Enthalpy content as a function of lipid accumulation in Rhodotorula glutinis

Microcalorimetry has been demonstrated to be a suitable on-line method for monitoring the lipid production phase of oleaginous yeasts. The choice of lipid extraction method for the oil accumulated by oleaginous yeasts is highly important both for accuracy when quantifying the lipid level and determining the fatty acid composition. The energy content of Rhodotorula glutinis increased from 23.0 kJ/g to 30.6 kJ/g dry biomass during the lipid-accumulating phase and was directly correlated to the analysed level of lipids, when an alkaline hydrolysis extraction method was used. Consequently, bomb-calorimetric measurements of the energy content were shown to be an indirect method of quantifying the lipid content in oleaginous yeasts. The fatty acid composition remained rather constant during the batch growth of Rh. glutinis with approximately 70% unsaturated C18 fatty acids. The high energy content as well as the fatty acid composition of Rh. glutinis makes this yeast a better candidate for use as aquaculture feed compared with the commonly used Saccharomyces cerevisiae.