Derivatization of Soyasapogenol A through Microbial Transformation for Potential Anti-inflammatory Food Supplements.

For the optimum use of soyasaponins isolated from soybean cake and to explore the potential anti-inflammatory agents from pentacyclic triterpenes as natural food supplements, microbial transformation of soyasapogenol A was carried out. Four strains of microbes, including Bacillus megaterium CGMCC 1.1741, Penicillium griseofulvum CICC 40293, Bacillus subtilis ATCC 6633, and Streptomyces griseus ATCC 13273, showed robust catalytic capacity to the substrate. Preparative biotransformation and column chromatographic purification led to the isolation of 10 novel and 1 reported metabolites. The structure elucidation was performed using 1D/2D NMR and HR-ESI-MS analytical method. Several novel tailoring reactions, such as allyl oxidation, C-C double bond rearrangement, hydroxylation, dehydrogenation, and glycosylation, were observed in the biotransformation. In the follow-up bioassay, most of the metabolites exhibited low cytotoxicity and potent inhibitory activity against the production of nitric oxide (NO) in RAW 264.7 cells stimulated by lipopolysaccharide. Especially compound 6 (3-oxo-11α,21β,22β,24-tetrahydroxy-olean-12-ene) showed comparable activity to the positive control of quercetin with an IC50 value of 16.70 μM. These findings provided an experimental approach to achieve the derivatization of natural aglycons in soybeans through microbial transformation for developing potent anti-inflammatory food supplements.