Optimization of Enzymatic Hydrolysis of Manihot esculenta Root Starch by Alpha-Amylase and Glucoamylase Using Response Surface Methodology

Abstract

Cassava starch hydrolysis was investigated in this study using alpha amylase and glucoamylase. The effects of process variables, namely: temperature, pH and time were studied and optimized for hydrolysis of cassava (Manihot esculenta) flour to glucose syrup. Three levels of process variables were used for the study. The three levels of process variables were: temperature (60, 67 and 74 ^oC), time (1.5, 2.0 and 2.5 h) and pH (4.5, 5 and 5.5). A polynomial regression model was developed using the experimental data. The results showed that production of reducing sugar was strongly affected by the variation of variables on alpha amylase and glucoamylase hydrolysis of cassava starch. The fit of the model was expressed by the coefficient of determination R² which was found to be 0.948 indicating that 94.8 % of the variability in the response can be explained by the model. The value also indicates that only 5.2 % of the total variation is not explained by the model. This shows that equation (2) is a suitable model to describe the response of the experiment pertaining to reducing sugar production. The statistical significance of the model was validated by F-test for analysis of variance (p ? 0.05). For alpha amylase and glucoamylase hydrolysis, the optimum value of temperature, time and pH were found to be 74 ^oC, pH 5.5 and time 1.5 h. The maximum reducing sugar production at optimum condition was 257 g/l representing 73.43 % conversion or 73.43 dextrose equivalent (DE).

Key words: cassava starch, hydrolysis, factorial design, glucose syrup, dextrose equivalent.