Soybean molasses: a promising substrate for the production of microbial oil by Phaffia rhodozyma

Soybean molasses represents a promising substrate for the production of high-value bioproducts, particularly in the cultivation of Phaffia rhodozyma, a yeast classified as GRAS (Generally Recognized as Safe). Although this yeast is well known for carotenoid synthesis, its potential for lipid accumulation remains largely unexplored. In this study, oil production by P. rhodozyma was evaluated using soybean molasses as the sole carbon source. The yeast was cultured in a 5 L bench-scale bioreactor (100 g·L⁻¹ substrate, 300 rpm, 1 vvm, 25°C) and the biomass was subsequently spouted bed drying. Lipids were extracted following the Bligh and Dyer method. After 144 h, 12.59 g.L⁻¹ of biomass was obtained, containing 154.23 µg·g⁻¹ of astaxanthin and 85.91 µg·g⁻¹ of β-carotene. Lipid yield reached 34.9% (w.w- 1), corresponding to a C/N ratio of 44.39 in the cultivation medium. Fatty acid analysis revealed a predominance of oleic acid (66.98%), with a saturated/unsaturated ratio of 0.24, iodine value of 74 g.I2.100 g⁻¹, saponification value of 161 mg KOH.g⁻¹, acidity of 5.02 mg KOH.g⁻¹, and peroxide value of 3.19 mEq O₂.kg⁻¹. These results demonstrate the potential of P. rhodozyma cultivated on soybean molasses to produce microbial oil with high nutritional and functional value, favorable lipid composition, and oxidative stability, highlighting the need for optimization strategies in the oil recovery step to enable future applications in the food industry.