Chemical composition and in vitro antibacterial activity of bark extractives and suberin monomers from Pinus brutia and Pinus nigra

In this study, the structure and amount of lipophilic and hydrophilic extractives were determined in the bark of Pinus brutia and Pinus nigra, which is considered as a waste material. Bark samples were extracted first with hexane for lipophilic extractives, and then with acetone:water (95:5, v:v) and methanol:water (4:1, v:v) for the hydrophilics. Furthermore, the structure and the amount of suberin monomers were determined by alkaline hydrolysis from extractive-free bark samples. The hexane extracts of both P. brutia (15.48 mg/g) and P. nigra (15.69 mg/g) were found to be similar. However, the results of acetone:water (119.47 mg/g) and methanol:water (242.12 mg/g) of P. brutia bark were remarkably higher than P. nigra. Resin and fatty acids in lipophilic extractives, sugars and phenolics in hydrophilic extractives were determined as main component groups. In the suberin monomers, fatty acids and dioic acids were the major groups. In these groups, acid 14:0 (4.04 mg/g in P. brutia), acid 22:0 (6.27 mg/g in P. nigra) and acid 1,18-dioic-18:1 were found to be the most abundant compounds. Anti-bacterial tests were carried out by using Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) strains with agar well diffusion method. In addition, the minimum inhibitory concentrations (MICs) of the extracts were also determined by using the micro-dilution method. It was determined that hexane extracts and suberin monomers had no antibacterial effect, while acetone:water (20.0 mm. in P. brutia and 15.7 mm. in P. nigra) extracts of both species had high inhibition zone on S. aureus. The minimum inhibitory concentration of these extracts ranged from 6.25 to 15 mg/ml.