Identification and quantification of the major phenolic constituents in Juglans regia L. peeled kernels and pellicles, using HPLC-MS/MS

Abstract

This study was designed to identify and quantify the major phenolic constituents in peeled kernel and pellicle of the walnut Juglans regia L. Data were compared across six different cultivars: 'Fernor', 'Fernette', 'Franquette', 'Sava', 'Krka' and 'Rubina'. High-performance liquid chromatography coupled with mass spectrometry was used to identify and quantify these compounds. Nineteen ellagitanins, 12 ellagic acid derivatives, 4 anthocyanins and 5 other phenols were identified in the pellicle of these walnuts, and 15 dicarboxylic acid derivatives and 1 phenol in the peeled walnut kernels. Thirteen previously unreported compounds were identified in the peeled walnut kernels, and 14 in the walnut pellicle. Hydrolysable tannins were the main phenolic compounds identified in the walnut kernels, and accounted for 31.0% to 35.1% of the total phenolics analysed. The highest intake of total phenolics content per walnut kernel can be obtained by consumption of 'Franquette' and 'Rubina', with the lowest for 'Krka'.

Keywords: Juglans regia L.; Peeled kernel; Pellicle; Phenolic compounds; Tannins.