Proanthocyanidin-rich extract from Pinus radiata bark: Mild-alkaline extraction and characterization

Abstract

This study assessed the efficacy of mild-alkaline extraction from P. radiata bark in obtaining proanthocyanidin (PA)-rich extracts. When the bark was treated with three types of bases—Na2CO3, NaHCO3, and NaOH—at varying concentrations, the extract yields increased with higher concentrations. When the pH of the extracts exceeded 7, the PA content and antioxidant activity were remarkably reduced. This result suggests that the pH holds a greater effect in the alkaline extraction of the bark rather than the type of base used. Among the bases used, NaHCO3 was selected and the extraction conditions of pine bark were examined at a concentration where the pH of the extract did not exceed 7. The extraction time during mild-alkaline extraction using 0.2% NaHCO3 was reduced compared to water-only extraction at the same temperature. Moreover, the extract yields were over 10% higher than those of water extraction, and the dried extracts exhibited good solubility in water. The mild-alkaline extracts were characterized using FT-IR and 13C NMR spectroscopic techniques, and acidic alcoholysis. Analyses of the spectra of the mild-alkaline extracts showed similarities to that of pure PA and hot water extract. This result indicated that PA in the bark was not significantly affected during mild-alkaline extraction.