FOOD ENGINEERING REVIEWS

Recent demands from consumers for fresh-like quality foods with less and/or no artificial additives have introduced innovative processing technologies. These technologies due to their potential for food processing with preservation of important properties may cause to introduce new products in the market, to improve the competitiveness of the food, to eliminate the use of some artificial food additives, and to reduce energy cost. Pulsed electric fields for microbial and enzyme inactivation, shelf-life extension, moderate electric fields for yield and extraction, and ohmic heating are among these novel technologies that are based on the application of electric current on food materials. It has been well established that these technologies can successfully be applied to different food products. Among all, fruit juices have special importance due to the suitability of their physical properties to be processed by the electrotechnologies. This article covers the fundamentals of these technologies, their current use, research activities, and trends

Responses of plant cells and tissues to pulsed electric field treatments

Cell membrane electroporation/permeabilization may be achieved without affecting cell viability through strict control of the electric pulse parameters. This process is referred to as reversible permeabilization. Even if the cells survive the electric field treatment, they are subjected to stress due to the opening of pores and the struggle of the cells to recover their normal functionality. Very little is known about what actually occurs in the cell and its membranes at the molecular level upon reversible electroporation, and the physiological responses to pulsed electric field (PEF)-induced stress are still largely unknown. This chapter explores the current state of the art on the influence of the complexity of plant tissues on electroporation. Focusing on reversible electroporation, metabolic responses of plant cells and tissues induced by PEF application are also reviewed. One of the first challenges when electroporating plant tissue is their heterogeneous structures where cells vary in shape, size, and cell wall structure. This heterogeneity influences the effect of different electric fields protocols aiming at permeabilizing all cells in the tissue. Once cells are reversibly permeabilized, physiological responses to PEF-induced stress include the production of reactive oxygen species, mobilization of stored energy, activation of stress-related genes, and the production of secondary metabolites. The application of reversible PEF has also been shown to barley seed germination as well as to increase the strength of the cell wall in potatoes and, in consequence, their textural properties. This chapter finishes by revising the effect of reversible PEF on protoplasts (plant cells where the cell walls have been removed) and, in consequence, on the regeneration of new plants. Overall, reports on reversible permeabilization of plant cells and tissues are not common in the literature; however, they have laid the foundation for a fascinating area of research and technological innovation