Effects of temperature and humidity on drying kinetics, final quality and cell wall pectin content of wolfberry ( Lycium barbarum )

The effects of four groups of hot-air drying methods, including constant temperature (50 °C) and constant humidity (10%) (CTCH), constant temperature (50 °C) and variable humidity (60%-47%-35%-23%-10%) (CTVH), variable temperature (40 °C-46 °C-52 °C-58 °C-64 °C) and constant humidity (10%) (VTCH), variable temperature (40 °C-46 °C-52 °C-58 °C-64 °C) and variable humidity (60%-47%-35%-23%-10%) (VTVH), on the drying kinetics, product quality and the content of pectin polysaccharides in cell wall of wolfberry were studied. Among them, VTVH showed the highest drying efficiency with the shortest drying time of 13 h, which was 9.52% shorter than that of CTCH, and the highest effective water diffusion coefficient for wolfberries (9.356 × 10−9 m2·min−1). After VTVH drying, samples showed the highest polysaccharides content (46.48%) and rehydration rate (52.24%), as well as the lowest color difference (6.07) and shrinkage rate (66.38%). The content of water-soluble pectin (WSP) in wolfberry was the highest under VTCH drying condition, which was 48.67% higher than that of CTVH drying condition.