## 1 Introduction  
Apples are an important source of sugars, amino acids, proteins, organic acids, vitamins and minerals in the human diet. This is important because it is recommended that they are eaten fresh. However, they are perishable products with a high metabolism and respiration rate, which are responsible for their limited shelf life [1]. Improvements in the postharvest treatment of fresh fruit are very important for increasing food availability [2] because losses during postharvest handling can reach 25-28% [3]. Apples have varied nutritional qualities that are lost during postharvest processing. Losses that occur during storage depend on external and internal conditions. The temperature and relative humidity during postharvest handling activities have the greatest impact on the storage efficiency of apples and the quality characteristics of fruit and thus, affect their shelf life [4, 5]. They affect, for example, fruit firmness, weight loss, titratable acidity and the content of soluble solids [6]. During ripening, there is a process of pectin degradation that plays an important role in cell wall degradation, which also has an effect on the shelf life of fruit [7]. Proper postharvest handling involves altering the natural conditions of the product in order to prolong their postharvest life [8]. Therefore, there is a need to find a new method for reducing the softening and senescence and prolonging the shelf life of fruit that are kept at room temperature after storage. This would provide a much-needed improvement in postharvest technology. This need can be met using physical methods (high voltage electric field, UV-C light, IR radiation, microwave radiation, etc.). The use of an alternating magnetic field (AMF) also has the potential to meet this need. AMFs are naturally occurring, easy to use, low on energy consumption and safe for the environment [9]. Magnetic fields have been reported to exert a positive effect on living organisms by influencing metabolic pathways [10; 11; 12]. Magnetic fields can change the selective permeability of a membrane, the position of the main membrane components (protein and lipid domains) and the molecular position of the electric charge. This can affect turgor pressure variations. The above changes may affect the rate of the physical, biochemical and physiological processes of the tissue of biological material. They also influence the activation of protein synthesis, thus increasing the viability of organisms [13; 14; 15; 16]. Alternating magnetic fields (AMFs) have been used by researchers to treat seedlings, plants, fruit and irrigated water. Numerous scientists have reported the positive effects of AMFs on plant growth. The treatment of plant crops with a magnetic field increases the germination rate, size and dry weight of the plant. After the application of a magnetic field, there can also be improvement in the parameters of fruit growth, such as an increase in the number of leaves, the leaf surface, the macroelement content in the leaves and the number of flowers and fruit per plant. A variable magnetic field can also increase the total fruit yield as well as the average weight of the fruit [17]. High voltage electric fields (HVEFs) can be used to extend the shelf life and improve the quality of fruit and vegetables. The electric field reduces the rate of cellular respiration and ethylene production, thus extending the postharvest shelf life. The electric field increases the action of the SOD, APX and CAT enzymes and increases the concentrations of reduced glutathione, ascorbic acid and polyphenols [17]. UV-C light has direct and indirect inhibitory and damaging effects on living cells; therefore, it is widely used for disinfection purposes. UV-C light stimulates the synthesis and accumulation of health-promoting phytochemicals before and after harvest, extends the shelf life of fruit and vegetables and stimulates the mechanisms of adaptation to biotic and abiotic ranges.