Fed-batch strategies for growing β-carotene enriched yeast Rhodotorula paludigena using untreated molasses

The β-carotene-rich yeast Rhodotorula paludigena CM33 was grown in a 22-L bioreactor using sugarcane molasses in combination with several distinct fed-batch strategies: DO (dissolved oxygen)-stat; stepwise feeding; and hybrid feeding (an initial exponential feeding phase followed by a DO-stat operation). The impacts of feeding strategies on biomass production, carotenoid production and nutrient conversion efficiencies were evaluated. The stepwise feeding proved most effective, achieving: a final dry biomass concentration of 73.1 ± 2.7 g L⁻¹; a β-carotene titer of 181.9 ± 1.0 mg L⁻¹; a biomass volumetric productivity of 1.33 ± 0.05 g L⁻¹ h⁻¹; and β-carotene productivity of 3.31 ± 0.02 mg L⁻¹ h⁻¹. However, with this feeding strategy the sugar and nitrogen conversion efficiencies were the lowest: the β-carotene yield on total sugar was 0.92 ± 0.00 mg g⁻¹ and its yield on nitrogen was 5.47 ± 0.06 mg g⁻¹. In contrast, the DO-stat operation was the most resource efficient, providing a biomass yield on sugar of 0.47 ± 0.02 g g⁻¹, a biomass yield on nitrogen of 2.64 ± 0.05 g g⁻¹, a β-carotene yield on sugar of 1.08 ± 0.04 mg g⁻¹, and β-carotene yield on nitrogen of 6.08 ± 0.08 mg g⁻¹. The hybrid strategy resulted in intermediate values of the various performance parameters. Raw sugarcane molasses proved to be excellent for high-cell-density culture of R. paludigena. A compromise between productivity and resource use efficiency may be required for commercial production of β-carotene especially if the substrate is expensive compared to the product.