On the effect of ultrasound-assisted atmospheric freeze-drying on the antioxidant properties of eggplant

Abstract

The low operating temperatures employed in atmospheric freeze-drying permits an effective drying of heat sensitive products, without any impairment of their quality attributes. When using power ultrasound, the drying rate can be increased, thus reducing the process duration. However, ultrasound can also affect the product quality. The aim of this study was to evaluate the effect of various drying process variables, namely air temperature and velocity, ultrasound power and sample size, on the antioxidant properties of eggplant (Solanum melongena L.) samples. For this reason, drying experiments were carried out at different drying temperatures (-5, -7.5, -10 °C), power ultrasound levels (0, 25, 50 W; 21.9 kHz) and air velocities (2, 5 m s) using different sample sizes (8.8 mm and 17.6 mm cube side). The ascorbic acid content (Jagota and Dani method), total phenolic content (Folin-Ciocalteau method), and the antioxidant capacity (FRAP method) of the dried products were considered as quality indicators of the dried samples. The increase in air velocity and temperature, as well as the sample size, significantly reduced the antioxidant potential of the dried samples (p-value < .05). For a given sample size, the application of ultrasound, at the acoustic power levels tested, did not produce significant effects on the antioxidant indicators considered. Temperature measurements inside the drying sample showed a non-negligible temperature rise when acoustic power was applied.

The effect of ultrasound pre‐treatment on quality, drying, and thermodynamic attributes of almond kernel under convective dryer using ANNs and ANFIS network

“…It is a nonthermal method in which the physical and sensory properties of food are preserved and applied to assess the food properties. Through this method, processing time is reduced and integrated by other methods, then efficiency of the method will be increased (Arvanitoyannis, Kotsanopoulos, & Savva, ; Colucci, Fissore, Rossello, & Carcel, ; Fan, Zhang, & Mujumdar, ; Mothibe, Zhang, Mujumdar, Wang, & Cheng, ; Rodríguez, Eim, et al, 2017; Rodríguez, Gomes, Rodrigues, & Fernandes, ).…”

Freeze-Drying of Plant-Based Foods

“…More recently, power ultrasound proved to be an effective, nontoxic, and environmentally friendly way to speed the AFD process [126]. Repeated compression-expansion cycles generated by the ultrasound helps to create of micropathways in the solid to ease the vapor flow and microstirring at the-solid fluid interface, reducing the external mass transfer resistance [127]. Moreover, the additional exertion of a mild heating effect increased the interest in the ultrasound-assisted atmospheric freeze-drying of thermally sensitive products.…”

“…Eggplant cubes [127] To evaluate the effect of air temperature and velocity, US power, and sample size on vitamin C, total phenolic, and antioxidant capacity of eggplant during US-assisted AFD Power ultrasound is a promising technology for accelerating the AFD process, but attention must be paid to the optimization of the operating conditions in order to limit the thermal effects of acoustic energy and to ensure the preservation of the nutritional properties of the samples.…”

Changes in unfrozen water content and dielectric properties during pulse vacuum osmotic dehydration to improve microwave freeze‐drying characteristics of Chinese yam

“…The results were expressed as rehydration ratio (mass after rehydration/mass before rehydration). The determination of TPC was undertaken according to the method of Colucci et al, 24 and the results were expressed as gallic acid equivalents (GAE) in grams of GAE per kilogram dry weight (DW). Color indicators measurement was carried out by a CR-400 model colorimeter (Onica Minolta Co., Tokyo, Japan).…”