Conventional method and microwave drying kinetics of Laurus nobilis leaves: effects on phenolic compounds and antioxidant activity

Cinética da secagem convencional e por micro-ondas de folhas de Laurus nobilis: efeitos sobre os compostos fenólicos e a atividade antioxidante

Abstract

Laurus nobilis constitutes one of the usually studied Mediterranean trees due to its therapeutic effects, nutritional properties, and ornamental use. In the current investigation, a comparative study was conducted between two types of drying methods, a microwave-assisted drying (MWD) (from 180 to 900 W) and a conventional method (open-air and oven-drying using temperatures from 40 °C to 120 °C). Drying kinetics were carried out as a function of moisture content according to time. Total Phenolic Content (TPC) as well as reducing power of obtained products were determined. Kinetic results showed that the time required for dried bay leaves became shorter as temperature and microwave power increased; drying with the microwave was much more efficient than conventional methods (open-air and oven-drying). Antioxidants of the Laurus nobilis leaves were better conserved using open-air and microwave drying. Our results underlined a significant correlation between TPC and reducing power. Microwave drying using 300 W during 130 s was the most efficient combination that provided dried bay leaves with the highest content of phenolic compounds and antioxidant activity.

Keywords:
Bay leaf; Open-air drying; Oven drying; Microwave drying; Phenolic compounds; Antioxidant capacity