ENZYMATIC FLOW-INJECTION DETERMINATION OF LACTOSE IN MILK WITH ONLINE DIALYSIS

Milk samples were analysed to determine their lactose content by using flow injection (FI) and incorporating immobilized beta-galactosidase and glucose oxidase-mutarotase bioreactors. A dialysis unit was placed after the injection valve to avoid the need for sample pre-treatment. The methodology was based on the chemiluminescence determination of hydrogen peroxide produced by the enzymic reactions, with use of an alkaline reagent containing luminol and hexacyanoferrate(III). Linearity was observed over the concentration range 20-200 mmol 1-1 with lactose as standard (r = 0.9995), and 20 milk samples h-1 could be analysed. Comparisons were made with high-performance liquid chromatography and chloramine-T methods. The enzymic Fl method afforded a low relative standard deviation (0.49%) and was free from interference. Additionally, the proposed method was simple and did not require precipitation of proteins, or filtration or centrifugation. The enzymic reactors were stable for 6 months when used daily at optimum pH.