Microwave Heating as a Pretreatment for Convective Drying to Produce Carrot Snacks: A Study of Drying Kinetics, Physicochemical, and Structural Properties

Abstract

In this study, carrot slices were dehydrated using microwave (MW) pretreatment compared to conventional convective drying (CCD) alone at two air temperatures (60 °C and 80 °C). The treatments included CCD60, CCD80, MW+CCD60, MW+CCD80, with freeze-drying (FD) as the control. The research aimed to analyze the kinetics of water removal to evaluate the efficiency of the different drying methodologies.Additionally, the physicochemical properties of the dehydrated carrot slices were examined, including: rehydration ratio (RR), texture, antioxidant capacity, shrinkage. Besides the ultrastructure via transmission electron microscopy (TEM) was measured.The results indicated that the processing time during MW+CCD led to significant time savings of 66 % and 57 % for temperatures of 60 °C and 80 °C, respectively. The fitting of the drying curves to the Page model revealed a diffusion mechanism for CCD (n>1) and a sub-diffusion mechanism for MW+CCD (n<1). Notably, microwave pretreatment improved the rehydration ratio and resulted in less shrinkage compared to CCD. The crispest samples were found to be FD, followed by MW+CCD60 and MW+CCD80.Furthermore, the use of MW pretreatment significantly enhanced antioxidant capacity, comparable to that of CDD samples. Ultrastructural analysis showed that MW treatment disrupted cell membranes and altered cell wall structure, which was associated to the lack of appreciable diffusive processes in MW+CCD drying.These findings highlight the potential advantages of incorporating microwave technology as a pretreatment in the dehydration process of carrot slices. This approach aligns with the goal of producing high-quality, convenient, and nutritionally valuable vegetable-based snacks. This work led to a significant improvement in the final product quality parameters like texture, shrinkage, rehydration and antioxidant compounds compared to CCD.