Conversion of endogenous phenolic acid in brown rice by bioextrusion of mesophilic α-amylase

Abstract

Thermomechanical process is the most commonly used for treating grains but inevitably cause loss of endogenous bioactive ingredients such as phenolics. This work investigated the phenolic retention of brown rice via bioextrusion at different concentration gradients of mesophilic α-amylase (MαA, 0–2000 U/g), and determined the conversion of individual phenolic acids at both free and bound forms. Results showed that extrusion promoted the release of phenolics but lead to a great loss of them. While the phenolic retention of brown rice was significantly increased with increasing MαA levels up to 1000 U/g (twice more than that of traditional extrudate), which simultaneously modified rice matrix from big granules to small ones by SEM observation. The viscosity of bioextruded brown rice was decreased significantly but negatively relating to phenolic retention. Extrusion kinetics revealed that mechanical input and residence time had obvious effects on starch gelatinization which ultimately influence the presence of phenolics.