Conductometric Determination of Phenolic Groups in Mixtures Such as Isolated Lignins

Sarkanen, K. V.; Schuerch, Conrad

doi:10.1021/ac60104a011

Cited by 30 publications

(6 citation statements)

References 31 publications

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“…O teor de OH fenólicos e carboxílicos foram determinados por titulação condutivimétrica (SARKANEN; SCHUERCH, 1955;ZAKIS, 1994). Cerca de 0,200 g de amostras foram solubilizadas em água (30,00 mL).…”

Section: Determinação De Oh Fenólicos E Carboxílicosunclassified

Análise de compostos bioativos, grupos ácidos e da atividade antioxidante do café arábica (Coffea arabica) do cerrado e de seus grãos defeituosos (PVA) submetidos a diferentes torras

Morais¹,

Aquino²,

Nascimento³

et al. 2008

Ciênc. Tecnol. Aliment.

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O Brasil apresenta um parque cafeeiro complexo e diversificado, dispõe de grandes extensões de terra de diferentes altitudes e produz, conseqüentemente, uma grande variedade de tipos de bebidas, o que o favorece em relação aos outros países concorrentes. Além disso, o País lidera o processo de desenvolvimento tecnológico, com destaque para a irrigação, fertirrigação e mecanização NAKAZONE, 2004). Na produção do café arábica, o Brasil de destaca por possuir o menor custo de produção e alta produtividade, o que lhe garante a competitividade no mercado internacional. AbstractThis work reports the results of the investigation of bioactive compounds (chlorogenic acids, trigonelline, caffeine, total phenolics, and proanthocyanidins), total acid groups, and the antioxidant activity of the Arabian coffee (Coffea arabica) from the Brazilian cerrado (vast tropical savannah) (Minas Gerais state) and its defective beans (Black, green, and sour beans). The samples were prepared using three roasting degrees: light (180 ± 10 °C; 6,0 ± 1,0 minutes), medium (180 ± 10 °C; 8,0 ± 1,0 minutos), and dark (180 ± 10 °C; 10,0 ± 1,0 minutes). Considering the average of the three roasts per coffee and defective beans, the difference observed for the content of all constituents listed above was not significant (p > 0,05). Exceptions are the content of acid hydroxyl groups, which were slightly greater in the coffee defective beans and the content of caffeine, calculated using the semi-quantitative method, which was higher in the coffee itself. Both the coffee and its defective beans presented scavenging activity against DPPH . radical; however, the coffee antioxidant activity was always higher. The variations observed in the content of caffeine, total phenols, proanthocyanidins, phenolic acid groups, trigonelline, and chlorogenic acid levels can not explain the higher antioxidant activity observed for the medium roasted coffee (EC50 of 2,3 mg.mg -1 of DPPH . ). Keywords: DPPH . ; EC50; savannah coffee; roasted coffee. ResumoO presente trabalho estudou os compostos bioativos (ácidos clorogênicos, trigonelina, cafeína, fenóis totais e proantocianidinas), grupos hidroxila ácidos e atividade antioxidante de um café arábica proveniente do Cerrado Mineiro e de seu PVA (grãos pretos, verdes e ardidos). As amostras foram preparadas nas torras clara (180 ± 10 °C; 6,0 ± 1,0 minutos), média (180 ± 10 °C; 8,0 ± 1,0 minutos) e escura (180 ± 10 °C; 10,0 ± 1,0 minutos). Considerando-se a média das três torras do café e do PVA, a diferença observada no teor de todos os constituintes acima não foi significativa (p > 0,05), exceto com o teor de grupos hidroxila ácidos que foi ligeiramente superior no PVA e cafeína calculada pelo método semiquantitativo que foi superior no café. Portanto, dentre esses constituintes, os compostos com grupos ácidos seriam os únicos que poderiam contribuir para explicar a grande diferença de sabor existente entre o café de grãos sadios e o de PVA. Tanto o café como o PVA apresentaram atividade seqüestradora do radical DPPH . nas...

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Section: Determinação De Oh Fenólicos E Carboxílicosunclassified

Análise de compostos bioativos, grupos ácidos e da atividade antioxidante do café arábica (Coffea arabica) do cerrado e de seus grãos defeituosos (PVA) submetidos a diferentes torras

Morais¹,

Aquino²,

Nascimento³

et al. 2008

Ciênc. Tecnol. Aliment.

