Deep eutectic solvent extraction and AB-8 resin adsorption for rambutan shell polyphenol: Profiling and bioactivity...

Rambutan shell, a major agro-industrial by-product, is a promising source of bioactive polyphenols. This study aimed to optimize polyphenol extraction from the rambutan shell of Baoyan NO.7 (BY-7) using deep eutectic solvent (DES) and to purify the extract with AB-8 resin. The adsorption mechanism was elucidated, and the polyphenol profile was characterized via next-generation metabolomics (NGM). The optimized extract showed high total phenolic (178.89 mg GAE/g), flavonoid (152.93 mg RE/g), and proanthocyanidin (41.89 mg CE/g) contents, along with potent antioxidant (DPPH: 7061.49, FRAP: 6925.34 μmol TE/g) and anti-glycemic activities (α-amylase IC₅₀: 2.62 mg/mL; α-glucosidase IC₅₀: 70.78 μg/mL). Adsorption followed Langmuir and pseudo-second-order kinetic models, indicating a spontaneous process. To the best of our knowledge, proanthocyanidin B1 was identified in the rambutan shell of BY-7 for the first time. Significant correlations were found between 11 polyphenols and the bioactivities. This work provides a theoretical foundation for valorizing rambutan shell resources.