MODELLING OF THE THERMAL KINETICS OF COLOUR CHANGE IN HAZELNUTS DURING ROASTING
The colour changes that occur in hazelnuts Corylus avellana during the dry roasting process were experimentally studied in order to determine the magnitudes of the parameters for a corresponding colour change model. Roasting times were 60 minutes and a number of roasting temperatures in the range from 120 °C to 180 °C were analysed. The colour progression of both whole hazelnuts and ground hazelnuts was quantified using the Hunter L, a, b tristimulus values approach. The L, a, b values obtained from the colour measurements showed that the lightness, L values, have less variation and the most precise response to time and temperature change. Furthermore, ground form hazelnut colour is significantly more sensitive to both time and temperature changes than whole hazelnut colour. Thus L values of ground hazelnuts were used in the modelling of colour change during hazelnut roasting. Statistical analysis of the data demonstrated that the colour parameter, L was best represented by a first order process. The rate constant was assumed to have an Arrhenius-type dependence on temperature. The activation energy, Ea and the frequency (pre-exponential) term, k∞ were determined as 56.74 kJ mol-1 and 1399 s-1 respectively for the conditions studied. Theoretical equations, based on the Exponential Integral function, to predict first order quality changes when product temperature is varying exponentially were developed. These equations were validated by comparison with the experimental colour data extracted from the non-isothermal region of the roasting process. Good agreement was obtained between the experimental results and theoretical colour change predictions.
Demir, A.D., Frías, J.M., Abodayeh, K., Cronin, K. and Oliveira, F.A.R. (2001). MODELLING OF THE THERMAL KINETICS OF COLOUR CHANGE IN HAZELNUTS DURING ROASTING. Acta Hortic. 566, 317-322
Quality kinetics, colour responses, Arrhenius temperature dependence, activation energy, and exponential integral