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The effect of ultrasound pretreatment on drying kinetics and physical properties as color and rehydration rate of dried apple slices was investigated. Apple samples var. Idared were submitted to ultrasonic treatment using 21 and 35 kHz for 30 min in an ultrasound bath securing sound intensity of 3 and 4 W/cm 2 , respectively. After pretreatment, the material was dried in a convective oven at 70C and at an air velocity of 2 m/s. The sonication reduced drying time by 13-17% in comparison with the untreated sample. Ultrasound treatment changed the color of apples tissue by decreasing the value of a* parameter and increasing the dried material lightness, chromaticity and the value of b* coefficient. Moreover, obtained results showed that there was a significant effect of pretreatment on rehydration properties as compared with untreated apple tissue. PRACTICAL APPLICATIONSThe most energy-consuming processes existing in the food technologies are the processes based on heat and/or mass transfer, for instance drying. Thus, a lot of attention is paid by researchers to conserve the energy and minimally change the physicochemical properties of food, which shape its quality. Additionally, increasing growth of consumers' expectations and their nutritional knowledge stimulate to seek some new solutions even more. Aforementioned is a reason why nonthermal technologies as ultrasound seem to be the one of the most interesting propositions.

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According to the U.S. Energy Information Association (EIA), world energy consumption will increase by 56% in 2040. Therefore, a lot of effort is being dedicated to maintaining economic development with minor impact on the environment. This can be done altering existing technologies or introducing completely new technologies. Due to the fact that drying can be considered one of the most energyconsuming processes, researchers have focused on ways to save energy while minimally changing the physicochemical properties of food, which shape its quality. Additionally, the increasing growth of consumer expectations and their nutritional knowledge have further stimulated efforts to seek new solutions. Non-thermal technologies such as pulsed electric field (PEF), ultrasound (US), and high hydrostatic pressure (HHP) seem to meet the expectations of both producers and consumers. This article reviews the impact of PEF, US, and HHP on drying kinetics and the quality attributes of dried food. INTRODUCTIONThe increase in food prices and the huge energy expenditures on foodstuff drying are the main reasons for the growing interest in drying process intensification. Conventional dewatering methods are progressively complemented by novel techniques which could give a high-quality product at lower production costs. Among the currently proposed solutions, non-thermal techniques such as ultrasound (US), pulsed electric field (PEF), and high hydrostatic pressures (HHP) are extremely noteworthy for drying of heat-sensitive foods since their application is not connected with a high increase in material temperature. In addition to dehydration, [1][2][3][4][5][6] several examples of the use of these technologies in food processing can be found in the scientific literature. In general, the possible applications of non-thermal technologies ( Fig. 1) are connected with food preservation [7][8][9][10][11] or enhancement of heat and=or mass-based processes. [12][13][14][15][16][17]

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