Thermal Behaviour of Amylose-g-Poly (Styrene) Graft Copolymer

The graft copolymer amylose-g-poly (styrene) was prepared by Fe²⁺-H₂O₂ initiation method. Thermal analyses of grafted samples having different styrene content have been carried out in nitrogen atmosphere. Thermal stability of amylose has been found to increase when it is grafted. Chatterjee and Freeman-Anderson methods have been applied to TG-data (Thermogravimetric Data). TG showed that degradation occurred through two distinct steps. DTA (Differential Thermal Analysis) of all samples having different degrees of grafting indicated that graft copolymers decompose before melting. From the DSC (Differential Scanning Calorimeter) study it is revealed that TG of graft copolymers is independent of the degree of grafting.     

Purification and characterisation of β‐mannanase from Lactobacillus plantarum (M24) and its applications in some fruit juices

β‐Mannanase was purified 2619.05‐fold from the Lactobacillus plantarum (M24) bacterium by ammonium sulphate precipitation and ion exchange chromatography (DEAE‐Sephadex). The purified enzyme gave two protein bands at a level of approximately 36.4 and 55.3 kDa in the SDS‐PAGE. The purified mannanase enzyme has shown its maximum activity at 50 °C and pH 8, and it has been also determined that the enzyme was stable at 5–11 pH range and over 50 °C. The V_max and K_m values have been identified as 82 mg mannan mL^?1 and 0.178 mm , respectively. The effects of some metal ions such as Fe²⁺, Ca²⁺, Co²⁺, Ni²⁺, Mn²⁺, Cu²⁺ and Zn²⁺ on the mannanase enzyme have been also investigated, and it has been determined that all metal ions had significant effects on the activation of the mannanase enzyme. In addition, the effectiveness of the purified mannanase enzyme on the clarification of some fruit juices such as orange, apricot, grape and apple has been investigated. During the clarification processes, the enzyme was more effective than crude extracts on the clarification of the peach juice with a ratio of 223.1% at most.     

Synthesis of Poly(Methacrylic Acid-)Starch Graft Copolymers Using Mn-IV-Acid System

When starch was treated with KMnO₄ solution, MnO₂ was deposited overall the starch. The amount of MnO₂ deposited relied on the KMnO₄ concentration. Subjecting the MnO₂-containing starch to a solution consisting of monomer (methacrylic acid, MAA) and acid (citric, tartaric, oxalic or sulphuric acid) resulted in formation of poly(MAA)-starch graft copolymer. The magnitude of grafting, expressed as meq. -COOH/100 g starch, was determined by amount of MnO₂ deposited, MAA concentration, temperature and duration of polymerization as well as kind and concentration of the acid. Incorporation of cations such as Fe⁺³, Cu⁺² and Li⁺¹ had a significant effect on grafting. The highest extent and rate of grafting were obtained with citric acid and the least with sulphuric acid; tartaric acid stood in-mid-way position. The magnitude of grafting increased as the acid concentration increased till a certain concentration beyond which grafting levelled off. Similar trend was observed when the magnitude of grafting was related to the amount of MnO₂ deposited. The extent and rate of grafting increased by raising the polymerization temperature from 30° to 50°C then decreased by raising the temperature further from 60° to 70°C. On the other hand, grafting enhanced significantly by addition of Fe⁺³, Cu⁺² or Li⁺¹ and followed the order Fe⁺³ > Cu⁺² > Li⁺¹. A tentative mechanism for grafting of starch with MAA using MnO₂-acid system was elucidated.     

A Study on Chain Transfer and Grafting of Amylose-g-Poly(Styrene)

Amylose-g-poly(styrene) has been prepared by Fe^2+- H₂O₂ initiation method. Evaluation of chain transfer constant and analysis of the kinetic data indicated a decrease in the extent of the termination of homopolymer and graft copolymer radicals. It also showed an increase in yield of the graft copolymer.     

