Optimisation of Combined Acid and Enzymatic Hydrolysis of Cocoyam Starch to Produce Fermentable Hydrolysate

Dilute acid hydrolysis and enzymatic hydrolysis were sequentially combined for the purpose of producing fermentable hydrolysate from cocoyam starch. A three variable Box Behnken design was used to study the effect of temperature, time and acid concentration for the acid hydrolysis step while for the enzymatic hydrolysis step, the variables optimised were temperature, time and pH. A total of 17 individual experiments were generated for each step of the hydrolysis and were used to develop regression models for each step. The regression models developed to represent the acid and enzymatic hydrolysis steps were statistically significant (p<0.05) and did not show lack of fit (R2>0.9). For the acid hydrolysis step, the regression model predicted the maximum sugar concentration to be 79.81 g/L at optimum temperature 100°C, time 11.66 min and acid concentration 1.5% w/w. For the enzymatic hydrolysis step, the regression model predicted the maximum sugar concentration to be 93.44 g/L at optimum temperature 58ºC, time 55 min and pH of 5.5.