The kinetics of colour and fluorescence development in concentrated milk systems

The kinetics of colour and fluorescence development were studied in aqueous systems containing whole milk powder (WMP) and sucrose (S) at three WMP/S ratios (R=0.30, 0.68, 1.06) and three temperatures (T=105, 122.5, 140 °C). At each testing time, the colour parameters Kubelka-Munk index (K/S), lightness (L), optical density (OD), absorption coefficient (K), dominant wavelength (DWL) and fluorescence (F) were determined. F and 100/L were the most appropriate parameters to study non-enzymatic browning in concentrated milk systems. Adequate models (r2>0.96) developed to analyse the effect of T and R on the rate constants, showed that colour parameters and their kinetic coefficients were mainly affected by temperature. The influence of R was more relevant at high temperatures. The activation energies and Q10 values obtained for K/S, 100/L, F and OD were in the range 81–159 kJ mol−1 and 1.8–3.8, respectively. F and reflectance properties showed different dependence on temperature and R, reflecting that although related, they do not have the same origin and significance.