Effects induced by the nodulation with Bradyrhizobium japonicum on Glycine max (soybean) metabolism and antioxidant potential

This study was conducted in order to assess the effect of the inoculation of Glycine max (soybean) with Bradyrhizobium japonicum on the metabolite profile and antioxidant potential of its aerial parts. Extracts containing phenolic compounds and organic acids were analysed by HPLC–DAD and HPLC–UV, respectively. Volatiles profile was determined by HS-SPME/GC–IT-MS. The antioxidant activity of acidic and methanolic extracts was assessed against DPPH. Nodulation caused by B. japonicum led to an increase in the contents of phenolic compounds and organic acids. The same was observed for volatile compounds, with compounds like linalyl acetate, menthyl acetate and α-farnesene being detected only in inoculated plants. The phenolic extracts showed stronger antioxidant capacity than the organic acid extracts. In addition, extracts from plants nodulated with B. japonicum exhibited significantly higher antioxidant activity than control samples. These findings suggest that the inoculation with nodulating B. japonicum strains may be employed to manipulate the content of interesting metabolites in G. max aerial parts.

Research highlights
► Glycine max (soybean) establishes symbiotic relationships with nodulating bacteria.
► Effect of the inoculation with Bradyrhizobium japonicum on soybean aerial parts.
► Inoculation led to higher contents of phenolics, organic acids and volatiles.
► Extracts from inoculated plants exhibited stronger antioxidant activity.