Twin‐Screw Extrusion of Rice, Millet, and Spinach Powder Blends: Extrudate Characteristics and Determination of Optimum Processing Condition

ABSTRACT Rice‐millet composite flour blended with powdered water spinach was extruded using a co‐rotating twin‐screw extruder. A response surface methodology (RSM) with a Box–Behnken design (BBD) was employed to evaluate the effects of independent variables, including barrel temperature (120°C–140°C), feed moisture (5%–15%), and screw speed (300–350 RPM), on product characteristics. These responses included expansion ratio, bulk density, true density, water activity, total color difference, hardness, crispiness, water solubility index (WSI), water absorption index (WAI), and anthocyanin retention. Multiple regression models were developed to assess the influence of each variable. The extrusion conditions of 114.6°C barrel temperature, 5% feed moisture, and 314 RPM screw speed resulted in extrudates with high anthocyanin retention, moderate hardness (305 kg), and desirable texture and acceptability. Future research should focus on cost‐effective large‐scale production, shelf‐life enhancement, ingredient diversification, and regulatory compliance to support commercialization. The findings confirm the potential of incorporating water spinach powder into rice‐millet composite flour to develop nutrient‐rich extruded snack foods.