Statistical Modeling and Optimization of Processing Conditions of Twin-Screw Extruded Rice-Legume Instant Breakfast Gruel

New product development using extrusion cooking, low cost raw materials to meet consumer preference for convenient products are increasingly becoming popular in the field of Food Engineering. The raw materials are usually complex biological materials that may undergo different transformations due to high temperature, pressure and shear in the extruder. This study investigated the effects of extrusion cooking conditions on the physical and functional characteristics of rice-cowpea breakfast gruel and modeled the relationship between the input and output variables for optimum product quality. Fifteen composite blends based on central composite rotatable design (CCRD) in a response surface methodology (RSM) were formulated and extruded at different extrusion conditions of barrel temperature, feed moisture content and rice-legume ratio in the feeds. Data generated from the analysis of the extruded products were fitted to second-order polynomial equation with optimal point located. Results showed significant (p≤0.05) variation in physical and functional characteristics of the extrudates studied. The optimal points for process conditions were obtained at 120oC barrel temperature, 20% feed moisture and 24% feed cowpea composition respectively at desirability value of 0.907, for product quality of 126.14 (expansion index), 0.214g/cm3 (bulk density), 6.83(water absorption index), 8.46 (water solubility index), 99.02% (dispersibility) and viscosity of 12.83Nm2. Fitted models indicated significant coefficients with adjusted R2 of 94.70%, 88.00%, 99.70%, 99.10%, 95.90% and 83.00% respectively for expansion index, bulk density, water absorption and solubility indices, dispersibility and viscosity, while the lack-of-fit test p-values were 0.608, 0.485, 0.513, 0.505, 0.297 and 0.200 respectively. It was concluded that the fitted models could be used to adequately represent the experimental data in their natural state and when extrusion variables are carefully selected, rice-cowpea blends could produce quality gruel of optimum quality for breakfast or complimentary feeding.