Protein precipitation activity of refined proanthocyanidin fractions

Proanthocyanidins (PAs) are plant specialized metabolites, which consist of flavan-3-ol type subunits. PAs possess a variety of bioactivities such as anthelmintic activity against ruminant gastrointestinal nematodes [1], [2]. PAs are found in multiple legume species and thereby they could form a solution to the global problem of ruminant gastrointestinal nematodes [3]. In biological activity studies, PAs have been usually utilized either as plant material or crude extracts and fractions. Usually PA composition of a single plant species can be extremely complicated consisting of even hundreds of compounds with different flavan-3-ol combinations. Thus, the structural complexity of PAs makes the structure–bioactivity linkage examinations challenging.

The aim of this study was to utilize chromatographically refined PA fractions produced from 11 Finnish plant species [4] to study their protein precipitation capacity (PPC) – the most probable mode of action of PAs against nematodes – via novel well plate reader method. The fractionation is illustrated in [Fig 1]. The refined fractions were analysed for their subunit content, polymer size and galloylation by UPLC-MS/MS [5]. The novel well-plate reader method was a turbidimetry based measurement of the insoluble complex formed during the PA–protein interaction. This approach revealed how the PPC of a complex PA mixture is divided in different retention time areas and how the PA subunit content, polymer size and galloylation affect the PPC.

Fig. 1 UPLC-DAD (λ = 280 nm) chromatogram comparison of pre-purified PA fraction (original PA mixture) and refined PA fractions (individual PA fractions).

• References

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