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Production of xylitol by the yeast Komagataella pastoris
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Xylitol is a sugar alcohol that can replace sucrose, is tolerated by diabetics and has several clinical applications. Currently, xylitol is manufactured on a large scale through a chemical process, but there is a search for alternative processes that are environmentally friendly and more cost-effective.
In this thesis, the biotechnological production of xylitol has been examined as an alternative to the chemical process, using the yeast Komagataella pastoris to produce xylitol from glucose/xylose mixtures. Different parameters, namely, pH, temperature, xylose concentration, the presence of arabinose as substrate and dissolved oxygen were tested.
This work demonstrated that the best pH value for xylitol synthesis was 7.0 - 7.5 that resulted in 4.04 g/L of xylitol, with a volumetric productivity of 0.024 g/L.h and a specific productivity 0.35 gxylitol /gCDW.
Cultivation with initial pH value 7.00 and 37 ºC, in fully aerobic conditions, and changing the pH to 6.4 at 72 h of cultivation, resulted in the highest xylitol concentration of this study: 12.00 g/L, concomitant with a volumetric productivity of 0.071 g/L.h and a specific productivity of 1.41 gxylitol/gCDW.
Limiting oxygen conditions resulted in a xylitol concentration of 5.81 g/L, with a specific productivity of 0.33 gxylitol/ gCDW, and a volumetric productivity, of 0.035 g/L.h.
Several concentrations of xylose in the glucose/xylose mixtures were tested. The highest xylitol production was obtained with 60 g/L of xylose. Reducing the xylose concentration resulted in lower xylitol production.
Interestingly, it was observed for the first time that K. pastoris was able to synthesize arabitol using arabinose as substrate, with the arabitol concentration reaching 3.15 g/L on cultivation at 37 ºC under oxygen limitation. This feature opens up the possibility of using this process for the synthesis of both sugar alcohols, xylitol and arabitol, being apparently possible to tune the synthesis of each product by altering the cultivation conditions.
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Palavras-chave
Xylitol Xylose Xylose reductase (XR) Yeast Komagataella pastoris