Effect of the pretreatment methods on extraction yield of polyphenol and chlorogenic acid from Elsholtzia cilliata leaves

Studies have shown that Elsholtzia ciliata (Thunb.) Hyland (ELC) contains many health-promoting bioactive compounds. The leaf cell wall of ELC must be adequately pretreated and disrupted to improve the extraction efficiency of total polyphenol content (TPC) and chlorogenic acid (CGA). This paper examined the effects of many pretreatment methods on extracting TPC, CGA, and antioxidant activity according to DPPH (AA according to DPPH) from ELC leaves. These pretreatment methods were convection drying, blanching (BL), blanching combined with freezing (BF), and blanching combined with freezing plus microwave assistance (BFM). The results indicated that blanching at 80 o C for 90 sec and freezing at -18 o C for 24 h significantly increased TPC and CGA contents from ELC leaves. In order to improve the extraction yield, the pretreated ELC was then extracted at a temperature of 70 o C for 75 min with a material -to-solvent ratio of 1/8 , the ethanol 60%, and pH 3. Under these conditions, the extraction yield for TPC, chlorogenic acid, and AA according to DPPH were 51.8%, 36%, and 46.4% (compared with the total content in raw materials), respectively. SEM micrographs recorded the cell structure disruption of the pretreatment methods, and UPLC analysis determined the bioactive components. These findings highlight the importance of pretreatment and extraction in maximizing the yield of bioactive compounds from ELC leaves and the potential of ELC in functional food. • Pretreatments improved extraction of TPC, CGA, and antioxidant activity. • Blanching (80°C, 90s) and freezing (-18°C, 24h) enhanced extraction yields. • Optimum extraction: 70°C, 75 min, 60% ethanol, pH 3, M/S ratio 1/8. • Yields: TPC 51.8%, CGA 36%, AA 46.4% vs raw material.