Browning kinetics evaluation using image processing techniques

Colour changes in peach ‘Extra’ jam owing to thermal treatment at different temperatures (80°C, 85°C, 90°C and 95°C) were investigated. Browning kinetics were assessed on jam samples brought just after concentration phase in order to determine the effect of the thermal treatments, subsequent to this step, that take place during the production process (hot bottling, final pasteurization). Colour measurements were performed applying image processing techniques on images acquired through a flatbed scanner as well as by traditional measurements with colorimeter. CIELAB colour space was considered using lightness (L*), colour difference (ΔE) and a* parameters to describe browning evolution with time at the considered temperatures. A first order kinetic model was applied to L* changes. A kinetic model based on a two-stage mechanism was employed to describe a* evolution. Colour difference was modeled with both kinetics even if the two-stage model better describe the evolution of this parameter. Experimental data strongly fit with the adopted models except for the treatment at 80°C in which colour changes resulted almost negligible.