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Valorizing Red Seaweed Spent Biomass into Reducing Sugars for β-Carotene Production by Rhodotorula paludigena
(2026-05-01)
Kongsinkaew, Chatchol
;
Tangsattayatithan, Chutipol
;
Chittapun, Supenya
;
Phiphatbunyabhorn, Parivat
;
Laemthong, Tunyaboon
Seaweed bioactive extraction generates de-extracted residual solids that remain carbohydrate-rich but are often underutilized. This study developed an integrated valorization route for Gracilaria fisheri spent biomass to produce fermentable sugars for β-carotene production by Rhodotorula paludigena CM33. Reducing sugar production was optimized using response surface methodology (Box–Behnken design) by varying reaction time, sulfuric acid concentration, and biomass loading at 90 °C. The predicted optimum (47.39 min, 2.50% (w/v) H<inf>2</inf>SO<inf>4</inf>, and 7.13% (w/v) biomass) yielded 22.41 g/L reducing sugars and was validated experimentally at 22.22 ± 0.19 g/L, indicating that the model reliably predicted reducing sugar production. The optimized condition was scaled up in a 22 L bioreactor with sequential acid hydrolysis followed by enzyme-assisted hydrolysis, increasing reducing sugars from ~30 to ~40 g/L. FTIR and SEM analyses indicated progressive modification of the carbohydrate matrix across processing stages. Batch cultivation of R. paludigena on the hydrolysate showed that ammonium sulfate supplementation significantly increased biomass, whereas β-carotene titers were not significantly different. Repeated-batch operation on non-supplemented hydrolysate sustained production over four cycles with β-carotene titers of 13.75–17.27 mg/L, demonstrating the operational feasibility of the hydrolysate-based system. Overall, this work demonstrates a practical seaweed biorefinery approach to upgrade G. fisheri spent biomass into sugars and carotenoid-rich yeast biomass.
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Fed-batch strategies for growing β-carotene enriched yeast Rhodotorula paludigena using untreated molasses
(2025-11-01)
Kongsinkaew, Chatchol
;
Chisti, Yusuf
;
Ketudat-Cairns, Mariena
;
Chittapun, Supenya
;
Pornpukdeewattana, Soisuda
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.

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