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

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.

摘要 月桂树（Laurus nobilis）因兼具治疗功效、营养特性与观赏价值，是地中海地区常被研究的树种之一。本研究针对两种干燥方式开展对比试验：微波辅助干燥（Microwave-assisted Drying, MWD）（功率范围180~900 W）与传统干燥方式（自然晾干及40~120 ℃条件下的烘箱干燥）。本研究基于水分含量随时间的变化规律测定了干燥动力学参数，并对所得样品的总酚含量（Total Phenolic Content, TPC）与还原能力进行了检测。动力学结果表明：随着干燥温度与微波功率的提升，干燥月桂叶所需时长显著缩短；微波辅助干燥的效率远高于传统干燥方式（自然晾干与烘箱干燥）。采用自然晾干与微波辅助干燥的方式，可更好保留月桂叶中的抗氧化成分。本研究结果证实，总酚含量与还原能力之间存在显著相关性。采用300 W微波功率干燥130 s为最优工艺组合，可使所得干燥月桂叶拥有最高的酚类物质含量与抗氧化活性。