Lipid production by the yeast Lipomyces starkeyi grown on sugars and oil palm empty fruit bunch hydrolysate

Abstract

Lipid accumulation by the yeast Lipomyces starkeyi grown on various carbon (C) sources (glucose, xylose, hydrolysate of oil palm empty fruit bunch (OPEFB)) is reported. In media with glucose as the main C-source, a glucose concentration of 60–80 g L−1 was optimal for producing microbial biomass and lipids. Glucose at 60 g L−1 afforded a final dry biomass concentration of 21.2 g L−1 with a 35.8% lipid content. The biomass concentration was reduced to 18.7 g L−1 if the glucose was 80 g L−1 and the lipids were reduced to 11.8%. With pure xylose (80 g L−1), the final biomass concentration was 14.0 g L−1 and the lipid content of the biomass was 42.1%. A 4:1 by mass mixture of glucose and xylose was used to simulate a typical hydrolysate of OPEFB. With this mixture (glucose = 64 g L−1, xylose = 16 g L−1), the maximum biomass concentration was 17.9 g L−1 and the lipids in the biomass exceeded 37.9%. A hydrolysate of OPEFB was prepared by enzymatic hydrolysis of the alkali-pretreated OPEFB. With this hydrolysate as the main C-source, the final yeast biomass concentration was 14.9 g L−1, but the lipid content in the biomass was only 6%. The lipid content of the yeast biomass could be raised to >40% by using a hydrolysate diluted with distilled water. Apparently, dilution alleviated the effects of inhibitory compounds that formed during hydrolysis of lignocellulosic biomass with the commercial enzymes. The lipid yield on C-sources was 0.162 g g−1 in a medium with a C:N mole ratio of 71.7:1.