Effect of different pretreatment methods on drying characteristics and quality of wolfberry (Lycium barbarum) by radio frequency-hot air combined segmented drying

Abstract

Abstract In this study, fresh wolfberry in the current season was used as the experimental material and a radio frequency (RF)-hot air combined segmented drying process was adopted for berry preservation. Ultrasonic treatment, hot water blanching, sucrose infiltration, ultrasonic & blanching, ultrasonic & infiltration, and NaOH and NaCl solution impregnation were used for pre-treatment of combined drying. Taking natural drying and conventional Na2CO3 dewaxing treatment as the control group, the effects of different pretreatment methods on drying characteristics, quality, and microstructure of wolfberry during combined drying were investigated. The drying time after ultrasonic and blanching pretreatment was the shortest(13.5h), which effectively retained total flavonoids(1.79mg/g) and enhanced their antioxidant activity(I = 60.78%). NaCl impregnation treatment significantly increased the total phenol content(8.77 mg/g). The retention rate of soluble sugar (0.73 g/g), ascorbic acid (3.96mg/100g), betaine(2.72%), and other nutrients increased significantly after ultrasonic and infiltration treatment, while the color, rehydration rate and microstructure were better than other treatment methods. The Weibull distribution function can accurately describe the RF-hot air combined drying process of Lycium barbarum after different pretreatment, and simulated results were consistent with the results of the combined drying characteristic curve of Lycium barbarum. The aim of this study was explored suitable pretreatment methods to improve the drying rate and ensure the quality of dried products of wolfberry.