Catalyzes the reversible epimerization of cellobiose to 4-O-beta-D-glucopyranosyl-D-mannose (Glc-Man). Catalyzes epimerization but also isomerization for beta-1,4- and alpha-1,4-gluco-oligosaccharides. Can use cellobiose, lactose, cellotriose, maltose and maltotriose. D-cellobiose = beta-D-glucosyl-(1->4)-D-mannopyranose kcat is 169 min(-1) for cellobiose. kcat is 89.4 min(-1) for lactose. Optimum pH is 7.0. Optimum temperature is 70 degrees Celsius. Monomer. Belongs to the cellobiose 2-epimerase family.