Catalyzes the selective oxidation of C1 hydroxyl moieties on mono- and disaccharides with concomitant reduction of molecular oxygen to hydrogen peroxide. This results in the formation of the corresponding lactones, which typically undergo spontaneous hydrolysis. Glucooligosaccharide oxidase is able to oxidize the monosaccharide D-glucose as well as the disaccharides maltose, cellobiose, and lactose. In addition, it shows high selectivity for cello- and maltooligosaccharides, indicating that glucooligosaccharide oxidase prefers oligosaccharides with a beta-D-glucosyl unit on the reducing end and additional sugar units linked by alpha- or beta-1,4 glucosidic bonds. beta-lactose + O2 = H2O2 + lactobiono-1,5-lactone D-cellobiose + O2 = D-cellobiono-1,5-lactone + H2O2 D-cellotriose + O2 = D-cellotriono-1,5-lactone + H2O2 D-cellotetraose + O2 = D-cellotetraono-1,5-lactone + H2O2 D-cellopentaose + O2 = D-cellopentaono-1,5-lactone + H2O2 D-cellohexaose + O2 = D-cellohexaono-1,5-lactone + H2O2 Binds 1 FAD per subunit in a bicovalent manner. Optimum pH is 10. Stable from pH 5 to pH 11. Optimum temperature is 50 degrees Celsius. The FAD cofactor is bound via a bicovalent 6-S-cysteinyl, 8alpha-N1-histidyl FAD linkage. Belongs to the oxygen-dependent FAD-linked oxidoreductase family.