Effect of moderate electric field on rheological properties, cell wall components, and microstructure of apple tissue

The synergistic effect of electrical and thermal treatment on the microstructure and rheological characteristics of apple tissue under moderate electric field (MEF) is poorly understood. This study investigated the effects of electric field strength and temperature on stress relaxation characteristics, cell microstructure, and cell wall components of apple tissue to understand the relationships between the parameters of the rheological equation and cell wall components. The stress relaxation curves of MEF-treated apple tissues were significantly different from those treated with the traditional water bath method at the same temperature (p < 0.05). Higher electric field strength and temperature significantly reduced the elasticity and viscosity of apple tissue. The contents of water-soluble pectin (WSP), chelator-soluble pectin (CSP), Na2CO3-soluble pectin (NSP), and hemicellulose all decreased with an increase in temperature. At the same temperature, under the applied electric field, WSP decreased while CSP and NSP increased in apple tissue. In addition, increasing electric field strength increased WSP and decreased CSP, NSP, and hemicellulose. The decrease in CSP, NSP, and hemicellulose contents and increased electropermeability of the cell membrane were the main reasons that derived viscoelasticity changes in apple tissue under MEF. Furthermore, the temperature was the main reason for plasmolysis in apple tissue cells and induced decomposition of the cell wall and dissolution of the cell membrane. The electric field promoted the electropermeability of the cell membrane increasing the decomposition of the cell wall. These findings increase our understanding of the MEF pretreatment technology for the processing of fruits and vegetables.