Methods for fermentation of xylose and hexose sugars

Methods and systems for the isomerization and fermentation of xylose and hexose sugars using an immobilized enzyme system capable of sustaining two different pH microenvironments in a single vessel are disclosed. Bilayer particles are dispersed in a mixture comprising an ionic borate source and xylose. The bilayer particles have an inner of a xylose isomerase having a pH of 6 or above, and an outer region having a second enzymatic activity at an acidic pH