Pressurized Hot Water Treatment of Wheat Bran Under Mild Acidic/Alkaline Conditions to Boost Polyphenol Release and Recovery

Abstract Wheat bran (WB) is a food industry side-stream and it has attracted notable attention as a bioresidue of high abundance. WB contains mainly cell wall-bound ferulic acid, and its liberation and recovery requires alkali- or acid-catalyzed cleavage. This work was thus carried out to examine acid- and alkaline-catalyzed hydrothermal treatments as effective means of generating polyphenol-enriched extracts, by employing mild catalysts, such as citric acid and sodium carbonate. The study included the implementation of pressurized aqueous media, to test their effect under various temperature and time combinations, and the treatments were assessed by severity-based models. The most efficacious treatment was found to be the alkali-catalyzed process, which at 150 °C and 5 min provided total polyphenol yields of approximately 25 mg ferulic acid equivalents per g dry WB mass. The chromatographic analyses of the extracts confirmed that the sodium carbonate-catalyzed treatment produced ferulic acid-enriched extracts, whereas a feruloyl pentose was the predominant metabolite in the extracts obtained with citric acid catalysis. The examination of the antioxidant activity also confirmed that the extracts containing the feruloyl pentose might be more potent than those enriched in ferulic acid. In this study, it was shown for the first time that pressurized water and mild alkaline catalysis may afford WB extracts with high feruloyl pentose concentration and enhanced antioxidant activity, within only 5 min of processing time. Such a finding may form the basis for developing a highly efficient and green methodology to produce bioactive compounds from WB or similar residual industrial biomaterials.