Potential of soybean molasses as the sole nutrient source in the cultivation of carotenogenic yeasts.

The main goal of this study was to evaluate the potential of four yeasts-Rhodotorula mucilaginosa CCT 7688, Sporidiobolus pararoseus CCT 7689, Pichia fermentans CCT 7677, and Phaffia rhodozyma NRRL Y-17268-to produce carotenoids using soybean molasses as the sole nutrient source. Initially, they were cultivated in the medium-containing soybean molasses (C1, 34.32 g L^-1) and compared to the standard medium Yeast Malt (YM). R. mucilaginosa showed similar performance in both media. S. pararoseus had better performance in soybean molasses than in YM, since biomass and carotenoid production was higher. On the other hand, P. fermentans showed higher growth in soybean molasses, but pigment production was lower. P. rhodozyma outperformed in soybean molasses, resulting in higher biomass production (7.21 g L⁻¹), total carotenoid production, expressed as β-carotene (129.49 µg g⁻¹ and 914.71 µg L⁻¹), and astaxanthin production (188.25 µg g⁻¹ and 1388.84 µg L⁻¹). In addition, the use of soybean molasses showed potential to reduce about 90% of culture medium costs, in the case of this strain, in comparison with YM. Thus, P. rhodozyma was selected for the assays at different soybean molasses concentrations: 100 (C2), 150 (C3), 200 (C4), and 250 (C5) g L⁻¹. The best results were observed at C3, which provided significant increase in biomass (15.73 g L⁻¹) and total carotenoids, expressed as β-carotene (2229.30 µg L⁻¹) and astaxanthin (3519.65 µg L⁻¹). Compared to the initial medium (C1), gains exceeded 150% in some parameters, demonstrating that soybean molasses is an efficient, low-cost cultivation substrate with high potential to enable yeasts to produce carotenoids.