Effect of different drying methods on drying characteristics, colour, total phenolic content and antioxidant activity of sliced green table olives

Abstract

This study analysed the effects of convective (50 and 75°C), microwave (90 and 160 W) and combined microwave-convective (90 W-50°C, 90 W-75°C, 160 W-50°C and 160 W-75°C) drying methods on the drying characteristics, colour, total phenolic content and antioxidant activity of sliced green table olives. The shortest drying time was found with the combined microwave-convective 160 W-75°C method, and it was found that the combined microwave-convective method provided the greatest time savings in comparison to other methods tested. According to the test results, the drying rate of samples increased with increasing convective temperature and microwave power. Based on the statistical tests used for evaluation, the Midilli et al. model was found to be the best model to explain test data for sliced green olives samples under all drying conditions. While the colour values L*, b*, and chroma and hue angle decreased, the colour value a* increased in dried sliced green olive samples. It was found that the 160 W microwave method gave colour values closest to those of fresh samples. Among the different drying treatments, the values to closest those of fresh green olive samples with respect to total phenolic content and antioxidant activity were achieved with the 160 W-75°C combined microwave-convective drying method.