Influence of extraction conditions on phenolic yields from pine bark: assessment of procyanidins polymerization degree by thiolysis

Pinus pinaster extract is a polyphenol-rich food supplement containing diverse types of flavonoids. The latter are known to have strong antiradical activity and thus different beneficial effects on human health. A 23 experimental design was performed to study the effect of temperature, contact time and liquid–solid ratio on the ethanol extraction efficiency. High values of phenol yields (17.0 ± 0.00 eq. g gallic acid/l) and antiradical activity (85.6 ± 3.94 DPPH inhibition percentage) were detected at 50 °C (values varied between 25 and 50 °C), at 90 min (between 30 and 90 min) and at a 5:1 liquid–solid ratio (between 5:1 and 10:1). A subsequent HPLC analysis allowed identification of the phenols occurring in the extracts. Previously, an aqueous extract (A), and another one soluble in both water and ethyl acetate (OW), were obtained after fractionation and subjection to thiolysis. The main monophenols detected were catechin > epicatechin in the A fraction and dihydroquercetin > catechin > epicatechin in the OW one. In the former fraction, the average degree of polymerization (DPn¯) of procyanidins was 7.0, while only oligomer phenols with DPn¯=3.0 were found in the OW fraction.