Composition, antioxidants content and antioxidant activity of walnut residues, a by-product of oil extraction in China

As by-products of walnut (Juglans regia L.) oil production, walnut residues are rich in polyphenols. The antioxidants content and antioxidant activities of walnut residues, which were obtained from three regions of China, were investigated in this study. Moreover, the correlation between polyphenols content and their antioxidant activities were analysed. The results showed that, for each walnut residue ethanolic extracts (WREE), there was a positive correlation between total polyphenols and antioxidant activity. Additionally, walnut residue ethanolic extracts from Xinjiang province (WREE-XJ) with the highest total polyphenols content possessed the highest antioxidant activity, which further de monstrated that polyphenols contributed to the antioxidant activity of the extracts. Furthermore, high resolution mass spectrometry was used to study the polyphenol composition of WREE-XJ. Results showed that the majority of WREE-XJ phenolics were procyanidins, gallic acids, ellagic acids, quercetin and their corresponding carbonyl compounds (glycosides).