Innovative approach to determine the effect of pulsed electric fields on the microstructure of whole potato tubers: Use of cell viability, microscopic images and ionic leakage measurements

Abstract

The aim of this study was to gain an in-depth understanding of the effect of pulsed electric fields (PEF) on the microstructure of potato tubers. The effect of peeling prior to PEF was also studied. Whole potato tubers were subjected to PEF at a constant frequency of 50Hz, over a range of electric field strengths (0.2 to 1.1kV/cm) and energy levels (1 to 10kJ/kg). To determine the uniformity of the PEF effect across the potato tuber, cell viability was assessed using tetrazolium salt staining. To evaluate the effectiveness of PEF processing the leakage of ionic species from the tubers was measured using atomic absorption spectrophotometry and FESEM-EDS analysis. In addition the influence of PEF on cell disruption and microstructural damage was assessed using scanning electron microscopy (Cryo-SEM). As the electric field strength and energy increased potassium ion leakage and electrical conductivity of the medium increased. The orientation of the tuber towards the electrodes and the presence of the skin greatly affected the impact of PEF on cell disruption and viability. At electric field strengths of 0.3kV/cm and above, potato cells located in the pith (inner medulla) showed more damage and had a higher proportion of cell death compared to cells located in the outer medulla. This is the first study to provide visual evidence that the application of electric fields to solid, living foods, such as potato tubers, results in an uneven distribution of cell damage and death owing to the presence of vascular bundles and cells that vary in their resistance to electric fields.