In this research, ‘Ahmad Aghaei’ pistachio cultivar harvested from Iran in 2011 was supplied by the Pistachio Research Institute. The effect of roasting times (5, 10, 15, 20, 25 and 30 min) and temperatures (120, 130, 140, 150 and 160 °C) on the colour of pistachio nuts was investigated. Initially, the L value (lightness) decreased for all temperatures and then increased for 120 and 130 °C with increases in roasting temperature and time. Values of a (redness) and ΔE (colour difference) for pistachio samples showed an increase while b decreased. Changes in L, a and b (yellowness) values of pistachio were used to develop and to validate a numerical dynamic model. The developed prediction models satisfactorily described the colour development as a function of roasting temperature and time for L, a, b and ΔE of ground-state measurements. As a result of variance analysis, the effects of the roasting process on colour values of pistachios were found to be statistically significant. In addition, changes in colour values gave high R2 and the obtained nonlinear equations may be utilised to determine the optimum roasting degree based on time and temperature. A reverse approach for modelling is used in order to establish that it is possible to obtain the optimal condition directly from the experimental data modelling step.
