Functional group changes and chemical bond-dependent dielectric properties of lotus seed flour with microwave vacuum drying

Microwave vacuum drying (MVD) was applied to dehydrate lotus (Nelumbo nucifera Gaertn.) seeds. This paper evaluated the changes of molecular, crystalline, and morphological structural properties of lotus seeds after MVD. The results showed the frequency of δ(CH) bending, β(CH), ν(OH), and carbon–oxygen double bonds (C = O) increased with increasing microwave power density. Moreover, as microwave power density increased, the transition enthalpy of crystallinity gradually increased, which was related to the formation of crystalline starch, re-crystallization, and complexes of starch–lipid structure depending on the hydrogen bonds formed. The MVD process resulted molecular polarity of lotus seeds, whereas the dielectric properties also changed. The dielectric properties interacted with the changes of molecules and crystalline structure. The morphology of lotus seed flour changed because the shape of starch granules was disrupted and the granules became aggregated with nonstarch components as the microwave power density increased. All these results explain the interactions among polymer molecules in lotus seeds dried by MVD.