Antioxidant activities and useful components of Korean Walnut (Juglans sinensis) kernels

Walnut (Juglans sinensis Dode, Juglandaceae) kernels contain high levels of phenolic compounds which show antioxidant properties [1]. The aims of this study were (a) to extract the phenolic fractions from walnut kernels, and to examine their antioxidant potentials, and (b) to determine the total phenolics for evaluating the correlation between antioxidant potential and total phenolics. Walnut kernels were collected from the walnut trees grown in the Korea Forest Research Institute (Suwon). Dried walnut kernels were finely ground, extracted twice with ethanol (EtOH) and then evaporated to give the crude extract. The crude extracts of walnut kernels were successively partitioned with various organic solvents in the order of dichloromethane (DCM), ethyl acetate (EtOAc) and butanol (Bu). From in this study, we could suggest that ethyl acetate fraction has the highest antioxidant and total phenolic content among others. Total phenolics in walnut EtOH extract (WE), DCM fraction (WD), EtOAc fraction (WEA), and Bu fraction (WBu) were 83.9 ± 4.4, 43.6 ± 14.3, 360.4 ± 8.8, and 189.3 ± 19.9 mg/g, respectively, while the free radical scavenging activities of the extract/fractions were 70.5 ± 7.3 (WE), 31.0 ± 6.4 (WD), 90.1 ± 0.5 (WEA), and 90.0 ± 1.3% (WBu) at 100 µg/ml. A linear correlation was also found between free-radical scavenging activity and total phenolics. From the correlation data, we can also conclude that the antioxidant activity of walnut kernels is also closely correlated with the total phenolics.

Keywords: antioxidant activity, vitamin C, Juglans sinensis, walnut kernels.

References:

[1] Diana OL, Maestri DM, Perello M. Matinez ML. Phenolic from Walnut (Juglans regia L.) kernels: Antioxidant activity and interactions with proteins. Food Chem 2008; 107: 607 – 612