Response Surface Optimization of Bath Type Ultrasound-Assisted Extraction (UAE) of Native Starch from Fresh Cassava Tubers

The objective of this study was to calculate the optimum conditions for extraction of starch from fresh cassava tubers using response surface methodology (RSM). In this study, Box-Behnken response surface design (BBD) was used to optimize the extraction process conditions (3 independent process factors at 3 levels with 17 runs) and to evaluate the main, linear and combined effects of cassava starch extraction conditions. The independent process variables selected in this study were sonication power (50, 75, 100 W), sonication time (10, 20, 30 min) and solid to solvent ratio (10, 20, 30 g/ml). The non-linear second order polynomial quadratic regression model was used for experimental data to determine the relationship between the independent process variables and response. Design Expert software (version 10.0.2.0) was used for regression analysis and Pareto analysis of variance (ANOVA). Ground cassava paste of 50 g was mixed with a proper quantity of distilled water. The suspension was directly placed in the bath sonicator (operating frequency of 33 ± 3 kHz, input voltage of 240 V and heating strength of 150 W), desired sonication power (W), sonication time (min) and solid to solvent ratio (g/ml) were maintained by means of controller. The optimal conditions of the selected variables were obtained using derringer’s desirability function as sonication power of 63.32 W, sonication time of 15.59 min and solid to solvent ratio (SS) of 19.19 g/ml) with a desirability value of 0.76. The maximum experimental cassava starch yield was 83.20% which was 8.2% higher than that of conventional wet extraction method. Under the optimized extraction conditions, the selected variables were validated (n=3), a mean starch yield of 82.28 ± 1.12% was obtained with adjusted R2 value of 0.85. Compared with wet extraction technique, UAE required shorter extraction time and yielded higher percentage of extraction recovery. Thus, UAE could be very effective for increasing the percentage recovery of starch from fresh cassava tubers.