Short communication: Nutrient consumption patterns of Lactobacillus acidophilus KLDS 1.0738 in controlled pH batch fermentations

This work focused on elucidating the nutrient consumption patterns of Lactobacillus acidophilus to guide the design of media for high-cell-density culture. We investigated the nutrient consumption patterns of L. acidophilus KLDS 1.0738 in chemically defined media in controlled pH batch fermentations. The most abundantly consumed amino acids, vitamins, ions, and purines and pyrimidines were Glu and Gly, pyridoxine and nicotinamide, K⁺ and PO₄^3?, and guanine and uracil, respectively. The highest consumption rates for amino acids, vitamins, ions, and purines and pyrimidines were Asp and Arg, folic acid and pyridoxine, Fe²⁺ and Mn²⁺, and uracil and thymine, respectively. Furthermore, most of the amino acids, as well as guanine, thymine, pyridoxine, folic acid, nicotinamide, Mg²⁺, PO₄^3?, and K⁺ had the highest bioavailability from the end of the lag growth phase to the mid-exponential growth phase. The overall consumption of glucose, adenine nucleotides, 2'-deoxyguanosine monohydrate, calcium pantothenate, Fe²⁺ and Mn²⁺ decreased with increasing average growth rate, indicating more effective use of these nutritional components at a higher average growth rate, as biomass yield based on nutritional component consumption increased. Our findings help to formulate complex media for high-cell-density cultivation and provide a theoretical basis for L. acidophilus feeding strategies.     

Effects of metal ions on growth, β-oxidation system,and thioesterase activity of Lactococcus lactis

The effects of divalent metal ions (Ca²⁺, Mg²⁺, Fe²⁺, and Cu²⁺) on the growth, β-oxidation system, and thioesterase activity of Lactococcus lactis were investigated. Different metal ions significantly influenced the growth of L. lactis: Ca²⁺ and Fe²⁺ accelerated growth, whereas Cu²⁺ inhibited growth. Furthermore, Mg²⁺ inhibited growth of L. lactis at a low concentration but stimulated growth of L. lactis at a high concentration. The divalent metal ions had significant effects on activity of the 4 key enzymes of the β-oxidation system (acyl-CoA dehydrogenase, enoyl-CoA hydratase, L-3-hydroxyacyl-CoA dehydrogenase, and thiolase) and thioesterase of L. lactis. The activity of acyl-CoA dehydrogenases increased markedly in the presence of Ca²⁺ and Mg²⁺, whereas it decreased with 1 mmol/L Fe²⁺ or 12 mmol/L Mg²⁺. All the metal ions could induce activity of enoyl-CoA hydratase. In addition, 12 mmol/L Mg²⁺ significantly stimulated activity of L-3-hydroxyacyl-CoA dehydrogenase, and all metal ions could induce activity of thiolase, although thiolase activity decreased significantly when 0.05 mmol/L Cu²⁺ was added into M17 broth. Inhibition of thioesterase activity by all 4 metal ions could be reversed by 2 mmol/L Ca²⁺. These results help us understand the effect of metal ions on the β-oxidation system and thioesterase activity of Lactococcus lactis.     

Biochemical properties and potential endogenous substrates of polyphenoloxidase from chufa (Eleocharis tuberosa) corms

Polyphenoloxidase (PPO) was partially purified from chufa corms through ammonium sulphate precipitation and dialysis. Biochemical properties of chufa PPO were analysed using exogenous substrate catechol. Optimal pH and temperature for PPO activity were 5 and 45 °C. Ethylenediaminetetraacetic acid disodium salt and l-cysteine could not inhibit the PPO activity. However, sodium thiosulphate pentahydrate exhibited the strongest inhibiting effect, followed by ascorbic acid and anhydrous sodium sulphite. Except for K⁺, other metal ions such as Zn²⁺, Cu²⁺, Fe³⁺, Ca²⁺, Fe²⁺ and Na⁺ accelerated the enzymatic reaction between catechol and PPO. Kinetic analysis showed that the apparent K_m and V_max values were around 10.77 mM and 82 units/ml min. In addition, (−)-gallocatechin gallate, (−)-epicatechin gallate and (+)-catechin gallate isolated and identified from chufa corms were supposed to be the potential endogenous PPO substrates due to their ortho-diphenolic or pyrogallolic structures. These polyphenols might be catalysed by PPO, resulting in the browning of chufa corms after fresh-cut processing.     

