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Glucose oxidase is a highly specific enzyme (for D-glucose, but see Chapter 8), from the fungi Aspergillus niger and Penicillium, which catalyses the oxidation of b-glucose to glucono-1,5-lactone (which spontaneously hydrolyses non-enzymically to gluconic acid) using molecular oxygen and releasing hydrogen peroxide (see reaction scheme [1.1]). It finds uses in the removal of either glucose or oxygen from foodstuffs in order to improve their storage capability. Hydrogen peroxide is an effective bacteriocide and may be removed, after use, by treatment with catalase (derived from the same fungal fermentations as the glucose oxidase) which converts it to water and molecular oxygen:

catalase                        
2H₂O₂ 2H₂O + O₂         [4.4]

For most large-scale applications the two enzymic activities are not separated. Glucose oxidase and catalase may be used together when net hydrogen peroxide production is to be avoided.

A major application of the glucose oxidase/catalase system is in the removal of glucose from egg-white before drying for use in the baking industry. A mixture of the enzymes is used (165 U kg^-1) together with additional hydrogen peroxide (about 0.1 % (w/w)) to ensure that sufficient molecular oxygen is available, by catalase action, to oxidise the glucose. Other uses are in the removal of oxygen from the head-space above bottled and canned drinks and reducing non-enzymic browning in wines and mayonnaises.