From UPLC-Q-TOF-MS/MS profiling to functional insights: Bound phenolics dominate antioxidant and α-glucosidase inhibitory activities in five Chinese jujube varieties

Jujube fruits are recognized for their significant medicinal value, which varies according to their varieties and geographical origin. However, the specific contributions of individual bioactive compounds to antioxidant and antidiabetic activities in certain cultivars remain unclear. Therefore, this study examined the structural properties of the free (FF), bound (BF), and esterified (EF) fractions, along with their antioxidant and antidiabetic activities, in five Chinese jujube cultivars. Our results demonstrated that the BF fraction had significantly higher (p < 0.05) levels of total phenols, flavonoids, and alkaloids as well as antioxidant activities (FRAP, DPPH, ABTS, H₂O₂, and O₂^- assays) compared with FF and EF, whereas the FF fraction exhibited the highest total triterpenoid content.Among the five jujube cultivars and their respective fractions, Ban Zao and Po Zao showed the highest phenolic content and strongest antioxidant capacity. A similar trend was observed for α-glucosidase (α-Glu) inhibition, with the BF fraction showing the strongest activity, particularly in fractions prepared from Ban Zao and Po Zao varieties. The antioxidant and antidiabetic activities were further supported by Pearson correlation analysis, indicating a strong positive relationship between phenolics content and their bioactivity. UPLC-Q-TOF-MS/MS analysis revealed a total of 88 compounds across the three fractions (FF, EF, and BF), including five flavonoids, two alkaloids, and six triterpenoids that were reported for the first time. The antidiabetic activities of key compounds were evaluated through in silico analysis, which demonstrated strong binding affinities to the α-Glu active site, particularly for flavonoids. This study highlights the strong antioxidant and α-Glu inhibitory activities of the bound compounds found in Chinese jujube varieties, particularly Ban Zao and Po Zao varieties, emphasizing their potential as valuable sources of natural antioxidants and promising functional food ingredients.