ABSTRACT
The growth performance and intracellular lipid production potentiality of two identified yeast stains Candida tropicalis (S5) and Issatchenkia orientalis (D5) in N-limited medium under different carbon, nitrogen sources, carbon/nitrogen ratio and temperature was studied. Among all carbon sources, glucose was the best in lipid weight, lipid content, lipid yield and lipid productivity. The increases in cell biomass reached its maximum value by use of yeast extract in Candida (8.62 gL-1) and 10.25 gL-1 for Issatchenkia using peptone. However, urea was the preferable N source for lipid production in both strains. On the other hand, KNO3 proved to be the lowest values treatment in the cell biomass and lipid production for both strains. The interaction treatments yeast extract + (NH4) SO4 was convenient for oil yield parameters in Candida. The data showed that the maximum cell biomass was obtained at 54 and 100 C/N ratio for Candida and Issatchenkia, respectively. The data also exhibited that designated sharp increases in lipid weight, lipid content and lipid productivity were developed by the two yeast strains reached their maximum values at C/N ratio 115 (1.0 gL-1, 27.77%, 0.20 gL-1) for Candida tropicalis and C/N ratio 100 (3.37 gL-1, 30.92%, 0.67 gL-1) for Issatchenkia orientalis. Further increase in C/N ratio resulted in drop in lipid weight; this drop was slight in Candida above 115, whereas it was drastically in Issatchenkia after C/N 100. The result of effect of temperature degree on cell biomass and lipid production showed that the temperature degree of 30°C was the best for yeast growth and also for lipid production.
ABSTRACT
Two oleaginous yeast strains identified as Issatchenkia orientalis D5 and Candida tropicalis S5 were evaluated for oil production under optimized growth factors. Both strains were inoculated in 2L of optimal fermentation broth medium for 9 days. Sample was taken periodically (24 hrs.), The data exhibited that cell biomass was gradually increased along with time sample to reach maximum values of cell dry weight (11.22 & 13.30 gL-1) after 8 and 9 day at consumed sugar equal to 79.52 and 156.29 gL-1 for Candida and Issatchenkia. It was found that Candida gave the highest values of lipid weight, lipid content, lipid yield, conversion coefficient and lipid productivity after 6 days being 2.16 gL-1, 34.17%, 2.70%, 2.73% and 0.36 gL-1/day, while Issatchenkia recorded the highest lipid concentration and lipid yield after 4 days of the fermentation period being 3.24 gL-1 and 2.06%. The specific growth rate, doubling time, multiplication rate and number of generation were 0.317 day-1, 2.18 days, 0.458 day-1 and 1.37 for Candida and reached to 0.275 day-1, 2.52 days, 0.396 day-1 and 0.793 for Issatchenkia. The data proved that the strains Issatchenkia orientals and Candida tropicalis could be used as feedstock producers for microbial lipid production.