Impact of High-Shear Extrusion Combined With Enzymatic Hydrolysis on Rice Properties and Chinese Rice Wine Fermentation

Abstract

To better understand how high-shear extrusion combined with enzymatic hydrolysis affects the rice properties and subsequent fermentation, a twin screw extruder incorporated with rice treatment with thermostable α-amylase was used for simultaneous saccharification and fermentation (SSF) of Chinese rice wine. Seven pretreatment methods for rice were compared, and their impacts on rice properties and quality indices of final wine were studied. Enzymatic extruded rice had higher water solubility index (WSI), extent of gelatinization (GE), but lower water absorption index (WAI) and viscosity than those of other treated rice due to a strong synergy of shear action and enzymatic hydrolysis on the degradation and gelatinization of starch. The modification of enzymatic autoclaved rice was smaller than that of enzymatic extruded rice mainly for the lack of mechanical shearing force. Although extrusion with smaller particle size tended to have higher susceptibility to enzyme, the effect was not dramatic. This implied that manipulating particle size had limited effect on the modification of rice properties. Correlation analysis showed that the ethanol yield (EY), fermentation efficiency (FE), amino acid (AA), and soluble solid content (SSC) of finished rice wine increased as rice properties improved by enzymatic extrusion. Overall, simultaneous high-shear extrusion and enzymatic hydrolysis can be an attractive alternative to obtain modified rice with desirable properties for manufacturing Chinese rice wine or other fermentation products.