Antioxidant phenolics and their microbial production by submerged and solid state fermentation process: A review

•Phenolics from natural sources can replace use of hazardous synthetic antioxidants.•Microbial fermentation is a powerful method for production/extraction of phenolics.•Phenolics are either produced by microorganisms or released from the substrate.•We reviewed production of antioxidant phenolics by SmF and SSF processes.•Antioxidant activity improvement of cereals & legumes by SSF is thoroughly discussed.

BackgroundBioactive phenolic compounds have recently received great attention in the food and clinical sectors due to their antioxidant potential. Extensive studies have been carried out to explore antioxidant potential of different phenolics from various natural sources in order to replace the use of health hazard synthetic antioxidants in food products.Scope and approachThe present review aims to provide an update of existing state-of-art and future prospect of both submerged fermentation (SmF) and solid-state fermentation (SSF) processes for the production/extraction of bioactive phenolics utilizing various substrates and microorganisms. Studies on enhancement of antioxidant potentials by increasing phenolics content of food materials including cereals and legumes by mainly SSF are reviewed and discussed thoroughly.Key findings and conclusionsMicrobial fermentation processes have been established as a potent tool for the production of antioxidant phenolic compounds due to their cost-effectiveness and environmental advantages. Extraction of phenolics through fermentation process is by far a more efficient process considering that conventional extraction methods using organic solvents do not allow complete release of bound phenolics from plant materials. During fermentation process, antioxidant phenolics are either produced by microorganisms through secondary metabolic pathway or released from the matrix of the substrate by extracellular enzymatic action. Fermentation technology is no doubt proving to be a boon for the food industry; however, extensive in vivo and toxicological researches are essential before the application of antioxidant-rich fermented foods for human health benefits.