Solvent extraction and analysis of phenolic compounds derived from spent sulphite liquor for enhanced succinic acid fermentation

Spent sulphite liquor (SSL), a by-product derived from the acidic sulphite pulping process of Eucalyptus globulus wood chips, is rich in fermentable sugars (mainly xylose) formed during the hydrolysis of hemicellulose. This study focuses on the improvement of succinic acid production via fermentation of sugars contained in SSL. Except sugars, SSL contains several compounds with inhibitory effect on microbial growth and succinic acid production. Low molecular weight phenolic compounds generated from the degradation of lignin have a toxic effect to the microorganisms employed, mainly through loss of membrane integrity. The removal of phenolics from SSL could enhance product yield and final succinic acid concentration. Furthermore, as the crude extracts present antioxidant activity, it is worthwhile to be evaluated as potential co-products for value-added applications.

The aim of this study is the removal and analysis of low molecular weight phenolic compounds from SSL via solvent extraction with ethyl acetate. The total phenolic content of the crude extracts was estimated by the Folin- Ciocalteu colorimetric method and their antioxidant activity by the DPPH• (1,1-diphenyl-2-picrylhydrazyl radical) scavenging method. The qualitative and quantitative determination of the extract was carried out by HPLC analysis. Gallic acid, vanillic acid, syringic acid and syringaldehyde were the predominant phenolic compounds. The pre-treated SSL was used for microbial succinic acid production with two wild-type bacteria strains, i.e. Basfia succiniciproducens and Actinobacillus succinogenes. Experiments were implemented in both Duran bottles and bench-top bioreactors giving an increase of 62% on succinic acid production when pre-treated SSL was used.