Phenolic Profile and Antioxidant Activity of Fractions of Procyanidin-Rich Hawthorn (Crataegus monogyna Jacq.) Bark Extract Separated by Low-Pressure Liquid Chromatography

Plant materials rich in proanthocyanidins are fractionated to determine the structure of these compounds and relate it to bioactivity. The aim of this study was to fractionate a procyanidin-rich hawthorn bark extract using low-pressure liquid chromatography and to determine the compound profile and antioxidant activity of the obtained fractions. We identified and quantified the phenolics of four fractions (I-IV) separated on a Toyopearl HW-40S column with methanol as the mobile phase, using HPLC-DAD and LC-ESI-MS techniques. The antioxidant activity was determined to comprise ABTS^•+ and DPPH^• scavenging activity, ferric-reducing antioxidant power (FRAP), and inhibition of β-carotene-linoleic acid emulsion oxidation. Characteristic data were subjected to principal component analysis (PCA). Fraction I contained mainly (-)-epicatechin (741.3 mg/g) and a lower amount of flavones and quercetin derivatives (100.7 mg/g). Fraction II was almost pure procyanidin B2, which accounted for 88.8% of the total phenolics. The subsequent fractions were rich in B-type procyanidin dimers, trimers, and tetramers. FRAP and antiradical activity against ABTS^•+ and DPPH^• of the fraction containing low-molecular weight phenolics was lower than those of the fractions with procyanidin oligomers. The antioxidant activity of fractions II-IV ranged from 8.95 to 9.28 and from 6.45 to 6.71 mmol TE/g in the ABTS and DPPH assays, respectively. Their FRAP was in the range of 17.67-21.06 mmol Fe²⁺/g. According to PCA, the procyanidin dimers of fractions II and III were associated with antioxidant activity in these assays. In turn, the procyanidins with the highest degree of polymerization (trimers and tetramers) present in fraction IV were related to the antioxidant activity measured in the β-carotene-linoleic acid emulsion system. Overall, the separation of purified hawthorn bark extract using low-pressure Toyopearl HW-40S column chromatography resulted in a fraction rich in procyanidin B2, as well as fractions containing procyanidins with an increasing degree of polymerization, all with high levels of antioxidant activity under various conditions and the potential for future applications in food, pharmaceuticals, and cosmetics products.