Application of power ultrasound on the convective drying of fruits and vegetables: effects on quality

Abstract

Drying gives rise to products with a long shelf life by reducing the water activity to a level that is sufficiently low to inhibit the growth of microorganisms, enzymatic reactions and other deteriorative reactions. Despite the benefits of this operation, the quality of heat sensitive products is diminished when high temperatures are used. The use of low drying temperatures reduces the heat damage but, because of a longer drying time, oxidation reactions occur and a reduction of the quality is also observed. Thus, drying is a method that lends itself to being intensified. For this reason, alternative techniques are being studied. Power ultrasound is considered as an emerging and promising technology in the food industry. The potential of this technology relies on its ability to accelerate the mass transfer processes in solid-liquid and solid-gas systems. Intensification of the drying process with power ultrasound can be achieved by modifying the product behavior during drying, using pre-treatments such as soaking in a liquid medium assisted acoustically or, during the drying process itself, by applying power ultrasound in the gaseous medium. This review summarises the effects of the application of the power ultrasound on the quality of different dried products, such as fruits and vegetables, when the acoustic energy is intended to intensify the drying process, either when the application is performed before pretreatment or during the drying process. © 2017 Society of Chemical Industry.

Drying characteristics and optimization of ultrasound‐strengthened cold air drying combined with sequential far‐infrared radiation drying on potato

“…On the other hand, the cavitation effect could generate enormous tiny cavities with violent kinetic energy and compression energy inside potato tissue (Liu, Zeng, Hu, & Sun, 2020; Sun, Liu, et al, 2017). Similar phenomenon was observed in other studies (Liu, Zeng, Wang, Sun, & Xi, 2019; Rodiuguez et al, 2018). García‐Pérez, Carcel, Riera, and Mulet (2009) also stated that the application of ultrasound enhanced the effective water diffusion coefficient and the D eff is linearly proportional to ultrasonic power.…”

Ultrasound assisted low‐temperature drying of kiwifruit: Effects on drying kinetics, bioactive compounds and antioxidant activity

“…From the figures obtained for the diffusion coefficient and the mass transfer coefficient, it could be concluded that the use of acoustic energy contributed to the acceleration of the drying process, not only decreasing the external resistance but also increasing the water mobility inside the food. The mechanical vibration produced by the ultrasound application affected both the internal resistance to the mass transport, by successive compressions and expansions of the material (‘sponge effect’), and the external resistance to the mass transport due to the reduction of the boundary layer, which eased the vapor transfer rate from the solid surface to the drying air . The sum of both effects led to an improvement in the water release during the drying process.…”

“…The mechanical vibration produced by the ultrasound application affected both the internal resistance to the mass transport, by successive compressions and expansions of the material ('sponge effect'), and the external resistance to the mass transport due to the reduction of the boundary layer, which eased the vapor transfer rate from the solid surface to the drying air. 29 The sum of both effects led to an improvement in the water release during the drying process.…”

The Effect of Hybrid Drying (Convective-Microwave-Ultrasound) on the Bioactive Properties of Osmo-Treated Sour Cherries

“…Literature data indicate that, depending on the cultivar, the anthocyanin content in ready-to-eat dried sour cherry snacks can range from 80 to as much as 320 mg of anthocyanins in 100 grams of product (Konopacka & Mieszczakowska-Frąc 2014). Also the choice of modern drying techniques, such as microwaves or ultrasound, can reduce the drying time or lower the process temperature, and thus contribute to better preservation of bioactive ingredients in the dried product (Wojdyło et al 2014b;Calín-Sánchez 2015;Fan et al 2017;Figiel & Michalska 2017;Horuz et al 2017;Onwude et al 2017;Rodríguez et al 2017). As the application of the microwave technique for drying of perishable fruits has been confirmed to be highly effective (Michalska et al 2016;Zielinska & Michalska 2016), the application of ultrasound in drying processes still remains at the experimental stage (Konopacka et al 2015a).…”