Production of Single Cell Oils from Glycerol By Oleaginous Yeasts

Introduction: A surplus of crude glycerol is obtained as the by-product of biodiesel manufacturing and has became a waste product whose applications are lacking. Thus, the use of crude glycerol as substrate for fermentation processes yielding valuable products is attractive. In this study, the utilization of glycerol as a growth substrate for the cultivation of oleaginous yeasts has been explored. Methods: 40 environmental yeasts belonging to 19 different species were screened for the ability to grow and produce intracellular lipids at 30 ◦C in a medium containing glycerol excess (C:N = 48:1). The most promising strain was challenged for lipid production under increasing C:N ratios, in batch and fedbatch bioreactor processes. Lipids were extracted from lyophilized biomass and determined gravimetrically. GC-MS analysis of fatty acids methyl-esters was performed. Results: Three out of 40 strains, belonging to the species Candida freyschussii, Pichia farinosa, and Saccharomyces spencerorum, depleted 40 g/L glycerol within 120 h and produced intracellular lipids. C. freyschussii sp. produced the highest amount of lipids, accounting for the 30% of biomass dry weight and the 8% of glycerol conversion. C16 and C18 (C18, C18:1, C18:2, and traces of C18:3) were the most abundant fatty acids, accounting for the 40 and 55%, respectively, with an unsaturation index of 0.9. Lipid production was positively affected by glycerol concentration and was the highest (30% of biomass weight) with 40 g/L glycerol. Since glycerol inhibited the growth of C. freyschussii sp. above 40 g/L, fed-batch processwasdeveloped.When50% glycerolwasfed, lipids increased up to 48% of biomass. Discussion: This study represents the first proposal of a biotechnological application of C. freyschussi, a rare non-albicans Candida. The yeast resulted oleaginous and a good candidate for the production of single cell oils from glycerol.