Evaluation of the waste from cassava starch production as a substrate for ethanol fermentation by Saccharomyces cerevisiae

Cassava starch production waste (cassava pulp) has been proposed as a high potential ethanolic fermentation substrate due to its high residual starch level and the small particle size of the lignocellulosic fibers. Saccharification of the residual starch from a 3% (w/v) dry weight basis (DS) of cassava pulp by alpha-amylase (100 degrees C, 10 min) and glucoamylase (60 degrees C, 2 h) resulted in a glucose yield of 22.6 g/l [67.8% (w/w) DS of cassava pulp] and in lignocellulosic fibers at 0.5 g/g DS cassava pulp. Pretreatment of the lignocellulosic fiber with dilute sulfuric acid and calcium hydroxide at 121 degrees C, 15 lb/in(2) for 30 min increased and decreased, respectively, its susceptibility to cellulase hydrolysis. Under the optimal conditions found, pretreatment of 6% (w/v) DS lignocellulosic fiber by 2% (w/v) H(2)SO(4) for 30 min, followed by saccharification by cellulase (40 degrees C, 9 h), yielded a glucose level of 26.6 g/l [79.8% (w/w) DS of the cassava pulp]. The starch and lignocellulosic fiber hydrolysates obtained from 30 g cassava pulp and 60 g H(2)SO(4) pretreated lignocellulosic fiber were fermented by Saccharomyces cerevisiae, without the need for (NH(4))(2)SO(4) supplementation, to yield ethanol levels of 9.9 and 11.9 g/l, respectively, after 48 h.