Identification and quantification of free, esterified, glycosylated and insoluble-bound phenolic compounds in hawthorn berry fruit (Crataegus pinnatifida) and antioxidant activity evaluation

For the first time, characteristics of free (FPCs), soluble esterified-bound (SEBPCs), soluble glycosylated-bound (SGBPCs) and insoluble-bound (ISBPCs) phenolic compounds in Chinese organic hawthorn berry (Crataegus pinnatifida) were investigated along with antioxidant activity. A total of 22 phenolics were identified and quantified by HPLC-ESI-MS/MS, with the most abundant being (−)-epicatechin (750 ± 4 μg/g dw)>procyanidin B2 (375 ± 3 μg/g dw)>(+)-catechin (305 ± 5 μg/g dw)>chlorogenic acid (256 ± 4 μg/g dw). Overall, flavonoids were the predominant phenolic sub-class in FPCs, ISBPCs and SEBPCs, whereas SGBPCs mostly existed as phenolic acids. In addition, more than 85.0% of procyanidins were found in FPCs, and no procyanidins were presented in SGBPCs. (+)-Catechin, (−)-epicatechin and protocatechuic acid were the main phenolics in ISBPCs, FPCs/SEBPCs and SGBPCs, respectively. 35.3–37.8% of antioxidant activity in hawthorn berry were contributed by FPCs, followed by ISBPCs (25.0–27.0%)>SEBPCs (23.4–25.7%)>SGBPCs (9.4–15.7%), and significant positive correlations were observed between phenolics and antioxidant activity. Interestingly, antioxidant activity of ISBPCs in peel (103 ± 2–125 ± 4 μmol Trolox/g dw) was significantly higher compared to pulp (61.3 ± 1.3–67.3 ± 1.4 μmol Trolox/g dw) as well as phenolics (1000 ± 35>368 ± 29 μg/g dw). The outcomes would help to provide better understanding of the functional activities of hawthorn berry and help utilize the advantage of this “medicine food homology” fruit for the application in food and pharmaceutical industries.