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“…The original method was developed by Sarkanen and coworkers (Sarkanen and Schuerch 1955) A Radiometer CDM 210 conductometer with a Radiometer CDC 641T temperature compensated measuring cell were used, together with a Metrohm 702 SM Titrino automatic buret filled with 1.002 M LiOH. The phenolic charge was determined at the intersection of the two extrapolated straight lines, a salt line of low slope obtained during the neutralization of acid functions and a line of high slope obtained after complete neutralization.…”

Section: Determination Of Phenolic Groupsmentioning

confidence: 99%

Physico-Chemical Characterization of a Fractionated Kraft Lignin

Norgren¹,

Lindström²

2000

Holzforschung

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A kraft lignin was leached from a softwood pulp and fractionated by ultrafiltration. The fractions were characterized in respect to phenolic group content, molecular weight distributions and self-diffusion coefficients. The 1 H-Pulsed Field Gradient (PFG) NMR self-diffusion measurements and the High-Pressure Size Exclusion Chromatography (HPSEC) analysis of the fractions, were seen to correlate fairly well.From the self-diffusion measurements, the mass-weighted median hydrodynamic radii of the diffusants in the fractions, were calculated assuming spherical fragments.Furthermore, the content of phenolic groups in the fractions, was found to decrease by increasing hydrodynamic radius and molecular weight, but the calculated median surface charge densities of the macromolecules, were determined to be constant in the range of oligomers up to at least 65 structural units.

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“…The method was checked with vanillin showing good reproducibility. \ Phenolic hydroxyl content.The phenolic hydroxyl contents were determined by conductometric titration (Sarkanen and Schuerch 1955). Lignin (0.24 g) was first dissolved in acetone (3 ml), then ethanol (6 ml) was added and next, water (9 ml) was added dropwise, with constant stirring, at 20 °C.…”

Section: Elemental Analysismentioning

confidence: 99%

Solvent Effects on Organosolv Lignin fromPinus caribaea hondurensis

Balogh¹,

Curvelo²,

Groote³

1992

Holzforschung

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Keywords Lignin analysis Organosolv lignin Molccular wcight (Mini, Mw and MWD) dctcrminations Hilücbrand's solubility paramctcr Sawdust Pinus caribaea hondurensis SummaryLignin from Pinus caribaea hondurensis sawdust (pre-extracted with bcnzenc/mcthanol 1:1) was obtaincd by pulping using ninc diffcrent organic solvcnts (in 9:1 mixturcs with 2.0 N HC1 aqucous Solutions) in a stainlcss stcel rcactor at 125 °C for six hours.Thc obtaincd lignins wcrc charactcrizcd by chcmical analysis (clcmcntal analysis, mcthoxyl and phcnolic hydroxyl groups) and by infrarcd spcctroscopy. Morcovcr, the avcrage molccular wcights (Mn, Mw and MWD) werc dctcrmincd by vapor phasc osmomctry and high pcrformancc-size exclusion chromatography and shown thrcc diffcrent pattcrns according to thc solvent mixturcs cmploycd. The yields of lignin dcpcnd on the acccssibility and nuclcophilicity of thc solvcnts äs well äs on thc lignin solubility, and are rclatcd to thc Hildcbrand's solubility paramctcrs ( ) of the solvent mixturcs. The plot of lignin yields against 6 show a charactcristic "Bell shapc" curvc wilh maximum at 23 MPa l/2 corrcsponding to thc lignin solubility paramctcr. IntroductionPulping processes can be divided into three main groups, depending on the solvent System employed: -Aqueous processes: These pulping processes use water äs solvent and inorganic reagents to cleave the protolignin to water soluble fragments. The inorganic reagents are generally used in high concentrations and the processes are carried out at high temperatures and pressures. -Organosolv processes: These processes use organic solvents, commonly in association with water and, in the most cases, an acid catalyst. In the acid catalyzed organosolv processes, water acts äs nucleophilic agent and reacts with reactive centers (which have been activated by the catalyst) in the protolignin. Organosolv processes generally use lower temperatures and pressures than the aqueous processes, and differ from in the recovery of the Chemicals, in organosolv processes only the solvent has to be recovered. -Mixed processes: The solubilization power of the organic solvents can be used in association with water and inorganic reagents producing mixed processes. These Systems are also performed at high temperatures and pressures and the inorganic reagents have to be recovered due to economical reasons. Organosolv processes making use of alkaline reagents are included in this group.

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Conductometric Determination of Phenolic Groups in Mixtures Such as Isolated Lignins

Cited by 30 publications

References 31 publications

Análise de compostos bioativos, grupos ácidos e da atividade antioxidante do café arábica (Coffea arabica) do cerrado e de seus grãos defeituosos (PVA) submetidos a diferentes torras

Análise de compostos bioativos, grupos ácidos e da atividade antioxidante do café arábica (Coffea arabica) do cerrado e de seus grãos defeituosos (PVA) submetidos a diferentes torras

Physico-Chemical Characterization of a Fractionated Kraft Lignin

Solvent Effects on Organosolv Lignin fromPinus caribaea hondurensis

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