Oligomeric proanthocyanidins (OPC) rich extracts (OPCEs) were isolated by sequential extraction from the bark of the deciduous trees grey alder (Alnus incana), black alder (Alnus glutinosa) and goat willow (Salix caprea). The yields of OPCE from all barks under study were rather similar and varied between 12.3% and 15.4% based on the oven dry (o.d.) bark. Content of proanthocyanidins in OPCEs ranged from 16.6% to 25% based on o.d. extract. The OPCEs were characterised by means of antioxidant activity with ABTS˙+ and DPPH˙ radical scavenging tests. All extracts being introduced into lipid-based substrates, i.e. mayonnaise and a basic composition of a cosmetic cream, showed antioxidant activity comparable to the reference commercial antioxidant tert-butylhydroquinone (TBHQ). The results of in vitro tests have revealed that the OPCEs could be useful for the human organism as they activated malfunctions of amylase, inhibited pancreatic lipase activity (duodenal digestion model), decreased lipid absorption in blood and decreased pyruvate level in blood plasma essential for regulation of carbohydrate metabolism. The data obtained confirms the advantages of OPC and OPCEs applications as an antioxidant additive for food, cosmetic and health industries.
The antioxidant activities (AoAs) of 50 different technical lignins have been determined. The lignins of various botanical origins (annual plants, coniferous trees, and deciduous trees) were isolated and fractionated by different techniques (delignification by alkali, kraft process, fast pyrolysis, and hydrolysis). The structure and the functionality of lignins were characterized by functional group analyses (phenolic OH, carboxyl, and methoxyl groups), analytical pyrolysis pyrolysis/gas chromatography/mass spectrometry/flame ionization detector (Py-GC/MS/FID), electron paramagnetic resonance, size exclusion chromatography, and titrimetric methods, and the AoAs were evaluated as the capacity to scavenge the DPPH· and ABTS·+ free radicals. The relationship between the lignin structure and the AoA was characterized by pair correlation, partial correlation, and multivariate regression analyses, including correlated components regression. The results were compared with those of lignin model compounds and low molecular weight phenylpropanoids. It has been shown that molecular weight does not influence essentially the AoA of lignins. There is a relationship between the activities of low and high molecular weight polyphenols; their mechanisms of action are also similar. The structure-related AoA of lignins has been quantified for the first time.