Iron binding by tannic acid: Effects of selected ligands

South, Paul K.; Miller, Dennis D.

doi:10.1016/s0308-8146(98)00040-5

Cited by 85 publications

(61 citation statements)

References 19 publications

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“…Absorbance characteristics of the tannin-iron solutions A variety of catechols and Fe 3+ form complexes with broad absorption curves and with maxima (λ-max) in the region 550-580 nm (Imsgard et al 1971). Fe 3+ complexes formed with tannic acid also show a broad absorption curve with λ-max around 560 nm (South, Miller 1998).…”

Section: Abbreviationsmentioning

confidence: 99%

“…To prevent iron from binding to tannins, various complexing agents have been screened as ligands and ethylenediaminetetraacetic acid (EDTA) is a very efficient one with very high affinity for iron, thus removing the latter from complexes with tannins (South, Miller 1998 (Ghosh, Ni 1998;Ni et al 1999). Compared with complexes of iron ions with catechols, the stability constant of the DTPA-Fe 3+ complex is higher [10 28.6 with a coordination stoichiometry of 1:1 DTPA:iron (The Dow Chemical Co)].…”

Section: +mentioning

confidence: 99%

“…Other phenolic compounds present in the trees, such as tannins and other extractives can also form coloured complexes with metals (Ni et al 1999;South, Miller 1998).…”

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confidence: 99%

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Tannin-iron impregnated thermomechanical pulp. Part I: Effects of extractions and heat on brightness

Friman

Höglund

Högberg

et al. 2004

Nordic Pulp &Amp; Paper Research Journal

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SUMMARY:Tannins are polyphenolic compounds found mainly in bark. When reacting with iron, they form strongly coloured complexes, which through contamination from the bark may induce a brightness decrease of mechanical pulps. Wood itself contains phenolic compounds, which can form coloured complexes with iron. We have investigated gallotannin as a model for metal-binding sites in the pulp. The behaviour of tannin-iron complexes in solution and in pulp has been studied. In aqueous solution, the tannin-iron complexes can be decolourised by the addition of diethylenetriaminepentaacetic acid (DTPA). The colour of the tannin-iron complexes was very pHdependent. Thus in solution, these were decolourised at low pH and at high pH the spectral characteristics were changed substantially. We have studied the effects on brightness and heatinduced brightness loss of the impregnation of thermomechanical pulp (TMP) with 30 parts per million iron (ppm i.e. mg/kg) either as iron or tannin-iron as well as the possibility to decrease such effects by using various solvent extractions. The tanniniron impregnation causes a decrease in ISO-brightness of approximately 3% and an increase in the light absorption coefficient (k) by approximately 2 m 2 /kg at the tannin-iron absorbance maximum, 565 nm. These effects are approximately ten times higher than those observed for the pulp only impregnated with iron. Extraction with 1% by weight of DTPA provides a way to reduce the brightness decrease induced by the tanniniron complexes and the observed decrease can be attributed to removal of iron from the pulp. Acid extraction was the most efficient way to reduce the iron content in the pulps and to decoulorise the tannin-iron impregnated pulp. However, after acid extraction of iron impregnated pulps, new chromophores were evidently formed. Addition of the reducing agent, sulphite, to extractions had no effect on the iron removal or the brightness of the impregnated pulps. The heat-induced brightness loss is not influenced by the addition of tannin-iron or iron. The brightness loss caused by heat was lower for pulps extracted with DTPA. ADDRESSES OF THE AUTHORS:Linda Friman (linda.friman@mh.se), Hans Höglund (hans.hoglund@mh.se) and Hans-

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Section: Abbreviationsmentioning

confidence: 99%

Section: +mentioning

confidence: 99%

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Tannin-iron impregnated thermomechanical pulp. Part I: Effects of extractions and heat on brightness

Friman

Höglund

Högberg

et al. 2004

Nordic Pulp &Amp; Paper Research Journal

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“…Fairweather-Tait et al, (1989) showed that Fe and Zn retention from extruded mixtures made with bran and flour and consumed with milk did not differ from that of the product, used in the same way, but not extruded. Furthermore, the effect of inhibitors can be minimized by the addition of adequate absorption enhancers such as ascorbic acid, citric acid and Na 2 EDTA (South & Miller, 1998). Besides that, micronutrient fortification is becoming an almost generalized practice; however in most cases nutrient bioavailability is ignored.…”

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confidence: 99%

Use of Soybean in Cereal Based Food Formulation and Development of Nutritionally Improved Foods

Drago¹,

Lassa²,

Torres³

et al. 2011

Soybean and Nutrition

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“…Tannins are a group of wood components containing many phenolic groups, which can form coloured complexes with metal ions, such as Fe 3+ (South, Miller 1998).…”

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confidence: 99%

Tannin-iron impregnated thermomechanical pulp Part II: Bleachability and brightness reversion

Friman

Höglund

Högberg³

et al. 2004

Nordic Pulp &Amp; Paper Research Journal

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SUMMARY:Tannins are polymeric, phenolic constituents found in the bark of pine and spruce. When reacting with iron ions, tannins form strongly coloured complexes. Thus, the presence of bark in the mechanical pulping process leads to decreased brightness of the pulp. In order to evaluate the effects of the presence of iron on the properties of pulp, we have impregnated thermomechanical pulp (TMP) with 30 parts per million (ppm i.e. mg/kg) iron either as Fe 3+ or as tannin-iron complexes and studied how such treatments affect bleachability and heat-induced brightness reversion. The bleaching agents studied are hydrogen peroxide and sodium dithionite. Treatment of the tannin-iron impregnated pulp with 1% by weight of diethylenetriaminepentaacetic acid (DTPA) before bleaching with 4% hydrogen peroxide almost eliminated the brightness loss caused by the impregnation. Such a treatment also removed all of the added iron from both the tannin-iron and FeCl 3 impregnated pulps. Approximately 5% more of the added peroxide was required for oxidation of the tannins in the tanniniron impregnated pulp. Contrary to what was observed with peroxide bleaching, dithionite bleaching did not reduce the amount of iron in the pulps. Instead, the added iron and tanniniron negatively affected the dithionite bleaching, even if the pulps were extracted with DTPA before bleaching. It should therefore be advantageous to first bleach with peroxide, which removes most of the iron, and then with dithionite. Compared with dithionite, peroxide yields a more efficient bleaching. The reason for this is that the former reduces the light absorption coefficient, the k-value, more efficiently in the whole visible spectrum, whereas dithionite reduces it mainly at shorter wavelengths. In our experiments, the addition of tannin-iron or FeCl 3 to the untreated pulp did not increase heat-induced brightness reversion. This is supported by the fact that although extraction of the samples with DTPA before bleaching lowered the iron content slightly, it did not affect the brightness reversion. The initial brightness reversion of the dithionite bleached pulps was larger than that observed for the peroxide bleached pulps. ADDRESSES OF THE AUTHORS:Linda Friman (frimanlinda@hotmail.com), Hans Höglund (hans.hoglund@mh.se) and Hans-Erik Högberg

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Iron binding by tannic acid: Effects of selected ligands

Cited by 85 publications

References 19 publications

Tannin-iron impregnated thermomechanical pulp. Part I: Effects of extractions and heat on brightness

Tannin-iron impregnated thermomechanical pulp. Part I: Effects of extractions and heat on brightness

Use of Soybean in Cereal Based Food Formulation and Development of Nutritionally Improved Foods

Tannin-iron impregnated thermomechanical pulp Part II: Bleachability and brightness reversion

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