Antimicrobial and Antioxidative Activities of the Extracts from Walnut (Juglans regia L.) Green Husk

Abstract

Several studies suggest that regular consumption of walnuts may have beneficial effects against oxidative stress-mediated disease such as cancer. The present study reports the total phenolic and flavonoid contents, together with the antioxidant and antibacterial activities of several solvent extracts (methanol, n-hexane, ethyl acetate, n-butanol, and water) obtained from walnut (Juglans regia L.) green husk. MIC (minimal inhibitory concentration) values of the walnut extracts for 8 human pathogenic bacteria strain were determined using agar dilution method. Antioxidant activity of extracts were assessed using DPPH (1,1-diphenyl-2-picrylhydrazyl) and ABTS (2,2'-azino-bis-(3-ethylbenzothiazoline-6-sulphonic acid)) assays, EC50 of DPPH and ABTS scavenging activities, and determination of total phenolic and flavonoid content and its correlation with DPPH and ABTS scavenging capacities. Among the six extracts, ethyl acetate extract (EtOAc Ex) showed the highest antimicrobial activity at 3.2 mg/ml of MICs against Staphylococcus aureus SG511. Total flavonoids and polyphenol contents of EtOAc Ex were 42.48 mg of quercetin equivalents (QE)/g and 223.25 mg of gallic acid equivalents (GAE)/g respectively. The highest antioxidative potential was shown by the sample extracted with EtOAc Ex (EC50=13.43 μg/ml for DPPH and EC50=41.83 μg/ml for ABTS radical scavenging activity assay). These results showed that J. regia green husk extracts can be used as an easily accessible source of natural antibacterial agents and natural antioxidants.

Traditional Applications, Ethnopharmacology, and Phytochemistry of Walnut Green Husk (Juglans regia L.): A Review

“…The sample extracted with EtOAc had the highest antioxidant potential (EC 50 = 13.43 μg/mL for 1,1diphenyl-2-picrylhydrazyl and EC 50 = 41.83 μg/mL for 2,2'-azinobis-(3-ethylbenzthiazoline-6-sulphonate) radical scavenging activity assay). 29 In addition, some scholars used the common method, reflux method, and ultrasonic method to verify the influence of different extraction methods on the extraction rate of total flavonoid and juglone (1) in WGH. The results showed that the contents of total flavonoid and juglone in the extract obtained by the ultrasonic extraction method were higher than those of the other 2 methods.…”

Effects of Phenolic Compounds on Walnut Bacterial Blight in the Green Husk of Hungarian-Bred Cultivars

“…The nut is surrounded by the green husk that contains many bioactive compounds, such as polyphenols, which include flavonoids, [ 6 , 7 ], also known as phenolics [ 8 , 9 , 10 ], and pectin, glucans [ 5 ] and chlorophyll [ 11 ]. The phytochemicals have antimicrobial, antifungal and antioxidant activities [ 8 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 ].…”

“…The phenolic compounds play an important role in the plant defence mechanisms against stress caused by many environmental factors and various pathogens [ 20 ]. They can inhibit the growth of mycelia and different bacteria up to 50%, but it is indicated that their inhibition effects depend on their concentration and the relationship between the juglone and phenolics present in the plant tissue [ 8 , 12 , 13 , 14 , 15 , 16 , 17 , 18 ].…”