Optimization and kinetic studies for enzymatic hydrolysis and fermentation of colocynthis vulgaris Shrad seeds shell for bioethanol production

Abstract

The key process parameters for the hydrolysis and fermentation of Colocynthis vulgaris Shrad seeds shell (CVSSS) were optimized using the Box-Behnken Design (BBD) of Response Surface Methodology (RSM). Kinetic study was also carried out. The proximate analysis of the CVSSS was done by the method of the Association of Organic and Applied Chemistry (AOAC). Enzymatic hydrolysis was experimented by using Aspergillus Niger as a crude enzyme isolated from soil at sawdust dump site and screened for cellulosic activities. Factors that affected the hydrolysis of the CVSSS were screened by using the Greco-Latin square design of experiment. However, for Saccharomyces cerevisiae, factors that affected the fermentation of the CVSSS were screened by using the same Greco-Latin square design of experiment. Meanwhile, the result of the proximate analysis revealed that the CVSSS had 73.54% cellulose which could be converted to bioethanol. It was established that temperature, pH and time had significant effect on hydrolysis, while the optimum results were obtained at 46.8 °C, 3.32 d, 5.68 and 59.87% for temperature, time, pH and glucose yield, respectively. Temperature, yeast dosage, pH and time had significant effect on fermentation, while the optimum results from optimization were found to be 33.58 °C, 7.0, 3.55 d, 1.65 g per 50 mL and 25.6% for temperature, pH, time, yeast dosage and ethanol yield, respectively. The kinetics of both the enzymatic hydrolysis and fermentation agreed with the Michealis-Menten kinetic model with the correlation coefficients (R2) of 0.9708 and 0.8773, respectively. However, from the error analysis, the experimental and predicted values had a very good relationship as described by Michaelis-Menten model.