ENZYMATIC FLOW-INJECTION DETERMINATION OF LACTOSE IN MILK WITH ONLINEDIALYSIS

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 h ydrogen peroxide produced by the enzymic reactions, with use of an alk aline 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 st andard deviation (0.49%) and was free from interference. Additionally, the proposed method was simple and did not require precipitation of p roteins, or filtration or centrifugation. The enzymic reactors were st able for 6 months when used daily at optimum pH.