Bioconversion of Soy Sauce Residue Treated with Steam Explosion into Ethanol by Meicelase and Mucor indicus

Steam explosion was attempted as a pretreatment for the efficient conversion of soy sauce residue into ethanol. The Simultaneous Saccharification and Fermentation (SSF) of steam-exploded soy sauce residue at a steam pressure of 10 atm and a steaming time of 5 min was carried out by using Meicelase and halotolerant Mucor indicus ATCC24905 and gave a maximum ethanol yield, i.e., 0.057 g-ethanol g-1 dry soy sauce residue, at a substrate concentration of 100 g L-1. This value corresponds to 1.9 times higher than that of untreated soy sauce residue, i.e., 0.030 g-ethanol g-1 dry soy sauce residue. At 200 g L-1 of steam-exploded soy sauce residue, though the ethanol yield was 0.052 g-ethanol g-1 dry soy sauce residue, the maximum ethanol productivity, i.e., 0.43 g-ethanol/L/h was obtained. Furthermore, the same ethanol yield and ethanol productivity were obtained at a substrate concentration of 100 g L-1 even if using the steam-exploded soy sauce residue without nutrient medium ingredients such as nitrogen sources and mineral salts.