Effects of oven, microwave and vacuum drying on drying characteristics, colour, total phenolic content and antioxidant capacity of celery slices

In this research, the effects of microwave (190, 375, and 680 W) vacuum (500, 600, and 700 mbar) and oven (70, 85, and 100 °C) drying methods on the total phenolics, antioxidant capacity, colour and drying characteristics of celery slices were studied. For the selection of the most suitable thin layer drying model, five mathematical models (Page, Modified Page, Logarithmic, Lewis, and Henderson and Pabis) have been applied to the treatments. In light of the statistical tests, Page and Modified Page models were considered the best to describe drying characteristics. Regarding the colour value changes during drying, L*, ΔEab and h° decreased, and a* increased. Additionally, both b* and C*ab increased with microwave and oven drying but decreased with vacuum drying. Dried celery had 38.51-75.34% less total phenolic content than fresh samples, while its antioxidant capacities was greater. The highest ferric-reducing ability of plasma (FRAP; 49.35±3.10 μmol TE/g dw) and cupric-reducing antioxidant capacity (CUPRAC; 33.29±1.02 μmol TE/g dw) resulted from microwave drying at 680 W, and the highest antioxidant capacity from the DPPH method (9.87±0.04 μmol TE/g dw) resulted from microwave drying at 375 W. In overall evaluation, microwave drying provided greater nutritional properties by increasing antioxidant capacity and gave the advantage of reduced drying times.