Multiphase drying of Calendula officinalis flowers in batch dryer | Višefazno sušenje cvasti nevena u šaržnoj sušari

The results of three-phase drying of Calendula officinalis L. in batch dryer, as well as changes of drying mode (open-circulating) in its second and third phase are discussed. The experiments include five different drying temperatures and plant material layer height. The drying temperature of 50 deg C, constant open mode and natural drying served as control. The mass of dried material, fuel consumption, temperature of lower and upper layer, total carotenoid content and total microbial count were measured. Also, the specific drying duration and the specific drying energy were calculated. The specific drying energy value was lower than that of the control, in all the three-phase drying groups. When drying with changed mode (open-circulating) was applied, the increase of the specific drying energy in final phase was smaller than in the control (constant open mode). The significant differences in moisture content between lower and upper layer of dried plant material were evident, pointing out the necessity of turning plant material during drying procedure. The content of total carotenoids was higher in lower layer, in all the experimental variants and lower by natural drying, pointing out that higher temperatures positively affected the total carotenoid content. The lowest total microbial count was obtained with the lower plant material layer while higher values were recorded in natural dried material. The highest values were recorded in fresh samples. Future investigations should be aimed at a constant temperature of drying agent in all phases, changing the drying mode (open-circulation) at app. 32% moisture content of plant material. In addition, plant layers should be turned after finishing first phase of drying (moisture content app. 32%). Also, the limit value of drying agent temperature should be defined to produce positive effects upon total carotenoid content. The recorded effect of relative humidity of drying agent upon total carotenoid content should be tested.