3.3. Colour change upon rehydration
Colour is an important quality criterion in foods and agricultural products. Undesirable changes in colour of food may lead to a decrease in its quality and marketing value. In this study,regardless of drying method, instant rice experienced colour change during drying. The results of colour parameters, as a function of microwave power (MW) and air temperature (T)for rehydrated instant rice, are presented in Fig. 3(a) and (b)for L* and DE*-values, respectively. An overall examination of the data of L* and DE*-values showed that the hot air drying had less influence on the colour of instant rice as compared to microwave drying and combined convective–microwave drying. When the datasets for microwave and combined drying were considered, the parameters L* tended to decrease faster significantly (p < 0.01) with MW and T. This indicated significant darkening of samples during drying, which increasedas microwave power increased. The parameters DE* tended to increase with significantly (p < 0.01) with MW and T. Thus,combination drying with MW = 560 W and T = 90◦C resulted insignificant darkening and colour change when compared to lower temperature drying, although it was the fastest method