Sprouting and solid-state bioprocessing by Rhizopus oligosporus increase the in vitro antibacterial activity of aqueous soybean extracts against Helicobacter pylori

Helicobacter pylori infection has been implicated as a major cause of gastric inflammation, peptic ulcer disease, and gastric cancer. While antibiotics have been the mainstay of current therapies for gastrointestinal disease linked to H. pylori infection, negative side-effects and antibiotic resistance issues have strengthened the need for alternative therapeutic strategies. In the search for new antimicrobial agents, much recent research has focused on the potential of dietary phenolic compounds. In this study, soybean extracts enriched for phenolic content via sprouting or solid-state bioprocessing by the dietary fungus Rhizopus oligosporus were investigated for in vitro antibacterial activity against H. pylori. Helicobacter pylori growth inhibition by soybean extracts was increased most effectively by 2d sprouting or 2d R. oligosporus bioprocessing. Anti-H. pylori activity was not associated with antioxidant activity, but was linked to extracts when activity of the phenolic-polymerizing enzymes guaiacol peroxidase (in sprouted soybean extracts) and laccase (in R. oligosporus-bioprocessed soybean extracts) were the highest. This suggests the potential involvement of polymeric phenolics in the anti-H. pylori activity of soybean extracts and possible mechanisms for such action are discussed.