High Value Antioxidants from Softwood Bark and Foliage

In the development of renewable sources of fuels and polymers, the forest industry will continue to be the source of the most abundant natural renewable carbon-rich resource on the planet. The development of efficient extraction and isolation methods could yield large quantities of high-value antioxidants from wood bark and foliage to supplement the fuels and chemicals derived from the hemi-cellulose, cellulose, and lignin in the forestry industry. Current research has focused on new methods of extracting and isolating cellulose, hemi-cellulose, and lignin. While focusing on these biopolymers is important to utilizing the high carbon content of wood, the extractives that make up the secondary metabolites of plants have gained increased interest due to their potent antioxidant activity and represents a new potential source of revenue for the pulp and paper, biorefinery, and timber industries. There are numerous secondary metabolites within tree bark and foliage that were extracted using an accelerated solvent extractor, ASE. Among these secondary metabolites are the stilbene and flavonoid compounds, which are derived through the stilbene and chalcone synthase enzymatic pathway, respectively. Resveratrol and piceatannol, two major stilbene compounds, were identified in black spruce, Norway spruce, white spruce, red spruce, and Eastern white pine bark and foliage and were quantified for the first time using HPLC-UV-MS and GC-MS techniques. Resveratrol has shown the ability to increase the lifespan in some model species and may be a high-value extractive. Relatively high concentrations of resveratrol (350-600 ppm) and piceatannol (400-650 ppm) were found in spruce bark. This concentration of resveratrol was equal to the values reported for Japanese knotweed (the main commercial source of resveratrol) and was up to 10-100 times more concentrated than grapes, wine, cocoa, peanuts, and blueberries. Catechin, epicatechin, and quercetion (flavonoid compounds) were also identified and quantified in spruce, pine, and fir species with white spruce bark containing the most abundant source of catechin (3600 ± 100 ppm). Bark, which is currently burned as wood fuel in pulp processing, may be a good source of high-value chemicals and antioxidants. Spruce bark, in particular, shows promise for its high stilbene and flavonoid content. The antioxidant potential of these species (tamarack, balsam fir, Eastern white pine, red pine, black spruce, Norway spruce, white spruce, and red spruce), which are important to the Maine forest industry, were all tested through various colorimetric assays based on food and beverage procedures (Folin-Ciocalteu's total phenolic assay, B-carotene bleaching assay, DPPH free radical scavenging assay) and showed greater antioxidant activity than most vegetables and fruits reported in the literature. The use of bark and foliage extracts as functional food additives would enable the forestry industry to enter a market that has shown 10-15% growth per year over that last decade and provide additional revenues to support the continued progress of a complete "biorefinery".