AIR-DRYING CHARACTERISTICS, EFFECTIVE MOISTURE DIFFUSIVITY AND ACTIVATION ENERGY OF GRAPE LEAVES

Abstract

Grape leaves were dried in a thin layer under hot air at 40, 50 and 60C m/s in the a cabinet dryer. The drying rate curves showed that the drying of grape leaves was characterized by a single falling rate period. Drying of grape leaves was greatly influenced by air temperature. Eight mathematical models available in the literature were fitted to the experimental data. The Wang and Singh and Midilli et al. models gave the best fits for each drying curve; based on the statistical tests, namely, coefficient of determination (R2), mean relative percent error (P), reduced chi-square (χ2) and root mean square error (RMSE). Fick's second law model was used to calculate the effective moisture diffusivity, which increased with temperature from 4.13 × 10−10 to 1.83 × 10−9 m2/s, with estimated activation energy value of 64.56 kJ/mol. The rehydration capacity was found to decrease with an increase in rehydration temperature. PRACTICAL APPLICATIONS Grape leaves are extremely perishable. Because of their short shelf life under normal ambient conditions of temperature and humidity, their preservation has assumed importance. Drying, which is the oldest of food preservation practiced by mankind, is the most important process to preserve agricultural products because it has a great effect on the quality of the dried products. The objective in drying foods is the reduction of the moisture content to a level that allows safe storage over an extended period. In this study, drying characteristics of grape leaves were studied in a convectional hot air-dryer. The effect of air temperature on drying and rehydration characteristics was determined. For the optimal products, the drying characteristics, namely drying time and rehydration capacity, are considered.