Exploring overlooked non-extractable phenolics in pecan nut residues through an LC-MS-based approach

This is the first study to report bound (non-extractable) phenolic compounds (NEP) in pecan nut processing residue (PPR), a source of bioactive compounds. NEP constitutes a significant fraction of total phenolics in plants and contributes to health-related effects yet remains underexplored. Previous studies on PPR focused on the extractable fraction (EP), reporting about 35 phenolic compounds and associated bioactive properties. Using LC-MS/MS, we annotated 61 phenolic compounds (Levels 1-3), including the first reported tetramers and pentamers of condensed tannins in PPR. NEP accounts for 30% of total phenolics and is enriched in condensed tannins (approximately 50% of its profile), contrasting with the phenolic acid-dominated EP. Notably, NEP exhibits 2.8-fold higher specific antioxidant activity, demonstrating that bound phenolics disproportionately contribute to PPR antioxidant capacity. These findings advance understanding of PPR's phenolic composition and support its valorization as a functional ingredient for food and health applications.