Comparative analytical and antioxidant activity studies on a series of<i>Fagus sylvatica</i>L. leaves extracts

Abstract

This paper was aimed at analytical and antioxidant activity studies on a series of European beech (Fagus sylvatica L.) leaves extracts in order to select the most proper period of raw material harvesting and corresponding technological approach in the final purpose of obtaining some extracts with high antioxidant effect useful as new, industrial material protecting products. Thus, comparative thinlayer liquid chromatography (TLC) studies on five series of (70%) ethanol macerates (tinctures), corresponding to the five periods of beech leaves harvesting (May–July–September–early October–late October) revealed caffeic acid (chlorogenic acid isomers), apigenin, kaempferol, quercetin, and catechin derivates as being the common polyphenolic species; it must be mentioned that while spring leaves revealed the dominance of one major kaempferol diglycoside and only traces of chlorogenic acid and apigenin derivates, summer to early autumn leaves have shown the abundance of chlorogenic acid isomers and an increasing number of apigenin derivates, as well as the appearing of one new major kaempferol mono-glycoside; different, autumn late leaves emphasized the decline of chlorogenic acid isomers versus the augmentation of summer apigenin derivates, as of two quercetin and catechin derivates, visualized only as traces in summer to early autumn samples. Further, quantitative assays indicated total phenols contents (expressed as gallic acid equivalents/GAE) of 7.04–11.61–33.55–9.40–5.81 mg g−1 GAE and total flavonoids contents (expressed as rutin equivalents/RE) of 12.40–9.02–5.71–2.22–2.19 mg g−1 RE; among flavonoids, kaempferol glycosides levels of 2.92–2.01–1.38–0.52–0.17 mg g−1 were estimated (mean values). Once established September time as the most suitable period for leaves harvesting, antioxidant activity (AA) assessments of the subsequently beech leaves hot (70%) ethanol extracts indicated polar extracts as being moderate to augmented antioxidant products (49% ≤ AA ≤ 96%); differently, non-polar extracts indicated an augmented pro-oxidant effect (AA = −71%). The obtained results formed the foundation of new, anti-scale/anti-corrosion products based on beech leaves extracts.