Abstract
The antioxidant activity of the phenolic compounds present in industrial black liquors obtained from the two cooking processes (kraft and sulphite) used in Portugal to produce Eucalyptus globulus pulp was evaluated. The black liquors treated at several pH values were extracted with ethyl acetate. Phenolic fractions were further separated by liquid chromatography of the crude extracts of kraft liquor at pH = 6 and sulphite liquor at the original pH. Total phenolic content was determined in terms of gallic acid equivalents (Folin-Ciocalteu colorimetric method), and the antioxidant activity in the crude extracts at several pH values and in the separated fractions was measured using the DPPH test for radical scavenging capacity. The total phenolic content of crude extracts and separated fractions ranged from 92.7 to 181.6 and from 91.6 to 1,099.6 mg GAE/g, respectively, while the antioxidant activity index (AAI) ranged from 2.20 to 3.41 and from 2.21 to 11.47 respectively, showing very strong antioxidant activity in all studied cases. The fractions separated by column chromatography were submitted to mass spectrometry analysis and the results were compared to others in the literature of natural products, mainly from Eucalyptus, and the characteristic bands of functional groups were identified by 1H-NMR and FTIR. These methods allowed the identification of 17 phenolic compounds.
Highlights
Chemical pulping refers to the most often used processes to produce paper pulp and is based on the principle of lignin dissolution, enabling the liberation of fibers from the wood matrix
Both crude and separated fractions were analyzed in terms of gallic acid equivalents by the Folin-Ciocalteu method [21]; respective antioxidant activity index (AAI) were determined by the 2,2-diphenyl-1-picrylhydrazyl method proposed by Scherer and Godoy [22]
Considering that both delignification methods give rise to polysaccharide depolymerisation and that some sugars can remain after the ethyl acetate extractions performed and interfere with the determination by reducing the Folin-Ciocalteu reaction mixture, these figures only intend to provide a relative number for comparison between the two cooking processes
Summary
Chemical pulping refers to the most often used processes to produce paper pulp and is based on the principle of lignin dissolution, enabling the liberation of fibers from the wood matrix. Black liquors from the cooking process in kraft and sulphite pulp mills contain chemicals and dissolved wood substances. Phenols derived from biomass oils are valuable and useful chemicals They have some pharmacological properties and could have an inhibitor effect on the expression of HIV-1 gene [3]. Natural antioxidants may be used to preserve food from lipid peroxidation and oxidative damage occurring in living systems Their action in oil rancidity retardation or inhibition is noticed and assumes an industrial important role. The crude extracts were subjected to liquid column chromatography using 10%chloroform/ethyl acetate as eluent Both crude and separated fractions were analyzed in terms of gallic acid equivalents by the Folin-Ciocalteu method [21]; respective antioxidant activity index (AAI) were determined by the 2,2-diphenyl-1-picrylhydrazyl method proposed by Scherer and Godoy [22]. The separated fractions were characterized by 1H-NMR, mass and infrared spectroscopy
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