Improving the bioactivity of water-soluble alfalfa saponins using biotransformation

Medicago sativa L. is gaining attention as a sustainable plant-based food protein. Alfalfa saponins (ASs) typically exist in a glycosylated form in nature, which has poor cell membrane permeability, while the deglycosylated saponins may show better bioactivity. The AS was deglycosylated by β-glucosidase from Aspergillus niger, and the chemical structures and biological activities, including in vivo assays, of AS and deglycosylated AS (DAS) were determined. The results showed that the half maximal inhibitory concentration for 2,2-diphenyl-1-picrylhydrazyl inhibition of DAS was 29.5 µg/mL, demonstrating a significantly higher reducing capacity compared to AS (p < 0.05). The DAS induced 33.8% antibacterial activity against Escherichia coli and enhanced the proliferation of human airway epithelial cells (BEAS-2B) at a concentration of 125 µg/mL. In vivo experiments on C57BL/6 mice fed a high-fat diet demonstrated that high-level DAS treatment produced significantly greater hypolipidemic effects compared to AS (p < 0.05). Thus, the AS can be deglycosylated, which leads to an improvement in biological activity, particularly since the DAS exhibits significantly enhanced hypolipidemic activity. PRACTICAL APPLICATION: Alfalfa saponins were deglycosylated by β-glucosidase from Aspergillus niger, which contributed to increased bioactivity, particularly its hypolipidemic activity.