Saccharification, fermentation, and protein recovery from low-temperature AFEX-treated coastal bermudagrass

Coastal bermudagrass was pretreated by a low-temperature ammonia fiber explosion (AFEX) process, which soaked the grass in liquid ammonia and then explosively released the pressure. Saccharifying enzymes were systematically applied to the AFEX-treated grass corresponding to low, medium, and high loadings of cellulase/hemicellulase (from Trichoderma reesei), cellobiase, glucoamylase, and pectinase. Three-day sugar yields linearly correlated with the logarithm of the cellulase loading. Supplemental enzymes (cellobiase, pectinase) caused upward shifts in the lines. The linearity and upward shifts are consistent with the HCH-1 model of cellulose hydrolysis. The hydrolysis sugars were converted to ethanol using yeast (Saccharomyces cerevisiae). The solid residues were treated with proteases to attempt recovery of valuable proteins. The low-temperature AFEX pretreatment was able o nearly double sugar yields. At the highest cellulase loadings (30 IU/g), the best reducing sugar and ethanol yields were 53% and 44% of the maximum potential, respectively. Protein recovery was, at most, 59%.