A new pretreatment using ammonia gas absorption fiber expansion for saccharification of cassava pulp

Abstract

Cassava pulp (CP), a by-product from the cassava starch industry, is a potential resource for ethanol production. Ammonia gas absorption fiber expansion (AGAFE) was developed to accomplish efficient saccharification of CP. AGAFE was designed to be used under moderate pressure by directly adding compressed ammonia gas before rapidly releasing the pressure. Scanning electron microscopy analysis showed that the cell wall of AGAFE-pretreated CP was severely disrupted, while the fiber of the raw CP remained largely intact. Additionally, the concentration of glucose released from the hydrolysis of pretreated CP was higher than that obtained from raw CP using α-amylase and glucoamylase. The optimum pretreatment conditions for AGAFE were 0.2 MPa and 70 °C for 10 min, which resulted in saccharification of 83.16 % of the total starch in CP. In contrast, only 53.73 % saccharification was achieved when raw CP was directly hydrolyzed without pretreatment, suggesting that destruction of the starch and fiber in CP was necessary to obtain maximum saccharification. To confirm whether the AGAFE pretreatment influenced ethanol fermentation, a fermentation test using the hydrolysate from AGAFE-pretreated CP was carried out using Saccharomyces cerevisiae NCYC3233 and Kluyveromyces marxianus TISTR5925. When the hydrolysates containing 10.1 % (w/v) glucose were subjected to fermentation, 5.0 and 4.5 % (w/v) ethanol was produced, respectively, indicating that >85 % of the theoretical yields were achieved without inhibition from any mixture components. These results indicated that AGAFE is a useful pretreatment option for ethanol production from biomass containing starch and fiber such as CP.