Kinetic Study on Color Changes in Milk Due to Heat

Analysis of changes in terms of color difference (ΔE) and yellowness index (YI) permits evaluation of severity of heat treatment of milk. Both ΔE and YI increased at constant temperature following zero-order kinetics, at temperatures between 90 and 130°C for 1 to 60 min. Activation energy, according to the Arrhenius equation, was 101.8 and 117.5 KJ/mol for ΔE and YI, respectively. Comparison of instrumental and sensory data showed a minimum ΔE of 3.8 would be attained before visual perception of milk browning. Color values, such as ΔE or YI, are proposed as the simplest and most reproducible indices of commercial milk quality.