Abstract
The present study described the optimization of the extraction process with carbon dioxide in supercritical state for obtaining extractives, especially polyphenols from softwood bark, Norway spruce (Picea abies (L.) Karst.). Using a full 23 factorial design of experiments, the effect of varying the working parameters on the yield of extractives was studied for the following ranges: temperature 40–100 °C, pressure 1050–9000 psi (7.2–62 MPa), and concentration of EtOH/water co-solvent mixture 40–96.6%. In addition, total phenolics content and the antioxidant capacity of the spruce bark extract were determined. The optimum operating conditions for the yield of extractives were identified as 73 °C, 6465 psi (44.5 MPa), and 58% EtOH/water cosolvent concentration for a yield of 8.92%. The optimum conditions for achieving a total phenolics content of 13.89 mg gallic acid equivalent (GAE)/g dry extract were determined as: 45 °C, 1050 psi (7.2 MPa), and 96.6% EtOH/water mixture.
Highlights
Today, the increasing consumption of nonrenewable resources, such as oil, coal, and natural gas, is a worldwide problem
The effects of the selected variables were determined in the following ranges: temperature t = 40–100 ◦ C, cosolvent concentration c = 40–96.6% and pressure p = 1050–9000 psi
The cosolvent concentration had the most significant effect on the yield of extractives, followed by the temperature, while the pressure had a minimal effect on the yield of extractives
Summary
The increasing consumption of nonrenewable resources, such as oil, coal, and natural gas, is a worldwide problem. The supplies of these resources are limited and are expected to run out in a few years. Significant emphasis is placed on maximizing the exploitation of industrial biomass waste, such as tree bark, turning it into value-added products. Tree bark is gaining attention due to its unique composition and content of valuable biochemicals, i.e., extractives, and as an economically and ecologically significant material due its biodegradability, renewability, low cost, and large potential availability [1]. The wood processing industry does not currently use tree bark to its Molecules 2019, 24, 4049; doi:10.3390/molecules24224049 www.mdpi.com/journal/molecules
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