Oak barks as raw materials for the extraction of polyphenols for the chemical and pharmaceutical sectors: A regional case study

• Valorization of a regional abundant wood side-products for the second generation biorefinery and the production of pharmaceutical molecules.
• Impact of the storage conditions on the chemical composition and the ease of extraction of polyphenolic compounds.
• Impact of the growth of the tree on the chemical composition.
• Answer to the basic question: for the pharmaceutical sector, what is the optimum age of a tree yielding a maximum of polyphenols?

Despite their potential for chemical recycling, residues from forest harvesting and wood processing are mostly used for industrial applications with low added value (energy, paper pulp, and panels). Bark of both oak species, Quercus robur L. 1753, Quercus petraea (Matt.) Liebl. 1784 is a by-product from sawmill and pulp mill activities. Bark is mainly used as a fuel for the same wood plants. The aim of this study is to look at the feasibility of enhancing the value of this material through the extraction of bioactive molecules, such as polyphenols (i.e. catechin, gallic, and ellagic acids). First, the effect of industrial storage of logs and bark on their polyphenol content was explored. Then, referring to the selection of tan oaks in the past, the question of an optimum harvesting age is addressed in order to maximize the polyphenol content of the barks. In the end, molecular diversity of bark is examined through the identification of molecules of interest, using different chromatographic analyses. The results show an effect of the industrial context and an effect of the raw material age on the chemical properties of the bark. First investigations also highlight molecules of interest and the molecular diversity, which needs to be further explored.