Saccharomyces cerevisiae mutants altered in vacuole function are defective in copper detoxification and iron-responsive gene transcription

The metal ions, Cu^2+/+ and Fe^3+/2+, are essential co-factors for a wide variety of enzymatic reactions. However, both metal ions are toxic when hyper-accumulated or maldistributed within cells due to their ability to generate damaging free radicals or through the displacement of other physiological metal ions from metalloproteins. Although copper transport into yeast cells is apparently independent of iron, the known dependence on Cu²⁺ for high affinity transport of Fe²⁺ into yeast cells has established a physiological link between these two trace metal ions. In this study we demonstrate that proteins encoded by genes previously demonstrated to play critical roles in vacuole assembly or acidification, PEP3, PEP5 and VMA3, are also required for normal copper and iron metal ion homeostasis. Yeast cells lacking a functional PEP3 or PEP5 gene are hypersensitive to copper and render the normally iron-repressible FET3 gene, encoding a multi-copper Fe(II) oxidase involved in Fe²⁺ transport, also repressible by exogenous copper ions. The inability of these same vacuolar mutant strains to repress FET3 mRNA levels in the presence of an iron-unresponsive allele of the AFT1 regulatory gene are consistent with alterations in the intracellular distribution or redox states of Fe^3+/2+ in the presence of elevated extracellular concentrations of copper ions. Therefore, the yeast vacuole is an important organelle for maintaining the homeostatic convergence of the essential yet toxic copper and iron ions. © 1997 John Wiley & Sons, Ltd.     

Purification and characterization of chymotrypsins from the hepatopancreas of crucian carp (Carassius auratus)

Two chymotrypsins (chymotrypsin A and B) have been purified to homogeneity from the hepatopancreas of crucian carp (Carassius auratus) by ammonium sulphate fractionation and chromatographies on DEAE-Sepharose, Sephacryl S-200 HR, Phenyl-Sepharose and SP-Sepharose. The molecular masses of chymotrypsin A and B were approximately 28 and 27 kDa, respectively, by SDS–PAGE. Purified chymotrypsins also revealed single bands by native-PAGE. Optimum temperatures of chymotrypsin A and B were 40 and 50 °C, and optimal pHs were 7.5 and 8.0 using Suc-Leu-Leu-Val-Tyr-AMC as substrate. Both enzymes were effectively inhibited by serine proteinase inhibitors and slightly activated by metal ions such as Ca²⁺ and Mg²⁺, while inactivated by Mn²⁺, Cd²⁺, Cu²⁺, Fe²⁺ to different degrees. Apparent K_ms of chymotrypsin A and B were 1.4 and 0.5 μM, and K_cats were 2.7 S⁻¹ and 3.4 S⁻¹, respectively. Immunoblotting analysis using anti-chymotrypsin B weakly cross reacted with chymotrypsin A.     

Growth Inhibition of Listeria monocytogenes by Sodium Polyphosphate as Affected by Polyvalent Metal Ions

Sodium polyphosphate (SPP, average chain length = 13) increased the lag time of L. monocytogenes Scott A (Lm) in brain-heart infusion broth (BHI). Polyvalent metal ions (1–10 mM) reversed inhibition of Lm growth by 0.5% SPP (nominal 3.6 mM). 10 mM Ca²⁺ or Mg²⁺, 5 mM Fe³⁺, 2 mM Mn²⁺ or 1 mM Zn²⁺ added to SPP-containing BHI, pH 6.0, at 19°C resulted in growth comparable to control cultures. Fe²⁺ partially restored growth; Ni²⁺, Co²⁺, Cu²⁺ or Al³⁺ were ineffective. SPP inhibited growth at 28°C in BHI, pH 5.0, and Lm grew upon addition of Ca²⁺, Mg²⁺ or Mn²⁺, but not Zn²⁺ or Fe³⁺. Addition of 0.5% SPP to mineral-rich foods, such as pureed beef, green beans or sweet potatoes, did not delay growth.     

