Synergistic effects of pulsed electric fields and ohmic heating on red beetroot cooking performance

Abstract

Achieving uniform heating in whole vegetables during ohmic processing is challenging due to their heterogeneous structure and uneven electrical conductivity. This study aimed to use pulsed electric fields (PEF) prior to ohmic heating (OH) to equalise the electrical conductivity and thus improve the cooking performance of red beetroot. PEF treatments were carried out at electric field strength of E = 1.0 and 2.0 kV/cm, and specific energy input varied between 0.1 and 16.1 kJ/kg, varying the number of pulses. Two PEF pre-treatments were selected to assess the impact on cooking performance (1.0 kJ/kg and 4.0 kJ/kg). The cooking performance and quality of the cooked products were evaluated using temperature kinetics, thermal camera images of temperature distribution, analysis of mechanical properties and changes in optical properties (CIE lab). The results revealed that untreated beetroot exhibited an uneven temperature distribution and notable hardness variations across different beetroot areas. Both PEF pre-treated samples showed a homogeneous heat distribution, drastically reducing the hardness differences within the vegetable tissue. PEF-treated samples had hardness values comparable to those of commercially sold cooked beetroot after 14 min of cooking, whereas untreated samples did not reach the same values even after 21 min of cooking. Consequently, the combined use of PEF and ohmic heating has remarkable potential as an industrial application for cooking large, complex vegetables by equalising temperature distribution and reducing cooking time.