Effects of Extrusion Process Variables on the Physicochemical and Textural Properties of Isolated Rice Protein-Enhanced Low-Moisture Meat Analogs

In this study, the physicochemical and textural properties of isolated rice protein-enhanced low-moisture meat analogs (IRPE-LMMAs) were systematically evaluated in relation to key extrusion variables. A dry blend containing 10% isolated rice protein was processed by low-moisture extrusion cooking, and moisture content, barrel temperature, and screw speed were varied using a Box–Behnken response surface design. The quality characteristics of IRPE-LMMAs were assessed based on appearance, water-holding capacity, integrity index, nitrogen solubility index, springiness, cohesiveness, chewiness, and cutting strength. Among the tested variables, moisture content showed the most apparent influence on both hydration-related and texture-related properties. Higher moisture content tended to increase water-holding capacity, nitrogen solubility index, springiness, and cohesiveness, whereas chewiness and cutting strength decreased. These results indicate that increased moisture content improved water-related functionality and elastic properties but reduced firmness-related textural attributes. Barrel temperature and screw speed showed response-dependent effects, suggesting that their influence should be interpreted in combination with moisture content and the specific quality parameter considered. Response surface methodology based on chewiness identified a practical processing window within the experimental range of 39–40% moisture content, 141–144 °C barrel temperature, and 205–215 rpm screw speed. Supplementary exploratory regression analysis suggested that moisture content was a major contributor to the composite quality index, while firmness-related responses required separate consideration. Overall, the results indicate that isolated rice protein can be incorporated into LMMA formulations, and that process optimization should focus on balancing hydration, elasticity, and firmness according to the intended product quality.