Comparison of four pretreatments on the drying behavior and quality of taro (Colocasia esculenta L. Schott) slices during intermittent microwave vacuum-assisted drying

Effect of different pretreatments on drying behavior and quality of taro slices during intermittent microwave vacuum-assisted drying were investigated. Taro slices were subjected to the following pretreatments: blanching (B), blanching and freezing (B+F), blanching and immersion in maltodextrin solution (B+M), and blanching and immersion in maltodextrin solution and freezing (B+M+F). The reduction in amylose content, the increase in amylose to amylopectin ratio, the change of mechanical properties, the increase in sample bulk density and reduction in sample porosity and structure collapse during pretreatment processes facilitated heat and moisture transfer and quality changes during drying of taro slices. During drying process, all the pretreatment reduced the drying time of samples. The drying rate included a warming-up period and a falling rate period. The values of effective moisture diffusivity increased gradually as the moisture content decreased. The B+M+F pretreatment had the shortest drying time, the highest drying rate and the biggest effective moisture diffusivity. Moreover, for B+M+F pretreatment, the parameters including hardness, crispness, color, and microstructure had remarkable changes as compared with the other pretreatments.