Pine Bark as a Potential Source of Condensed Tannin: Analysis through Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), and Energy Dispersive X-ray (EDX)

Abstract

This study aimed to evaluate the tannin content in the bark of five pine species from a forest harvesting area of the Ixtlán de Juárez community, Oaxaca, México. The species studied were Pinus patula, Pinus ayacahuite, Pinus rudis, Pinus douglasiana, Pinus pseudostrobus. The bark samples were subjected to a drying, grinding, and sieving process. These compounds were extracted using two methods: by constant reflux with ethanol for three hours or in a water bath with distilled water for two hours. The percentage of total extract, Stiasny number, and condensed tannins were quantified. The quantitative number of condensed tannins present in the bark for each of the five species studied ranged from 0.65% to 5.14% for the ethanolic extracts and 0.14% to 1.46% for the aqueous extracts. Analysis by Fourier transform infrared spectroscopy (FTIR) identified polyphenolic compounds and functional groups characteristic of tannins. Analysis by scanning electron microscopy (SEM) and X-ray dispersive spectroscopy (EDX) provided the elemental analysis and chemical composition of the tannin extracts, respectively, finding trace elements of silver, cadmium, phosphorus, iodine, and sulfur, which are minerals present in the soil, meaning that through processes of micronutrient absorption, these can interact with the tannins or polyphenols in the barks of the tree species being studied. The results indicate that the bark of P. patula and P. ayacahuite have a higher concentration of condensed tannins, 5.14% and 4.71%, respectively, in the ethanol extraction, and may be susceptible to exploitation due to the amount of bark generated in forestry activities.