Improved [alpha]-amylase and Helicobacter pylori inhibition by fenugreek extracts derived via solid-state bioconversion using Rhizopus oligosporus

The present research investigated the enrichment of fenugreek (Trigonella foenum graceum) seed substrate with phenolic antioxidants and L-DOPA via fungal-based solid-state bioconversion (SSB) system. This approach using food grade fungus Rhizopus oligosporus, was chosen because it has been demonstrated to be effective in other seed and food substrates for improving health-relevant functionality and has long history of use for food processing in Asia. The protein content and beta-glucosidase activity of the substrate which reflects fungal growth, increased with incubation time in conjunction with enhanced phenolic content and also suggested its possible involvement in phenolic mobilization. The antioxidant activity assayed by beta-carotene bleaching and DPPH free radical scavenging methods both indicated high activity during early growth stage (days 4-6) followed by reduced activity during later growth stage (days 8-20). A direct association between higher phenolic contents during early growth stage (days 4-6) and antioxidant activity suggested a link to mobilization of polymeric and hydrophobic phenolic forms. The L-DOPA content of the fenugreek extract fluctuated during the course of bioconversion with higher levels during days 6-10 (1.5-1.7 mg/g DW). The SSB process substantially improved the in vitro porcine alpha-amylase inhibition activity by 75 % on day 4 which correlated to higher levels of total phenolics and related antioxidant activity of the extracts. The high alpha-amylase inhibitory activity also coincided with high L-DOPA content on day 6. These results have implications for diet-based diabetes management. The same bioconversion stage had Helicobacter pylori inhibitory activity, which has implications for ulcer management.