Optimization of solid-state fermentation conditions to improve phenolic content in corn bran, followed by extraction of bioactive compounds using natural deep eutectic solvents

The purpose of this study was to develop a sustainable method for producing antioxidant -rich extracts from corn bran. The technique involved solid-state fermentation (SSF) as a pretreatment method followed by natural deep eutectic solvents (NADESs)-based extraction. SSF was optimized with response surface methodology and the highest total phenolic content (TPC) of 3.31 mg gallic acid equivalent (GAE)/g dry weight (dw) was achieved. Fourteen different NADESs for extracting phenolic compounds in fermented corn bran were screened. The two most suitable NADES systems were selected for the recovery of bioactive compounds from fermented corn bran according to COSMOtherm software. The results showed that the corn bran extracts obtained through betaine: malic acid (3.86 mg GAE/g dw) and choline chloride:xylose (3.52 mg GAE/g dw) had significantly a higher TPC than the extract obtained through ethanol (3.11 mg GAE/g dw). Moreover, the selected NADESs extracted more ferulic acid, vanillic acid, and caffeic acid than ethanol according to the UPLC-qTOF-MS/MS results. The highest extraction levels of ferulic, p -coumaric, caffeic, and vanillic acids extracted by NADESs were 112.01, 30.53, 2.21, and 4.89 mu g/100 mL extract, respectively. The study demonstrated that SSF followed by NADES-base extraction is an efficient strategy for enhancing the phenolic content and antioxidant activity in corn bran. Industrial application: Corn bran is a significant by-product of the corn industry, with a global production volume of 8.78 million tons in 2021. It is a rich source of phenolic compounds, which are known for their antioxidant and health -promoting properties, making it attractive for food and pharmaceutical industries. However, the industrial application of corn bran poses a challenge as these phenolic compounds are mostly bound and insoluble. Our study demonstrated that Solid -State Fermentation (SSF) can significantly increased the total phenolic content of corn bran. By integrating SSF with the use of Natural Deep Eutectic Solvents (NADESs), our work not only improved the phenolic content of corn bran but also offered a sustainable and green approach to the extraction of bioactive compounds. This approach was highly desirable from an industrial perspective as it provided a costeffective and eco-friendly method for the production of bioactive compounds from corn bran.