New at-line flow cytometric protocols for determining carotenoidcontent and cell viability during Rhodosporidium toruloides NCYC 921batch growth

Rhodosporidium toruloides NCYC 921 batch growth was monitored as a means to evaluate the yeastbiomass potential as a source for the production of carotenoids and other lipids.Carotenoid content, cell viability and size were assessed by multiparameter flow cytometry. Thesaponifiable lipid fraction was assayed by gas–liquid chromatography.The carotenoid production increased during the stationary phase, reaching 78 g/g while the total fattyacid content attained 32% (w/w) at the end of the fermentation. The fatty acid profile was suitable forbiodiesel purposes.As the yeast cells entered the stationary phase, the proportion of cells with depolarised mitochon-drial membrane and cells with permeabilised cytoplasmic membrane increased, attaining 65% and 14%,respectively. Nevertheless, a high proportion of cells (82%) showed esterase activity.These results demonstrated that flow cytometry can be a powerful at-line technique to monitor thetotal carotenoids and cell viability during the yeast growth, being useful for the yeast process optimisationat lab and pilot scales