Abstract
Juglans regia L. (walnut tree) is a recognized source of bioactive compounds with potential health benefits. In this work, hydroethanolic extracts of J. regia leaves were obtained by heat assisted extraction from different Portuguese samples in two phenological stages (green and yellow leaves) aiming to assess the impact of seasonal variations. The samples were compared regarding their phenolic composition and bioactivity. Seventeen phenolic compounds were identified by liquid chromatography combined with a diode array detector and electrospray ionization mass spectrometer (LC-DAD-ESI/MSn): six phenolic acids, ten flavonoids and one tetralone derivative. The green leaves extracts presented a higher amount of total phenolic compounds (29.70 ± 0.03 mg/g extract) compared with the yellow leaves (23.26 ± 0.06 mg/g extract). In particular, yellow samples were richer in flavonoids (17.4 ± 0.2 mg/g extract; mainly quercetin-3-O-glucoside: 3.64 ± 0.01 mg/g extract), while the green ones presented higher phenolic acids content (16.7 ± 0.2 mg/g extract; mainly trans 3-p-coumaroylquinic acid: 6.9 ± 0.5 mg/g extract). Green leaves extract also presented higher antioxidant potential, achieving IC50 values around 32 ± 2 μg/mL and 26.8 ± 0.2 μg/mL for the oxidative haemolysis inhibition and the thiobarbituric acid reactive substances assays, respectively. Furthermore, only green leaves samples showed anti-inflammatory potential. The cytotoxic evaluations revealed similar anti-proliferative action of both extracts against the tumor cell lines tested. Also, an analogous anti-bacterial potential of the extracts was observed, with preferential action against Gram-positive clinical isolated bacteria, with lower minimum inhibitory concentration (MIC) values for Enterococcus faecalis and Listeria monocytogenes (MIC = 2.5 mg/mL). Therefore, the present study suggests the use of walnut leaves as a source of active ingredients without hepatotoxic effects to be used in different applications in the food or pharmaceutical areas.
Highlights
Medicinal plants have been used for centuries by different civilizations as therapeutic agents due to their preventive and curative properties (Tasneem et al, 2019)
The phenolic composition of the extracts of J. regia leaves was assessed for samples in two phenological stages
Peak 2 ([M−H]– at m/z 353) and peaks 3 and 4 ([M−H]– at m/z 337) were assigned as trans 3-O-caffeoylquinic acid and cis and trans 3-p-coumaroylquinic acid, respectively. These assumptions were taken into account, due to the hierarchical fragmentation pattern described by Clifford et al (2003), and by using literature data described by other authors, that identified these compounds in J. regia leaves (Amaral et al, 2004; Santos et al, 2013; Wichtl and Anton, 1999)
Summary
Medicinal plants have been used for centuries by different civilizations as therapeutic agents due to their preventive and curative properties (Tasneem et al, 2019). Juglans regia L. is spread across the globe, being walnut leaves widely used by the folk medicine as antiseptic, antiinflammatory, antidiabetic, anti-helminthic and antidiarrheic agents. They are traditionally used for the treatment of hyperhidrosis, ulcers and dandruff (Carvalho et al, 2010a; Cosmulescu et al, 2014).
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