Polyvinyl Alcohol Beads as a Robust and Reusable Carrier for Pichia fermentans WC1507 in Xylose-to-Xylitol Bioprocessing

The bioconversion of xylose into xylitol offers a sustainable approach to upcycle pentoses in lignocellulosic hydrolysates by leveraging the metabolic capabilities of ascomycetous yeasts. Scalable solutions, such as immobilized-cell systems, facilitate industrial bioprocessing by enabling easy biomass recovery, reusability, and maintenance of high cell concentrations without compromising productivity. Pichia fermentans WC 1507 has demonstrated remarkable efficiency in converting xylose to xylitol. In this study, its cells were immobilized in beads composed of 0.8% (w/v) alginate and 10% (w/v) polyvinyl alcohol (PVA) crosslinked with calcium and boric acid. While immobilization initially reduce yeast viability, it was progressively restored during the first utilization cycles of the PVA-immobilized cells. The PVA beads loaded with the cells were tested in four consecutive 7-day fermentation runs using a medium containing 120 g/L xylose. The experiments confirmed the excellent robustness of the PVA beads, that proved to be usable in stirred tank bioreactors for remarkably long periods. Across the four runs, fermentation efficiency improved, achieving stable xylitol yields of 60–63 g/L, with 54–56% conversion and a volumetric productivity of 450–470 mg/L/h under non-optimized conditions. These results highlighted the potential of P. fermentans WC 1507 for the valorization of xylose-rich hydrolysate and validated PVA matrices as durable biomass carrier for use in stirred bioreactor systems.