Kinetic modeling of xylitol production by <i>Pichia fermentans</i> NCIM 3638 under varied initial xylose concentrations.

Abstract

Xylitol, valued for its anticariogenic properties and low glycemic index, can be sustainably produced through microbial fermentation of xylose, thereby addressing the environmental limitations of conventional chemical synthesis. In this study, the effect of increasing xylose concentrations on substrate utilization efficiency and xylitol productivity by Pichia fermentans NCIM 3638 was systematically investigated. A maximum xylitol yield of 0.38 g/g xylose and a volumetric productivity of 0.25 g/L/h were achieved at an initial xylose concentration of 75 g/L and remained constant up to 100 g/L; however, both parameters decreased slightly when the xylose concentration increased to 110 g/L. The synthesized xylitol was subsequently confirmed by GC-MS analysis. Growth kinetics and xylose consumption were evaluated using three mathematical models, while five models were assessed to estimate the specific growth rate. Among them, the Hybrid Logistic-Monod model provided the best fit, estimating a µ max of 0.14 h- 1 at 110 g/L xylose. Xylitol production kinetics was successfully described using the Luedeking-Piret model, yielding a model-estimated maximum product yield coefficient of 0.66 g/g at 100 g/L xylose. Sensitivity analysis identified V m as a key parameter governing xylitol production, with a ± 30% perturbation in V m resulting in a proportional 30% variation in final xylitol titers at an initial xylose concentration of 100 g/L. The produced xylitol was crystallized and characterized using FTIR, XRD, and SEM analyses. Overall, the results highlight the strong metabolic potential of P. fermentans NCIM 3638 for efficient xylose to xylitol bioconversion and provide valuable insights for process optimization and scale-up. Graphical abstract Supplementary information The online version contains supplementary material available at https://doi.org/10.1007/s13205-026-05133-y.

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