Thin Layer Drying of Stinging Nettle (Urtica Dioica) Leaves in Cabinet Dryer and Selection of Appropriate Drying Model

Abstract

The present study was conducted to examine the drying kinetics of stinging nettle (Urtica dioica) leaves, both pretreated and untreated, in a cabinet dryer. The leaves were blanched at 90°C for one minute before drying at temperatures of 50, 55, or 60°C. The control group involved drying the leaves without any blanching. The drying of stinging nettle leaves followed only a falling rate period. Graphical and statistical analysis of the result showed that Midilli and Verma models were the best-fitted models for cabinet drying of stinging nettle leaves. The time required to dry unblanched leaves from an initial moisture content of ~8.54±0.86% db to a final moisture content of ~1.11±0.01% db was 90, 75, and 60 minutes at 50, 55, and 60℃, respectively. Similarly, the time required to dry blanched leaves was 75, 60, and 45 minutes at 50, 55, and 60°C respectively. The rehydration ratio of stinging nettle varied from 3.08±0.09 to 4.26±0.01 for unblanched and 3.40±0.15 to 4.52±0.07 for blanched product dried at 50-60℃. The Deff of leaves was increased from 1.2-2.5×10^-12m²/s for unblanched leaves and 2-3.1×10^-12m²/s for blanched leaves as the drying temperature increased from 50-60℃. The activation energy was estimated to be 65.2 kJ/mol for unblanched leaves and 38.9 kJ/mol for blanched leaves. Drying (at 55℃) retained 43% and 31% of total chlorophyll and β-carotene respectively while drying with blanching retained 38% and 57% total chlorophyll and β-carotene respectively.