Alkaline extraction of polyphenols for valorization of industrial spruce bark
Marc Borrega, Anna Kalliola, Marjo Määttänen, Anna S. Borisova, Atte Mikkelson, Tarja Tamminen
Abstract
Industrial spruce bark is an abundant side-stream from forest industries that contains tannins and other phenolic compounds that can be exploited in a variety of applications. In this study, alkaline extractions of spruce bark conducted under a wide range of process conditions showed that 20–27 % of the bark could be extracted as polyphenols, mainly tannins and some lignin. The polyphenols in alkaline extracts from two selected scale-up extractions, conducted at 100 °C with 15 % NaOH and at 160 °C with 24 % NaOH, were then recovered by acidic precipitation and tested as surfactants. Despite their different composition, the polyphenol-rich precipitates showed similar surface activity than a commercial biosurfactant, and were also soluble under neutral conditions. Moreover, sugar yields above 80 % could be obtained by enzymatic saccharification of the extracted bark residues. These results demonstrated that alkaline extraction is a promising technology for valorization of industrial bark side-streams.