Advances in the study of the kinetics of color and fluorescence development in concentrated milk systems

The kinetics of color and fluorescence development in systems containing whole milk powder (WMP), sucrose (S) and water were studied; the influence of three design variables: pH (6, 7 and 8), temperature (105, 122.5 and 140 °C) and WMP/S ratio (R = 0.3, 0.68 and 1.06) being particularly investigated. The Kubelka-Munk index (K/S), luminance or lightness (L), optical density (OD) and fluorescence (F), were measured at different reaction times. Reaction pseudo-order (n) varied between 0 and 1 and reaction rate constants for the development of fluorescence and the color parameters were found to be more dependent on temperature than on R at all measured pH values. Temperature dependence of CP was analyzed through the activation energy (E_a) values. The variables F and OD, which are related to the molecular aspects of the systems, showed the extreme values of E_a, while than K/S and 100/L, related to the macroscopic appearance or reflectance, showed intermediate E_a values and lower dependence with R and pH. When compared to the variables related to brown pigment development, fluorescence development showed a higher relative change, which shows its higher sensitivity as a reaction marker. The variables that most affected color and F development were temperature and protein concentration, respectively.