Digestive Characteristics and Stability of Walnut Polyphenols From Diaphragma juglandis Fructus, Walnut Pellicle, and Flowers of Juglans regia

This study investigated the ultrasound‐assisted extraction of polyphenols from three sources: Diaphragma juglandis fructus (DJF), walnut pellicle (WP), and flowers of Juglans regia (FJR). Initially, we assessed the transformation of walnut polyphenols through simulated gastric and gastrointestinal digestion using in vitro models. Then, we examined the stability of walnut polyphenols under various storage conditions and in the presence of exogenous additives. Our findings indicated that digestive enzymes facilitated the hydrolysis of tannins and the release of bound polyphenols, thereby increasing the polyphenol content in the extracts and enhancing their antioxidant potential. However, after exposure to intestinal fluid, the phenol content decreased significantly under the influence of bile, enzymes, and pH changes, which was correlated with a reduction in antioxidant capacity. Furthermore, walnut polyphenols exhibited robust thermal stability and were more suitable for dark storage in neutral environment with a neutral pH (3–7) and lower temperature. It can be speculated that oxidants, stabilizers, and metal ions may affect the stability of polyphenols. Overall, our study provides valuable insights into enhancing the bioavailability of walnut polyphenols and offers practical guidance for optimizing their processing and storage conditions.