Far-infrared radiation heating assisted pulsed vacuum drying (FIR-PVD) of wolfberry (Lycium barbarum L.): Effects on drying kinetics and quality attributes

Abstract

The drying kinetics of wolfberry was investigated in a pulsed vacuum dryer using far-infrared radiation heating at different vacuum pressure durations (10, 15, and 20min), ambient pressure durations (2, 4, and 6min) and drying temperatures (60, 65, and 70°C). The quality attributes such as colour, rehydration ratio, and microstructure of the dried products were also evaluated. Under appropriate conditions, FIR-PVD significantly lowers the drying time compared to hot air drying. The Weibull model was used to calculate the effective moisture diffusivity (Deff), which ranged from 3.72×10−10 to 7.31×10−10m2/s. The activation energy was 54.30kJ/mol determined by Arrhenius equation. The colour parameters of dried wolfberry dried by FIR-PVD were much similar to that of the fresh berries. The rehydration ratio of FIR-PVD dried wolfberry was 2.41 and 2.82 at drying temperatures of 70 and 60°C, respectively. Porous and fissured microstructure was observed on the surface of dried wolfberry, which can enhance drying kinetics as well as the rehydration process. By comprehensive considering the drying time and quality, drying temperature of 65°C, vacuum pressure duration of 15min and ambient pressure duration of 2min were proposed as the most favourable drying conditions for wolfberry.