Impact of applied ultrasonic power on the low temperature drying of apple

Abstract

Low temperature drying (LTD) allows high-quality dried products to be obtained, preserving the nutritional properties of fresh foods better than conventional drying, but it is a time-consuming operation. Power ultrasound (US) could be used to intensify LTD, but it should be taken into account that process variables, such as the level of applied power, have an influence on the magnitude and extension of the ultrasonic effects. Therefore, the aim of this work was to assess the influence of the level of applied ultrasonic power on the LTD of apple, analyzing the drying kinetics and the quality of the dried product. For that purpose, apple (Malus domestica cv. Granny Smith) cubes (8.8mm side) were dried (2m/s) at two different temperatures (10 and -10°C), without and with (25, 50 and 75 W) US application. In the dried apple, the rehydration kinetics, hardness, total phenolic content, antioxidant capacity and microstructure were analyzed to evaluate the impact of the level of applied ultrasonic power. At both temperatures, 10 and -10°C, the higher the ultrasonic power level, the shorter the drying time; the maximum shortening of the drying time achieved was 80.3% (at -10°C and 75 W). The ultrasonic power level did not significantly (p<0.05) affect the quality parameters analyzed. Therefore, US could be considered a non-thermal method of intensifying the LTD of fruits, like apple, with only a mild impact on the quality of the dried product.

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

“…The identified h m figures ranged from 3.86 × 10 −5 kg water m −2 s −1 at 5 °C (AIR) to 19.01 × 10 −5 kg water m −2 s −1 at 15 °C (AIR + US). In low‐temperature drying of apples at 2 m s −1 of air velocity and temperatures of 0 and 10 °C and 10 °C, with and without ultrasound application, higher h m figures were reported: 2.7–9.1 × 10 −4 and 4.3–10 × 10 −4 kg water m −2 s −1 , respectively, probably due to higher air velocity figures than in the present study (1 m s −1 ). Thus, external resistance to moisture removal was significantly different at 2 m s −1 of air velocity than 1 m s −1 of air velocity.…”

The effect of microwave and convective dryer with ultrasound pre‐treatment on drying and quality properties of walnut kernel

“…Among different types of pre-treatment, the application of high-power ultrasound waves enjoys the highest popularity since it produces higher quality final products and increases the drying rate at a lower temperature (Kowalski & Pawłowski, 2015;Ortuño, Pérez-Munuera, Puig, Riera, & Garcia-Perez, 2010;Schössler, Jäger, & Knorr, 2012). Santacatalina, Contreras, Simal, Cárcel, and Garcia-Perez (2016) investigated the effect of applying the power of ultrasound waves in dehydrating apples at low temperatures. To do so, apples were cut into cubic slices with 8.8 mm dimensions and dehydrated at two different temperatures of −10 and 10°C with the wind speed of 2 m/s and the ultrasound treatments with 25, 50, and 75 W powers without any ultrasound pre-treatment.…”

Accelerated mild heating of dry-cured ham by applying power ultrasound in a liquid medium

“…In these applications, ultrasound was used to intensify mass transfer, heat transfer or both phenomena simultaneously. Thus, as examples of mass transfer intensification, Ozuna, Cárcel, Walde, & Garcia-Perez (2014) shortened the drying time for salted cod by up to 50% (20 ºC, 20.5 kW/m 3 ), while Santacatalina, Contreras, Simal, Cárcel, & Garcia-Perez (2016) sped up the drying process of apple by up to 80% (-10 ºC, 32 kW/m 3 ). As far as the coupling of ultrasonic waves in heat transfer processes is concerned, it has been used in both cooling and heating processes.…”