Optimization of a minimal synergistic enzyme system for hydrolysis of raw cassava pulp

Abstract

Cassava pulp is an underused agricultural by-product comprising residual starch granules entrapped in cell wall polysaccharides, making it unique from other lignocellulosic wastes in terms of enzymatic processing. In this study, a synergistic system comprising a minimal set of enzymes tailor-made for efficient bioprocessing of raw cassava pulp was developed. The fiber-degrading enzyme mixture comprises an endoglucanase (Cel12), β-glucosidase (BGL), endo-β-1,4-xylanase (XYN) and endo-polygalacturonase (EPG) from Aspergillus aculeatus and a cellobiohydrolase I (Cel7A) from Talaromyces cellulolyticus was initially optimized using the experimental design approach. A glucose recovery yield of 91.3% based on the total starch and cellulose content was obtained from saccharification of cassava pulp using the combination of 5.0 mg g⁻¹ of fiber degrading enzyme mixture comprising Cel12, Cel7A, BGL, XYN and EPG in the ratio of 16.5 : 25.5 : 15.0 : 18.0 : 25.0 together with 0.5 mg g⁻¹ of raw starch degrading enzyme Stargen™ 002 with the degree of synergy of 1.43. Efficient hydrolysis was achieved without an energy-intensive pretreatment step, showing industrial applicability on saccharification and modification of cassava pulp and for further incorporation of these enzymes into ethanologens for consolidated bioprocessing.