Property Characterization and Lipid - Compositional Analysis of Lipid Granules Isolated from an Oleaginous Yeast Rhodotorula glutinis

Abstract

Preparative isolation of lipid granules from Rhodotorula glutinis, which has been studied for long time to produce edible lipids, was carried out by flotation method in Ficoll-linear density gradient. When the isolated lipid granules were suspended in a series of solutions containing varying concentration of osmotic stabilizer (sorbitol and mannitol) ranging from 0.8 M to 0 M, the lipid granules appeared to be disrupted at a concentration between 0.8 M and 0.7 M, and again at a concentration below 0.1 M, suggesting that lipid granules have a membraneous structure and that at least two types of lipid granules are present. Compositional analysis of lipids from lipid granules revealed that lipids are composed mainly of neutral lipids (87.8% of total lipids), predominantly as triacylglycerols (71.8%). Marked differences were observed in phospholipids between lipids of lipid granules and those of whole cells. The major components of phospholipids in lipid granules and in whole cells are phosphatidylcholine (38.6%) and phosphatidylserine (42.8%), respectively. In addition, significant differences were also observed in the fatty acid composition of phospholipids. As phospholipids are important structural components of membranes, these differences lead to the suggestion that the membrane of lipid granules may be distinct functionally and structurally from other membranes of yeast cells. The major fatty acid components of neutral lipids of whole cells and lipid granules are palmitic, oleic, and linoleic acid. However, degree of fatty acid unsaturation of neutral lipids of lipid granules was much lower than that of neutral lipids of whole cells