Development of a sugar platform and fermentation media from residues from alfalfa biorefining

Abstract

Biorefining of fresh alfalfa for protein production leads to a solid fibrous residue (pulp), and a liquid fraction (brown juice) after recovery of proteins by precipitation. In this study, potential uses of these side streams were investigated. Treatment of the pulp with 6% sodium chlorite resulted in 79.8% removal of lignin, while 89.1% of the glucan and 75.4% of the xylan was retained. Subsequent enzyme hydrolysis using cellulase at a loading of 10 FPU/g dry substrate for 48 h, converted 81.0% of the glucan to glucose and 79.3% of the xylan to xylose. Concentrations of 35.2 g/L glucose and 13.0 g/L xylose were obtained in the hydrolysate after using a biomass loading of 10% w/v, and deionized water for suspension during saccharification. The brown juice was investigated as a medium for fermentative production of L-lactic acid using the bacterium Lactococcus lactis KF 147. Fermentation of the brown juice without further additions yielded 12.8 g/L lactic acid. When the brown juice was supplemented with increasing amounts of pulp hydrolysate, from 15% to 70% v/v, the lactic acid yield increased to 17.4 and 28.8 g/L, respectively. Overall, these results show that converting the alfalfa pulp to a sugar platform for fermentation is feasible, and the brown juice may serve as a nutrient additive in the fermentation process.