Optimization of the process of freeze-drying and comparison with convective drying of Russian tarragon (Artemisia dracunculus L.).

Abstract

Drying is a conservation process that may adversely affect the nutritional and organoleptic properties of the product. The present study was developed in the Laboratory of food quality control, at the Universidad Nacional de Colombia, Medellín headquarters. The aim of this work was the experimental optimization of the freeze-drying process (LIO) of the Russian tarragon leaves (Artemisia drancunculus L.) to preserve, in the best possible way, its properties. We used a tray freeze dryer, where the material was frozen from 25 °C to -40 °C, at a speed of 0.22 °C/min. The optimization was carried out using response surface methodology with an optimal design, as a function of independent variable plate heating rates (0.03 - 0.06 °C/min) from -40 °C to 35 °C, holding the temperature of the plate at 35ºC for one hour. The dependent variables were moisture content, water activity (aw), antioxidant activity, color and drying time. The product dried in the optimum condition was compared with another drying by forced convection (SC). The freeze-drying time process presented statistically significant differences with the plate heating speed (VCP). LIO Optimal condition was obtained at a VCP of 0.06 °C/min for 20.8 hours. The dried products with both methods showing showed statistically significant differences in aw, moisture, DPPH, and color, but not in total phenol content. The LIO products showed better properties than SC products, preserving, in a best way, its color and antioxidant activity in comparison to fresh plant.