Influence of edible coatings pretreatment on the performance of microwave and combined microwave-hot air drying of kiwifruit

This study was conducted to investigate the influence of edible coatings on the qualitative and quantitative characteristics of kiwifruit subjected to drying processes involving both microwave and combined microwave-hot air drying methods. The coating was applied separately using potato starch, carboxymethyl cellulose (CMC), or pectin, at the optimal concentrations, through an immersion method prior to the drying process. Based on the findings, the microwave method exhibited a significant influence (p < 0.05) of power level on drying time. In the combined method at temperature of 80 °C and 90 °C, a reduction in drying time was observed in comparison to the microwave method. Among the ten common kinetic models assessed, the model proposed by Midilli et al. emerged as the most suitable. The highest observed diffusion coefficient, at 0.97 × 10⁻⁹ m²/s, was recorded for the pectin-coated samples subjected to drying under combined conditions of 450 W and 90 °C. Additionally, the energy consumption associated with the combined method, particularly at temperatures of 80 °C and 90 °C, was lower compared to the microwave method. Moreover, the application of coating and the combined drying method resulted in improved color parameters for the products. The CMC-coated sample dried at 450 W and 80 °C, exhibited the highest degree of rehydration compared to the other samples. Furthermore, the starch-coated samples displayed the highest concentrations of vitamin C (75.3704 mg/100 g) and total phenolic compounds (3458.9 mg/g). The pectin-coated sample exhibited the highest level of antioxidant capacity (0.1711 mg/g). Therefore, it is recommended to employ a combination of starch coating followed by pectin coating in the process of microwave-hot air drying for kiwifruit.