Sequential‐combined solar energy assisted hot air and hot air‐assisted radio frequency drying to produce high‐quality dried whole apricots: An optimization study for process parameters

Abstract

A solar energy assisted hot air (SAAD) and its sequential combination with hot airassisted radio frequency drying (HARFD) system was used to dry whole apricots.Sequentially combined drying conditions (pre-drying temperature (50-70°C), predrying time (300-1,140 min), distance between electrodes (77-85 mm), and radio frequency drying time (270-690 min)) were investigated and optimized using the Box-Behnken design for minimum browning and surface color and optimum texture and moisture content. Under optimum conditions of 63.5°C pre-drying temperature, 895 min pre-drying time, 77 mm distance between radio frequency electrodes, and 385 min radio frequency drying time; the moisture content, amount of browning products, total color change, and hardness were 22.31% ± 2.82%, 0.69 ± 0.03 (A 420 /g dry weight), 37.65 ± 2.23, and 1,293.46 ± 61.96 N, respectively. Sequential combination of SAAD with HARFD system provided high-quality whole apricots while reducing the processing time.Novelty impact statement: Sequentially combined solar energy assisted hot air and hot air-assisted radio frequency drying system was used for the first time to dry whole apricots and process parameters were optimized to produce high-quality products using response surface methodology. The results showed that the applied sequential drying technique is promising to produce commercially marketable apricots in a short time with acceptable quality characteristics. Consequently, the sequentially combined drying system could be an alternative technology in industry.

Characteristics and Quality Analysis of Radio Frequency-Hot Air Combined Segmented Drying of Wolfberry (Lycium barbarum)

“…The residual unevaporated free water on the surface of the material was lost with the air during the transfer process from RF to hot air drying, which resulted in a temporary increase in the drying rate. RF heating makes the wolfberries have a positive temperature gradient from the center to the surface, causing a vapor pressure difference and improving the drying rate, and the material enters a low-amplitude stable heating stage after the rapid heating stage [ 28 ].…”

“…Each dehydration time was 10 min. Final samples were immersed in 100% tert-butanol for 15 min and then placed in a vacuum freeze drying machine for processing [ 22 , 23 , 24 , 25 , 28 , 29 , 30 ]. The sample observation surface was placed upward and fixed on the scanning electron microscopy sample table with conductive tape after treatment, and the surface was coated with an ion sputter-coating instrument for 90 s, then placed under a scanning electron microscope.…”

“…It was reported that the total phenol content, shrinkage rate, and color change of bananas after RF treatment at the early stage of hot air drying showed an upward trend [ 26 , 27 ], and the rehydration rate and hardness of samples decreased. Hot air-assisted RF drying was also applied to the drying of apricots [ 28 , 29 ], and the experimental results showed that the drying process had significant effects on the color, antioxidant capacity, and β-carotene content of preserved apricots. In addition, the drying time was significantly reduced.…”