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

Abstract

To overcome the problems of a long conventional drying time, low energy efficiency, and poor product quality, a segmented drying approach was developed for fresh wolfberry (Lycium barbarum) using a radio frequency (RF)-hot air drying process, which was investigated under different parameters of plate spacing (80, 90, 100 mm), vacuum degree (0.015, 0.025, 0.035 Mpa), and hot air temperature (50, 55, 60 °C). Analysis of the wolfberry’s drying characteristics, comprehensive quality, and microstructure indicated that: combined drying was faster and less time-consuming than natural drying or hot air drying, and components such as polysaccharides, ascorbic acid, and betaine in wolfberries were effectively retained. Based on the acceptable drying rate, stable temperature application, and avoidance of arcing effects, the optimal combined segmented drying parameters were determined to be as follows: a plate spacing of 90 mm, vacuum degree of 0.025 MPa, and air temperature of 55 °C. For the dried wolfberries under these conditions, the total drying time was 17 h and the berries had an improved comprehensive quality, the content of total soluble sugars was 0.62 g/g, total phenol was 10.01 mg/g, total flavonoids was 2.60 mg/g, VC was 3.18 mg/100 g, betaine was 3.48%, oxidation resistance represented by an inhibition rate was 66.14%, color was better, and rehydration rate was 48.56%. The microstructure was more regular because of the special dielectric heating characteristics of RF vacuuming. Despite the differing drying characteristics of individual materials, the overall RF-hot air combined drying process was found to achieve high-quality dehydration of wolfberries.

Improving Drying Characteristics and Physicochemical Quality of Angelica sinensis by Novel Tray Rotation Microwave Vacuum Drying

“…The polysaccharide content was 179.92 mg/g at the drying temperature of 50 °C, which increased by 42.84% compared with that at 35 °C (125.96 mg/g). This may be due to the low drying temperature, which increased the time for the Maillard reaction and caramelization reaction between amino acids and polysaccharides, and therefore the polysaccharide content decreased [ 37 , 39 ]. It is also known that the polysaccharide contents of the samples were 140.96 mg/g and 141.80 mg/g at section thicknesses of 3 mm and 4 mm, which were higher than the polysaccharide contents at other thicknesses, indicating that the samples could retain the bioactive substances better under this condition.…”

“…Polysaccharide was determined by the sulfuric acid-phenol method [ 39 ]. A 0.005 mL extract was taken, 1.0 mL 9% phenol solution was added, fully mixed, added 3.0 mL concentrated H 2 SO 4 , shaken for 5 min, room temperature reaction for 30 min.…”

“…Antioxidant activity was determined by DPPH method [ 39 ]. An appropriate amount of extract was taken and added to 3.0 mL mol/L DPPH methanol solution, and shaken at room temperature for 30 min under dark conditions.…”

Study on drying characteristics and moisture content prediction model of Panax notoginseng taproot by using segmented drying of microwave vacuum combined with hot air

“…With the convert moisture content decreased from 40 g•g −1 to 20 g•g −1 , the drying time of microwave vacuum increased from 8 to 19.3 h, while the total drying time of reaching the storage moisture content decreased from 71 to 37.6 h. It could be seen that the use of segmented drying shortened the drying time. Xu et al (2022) studied drying characteristics of wolfberry by using segmented drying of radio frequency combined with hot air, Li et al (2020) studied drying characteristics of Huyou fruit by using segmented drying of microwave vacuum combined with freeze, indicating that segmented drying can shorten the drying time of drying method with long drying time (e.g., hot air and freezing) and achieve high quality dehydration. Due to microwave vacuum heated the sample from inside to outside, the heat transfer direction of the sample was the same, and the vacuum environment was conducive to the transfer of water.…”

Evaluation of the effect of ultrasonic pretreatment on vacuum far‐infrared drying characteristics and quality of Angelica sinensis based on entropy weight‐coefficient of variation method

“…Color is one of the important indexes to evaluate the quality of agricultural products. Xu et al (2022) found that compared with hot-air drying and radio-frequency drying, pretreatment shortened the total drying time, increased the drying rate, and reduced the Maillard reaction time (Çakmak et al, 2016;Jiang et al, 2022). To a certain extent, it inhibited the oxidative decomposition of natural active substances and the degradation of thermosensitive nutrients.…”