Study on the microbial fat production

Abstract

Studies were carried out to produce microbial fat as alternative source of this material. $\mbox{\underline{Rhodotorula}}$ $\mbox{\underline{gracilis}}$ (NRRL Y-1091) was chosen for this purpose and this yeast produced high amount of lipid(57.4\%; F.C. 22.0 and E.C. 38.3) cultured with ammonium sulfate and glucose as nitrogen and carbon source respectively. In batch culture on the 20-1 scale, fat content between 50 and 60 \% were obtained. The generation time was 15-20 hours and the protein content amounted to only 12-13\%. The specific growth rate of this batch culture was 0.047 $hr^{-1}$. It took 60 hours for $\mbox{\underline{Rh}}$. $\mbox{\underline{gracilis}}$ to produce maximum lipid content and biomass yield was also maximum value at that point. Extraction temperature of 60$^\circ$C was the best condition for extraction of lipid from ground yeast cell with chloroformmethanol(2:1) mixed solvent. At this condition the extraction rate was represented as follows: $$-dC/dt=3.03\times10^{-7}S^{2.48}C^{8.69}$$ where, C is the residual oil content in g oil/g inert solid, t is the extraction time in minutes, and S is specipic surface of the particle in $cm^2$/g. The characteristics of this lipid was very similar to those of plant oil. It was composed of neutral lipids 84.1 \%, glycolipid 13.7 \%, and phospho- and other polar lipids 2.2\%. This lipids had high proportion of essential fatty acids and contained oleic acid(55.6 \%), linoleic acid(12.5 \%), stearic acid(11.3 \%), palmitic acid(11.0 \%), and linolenic acid(4.5 \%) as major components. And this yeast containd all essential amino acids although the sulfur containing amino acids were very low. From the above mentioned results, it can be concluded that the lipid extracted from this yeast may be as human food and the defatted yeast cell can be used as food ingredient or animal feed succesfully.