Isoflavone aglycone-rich powder from soybean residue submerged fermentation using Lactobacillus fermentum 44197

Abstract

Soybean residue contains high amounts of isoflavones and proteins with utilisation limited to animal feed and fertiliser. This study investigated isoflavone bioconversion by Lactobacillus fermentum 44197 to enhance the biological activity of fermented soybean residue to serve as a functional food ingredient. Using liquid-state fermentation, growth of L. fermentum 44197 in soybean residue substrate was similar to growth in MRS substrate. β-Glucosidase produced by L. fermentum 44197 contributed to isoflavone bioconversion from glycosides to aglycones. Submerged fermentation in substrate containing 20% soybean residue and 4% glucose at 37 °C for 24 h produced the highest isoflavone aglycones (daidzein and genistein). Fermented soybean residue was dried by drum drying and exhibited high isoflavone contents (mg/100 g db): daidzin (2.24), genistin (5.33), daidzein (28.62) and genistein (66.07) that was named isoflavone aglycone-rich powder. The powder was an excellent source of isoflavone aglycones, protein and free amino acids, exhibiting high protein solubility between pH 3 and 9 and high water absorption (4.0 g/g). Results demonstrated the potential of L. fermentum 44197 for isoflavone bioconversion of soybean residue under submerged fermentation. Isoflavone aglycone-rich powder can also be used for bioactive compound enrichment and formulation of various functional foods and health foods, especially plant-based protein products.