Evaluation of the Degree of Polymerization of the Proanthocyanidins in Cranberry by Molecular Sieving and Characterization of the Low Molecular Weight Fractions by UHPLC-Orbitrap Mass Spectrometry.

Claudio Gardana,Paolo Simonetti

doi:10.3390/molecules24081504

Abstract

4-dimethylammino-cinnamaldehyde (DMAC) assays quantify total proanthocyanidins (PACs) but do not provide qualitative PAC molecular weight distribution information and cannot discriminate between A- and B-type PACs. We developed an efficient method for assessing PAC molecular weight distributions. The PACs from three commercial cranberry extracts (A1–A3) were fractionated by molecular sieves with cut-offs of 3, 10, 30, 50, and 100 kDa, and each fraction was analyzed by DMAC assays. A1, A2, and A3 contained 27%, 33%, and 15% PACs, respectively. Approximately 28 PACs, 20 flavonols, and 15 phenolic acids were identified by UHPLC-DAD-Orbitrap MS in A1 and A3, while A2 contained only flavan-3-ols. Epicatechin was the main monomer in A1 and A3, and catechin was the main in A2. Procyanidin A2 was the main dimer in A1 and A3, representing more than 85% of the total dimers, while it constituted approximately only 24% of A2. A1 and A3 contained quercetin, isorhamnetin, myricetin, and their glycosides, which were totally absent in A2. In A1 and A3 the PACs were mainly distributed in the fractions 30–3 and <3 kDa, while in A2 more than 70% were present in the fraction less than 3 kDa. Overall, obtained data strongly suggests that A2 is not cranberry-derived, or is adulterated with another source of PACs.

Highlights

Cranberry, Vaccinium macrocarpon, has various biological benefits for human health including the prevention of microbial adhesion in urinary tract infections (UTIs) [1], reduction in biofilm formation [2], antioxidant action [3], cholesterol reduction [4], and anticancer effects [5]
Procyanidin A2 was the main dimer in A1 and A3, representing more than 85% of the total dimers, while it constituted approximately only 24% of A2
The use of procyanidin A2 as a standard for the DMAC assay has been shown to underestimate total PACs content compared to cranberry-derived PACs

Summary

Introduction

Vaccinium macrocarpon, has various biological benefits for human health including the prevention of microbial adhesion in urinary tract infections (UTIs) [1], reduction in biofilm formation [2], antioxidant action [3], cholesterol reduction [4], and anticancer effects [5]. Several mechanisms have been proposed for the actions of cranberry in the prevention of UTIs, with attention especially on its interference with bacterial adhesion in the urinary tract [1]. Cranberry has a complex phytochemical composition including mainly flavon-3-ols, anthocyanins, aromatic acid, and monomeric flavan-3-ols together with oligomeric and polymeric proanthocyanidins (PACs), respectively [8]. Cranberry flavon-3-ols occur mainly as glycosylated forms of quercetin, myricetin, and kaempferol, respectively [10], and their total amount in the fruit is in the range of 0.3–0.5 mg/kg [11]

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Results