Determination of proteins by fluorescence quenching of Magdala Red

Magdala Red (MR) binding to protein causes a decrease in the fluorescence i ntensity of MR at 556 nm. Based on this, a new quantitative determination m ethod for proteins is developed. The linear range of this assay is 0.1-4.0 mu g ml(-1) of Bovine Serum albumin (BSA). The measurements can be made eas ily on a common fluorimeter. The reaction between MR and proteins is comple ted in 1 min, and the fluorescence intensity is stable for at least 2 h. Th ere is little or no interference from amino acids and most metal ions. The proposed method has been applied to the determination of protein in milk po wder and soybean milk powder and the results are in agreement with the resu lts by the other methods. (C) 2000 Elsevier Science B.V. All rights reserve d.