Metabolic response of organic fruits subjected to PEF assisted-osmotic dehydration

Organic food has been one of the fastest growing market sectors over the last few years. This is because there is an increase consumer demand for safe, healthy and environmental friendly food products, with high quality characteristics. It is important to highlight, that minimally processed fruits are still metabolically active tissue and therefore they are highly perishable. Thus, the aim of this work was to evaluate the effect of pulsed electric field (PEF) pre-treatment before osmotic dehydration (OD) on physiological changes in strawberry and kiwifruit tissues, in terms of respiratory activity and metabolic heat production measured by isothermal calorimeter (TAM-Air), cells damage evaluated by fluorescence microscopy and electrolytes leakage. Strawberry halves and kiwifruit quarter-slices were treated with PEF at two different electric field strengths (100 V/cm and 200 V/cm) using 100 near-rectangular shaped pulses, with fixed pulse width of 100 μs and repetition time of 10 ms. Afterwards, samples were subjected to OD treatments carried out in two different hypertonic solutions (40% w/w), one with sucrose and the other one with trehalose, both with addition of 1 % of CaLac. The results showed that the application of OD alone allowed to maintain the functionality of the membranes causing only a decrease in the endogenous heat production. The application of PEF as a pre-treatment had different effects depending on the intensity of the field applied. The application of low electric field strength (100 V/cm) generally preserved the cell viability, which was reduced drastically following OD treatment. On the contrary, the application of 200 V/cm caused the total loss of cell vitality, probably due to irreversibility of the electroporation.