Modelling the kinetics of textural changes in hazelnuts during roasting

The texture changes in hazelnuts that were dry roasted at four temperatures (120, 140, 160 and 180 °C), for times ranging from 5 up to 60 min were studied using instrumental analysis. Textural changes were determined from the force deformation curves obtained from compression tests. The first break point of the maximum force was used as a measure of texture. The magnitudes of the parameters for a corresponding texture change model were determined using linear regression. Statistical analysis of the data showed that the change in texture with roasting time was represented by a first-order reaction. The reaction rate constants were assumed to have an Arrhenius-type dependence on temperature. The activation energy, E_a and the frequency (pre-exponential) factor, k_∞ were determined as 22.5 kJ mol^-1 and 0.338 s ^-1 respectively. Theoretical equations, based on the exponential integral function (E₁), to predict texture changes when product temperature is varying exponentially were developed. These equations were validated by comparison with the experimental data. The results of this study showed that both time and temperature effects were significant (p < 0.001) on the textural changes in hazelnuts. The exponential integral prediction of texture change when product temperature varies during roasting was superior to the isothermal prediction throughout the process.