Response surface methodology for evaluation and optimization of process parameter and antioxidant capacity of rice flour modified by enzymatic extrusion

• RSM was used to evaluate and optimize the operating conditions of enzymatic extrusion for rice flour.
• Severe extrusion conditions resulted in low SME but high starch gelatinization and antioxidant activity.
• The retention ratio of total phenolic content in rice significantly increased with increasing moisture and enzyme levels.

For the purpose of investigating the effect of enzyme concentration (EC), barrel temperature (BT), moisture content (MC), and screw speed (SS) on processing parameters (product temperature, die pressure and special mechanical energy (SME)) and product responses (extent of gelatinization (GE), retention rate of total phenolic content (TPC-RR)), rice flour extruded with thermostable α-amylase was analyzed by response surface methodology. Stepwise regression models were computed to generate response surface and contour plots, revealing that both TPC-RR and GE increased as increasing MC while expressed different sensitivities to BT during enzymatic extrusion. Phenolics preservation was benefited from low SME. According to multiple-factor optimization, the conditions required to obtain the target SME (10 kJ/kg), GE (100%) and TPC-RR (85%) were: EC = 1.37‰, BT = 93.01 °C, MC = 44.30%, and SS = 171.66 rpm, with the actual values (9.49 kJ/kg, 99.96% and 87.10%, respectively) showing a good fit to the predicted values.