Modulation of Polyunsaturated Fatty Acid Production and Nutritional Lipid Quality Indices in Rhodotorula mucilaginosa 6S Using Molasses as a Sustainable Carbon Source

Microbial lipids produced by oleaginous yeasts are a sustainable alternative to conventional lipid sources because of their ability to generate nutritionally valuable fatty acids. This study evaluated the effects of carbon-to-nitrogen (C/N) ratio, modified through molasses concentration, and cultivation temperature (15 and 25 °C) on biomass production, lipid accumulation, fatty acid composition, and nutritional quality of lipids produced by the native yeast Rhodotorula mucilaginosa 6S. Biomass, lipids, sugar consumption, and growth kinetics were determined, while fatty acid composition was analyzed by gas chromatography and nutritional quality was assessed through lipid nutritional indices. Biomass production was mainly influenced by the C/N ratio, whereas temperature had the greatest effect on lipid accumulation and fatty acid composition. Cultivation at 25 °C enhanced lipid yield and productivity, while 15 °C promoted faster growth and higher accumulation of polyunsaturated fatty acids (PUFAs), resulting in lipids with superior nutritional quality. The combination of 15 °C and a C/N ratio of 12 produced the most favorable lipid profile, with higher unsaturation, improved PUFA/SFA and MUFA/SFA ratios, balanced ω-6/ω-3 and LA/ALA ratios, low atherogenicity and thrombogenicity indices, and a high hypocholesterolemic/hypercholesterolemic ratio. These findings demonstrate the potential of molasses as a sustainable substrate for producing high-quality microbial lipids.