Walnut leaves – influence of different extraction methods on the total phenol and flavonoid contents
Polyphenols are considered as one of the most important components of walnut leaves with many beneficial effects on human health. In this study, a microwave-assisted extraction (MAE) was compared with three other methods for the extraction of total phenols and flavonoids of walnut (Juglans regia L.) leaves. It was found that the extraction of total phenols and flavonoids from walnut leaves in MAE method for 4 minutes was higher than that of maceration extraction, ultrasonic extraction, and soxhlet extraction for 24 hours, 15 min, and 6 hours, respectively. Compared with other extraction methods, MAE reduced the extraction time. It was found that Blanching had no significant effect on the total phenols of walnut leaves. The highest content of total phenols was obtained in July. The antioxidant activity was measured by FRAP assay. The FRAP values of the sample extracts were significantly higher than Frap value of Trolox (P<0.05); it was revealed that this extract has a high antioxidant activity.
Walnut leaves are considered as a source of health care compounds and have been extensively used in traditional medicine for treatment of venous insufficiency and haemorrhoidal symptomatology. They are used as a medicine for their antidiarrheic, antihelmintic, depurative and astringent properties (1). Also, eratolytic, antifungal, hypoglycaemic, hypotensive, anti-scrofulous and sedative effects have been described (2). Phytochemicals, such as phenolic compounds, are beneficial for human health, decreasing the risk of degenerative diseases by the reduction of oxidative stress and inhibition of macromolecular oxidation (3). It has been shown that they have free radical-scavenging and metalchelating activity in addition to their reported anticarcinogenic properties (4). Phenolics analysis of walnut leave extract was performed by reversed-phase HPLC/DAD and 10 compounds were identified and quantified: 3- and 5-caffeoylquinic acids, 3- and 4-pcoumaroylquinic acids, p-coumaric acid, and flavonoids such as quercetin 3-galactoside, quercetin 3-pentoside derivative, quercetin 3-arabinoside, quercetin 3-xyloside, and quercetin 3-rhamnoside (5). The an ...