Drying kinetics of tobacco leaves based on Weibull function during stem drying stage and its color parameters

ObjectiveIn order to provide a theoretical reference for the optimization of curing process during stem drying stage,the changes of drying characteristics and color of tobacco midrib during stem drying stage was analyzed.MethodIn this study,the middle leaves of Yunyan 87 were used as experimental materials.Weibull distribution function was applied to analyze the drying characteristics of midrib during stem drying stage under different drying air velocities (low velocity,intermediate velocity and high velocity),relative humidity(12%,18% and 24%)and dry-bulb tempera-ture(60,64,68 and 72℃),and the color parameters of flue-cured tobacco leaves were also studied.ResultThe mois-ture dehydration of tobacco midrib was in a falling-rate drying process during stem drying stage,its drying rate was in-creased with the raise of air velocity,decrease of humidity or increase of dry bulb temperature.Weibull distribution func-tion could well describe the drying curves of tobacco midrib during stem drying stage.It was found that the scale parame-ter α decreased as air velocity increased,humidity decreased and dry bulb temperature increased.And there was a lower influence on the shape parameter β under different stem drying conditions.The moisture diffusion coefficient Dcalof tobac-co midrib during stem drying stage based on Weibull distribution was between 1.994×10-10and 4.026×10-10m2/s.The acti-vation energy Eafor drying of tobacco midrib was 56.57 kJ/mol.The brightness value L*,the color difference between the front and back of leaves?L* increased with the increase of air velocity,the color of tobacco leaves was bright yellow. The brightness value L*and the color difference between front and back of leaves?L* decreased with the increase of rela-tive humidity,while the redness value a*,yellowness value b*and color saturation C*increased gradually,the color of tobacco leaves was close to orange.In addition,the redness value a*increased with the raise of dry bulb temperature,the color of tobacco leaves was reddish brown.ConclusionHigh temperature,high humidity and low air velocity during to-bacco stem drying stage is benefit for improving the drying efficiency and increasing the color saturation of tobacco leaves.