PEF treatment for the valorization of agri-food byproducts

Cell membrane acts as a physical barrier when removing the intracellular substances (water, juices and solutes) from food tissues in common unit operations of food industry such as drying and extraction. The permeabilization of the cell membrane by means of food tissue pre-treatments may positively affect the mass transport rates, and, thus, higher yield and shorter residence time in the processing plants can be obtained. However, the conventional pre-treatments of the raw material utilized to increase the extraction yield, namely grinding, heating, addition of chemicals/enzymes, have a negative impact on the quality of the solutions and extracts (e.g., purity, turbidity, color, flavor and nutrient content). Pulsed electric fields (PEF) treatments has been proved to bea promising mild and more efficient physical method alternative to conventional cell disintegration techniques. The exposure of food tissue to an electric field of moderate intensity (0.5-10 kV/cm) and relatively low energy (1-10 kJ/kg), applied in the form of repetitive very short voltage pulses, typically from few μs up to 1 ms, induces thepermeabilization of cell membranes by electroporation, facilitating the release of liquids and valuable compounds from the inner parts of the cells. PEF pretreatment may exert a selective permeabilization of the membranes (tonoplast and plasma membrane), while the cell wall remains intact. Consequently, the yield and the purity of the extractsare improved. Moreover, since PEF is a non-thermal technology, the reduction of the impact on the thermo-sensitive and thermo-labile compounds in the extracts is avoided. Interestingly, PEF treatment can be used to recover valuable compounds from food wastes and by-products,which have been matter of concern by the agri-food industry due to their environmental impact. The compounds that can be recovered show great potential industrial applications as natural colorants (anthocyainins, carotenoids, betanines, etc.) or nutraceuticals(polyphenols). In this paper a brief description of the basic mechanisms of electroporation of plant tissues is presented and the experimental results on the recovery of valuable compounds from fruit and vegetable by-products are presented. The influence of PEF processing parameters on extraction effectiveness is also discussed.