The Antioxidant Activity of Phenolic Compounds Isolated from the Bark of Ryukyu Pine Trees (Pinus luchuensis Mayr.)

Background: Considering that many foreign tourists visit Okinawa, Japan, to purchase cosmetic products, there is an urgent need to create cosmetic products native to Okinawa. As the Ryukyu pine tree, which is endemic to Okinawa, has been used as a source of wood, investigating the possible use of its bark is recommended. Using this natural resource from Okinawa would aid in promoting the products of Okinawa’s unique brands. As a result, this study was designed to isolate useful materials for cosmetic production. Therefore, fractionation was conducted based on a few types of chromatographies, after which the extracted product of the Ryukyu pine tree (Pinus luchuensis Mayr.) bark was analyzed, and its polyphenol contents were compared. Methods: Bark of the Ryukyu pine tree cultivated in the northern mountainous region of the Okinawa Main Island was used for ASE extraction using ultrapure water at 130°C. DIAION HP20 with methanol and two HPLC fractionation types were subsequently used for phenolic compound isolation. Results: ASE extraction and HP20 and HPLC fractionations resulted in an isolation of several compounds: threo-1,2-bis-(4-hydroxy-3-methoxyphenyl)-propane-1,3-diol (compound 1; 0.03% w/w of an ASE extract), erythro-1,2-bis-(4-hydroxy-3-methoxyphenyl)-propane-1,3-diol (compound 2; 0.03% w/w of an ASE extract), catechin (0.11% w/w of an ASE extract), and vanillin (0.31% w/w of an ASE extract). In addition, the value of its antioxidant activity determined by the DPPH (2,2- diphenyl-1-picrylhydrazyl) radical-scavenging capacity assay was 3.3 mmol-trolox eq./g, 2.6 mmol-trolox eq./g, 9.7 mmol-trolox eq./g and 0.7 mmol-trolox eq./g for compound 1, compound 2, catechin, and vanillic acid, respectively. Conclusion: These phenolic compounds possess whitening and anti-aging potentials. Therefore, the Ryukyu pine tree bark would be a useful raw material source for cosmetic production.