Discovery and Characterization of Antioxidant Compounds in the Pericarp and Seed Byproducts of Different Litchi (Litchi chinensis Sonn.) Fruits.

Abstract

The processing of litchi (Litchi chinensis Sonn.) fruits generates substantial amounts of pericarp and seed by-products, which are candidate sources of antioxidant compounds but are underutilized. This study systematically investigated the total phenolic content (TPC) and in vitro antioxidant capacities (FRAP, ABTS, and DPPH values) of pericarp and seed extracts across eight commercial litchi cultivars. Qualitative LC-MS-based phytochemical profiling was further performed on the representative 'Bingli' cultivar. The results indicated that litchi seeds consistently exhibited significantly higher TPC and antioxidant activities compared to pericarps. Among the tested pericarps, the 'Nuomici' cultivar showed the highest TPC (10.29 ± 0.10 mg GAE/g dw) and antioxidant capacities. The 'Bingli' cultivar demonstrated the highest overall antioxidant activity among seeds (e.g., TPC of 33.92 ± 1.75 mg GAE/g dw and FRAP of 373.06 ± 4.64 μmol Fe(II)/g dw). LC-MS-based qualitative screening tentatively annotated several hydroxycinnamic acids and A-type procyanidins as putative phenolic constituents of the 'Bingli' litchi pericarp and seed extracts. Subsequent targeted HPLC analysis determined the concentrations of Procyanidin A2, revealing that it had a high concentration in the 'Xianjinfeng' and 'Bingli' seeds (1298.73 ± 54.87 and 1127.81 ± 67.22 μg/g dw, respectively). These findings indicate cultivar- and tissue-specific variations in litchi fruit by-products and suggest that the seeds of 'Bingli' and 'Xianjinfeng' are candidate sources of antioxidant phenolics for further investigation, pending validation in food models or biological systems.