Visualization of the frequency effect of pulsed electric field on enzymatic browning of peel ground tissue

The enzymatic browning behavior of a model ground tissue, banana peel, influenced by the frequency variable of pulsed electric field (PEF), has been visualized and studied. The tissue was PEF-treated with 15 µs pulse at 3.3 kV/cm using trains of 5, 15, and 30 pulses, each varying from 0.1 Hz to 10 Hz; images and electrical conductivity were recorded intermittently throughout the incubation. The degree of browning was quantified with a browning index (BI) term, and the uniformity of browning was visually assessed by inspecting the pattern of pigment distribution. Moreover, the degree of tissue disintegration was calculated using a conductivity-based tissue disintegration index (DI) and compared to the BI and specific energy input. Browning uniformity was found to be significantly affected and increased with decreasing frequency. The effect was most noticeable up to disintegration degree of about 63, DI, or when the frequency of 5 or 15 pulses was reduced from 1 Hz to 0.1 Hz. Remarkably, the decrease at 5 pulses resulted in a significant increase in BI without a substantial increase in DI. The observed effect has been attributed to increased electrophoretic mobility of browning agents along the extracellular path during 0.1 Hz pulsation. Furthermore, lowering the frequency to 0.1 Hz reduced the energy required for a browning level close to saturation by about 57% compared to 10 Hz.