Acid hydrolysis of brewers' industrial wastes and their use for lipid production by oleaginous yeasts

Abstract

© 2019, Japan Society on Water Environment. Brewers' spent grain (BSG) and spent yeast cell (SYC) are the wastes from mashing and fermentation process of beer. The compositions of BSG were 24.49 ± 0.91% hemicellulose, 20.86 ± 0.60% cellulose and 9.62 ± 0.40% lignin, while those of SYC were 46.97 ± 0.07% protein, 21.32 ± 0.08% carbohydrate and 5.73 ± 0.57% lipids. BSG and SYC were acid hydrolyzed using different solid loadings at 5-24%. The optimal solid loadings for BSG and SYC that gave maximum sugar concentration were 15% and 24%, respectively. Sugar compositions in BSG hydrolysate were 22.02 ± 0.8% glucose, 45.83 ± 1.53% xylose, and 32.13 ± 2.3% arabinose, while those found in SYC hydrolysate were 31.43 ± 0.38% glucose and 69.57 ± 1.04% mannose. Both hydrolysates were used as nutrient sources at the same sugar concentration of 40 g/L for cultivation of three oleaginous yeasts, Trichosporonoides spathulata JU4-57, Rhodotorula mucilaginosa G43 and Yarrowia lipolytica TISTR 5151. BSG hydrolysate gave higher biomass than SYC hydrolysate possibly due to a higher content of suitable sugars for cell growth. Among three yeasts, T. spathulate JU4-57 gave the highest lipid yields of 62.9 ± 5.67 and 39.9 ± 0.62 mg/g-substrate on BSG and SYC hydrolysates, respectively. This study may contribute greatly to low-cost production of oil sources for biodiesel production and may help to increase the environmental and economic sustainability of the brewery business.