Effects of pre-processing on the active compounds before drying Eucommia ulmoides leaves

Abstract

Aiming to provide a new way that preserves more active components in Eucommia ulmoides (EU) leaves, this paper utilizes 4 methods, i.e., microwave, steam, air heating, and frying, to process EU leaves before drying, and their respective effects on the leaves were evaluated. The antioxidant activity of EU leaves in vitro was measured by the DPPH free radical method; the contents of total flavonoids (TFC) and total phenols (TPC) were analyzed by spectrophotometry; and the contents of main active components were determined by high-performance liquid chromatography (HPLC). The results showed the pre-process improved the quality of the EU leaves. As a simple and fast process, the microwave process is the most effective technique in the retention of flavonoids and four active ingredients except aucubin. High power (800 W) and short time (2.5 min) are more conducive to the retention of active ingredients, with high antioxidant activity. Appropriate steam and frying processes also exhibited benefits for the active components. In particular, the samples treated with steam for 10 minutes showed great potential for industrial application with the highest antioxidant activity and polyphenol content. Therefore, proper pre-processing before drying should be conducted to effectively protect the active components of EU leaves.