Changes in electrical properties and void distribution of mung bean sprouts during hot water heating

Abstract

We investigated the relationships between electrical properties and tissue structures, including the cell membrane, and the voids of fresh and heated bean sprouts. The electrical properties, which were obtained by electrical impedance spectroscopy and equivalent circuit analysis, changed drastically within 60 s by heating at 70 °C. Confocal laser-scanning microscopy suggested that these changes are due to cell membrane damage. We also visualized void distribution using micro X-ray computed tomography imaging and the calculated porosity. The porosity decreased from 6.71% to less than 1% after 30 s of heating. The fresh samples showed several axially elongated voids with low sphericity (< 0.3) and high volume (> 10⁵ µm³), which then disappeared preferentially with heating. Moreover, extracellular resistance was highly correlated with porosity (R = 0.900). We suggest that the contribution of cell membrane and void conditions to the texture of bean sprouts for short heating times needs to be considered.