KINETIC DETERMINATION OF TOTAL CASEIN IN MILK AND DAIRY-PRODUCTS BY LONG-WAVELENGTH FLUORESCENCE DETECTION

A very simple and fast fluorometric method for the routine determinati on of total casein in food samples is described. It is based on the ap plication of kinetic methodology to the Indocyanine Green-cetyltrimeth ylammonium bromide-casein system by using stopped-flow mixing techniqu e and long-wavelength fluorescence measurements, which allow the tempo ral and spectral discrimination of the analytical signal. The electros tatic interaction between casein and the surfactant eliminates the que nching caused by the latter on the fluorescence of the dye, so that th e fluorescence intensity increment with time, which is measured in sim ilar to 2 s, is directly related to casein concentration. The dynamic range of the calibration graph is 3-100 mu g mL(-1), and the detection limit is 0.9 mu g mL(-1). The relative standard deviation is <2%. The proposed method was applied to the determination of total casein in m ilk samples and dairy products with a recovery of 96.8-103.1%.