Comparison of Acid and Enzymatic Hydrolysis of Jerusalem Artichoke Tubers for Fermentative Butanol Production

In this study, a central composite design and response surface methodology were used to study the effect of various hydrolysis variables on both acid and enzymatic hydrolysis of Jerusalem artichoke-derived inulin. It was found that quadratic model was able to predict inulin conversion as a function of all investigated factors in both types of hydrolysis. The models were confirmed by additional experiments and via analysis of variance (ANOVA). Subsequently, numerical optimization was used to maximize the inulin conversion (94.5% in enzymatic hydrolysis and 96% in acid hydrolysis) of Jerusalem artichoke powder within the experimental range. The optimum conditions for enzymatic inulin conversion were a temperature of 48°C, pH of 4.8, substrate concentration of 60 g.l^-1, and enzyme loading of 10 unit. g^-1_substrate in 24 hours. For acid hydrolysis using Sulphuric acid as catalyst, the optimum conditions were achieved at a temperature of 97°C, pH of 2.0, and in 35 minutes.

The hydrolysates of Jerusalem artichoke were fermented via solventogenic clostridia to acetone- butanol- ethanol (ABE). ABE yields of 0.33 g.g^-1 and 0.31 g.g^-1 were obtained using enzymatic and acid hydrolysates of Jerusalem artichoke, respectively. Acid hydrolysis produced HMF as fermentation inhibiting byproduct resulting in a lower yield compared to enzymatic hydrolysis. Therefore, enzymatic hydrolysis of Jerusalem artichoke was found to be a more effective method of hydrolysis for butanol production.