Vegetable soybean (Glycine max (L.) Merr.) leaf extracts: Functional components and antioxidant and anti-inflammatory activities.

Abstract

To investigate ways to extract greater dietary value from the leaves of the vegetable soybean (Glycine max (L.) Merr.) cultivar Kaohsiung No. 9 . Our results indicate that phenolic content and flavonoid content are highest in extracts prepared with 70% methanol and 70% ethanol. The 70% ethanol extracts also had the highest quercetin (135 ± 1.62 µg/g) and kaempferol (450 ± 1.35 µg/g) contents. These results show that flavonoids are a dominant class of compounds in these vegetable soybean leaf extracts and serve as their main source of antioxidants. At an extract concentration of 5 mg/ml, the 70% methanol extracts achieved good antioxidant effects, with a DPPH radical scavenging rate of 80%, and a reducing power of 88%. In assays of anti-inflammatory capacity using lipopolysaccharide-stimulated RAW 264.7 macrophages. The 70% methanol extracts displayed the most significant inhibition of nitric oxide (NO) synthesis, achieving up to 86% inhibition. As a similar trend was observed in expression levels of inducible nitric oxide synthase (iNOS), we deduced that vegetable soybean leaves may regulate NO synthesis through inhibiting iNOS. We also observed a significant decrease in cyclooxygenase (COX)-2 gene expression. Analysis of proinflammatory cytokine synthesis revealed that the 70% methanol and 70% ethanol extracts significantly reduced TNF-α, IL-6, and IL-1β synthesis, and increased the intracellular reduced glutathione/oxidized glutathione (GSH/GSSG) ratio from 8 to 12.8. These results indicate that vegetable soybean leaves possess antioxidant activities and exert inhibitory effects on inflammatory mediators, suggesting their potential for use as dietary supplements.