resumo
In Portugal, the cork and the pulp and paper industries are important economic sectors, however, generating substantial amounts of by-products. These byproducts could be exploited in added value applications, rather than being simply burned for energy production, as, for example, as a source of the valuable phenolic compounds. These compounds are known by their innumerous properties, as antioxidant, anti-inflammatory or even antithrombotic. In this study, the phenolic fractions of the most abundant cork and pulp industrial residues were characterised in detail, aiming at up-grading them. The phenolic fraction of the barks of Eucalyptus globulus, E. grandis, E. urograndis and E. maidenii as well as the cork from Quercus suber and the residues of its exploitation, namely, cork powder and black condensates, were obtained by conventional solid-liquid extractions. In the case of E. globulus bark, the potential application of green methodologies in the extraction of phenolic compounds was also evaluated, by using supercritical CO2 extraction. This approach was optimized by using surface response methodology. High-performance liquid chromatography coupled with mass spectrometry techniques were used in the identification and quantification of phenolic compounds. The total phenolic content was also accessed by the Folin- Ciocalteu method, mainly for comparative purposes. The characterization of the phenolic fraction of each extract was also complemented with antioxidant activity measurements, by using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging. Thirty phenolic compounds were identified as constituents of E. globulus bark, 17 of them referenced for the first time, namely, quinic, dihydroxyphenylacetic, and caffeic acids, bis-hexahydroxydiphenoyl(HHDP)-glucose, galloyl-bis- HHDP-glucose, galloyl-HHDP-glucose, isorhamentin-hexoside, quercetinhexoside, methyl-ellagic acid, methyl-ellagic acid (EA)-pentoside, myricetinrhamnoside, isorhamnetin-rhamnoside, mearnsetin, phloridzin, mearnsetinhexoside, luteolin and a proanthocyanidin B-type dimer. The phenolic composition of E. grandis, E. urograndis and E. maidenii bark was studied in this work for the first time. Thirteen, twelve and twenty four phenolic compounds were identified in E. grandis, E. urograndis and E. maidenii bark extracts, respectively. These compounds include quinic gallic, protocatechuic, chlorogenic and ellagic acids, methyl gallate, catechin, galloyl-bis-HHDPglucose, digalloylglucose, epicatechin, quercetin-glucuronide, dihydroxyisopropylchromone- hexoside, isorhamnetin-hexoside, ellagic acid-rhamnoside, taxifolin, quercetin-hexoside, dihydroxy-(methylpropyl)isopropylchromonehexoside, methyl-ellagic acid-pentoside, myricetin-rhamnoside, isorhamnetinrhamnoside, aromadendrin-rhamnoside, mearnsetin, mearnsetin-hexoside, eriodictyol, quercetin, isorhamnetin and naringenin. The analysis of the phenolic fraction of cork allowed to identify twenty two phenolic compounds, ten of them reported for the first times as its constituents, namely, quinic, salicylic and p-hydroxyphenyl-lactic acids, eriodictyol, naringenin, methyl gallate, brevifolin carboxylic acid, caffeic acid isoprenyl ester, isorhamnetin-rhamnoside and isorhamnetin. It were identified sixteen phenolic compounds in industrial cork powder, namely, quinic, gallic, protocatechuic, caffeic, ferulic and ellagic acids and methyl gallate, esculetin, brevifolin carboxylic acid, coniferaldehyde, caffeic acid isoprenyl ester, valoneic acid dilactone, ellagic acid-pentoside, ellagic acid-rhamnoside, isorhamnetinrhamnoside and isorhamnetin. From these, only ellagic acid was previously reported as constituent of cork powder. Likewise, thirteen phenolic compounds were identified on black condensate, twelve of them for the first time, namely quinic, gallic, p-hydroxyphenyl-lactic, protocatechuic, p-coumaric, caffeic and ellagic acids and vanillin, esculetin, coniferaldehyde, caffeic acid isoprenyl ester and eriodictyol. The supercritical extraction of phenolic compounds from E. globulus bark allowed to verify the parameters affecting the qualitatively and quantitatively the final extracts. The optimal conditions of those parameters were obtained. This technique showed to be selective to restrict classes of compounds, such as flavanones and O-methylated flavonols. This was also the first study involving the evaluation of the antioxidant activity of the phenolic extracts of E. grandis, E. urograndis and E. maidenii bark as well as of cork and the residues of their exploitation. The vast range of phenolic compounds identified in each vegetal source studied, as well as its outstanding antioxidant activities, all in the same range of the well known commercial antioxidant ascorbic acid, are, clearly, a contribute to the up-grading of these industrial by-products.
categoria
Química Fenóis Produtos florestais: Portugal Indústria da cortiça: Subprodutos Indústria do papel: Subprodutos
autores
Sónia Andreia Oliveira Santos
nossos autores
Sónia Andreia Oliveira Santos
Investigador Auxiliarorientadores
Carlos Pascoal Neto; Armando Jorge Domingues Silvestre