STUDIES ON YEAST LIPIDS USED AS LUBRICANT ADDITIVES

Abstract

The thesis entitled "Studies on Yeast Lipids used as Lubricant Additives" deals mainly with the isolation of the oleaginous yeast strains from soil samples, optimization of culture conditions for the growth and lipid accumulation for the selected strain, characterization and evaluation oflipids as lubricating base oil or its additives. An oleaginous yeast strain was isolated from oil impregnated soil sample and was identified as Rhodotorula minuta IIP-33. It is a pink coloured strain and the pink, colour of the strain is temperature sensitive. Growth and lipid accumulation parameters for the yeast strain R. minuta IIP-33 were optimized. The strain shows a maximum specific growth rate of 0.38 h" on glucose. The optimum pH and temperature for the growth ofthe strain are 4.5 and 30°C respectively. Activation energy for growth of the strain R. minuta IIP-33 is 117.83 KJ/mole. Lipid accumulation in an oleoginous yeast strain occurs under nitrogen limiting conditions. Optimum temperature for maximum lipid accumulation (50%) by the strain R. minuta IIP-33 is 32°C. Alipid yield of 0.507 is obtained at 32°C which decreases to 0.201 at 38°C. C/N ratio also affects the lipid yield and productivity of the strain R. minuta IIP-33 and this was observed by doing the continuous cultivation of the strain R. minuta IIP-33. Optimum dilution rate and C/N ratio for maximum lipid yield (0.183) is 0.15 h"1 and 17 respectively. Higher C/N decreases the lipid yield and productivity.

The best mode of operation for maximum lipid productivity is a continuous culture of the strain R. minuta IIP-33 followed by a plug-flow reactor operation. It gives a productivity of 1.24 g/l/h. Gas chromatographic analysis shows that the general fatty acid profile of lipid of R. minuta IIP-33 which consists of fatty acids ranging from Cg-C,8. R. minuta IIP-33 accumulates mainly palmitic and oleic acids and the percent of palmitic and oleic acids is highest at 32°C (14.80 and 30.50 respectively). At the lower post accumulation phase temperature of 16°C the content of nearly all the unsaturated fatty acids increases which degree of fatty acid unsaturation. Evaluation of the lipid sample for its lubricant properties namely viscosity index, pour point and flash point show that lipid sample as such cannot be used as a lubricant because of high pour point and low flash point however, blending with 90% mineral lube oil base reduces the pour point and increases the flash point which makes the lipid suitable to meet the requirements of a lubricant additive. Conversion of yeast lipids to fatty acid esters of suitable alcohols have a great scope for use as lube base oil. Lipids of R. minuta IIP-33 were converted to fatty acid esters of 2-ethyl hexanol and isobutanol and the esters were reported to have great potential to be used as lube base oil.