Optimization of drying conditions of Rheum ribes (Işkin) by response surface methodology and mathematical modeling of drying process

Rheum ribes is a herbaceous plant belonging to the Polygonaceae family. It is also known by the names of 'ışgın, uçkun, dağ muzu, yayla muzu' among the local people. The only species of Rheum genus grown in Turkey is Rheum ribes. In this study, convection drying conditions at 50 °C, 60 °C and 70 °C under the influence of osmotic pre-treatments of Rheum ribes (Işkın) plant and the quality parameters changing accordingly were investigated. Treatment with %0 %5 and %10 (w/w) salt solutions for 5 minutes, 20 minutes and 35 minutes was chosen as pre-treatment and independent variable. Drying behavior of Rheum ribes plant was investigated by mathematical modeling. Within the scope of the optimization of the drying conditions with the response surface method, 15 run was carried out according to the Box-Behnken experimental design with 3 center points and 12 drying conditions. Optimization with surface response method (RSM), drying kinetics and accordingly changing quality parameters (total phenolic content TPC, color analysis, sensory analysis, rehydration analysis) were investigated. The models explaining the drying behavior of Rheum ribes were Page and Modified Page models. L* value, hᵒ value, drying time, total phenolic content, drying rate and moisture ratio values of the dependent variables were found to be significant as a model (p<0.01). The optimum condition was determined as drying with hot air after 35 minutes of treatment in a 3.489% salt solution at 70ᵒC. Accordingly, L* value was 50.726, hᵒ value was 89.852, drying time was 210.85 min, total phenolic content was 60.93 mgGAE/g dm, the drying rate was found to be 0.082 g water/g dm min and the moisture ratio was 0.031.