Accumulation of secondary metabolites in response to antioxidant activity of turmeric rhizomes co-inoculated with native arbuscular mycorrhizal fungi and plant growth promoting rhizobacteria

• Increase in secondary metabolite contents of AMF inoculated turmeric rhizomes is reported.
• Inoculated rhizomes showed strong antioxidant activities over control.
• AMF ameliorate sustainable and quality production of turmeric rhizomes.

The present study was aimed at investigating the therapeutic potential of methanol crude extract of turmeric (Curcuma longa L.) rhizome co-inoculated with native arbuscular mycorrhizal fungi (Glomus, Gigaspora and Acaulospora sp.), phosphate solubilizer Bacillus megaterium and diazotrophic bacteria, Azospirillum amazonense and Azotobacter sp. To achieve the goals, parameters like free-radical (DPPH, ABTS) scavenging capacity, total phenolic contents, total flavonoids contents and percentage of curcumin content were examined. A significant increase of these secondary metabolites were observed in inoculated plants compared to non-inoculated controls revealing strong antioxidant activities of turmeric against DPPH and ABTS radicals in the range of 80–97%. The high amount of flavonoids (179.07–493.15 mg RE g−1), phenolic contents (83.07–151.54 mg GAE g−1) and percentage of curcumin (4.81–6.09%) present in all the methanolic extracts of dried rhizomes might be responsible for the observed antioxidant activity.