Evolution and modeling of colour changes of red pepper (Capsicum annuum L.) during hot air drying

In current work, the evolution kinetic models of moisture, surface colour (L∗, a∗, and b∗), natural pigment and non-enzymatic browning (NEB) of red pepper during hot air drying at drying temperatures of 60, 70, and 80 °C were investigated. The relationships between surface colour and natural pigment, as well as non-enzymatic browning were explored. Results showed that, the drying time of red pepper decreased with the increase of drying temperature, Weibull model fits the drying curves well. By comparing the fitting of kinetic models to the experimental data, it was found that the evolution kinetics of surface colour (L∗, a∗, and b∗) and NEB followed the Weibull and zero-order model, respectively. The degradation of natural pigment fitted well to both the Weibull and first-order model. The activation energy for L∗, a∗, b∗, natural pigment and NEB evolution were 42.47, 42.83, 44.92, 37.22, and 56.68 kJ/mol, respectively, which indicates that browning was most sensitive to heat. Furthermore, the surface colour parameters showed a positive correlation with natural pigment content, and a negative correlation with NEB. Equations to predict the concentration of the natural pigment in red pepper on the basis of CIELAB colour values were obtained.