Changes of γ-Aminobutyric Acid, Phytoestrogens, and Biofunctional Properties of the Isoflavone-Enriched Soybean (Glycine max) Leaves during Solid Lactic Acid Fermentation

Abstract

The present study documents the changes in the γ-aminobutyric acid (GABA), the total phenolic (TP), total flavonoid (TF), and isoflavone contents, the antioxidant activities and the digestive enzyme inhibition during the solid lactic acid fermentation of isoflavone-enriched soybean leaves (IESLs) with starters Lactiplantibacillus plantarum P1201 and Levilactobacillus brevis BMK184. The contents of glutamic acid (GA) and GABA remained almost unchanged during fermentation with P1201. In contrast, the contents of GABA increased from 144.24 to 173.09 and 175.59 mg/100 g, and the contents of GA decreased from 43.68 to 18.26 and 11.25 mg/100 g during the IESLs’ fermentation with BMK184 and the combined use of P1201 + BMK184, respectively. The total isoflavone content decreased during fermentation, but the isoflavone aglycone levels increased; in fact, the levels of daidzein and genistein were the highest after the use of P1201 + BMK184 (2265.57 μg/g) and BMK184 (1055.27 μg/g), respectively, at 72 h of fermentation. Correspondingly, the DPPH (90.90%), the ABTS (91.09%), and the hydroxyl (74.88%) radical scavenging activities, the ferric reducing/antioxidant power (2.45), as well as the α-glucosidase (49.86%) and pancreatic lipase (37.30%) inhibition activities exhibited their highest levels after fragmentation with P1201 + BMK184.