Enzymatic oxidation of lactose for lactobionic acid production: Effect of reaction conditions and dairy side stream compositions.

Lactobionic acid (LBA), a valuable compound with applications in food, cosmetics, and pharmaceutical industries, can be produced by enzymatic oxidation of lactose in dairy side streams. This study investigated the combination of lactose oxidase and catalase in skim milk, ultrafiltration permeate, nanofiltration retentate, sweet whey, and acid whey. The reaction was investigated under different enzyme dosages, with and without pH control, oxygen addition from stirring, and hydrogen peroxide addition for in situ oxygen generated by catalase. pH control by 1M sodium hydroxide reduced LBA concentration, while higher lactose oxidase dosage and hydrogen peroxide addition significantly increased yields; catalase dosage increase had little effect. Most side streams produced their highest LBA yields within 30 min with hydrogen peroxide addition and unstirred achieving between 45.74 - 49.67 mg/mL LBA. Nanofiltration retentate gave higher LBA concentrations (192.8 mg/mL) but lower percentage yields. These findings support enzymatic oxidation as a promising strategy for valorizing dairy side streams.