The impact of osmotic dehydration and microwave drying process conditions on the quality characteristics of celery roots (Apium graveolens l. Subsp. rapaceum)

In this study, celery roots were dried by the osmotic dehydration-assisted microwave drying method, and both osmotic dehydration (OD) and microwave conditions were optimized using response surface methodology (RSM). Utilizing a Box–Behnken experimental design, the drying time was minimized while maximizing the total phenolic compounds (TPC) in dried samples at different OD salt concentrations (10, 20 and 30 %), OD temperatures (30, 45 and 60 °C), OD durations (1, 2 and 3 h) and microwave powers (210, 350 and 490 W). The optimal drying conditions were identified as 15.05 % for OD salt concentration, 42.5 °C for OD temperature, 1.6 h for OD duration and 489.7 W for microwave power. Under these optimal conditions, the predicted values for time and TPC were 10 min and 104.38 mg GAE/100 g, respectively. The composite desirability value was 0.99 as a result of optimization. The experimental values for time and TPC were measured as 11 min and 97.45 mg GAE/100 g, respectively. The predicted and experimental values were found to be statistically similar to each other. A comparison with control groups designed to assess the effects of OD and microwave processes revealed that these processes significantly influenced both quality (TPC, antioxidant activity, color) and drying characteristics (drying time, rehydration rate). The greenness assessment value was calculated as 78 using the MoGAPI tool. Consequently, the application of OD pretreatment and use of the innovative microwave drying method as a final drying step in vegetable drying was successfully implemented to enhance the properties of the final product.