s Optimization of Single Screw Extrusion Processing Variables and Soy and Rice Flour Blend Formulations based on Physical Properties of Extrudates

Background: Extruded cereals and snacks are mainly carbohydrates. Most adults require more protein above RDA by restricting carbohydrates for many health benefits. A wide variety of soy protein-rich extrudates can be produced by blending with rice flour. However, optimum extrusion processing variables (i.e., screw speed, die temperature, and product formulations) are required for maximum retention of nutrients with desired product characteristics. Objective: The objective of this study was to optimize the extrusion operating conditions and soy flour and rice flour blend formulations for developing protein-rich cereal-like extrudates. Methods: Twenty formulations using CCRD with the combinations of soy flour content (43-77%), die temperature (123-157°C), and screw speed (250-350 rpm) were extruded using a single screw extruder. The physical properties (expansion ratio, density, porosity, hardness, crispness, color, and water solubility index) of extrudates were determined. The regression models and 3-dimensional response surface models were developed for each property of extrudates using RSM. Numerical and graphical optimizations were conducted based on the desirability to determine an optimum condition. Results: The regression models were able to predict the physical properties of extrudates with an accuracy of 75-90%, depending on their properties. The 3-dimensional response surface models indicated that the soy flour content, die temperature, and screw speed affected the physical properties of extrudates significantly (p < 0.05). Soy flour content (50-55%), die temperature (140-145°C), and screw speed (290-320 rpm) were very effective for the desired quality of soy flour and rice flour blend extrudates. Conclusion: The optimum condition is expected to be very useful for soy protein and rice flour blend extruded cereal-like product development commercially within the experimental range.