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. Hexose oxidase is able to oxidize a variety of substrates including D-glucose, D-galactose, maltose, cellobiose, and lactose. beta-D-glucose + O2 = D-glucono-1,5-lactone + H2O2 D-galactose + O2 = D-galactono-1,5-lactone + H2O2 D-maltose + O2 = D-maltobiono-1,5-lactone + H2O2 D-cellobiose + O2 = D-cellobiono-1,5-lactone + H2O2 beta-lactose + O2 = H2O2 + lactobiono-1,5-lactone Binds 1 FAD per subunit in a bicovalent manner. Optimum pH is 6 (PubMed:9108257, PubMed:11427234). A second pH optimum was found at pH 10 (PubMed:9108257, PubMed:11427234). Homodimer. Cleaved into 40 kDa and 29 kDa cleavage products, but the 2 polypeptide chains do not separate and seem to be physically linked together. 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. Was initially reported to use Cu(2+) as a cofactor (PubMed:4708670). However, cofactor composition could not be confirmed later (PubMed:9108257), and the discrepancies in the reported characteristics of the enzyme were suggested to originate from the characterization of a contaminating protein in PubMed:4708670.