Abstract:

In this study, the drying performance of lemon peel samples was investigated by drying processes with microwave, hot air and their combinations. Three different temperatures (40, 50 and 60°C) and three different microwave powers (90, 180 and 360 W) were used. Effects of drying conditions on drying rate and drying time were determined. Page and Modified Page models were found to be the best expressing models of the drying kinetics of lemon peels. With the increase in temperature and microwave power, the drying rate increased, while the drying time decreased. It was observed that the drying process performed with the combination of 60°C hot air and 360 W microwave had the highest drying rate with the shortest drying time of 24 minutes. The effect of drying processes on the color of lemon peels was determined by determining the L*, a*, b*, Hue angle, Chroma and ∆E* values and the color differences between fresh and dry samples. Due to the darkening of the samples under high microwave power, it was concluded that the use of 90 and 180 W is more suitable than 360 W. Total amount of phenolic substances increased in the dried samples compared to the fresh samples, while the antioxidant activity decreased. At 40°C, which has the longest drying time, the decrease in antioxidant activity was the highest with 85.54%. The drying process performed with the combination of 60°C and 360 W was the drying condition in which the total phenolic content increased the most with 186.11%.

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