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Convective and microwave drying characteristics, energy requirement and color retention of dehydrated nettle leaves (Urtica diocia L.) 

DOI: DOI:10.18805/lr.v0i0.8409    | Article Id: LR-323 | Page : 649-654
Citation :- Convective and microwave drying characteristics, energy requirementand color retention of dehydrated nettle leaves (Urtica diocia L.) .Legume Research.2017.(40):649-654

Fuat Lule and Turhan Koyuncu

flule@adiyaman.edu.tr
Address :

Faculty of Technology, University of Adiyaman, 02040 Adiyaman, Turkey.

Submitted Date : 6-10-2016
Accepted Date : 28-12-2016

Abstract

In this research, convective and microwave drying characteristics, energy requirement and color changes of nettle leaves (Urtica diocia L.) were reported. Samples of freshly harvested nettle leaves were dehydrated under three air temperatures of 50 °C, 60 °C and 70 °C and at three microwave power levels of PL-1, PL-2 and PL-3. Selected drying air velocity was 0.30 m/s for all temperatures. This is coming from the fact that it was understood from the preliminary studies that the temperature less than 50 °C and the air speed more than 0.30 ms-1 increase the drying time and energy requirement, extremely for these products. Nettle leaves were dehydrated from the initial moisture content of 320 (percentage dry basis) to a final moisture content of 7 % to 9 %. During convective drying experiments, product were weighted automatically by the balance per (5 to10) min. Data were transferred to the computer and processed by a software. During microwave drying, the product were weighted and data recorded manually per (15 to 60) min. The influence of drying method, drying air temperature and microwave power level have also been studied. Hunter L, a, b values system was also used to evaluate changes in total color difference (DE) on dried products. The results showed that convective drying air temperature and microwave oven power levels influenced the total drying time, total energy requirement, specific energy requirement and color difference for nettle leaves. The minimum specific energy requirement were determined as 6.95 kWhkg-1 and 23.63 kWhkg-1 for 70 °C and PL-2 respectively. 70 °C drying air temperature and PL-3 was found to yield better quality product in terms of color retention of Hunter L, a, b and  DE. As a result, to reduce drying energy consumption and to keep better color retention, convective drying can be recommended for this application.

Keywords

Color retention Convective drying Drying characteristics Energy requirements Microwave drying

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