Changes in nutritional compositions and digestive enzyme inhibitions of isoflavone-enriched soybean leaves at different stages (drying, steaming, and fermentation) of food processing

Isoflavone-enriched soybean leaves (IESLs) were processed for drying, steaming, and fermentation, and bioactive compounds and biological activities were analyzed. During food processing, the content of fatty acids, water-soluble vitamins, total phenolics, total flavonoids, and isoflavone-aglycones increased from dried IESLs (DrIESLs) to fermented IESLs (FeIESLs). Especially, oleic acid (53.4 → 113.1 mg/100 g, 2.1-folds), γ-aminobutyric acid (357.36 → 435.48 mg/100 g, 1.2-folds), niacin (19.0 → 130.6 mg/100 g, 6.9-folds), folic acid (9.7 → 25.5 mg/100 g, 2.6-folds), daidzein (270.02 → 3735.10 μg/100 g, 13.8-folds), and genistein (121.18 → 1386.01 μg/100 g, 11.4-folds) dramatically increased. Correspondingly, the antioxidant and digestive enzyme inhibitory activities increased. Therefore, solid-state lactic acid fermentation (SLAF) was suggested as a suitable technique for mass-processing IESLs. FeIESLs with SLAF have the potential to be utilized as a functional food. •IESLs enhanced bioactive compounds and biological activities associated with the SLAF.•Oleic acid and GABA in FeIESLs were 2.1 and 1.2-fold compared to DrIESLs.•Niacin and folic acid in FeIESLs were 6.9 and 2.6-fold compared to DrIESLs.•Daidzein and genistein dramatically increased in FeIESLs (3735.10 and 1386.01 μg/100 g).•Antioxidant and digestive inhibitory activities increased from DrIESLs→StIESLs→FeIESLs.