This study was undertaken to investigate the effects of hydrothermal treatments under mild acid and alkaline conditions on polyphenol release and recovery from wheat bran (WB). After an initial screening of various food-grade substances, strong evidence was raised regarding the potency of citric acid and sodium carbonate to provide WB extracts exceptionally enriched in polyphenols. Thus, these two catalysts were tested under various time and temperature combinations, and the processes were described by linear models based on severity factor. The most effective treatments were those performed with 10% of either citric acid or sodium carbonate, at a constant temperature of 90 °C for 24 h, providing yields in total polyphenols of 23.76 and 23.60 mg g-1 dry mass of ferulic acid equivalents, respectively. Liquid chromatography-mass spectrometry analyses revealed that, while the sodium carbonate treatment afforded extracts enriched in ferulic acid, treatments with citric acid gave extracts enriched in a ferulate pentose ester. The extracts produced from those treatments also exhibited diversified antioxidant characteristics, a fact ascribed to the different polyphenolic composition. To the best of the authors' knowledge, this is the first report demonstrating the effective release of ferulic acid and a ferulate pentose ester from WB, using benign acid and alkali catalysts, such as citric acid and sodium carbonate.
Keywords: acid catalysis; alkaline catalysis; antioxidants; ferulic acid; hydrothermal treatment; polyphenols; process severity; wheat bran.