Diffusion of thiocyanate and hypothiocyanite in whey protein films incorporating the lactoperoxidase system

The diffusion of the thiocyanate (SCN−) and hypothiocyanite (OSCN−) components of a lactoperoxidase system (LPOS) in whey protein isolate (WPI) films was investigated. Diffusion coefficients for these molecules were measured for the LPOS-incorporated WPI films prepared with different WPI:glycerol ratios (1:1, 3:1, and 5:1). WPI film disks were coated on the surfaces of smoked salmon samples, and the samples were stored at 4, 10 and 22 °C. The diffusion coefficients were determined by fitting a mathematical model to the amounts of SCN− and OSCN− released from the disks during a period of time. The diffusion coefficients for SCN− (D1) and OSCN− (D2) in the films were 0.19–5.2 × 10−12 m2 s−1 and 0.13–6.5 × 10−13 m2 s−1, respectively. The D1 and D2 decreased as the WPI:glycerol ratio increased and the storage temperature decreased. The Ea values for diffusion in 1:1, 3:1, and 5:1 WPI:glycerol films were 13.3, 29.5, and 35.6 kJmol−1, respectively, for SCN− and 15.8, 30.1, and 39.9 kJmol−1, respectively, for OSCN−.