Biovalorization of whole old oil palm trunk as low-cost nutrient sources for biomass and lipid production by oleaginous yeasts through batch and fed-batch fermentation

Biovalorization of whole old oil palm trunk (OPT) as low-cost nutrient sources for biomass and lipid production by oleaginous yeasts were intensively investigated. Oil palm sap (OPS) squeezed from OPT containing mainly glucose (52%), sucrose (28%), and arabinose (20%) was used directly while the residual OPT fiber was acid-hydrolyzed into fermentable sugars before use. The main sugars in OPT hydrolysate (OPTH) were arabinose (47%), xylose (35%), and glucose (18%). Six oleaginous yeasts including Rhodotorula mucilaginosa G43, Candida tropicalis X37, Trichosporonoides spathulata JU4-57, Kluyveromyces marxianus X32, Yarrowia lipolytica TISTR 5151, and Yarrowia lipolytica TISTR 5054 were screened. Among the strains screened, R. mucilaginosa G43 and C. tropicalis X37 gave the maximum lipid yields of 65-68 mg/g-sugar from OPS. When OPTH was used, Y. lipolytica TISTR 5054 grew best and produced higher yields of lipids (55-58 mg/g-sugar) than other strains. To manipulate the suitably high C/N ratio for lipid production, the fed-batch fermentations using various co-carbon sources were performed. Crude glycerol (CG), a byproduct from biodiesel production, was the best cocarbon source that could increase the lipid production up to 3.07 +/- 0.03 g/L from OPS and 1.80 +/- 0.06 g/L from OPTH. The preliminary mass balance revealed the practical biovalorization of whole felled OPT into yeast biomass and lipids that may greatly increase the competiveness of the bioenergy and palm oil industries.