Drying Kinetics and Quality of Barberry in a Thin Layer Dryer

The objective of this study was to investigate dehydration kinetics of barberry (Berberis vulgaris L.) at different drying temperatures (۶۰ ºC, ۷۰ ºC, ۸۰ ºC), air velocities (۰.۳ m s-۱, ۰.۵ m s-۱, ۱ m s-۱) with two types of pretreatment. Drying time and colour quality during dehydration were experimentally determined. Barberries were dried from the initial moisture content of ۷۳.۴۴% (w.b.) to the required moisture content of ۱۸% (w.b.). Dehydration kinetics was monitored by measuring barberries weights at regular intervals. Convective drying curves were obtained for the treated and untreated barberries. The effect of two dipping pretreatments on drying kinetics of barberries was also studied. The two pretreatments were thermal shocking by immersing barberries in hot water, followed by cold water cooling, and dipping in olive oil and food grade K۲CO۳. Colour of the dried product was altered significantly during drying. The results indicated that the use of low temperatures is adequate for preserving this property. The air temperature significantly affected drying time and hunter colour indices of barberries (P< ۰.۰۵). With heat shocking and treatment with olive oil and K۲CO۳, drying time was reduced to about ۴۰% and ۶۰%, respectively. The total colour change (ΔE) and hue angle (H) increased with temperature. Moisture transfer from the test samples was described by applying the Fick’s diffusion model for calculating the effective diffusivity. The effective moisture diffusivity (Deff) of barberry increased as the drying air temperature increased. The Deff values were higher for the treated samples than the untreated ones. These values were also higher for the samples treated with olive oil and K۲ CO۳ emulsion than those treated with hot water. The effective diffusivity of the untreated and the pre-treated varied between ۲.۵۷×۱۰-۱۳ and ۹.۶۷×۱۰-۱۲ m۲ s-۱, respectively. Higher colour change was observed in barberries treated with olive oil and K۲CO۳ emulsion. Statistical analysis showed that temperature and pretreatment had the most significant effect on drying time at p<۰.۰۱.