Background: Lipid-producing microorganisms, said to be oleaginous have been recognized
since several years. We had investigated the effects of medium components and culturing
situations on cell growth and lipid accumulation of oleaginous yeasts which were analytically examined
so as to enhance lipid yield for biodiesel production.
Objective: The main objective of this study was to explore oleaginous yeast, Yarrowia lipolytica
isolated from soil and optimization of culture conditions and medium components to obtained better
quality microbial oil for biodiesel production.
Methods: Fifty yeast strains were isolated from soil from different regions of Lahore and eleven of
them were selected for oil production. The isolated yeast colonies were screened to further check
their lipid producing capabilities by the qualitative analysis. Five yeast strains were designated as
oleaginous because they produced more than 16% of oil based on their biomass. To estimate the
total lipid content of yeast cells, the extraction of lipids was done by performing the procedure proposed
by Bligh and Dyer. The transesterification of yeast oils was performed by using different
methods. There were three different strategies customized to transesterifying microbial oil using
base catalyzed transesterification, acid catalyzed transesterification and enzyme-based transesterification.
After completion of transesterification, sample was used for fatty acid methyl esters
(FAMEs) were analyzed by gas-chromatograph with ionization detector type MS.
Results: The isolate IIB-10 identified as Yarrowia lipolytica produced maximum amount of lipids
i.e. 22.8%. More amount of biomass was obtained when cane molasses was utilized as carbon
source where it produced 29.4 g/L of biomass while sucrose and lactose were not utilized by IIB-10
and no biomass was obtained. Similarly, meat extracts showed best results when it was used as
nitrogen source because it resulted in 35.8 g/L biomass of Yarrowia lipolytica IIB-10. The culturing
conditions like size of inoculum, effect of pH and time of incubation were also studied. The 10% of
inoculum size produced 25.4 g/L biomass at 120 h incubation time, while the pH 7 was the optimum
pH at which 24.8 g/L biomass was produced by Yarrowia lipolytica IIB-10. GC-MS analysis
showed that biodiesel produced by transesterification contained similar fatty acids as found in vegetable
oil for this reason it is widely accepted feedstock for biodiesel production.
Conclusion: The analysis of fatty acids methyl esters showed the similar composition of microbial
oil as in vegetable oils and high amount of methyl esters were obtained after transesterification.
Therefore, potentially oleaginous yeast could be used to generate a large amount of lipids for biodiesel
production that will be the better substitute of petroleum-based diesel and will also control
the environmental pollution.