoculated soybean showed the highest polyphenol content. Additionally, the study found that the antioxidant activity was significantly higher in the inoculated legumes, with the A. sojae-treated red kidney bean demonstrating superior antioxidant properties. The extracts of these legumes also effectively inhibited several digestive enzymes, with treated legumes showing significantly greater inhibitory effects on a-glucosidase and a-amylase, which are critical for carbohydrate digestion. Moreover, both inoculated and non-inoculated samples displayed substantial inhibition of pancreatic lipase, an enzyme involved in fat digestion, suggesting potential benefits for managing obesity and diabetes. Overall, this research highlights the potential of using A. sojae to enhance the nutritional and health benefits of legumes.

Technical 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, including polyphenolics, 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 the food-grade fungi Aspergillus sojae (A. sojae) and evaluate the induced and non-induced-legume-extracts-for phytoalexins, phenolics, antioxidant capacity, and antiobesity and antidiabetic potentials. UPLC-DAD findings revealed that A. sojae enhanced the phytoalexin content in all the legumes. All induced legume extracts analyzed exhibited higher total polyphenol and total flavonoid contents. The induced soybean (SB-AS) showcased abundant polyphenols (4.85 mg GAE/g) compared to other legumes. Findings of UPLC-ESI-QTOF-MS/MS established that legumes contained substantial levels of phenolic acids in all the extracts. Results of in vitro antioxidant assays revealed significantly higher levels in induced legumes compared to the non-induced samples. Among all the legumes, higher antioxidant activity was observed by A. sojae-induced red kidney bean (RKB-AS) using DPPH and ABTS assays. Moreover, extracts were also screened for their ability to inhibit the digestive enzymes a-amylase and a-glucosidase. All the treated legume extracts effectively inhibited a-glucosidase across all concentrations (0.5-5 mg/mL), whereas the activity in non-induced legumes was markedly lower. Similarly, induced bean samples exhibited higher a-amylase inhibitory effects than non-induced samples. Additionally, inhibiting pancreatic lipase (an enzyme crucial in the conversion of fat to fatty acids) is advantageous in slowing the absorption of fat and lipids. Both induced and non-induced legume samples displayed significant inhibition of pancreatic lipase. Overall, this research highlights the potential of using A. sojae to enhance the nutritional and health benefits of legumes.