Evaluation of Turnip slice phenolic component increasing by osmosis treatment in Roselle extract and investigation of its hot-air drying kinetics

In this study, turnip slices was osmotic dehydrated in rosella extract for polyphenolic enrichment purpose which further dried using hot air drying technique. Osmotic process variables were the concentration of sucrose solution (30, 50 and 70 %), process time (40, 75 and 105 min) and the solution temperature (60, 70 and 80°C). The quality of osmotic dehydration-enrichment step was evaluated by measuring water loss, solid gain, weight reduction and phenolic compounds absorption. All variable were effective on measured parameters. Optimized osmotic condition were 35% of sucrose concentration, 105 min for process time and temperature of 80°C to reach the most desirable responses including maximum water loss and weight reduction and phenolic compounds absorption as well as minimum solid gain. Processed turnip slices at optimum condition were then air dried at 60, 70 and 80°C. Moisture ratio during drying time was measured for every temperature and used for determination of best drying kinetic model. 10 models were fitted to experimental data and the fitting quality was evaluated using statistical parameters. It was found that two term models predicts the moisture changes well. Effective diffusion coefficient s were 1.83E-9, 2.03E-9 and 3.04E-9 for 60, 70 and 80°C drying temperatures respectively. Arrhenius model was used for activation energy determination and it calculated as 25.12 Kj/mol.