Abstract
Sun, oven (50 and 70 degrees C) and microwave oven (210 and 700W) drying of onion slices were carried out to monitor the drying kinetics and quality degradation of the product. Page, "Modified Page" and "Midilli and Kucuk" models exhibited high coefficient of determination (R-2) values, ranging between 0.994 and 0.999. The calculated effective diffusivity (D-eff) values (m(2)/s) of onion slices for the sun, oven 50 degrees C and oven 70 degrees C, microwave 210 W and microwave 700W drying process were 8.339 x 10(-10), 7.468 x 10(-10), 1.554 x 10(-9), 4.009 x 10(-8) and 4.869 x 10(-8), respectively. Fresh and dried onion slices had high amounts of K (696.82-16357.55 mg/kg), Ca (69.64-340.03 mg/kg), Na (37.72-1895.43 mg/kg), Mg (3.31-964.77 mg/kg) and P (46.47-3384.07 mg/kg) minerals. The highest mineral values were determined in oven dried samples. Sun (L* 58.00 +/- 4.83, a* 0.27 +/- 0.10, b* 14.36 +/- 2.40) and microwave oven drying (210 W) (I.* 54.78 +/- 7.54, a* -0.71 +/- 0.09, b* 13.17 +/- 1.05) revealed better colour values in the dried products. The phenolic contents of microwave oven dried samples (1664.39 +/- 134.12 and 1623.59 +/- 140.02 for 210 W and 700W, respectively) were higher than those of the other dried onion slices. (C) 2010 Elsevier Ltd. All rights reserved.