Effects of washing with water on enzymatic saccharification and d-lactic acid production from steam-exploded sugarcane bagasse

Abstract

This study investigated the production of d-lactic acid from unutilized sugarcane bagasse using steam explosion pretreatment. The optimal steam pressure for a steaming time of 5 min was determined. The steam-exploded sugarcane bagasse was hydrolyzed using cellulase (Meicelase) and then the hydrolyzate was subjected to fermentation substrate. By enzymatic saccharification using Meicelase, the highest recovery of glucose from raw bagasse, 73.7 %, was obtained at a steam pressure of 20 atm. For extracted residue with water after steam explosion, the glucose recovery increased up to 94.9 % at a steam pressure of 20 atm. These results showed that washing with water is effective in removing enzymatic reaction inhibitors. After steam pretreatment (steam pressure of 20 atm), d-lactic acid was produced by Lactobacillus delbrueckii NBRC 3534 from the enzymatic hydrolyzate of steam-exploded bagasse and washed residue. The conversion rate of d-lactic acid obtained from the glucose concentration was 66.6 % for the hydrolyzate of steam-exploded bagasse without washing with water and 90.0 % for that derived from the extracted residue with water after steam explosion. These results also demonstrated that the hydrolyzate of steam-exploded bagasse (without washing with water) contains fermentation inhibitors and washing with water can remove them.