Effect of Pulsed Electric Field on colour, texture and microstructure of plant materials: Unraveling peeling mechanism

Aim: The food industry is actively developing new peeling techniques to reduce waste and enhance product quality. This study, conducted as part of the OnFoods project (www.onfoods.it), aimed to assess the effect of thermal (blanching) and nonthermal (pulsed electric field (PEF)) technologies on the peeling ability of fresh mango (M) and red bell pepper (RBP), focusing on their physical and microstructural c haracteristics. Method: Samples were subjected to a fixed electric field strength of 1.0 kV/cm and a bipolar pulse with specific energy (Ws) ranging from 0.8 to 8.2 kJ/kg. The effectiveness of PEF was compared with traditional peeling method: blanching (M: 94°C ± 2°C/1 and 3 min; RBP: 94°C ± 2°C /1 and 2 min). Moreover, peeling force, penetration assessments, colour measurement, and structural analysis were conducted to evaluate the effectiveness of the peeling process and understand its impact on the physical and structural analysis of the samples. Results: The blanched M and RBP samples showed a significant difference in terms of colour compared to untreated while PEF showed less impact. Regarding M samples, the force required to remove the peel decreased significantly for all treated samples. In comparison to the untreated samples, the highest Ws resulted in a greater reduction in peeling force, similar to that observed with blanching. On the contrary, RBP was not peelable after all treatments. Nonetheless, softer flesh was obtained for all treated samples compared to untreated ones for both M and RBP samples. High cell destruction was observed at high Ws (M: at 3.6 kJ/kg) and that was confirmed by microstructure analysis. This mechanism was correlated with the decrease in mechanical force required for peeling. In contrast, waxy nature of RBP skin created a significant barrier, resulting in unpeelable and less hardness due to its elastic behavior, thus both treatments did not disrupt the cell structures. Conclusion: PEF treatment effectively reduced the peel removal force in mangoes, similar to blanching, by better preserving their natural attributes. Microstructure analysis revealed significant cell destruction for mangoes, correlating with reduced peeling force. However, bell peppers were not peelable and their structure remained unaffected after all treatments.