Continuous Production of Ethanol from Starch UsingGlucoamylase and Yeast Co-Immobilized in Pectin Gel

摘要

This work presents a continuous simultaneous saccharification and fermentation(SSF) process to produce ethanol from starch using glucoamylase and Saccharomycescrevisiae co-immobilized in pectin gel. The enzyme was immobilized on macroporoussilica, after silanization and activation of the support with glutaraldehyde. The silica-enzyme derivative was co-immobilized with yeast in pectin gel. This biocatalyst was usedto produce ethanol from liquefied manioc root flour syrup, in three fixed bed reactors. Theinitial reactor yeast load was 0.05 g wet yeast/ml of reactor (0.1 g wet yeast/g gel), used inall SSF experiments. The enzyme concentration in the reactor was defined by runningSSF batch assays, using different amount of silica-enzyme derivative, co-immobilizedwith yeast in pectin gel. The chosen reactor enzyme concentration, 3.77 U/ml, allowedfermentation to be the rate-limiting step in the batch experiment. In this condition, usinginitial substrate concentration of 166.0 g/1 of total reducing sugars (TRS), 1 ml gel/1 ml ofmedium, ethanol productivity of 8.3 g/l/h was achieved, for total conversion of starch toethanol and 91% of the theoretical yield. In the continuous runs, feeding 163.0 g/1 of TRSand using the same enzyme and yeast concentrations used in the batch run, ethanolproductivity was 5.9 g ethanol/1/h, with 97% of substrate conversion and 81% of theethanol theoretical yield. Diffusion effects in the extra-biocatalyst film seemed to be re-duced when operating at superficial velocities above 3.7 x 10-4 cm/s.