Improved Co-Fermentation of Xylose and Glucose by Encapsulation of Saccharomyces Cerenvisiae

Abstract

Abstract Background: Presently the consumption of biofuels is increasing substantially. Fermenting lignocellulosic materials could be a cheap, environmentally friendly and sustainable solution to obtain biofuels like bioethanol, without the controversies arising from the use of potential food and feed sources. To access the fermentable sugars of the lignocellulosic matter, pre--‐treatment and hydrolysis must be performed. After these steps inhibitory compounds are present and can interfere with the fermentation. Encapsulation of yeast is a promising technique when the goal is to improve the fermentation productivity and dealing with lignocellulosic inhibitors, like furfural and hydroxymethylfurfural (HMF). Results: The encapsulation was performed with alginate--‐chitosan--‐alginate multilayer capsules. Therefore capsules were treated with 1.5% hydrolysed (3--‐Aminopropyl) triethoxysilane. Fermenting a 40 g/L initial sugars concentration the consumption rate for encapsulated yeast using glucose and xylose was: 1.2 g/gh and 0.3 g/gh in the presence of 1 g/L furfural; with 2 g/L furfural the consumption reached 1.3 g/g h and 0.2 g/gh and without inhibitor 1.5 g/gh and 0.6 g/gh for glucose and xylose respectively. Moreover the ethanol productivity for encapsulated cells using glucose and xylose together was higher, around 50%, when compared with free cells. It was also shown that the volumetric mass transfer coefficients of glucose and xylose have similar values, 3.30 and 3.45 cm3/min respectively. Conclusion: Encapsulation revealed to be efficient in promoting the co--‐consumption of C5 and C6 carbon sugars by recombinant Saccharomyces cerevisiae. There were visible improvements in ethanol yield in encapsulated cultures with glucose and xylose. Encapsulation also showed effectiveness in the presence of furfural.