Optimization of Reducing Sugar Concentration from Ulva fasciata Using Cellulase via Response Surface Methodology Techniques

Abstract

The enzymatic hydrolysis of a cellulose-bearing substrate such as green seaweed Ulva fasciata for the release of reducing sugars for subsequent conversion to bioethanol is generating considerable research interest. However, a major challenge in this process is the cost of enzymes. Crude enzyme extracts from Aspergillus inseitus isolated from indigenous U. fasciata was employed in this study to compare its hydrolytic efficiency with commercial cellulase CTec 2. The aim of the study was to model and optimize the hydrolysis process to predict and determine the concentration of reducing sugars obtained using response surface methodology with the application of the statistical tool, central composite design. Two most important influencing process parameters—hydrolysis time and enzyme dosage—were varied and used to conduct the optimization. The results showed that an optimal enzyme dosage of 0.25 U/g DM could yield a maximum reducing sugar concentration of 1.61 g/L at 6 h hydrolysis time for the commercial enzyme CTec 2 and 0.61 g/L at 12 h for enzyme extracts from A. inseitus, making the hydrolytic efficiency of CTec 2 only approximately 3 times better than crude enzyme extracts from A. inseitus based on reducing sugar concentration. A satisfactory coefficient of R2 of 0.9415 and 0.9493 for A. inseitus and CTec 2 respectively was obtained for the models which were experimentally verified. Careful concentration and purification of the crude enzyme extract from A. inseitus could make it an effective cellulase for hydrolysis processes resulting in cost reduction.