Identification and quantification of phenolic compounds in kernels, oil and bagasse pellets of common walnut (Juglans regia L.)

•Quantification of individual phenolics in walnut kernels, bagasse pellets and oils•Assessment of differences in major phenolic groups among walnut products•First report on individual phenolic quantification of walnut pellets/oils•The main polyphenolic subclass comprised hydrolysable tannins.•Glansreginin A and glansreginin B detected in all analyzed walnut products.

Individual phenolic compounds, total phenolic content and antioxidant potential were assessed in kernels, oils and bagasse pellets (residues of oil pressing) of different walnut cultivars. Twenty-seven phenolic compounds were detected in kernels and pellets conducting high-performance liquid chromatography-tandem mass spectrometry. The main polyphenolic subclass comprised hydrolysable tannins, which accounted approximately 60.80% (kernels) and 61.66% (pellets) of the total phenolics identified (TPI). Walnut oil was poor in phenolics and contained only six different compounds but due to their low content (from 0.15 to 1.44 μg g− 1) just two compounds have been identified. Glansreginin A and glansreginin B were detected in all analyzed walnut products. A comparison of average amount of total phenolic content revealed that walnut oil contains as much as 154 fold less phenolics (0.05 mg GAE g− 1 FW) compared to kernels (7.7 mg GAE g− 1 FW) or pellets (7.9 mg GAE g− 1 FW).