Effect of Culture Conditions on the Production of Microbial Oils from Mortierella sp.

Abstract

Microbial oils are the lipids obtained from microorganisms such as bacteria and fungi. They have the ability to produce oils under certain special culture conditions. Microbial oils might become one of the potential oil feedstocks for biodiesel production in the future. In the present work, the effects of culture conditions on the biomass and lipid production of Mortierella sp. were studied. The favourable pH, temperature and media were found to be 6.0, 25°C and yeast extract peptone glucose (YPG) media, respectively. Under these conditions, M. polycephala yielded the highest biomass (9.1 g/L) compared with M. vinaceae (8.2 g/L) and M. alpina (5.9 g/L); at pH 6.0, M. alpina yielded the highest biomass of 17.60 g/L compared with M. vinaceae, which produced 15.20 g/L and M. polycephala, 15.05 g/L. The effect of different media like YPG, fat producing media and potato dextrose broth was studied; a maximum growth of about 17.34 g/L was observed in M. alpina compared with M. polycephala (15.03 g/L) and M. vinaceae (15.63 g/L), respectively, in YPG media. The lipid content was found to be maximum in M. polycephala, i.e. about 1.95 g/L, and M. alpina was found to be the least yielding, i.e. about 0.007 g/L, at 25°C. Thin layer chromatography was performed using the isolated lipid extracts to determine the constituents, and it showed the presence of myristic, palmitic and stearic acids. The estimated iodine values were 81 g of I2/100 g of oil for the lipids extracted from M. polycephala, exhibiting higher unsaturated lipid contents than other two fungal species, i.e. M. vinaceae (79 g of I2/100 g of oil) and M. alpina (59 g of I2/100 g of oil). The acid values of the fungi followed a similar pattern as that of the iodine values as the free fatty acid content was more in M. polycephala. Peroxide values varied in M. polycephala (1.49 mg KOH/g oil) than those of M. vinaceae (1.20 mg KOH/g oil) and M. alpina (0.31 mg KOH/g oil). Hence, M. polycephala was the major strain considered for producing good quality oil compared with M. vinaceae and M. alpine, and it can be effectively utilised to produce microbial biodiesel.