Giant Amazonian fish pirarucu (Arapaima gigas): Its viscera as a source of thermostable trypsin

A trypsin was purified from pyloric caeca of pirarucu (Arapaima gigas). The effect of metal ions and protease inhibitors on its activity and its physicochemical and kinetic properties, as well its N-terminal sequence, were determined. A single band (28.0 kDa) was observed by SDS–PAGE. Optimum pH and temperature were 9.0 and 65 °C, respectively. The enzyme was stable after incubation for 30 min in a wide pH range (6.0–11.5) and at 55 °C. The kinetic parameters K_m, k_cat and k_cat/K_m were 0.47 ± 0.042 mM, 1.33 s⁻¹ and 2.82 s⁻¹ mM⁻¹, respectively, using BApNA as substrate. This activity was shown to be very sensitive to some metal ions, such as Fe²⁺, Hg²⁺, Zn²⁺, Al³⁺, Pb²⁺, and was highly inhibited by trypsin inhibitors. The trypsin N-terminal sequence IVGGYECPRNSVPYQ was found. The features of this alkaline peptidase suggest that it may have potential for industrial applications (e.g. food and detergent industries).     

Antioxidant and free radical scavenging potential of Achillea santolina extracts

The antioxidative activities of hydroalcoholic extract of Achillea santolina were investigated employing various established in vitro systems including total antioxidant activity in linoleic acid emulsion system, 1,1-diphenyl-2-picrylhydrazyl (DPPH), superoxide and hydroxyl radicals scavenging, reducing power, and inhibitory effect on protein oxidation as well as the inhibition of Fe²⁺/ascorbate induced lipid peroxidation in rat liver homogenate. Total phenolic and flavonoid content of A. santolina extract (ASE) was also determined by a colorimetric method. The results revealed that ASE has notable inhibitory activity on peroxides formation in linoleic acid emulsion system along with concentration-dependent quenching of DPPH and superoxide radicals. Furthermore, the extract showed both nonsite-specific (Fe²⁺ + H₂O₂ + EDTA) and site-specific (Fe²⁺ + H₂O₂) hydroxyl radical scavenging suggesting potent hydroxyl radical scavenging and chelating ability for iron ions in deoxyribose degradation model. A linear correlation between ASE and the reducing power was also observed (r² = 0.9981). ASE prevents thiobarbituric acid reactive substances formation in Fe²⁺/ascorbate induced lipid peroxidation in rat liver tissue in a dose-dependent manner. Moreover, free radical induced protein oxidation was suppressed significantly by the addition of ASE over a range of concentration. These results clearly demonstrated that A. santolina extract possess a marked antioxidant activity.     

Purification and some properties of α-amylase from post-harvest Pachyrhizus erosus L. tuber

α-Amylase, a starch splitting enzyme, was purified to homogeneity from post-harvest Pachyrhizus erosus L. tuber by successive chromatography on DEAE- and CM-cellulose columns. Purification achieved was 110 fold from the crude extract with a yield of 22.8%. SDS-PAGE showed a molecular weight of 40 kDa for the enzyme. The enzyme is of α-type as it lost total activity in the presence of EDTA, a chelating agent. It is a glycoprotein that contains 2.6% sugar as estimated by the phenol-sulfuric acid method. The enzyme displayed optimum activity at pH 7.3 and 37 °C with an apparent K_m value of 0.29% for starch as substrate. The enzyme was strongly inhibited by Cu²⁺, Fe²⁺ and Zn²⁺, moderately by Li²⁺, Hg⁺ and Cd²⁺ and slightly by Ag⁺, Mg²⁺ and K⁺. Calcium ion almost doubled the activity whereas Fe³⁺, Mn²⁺ and Na⁺ enhanced it appreciably.     

Identification of Galactaric Acid as an Intermediate Product of Breast Milk Digestion

The product forming after oxidative acid digestion of the breast milk and the usage of ethyl ether or petroleum ether to remove the fat by solvent extraction has been identified as galactaric (mucic) acid, C₆H₁₀O₈. This compound cannot be discarded, as its capability to form stable complexes with most important bioactive ions (Cu²⁺, Zn²⁺ Mg²⁺, and others) can lead to their vigorous sequestration from nitric acid solution before being measured by spectroscopic techniques.     

Characterization of purified xylanase from finger millet (<Emphasis Type="Italic">Eleusine coracana-</Emphasis>Indaf 15) malt

Xylanase (E.C. 3.2.1.8) was purified to apparent homogeneity from 96 h finger millet (Eleusine coracana, Indaf-15) malt by a three step purification procedure via ammonium sulphate fractionation, DEAE-cellulose ion exchange and Sephadex G-75 gel permeation chromatographies with a recovery of 4.0% and fold purification of 60. Xylanase, having a molecular weight of 29 ± 2 kDa was found to be monomeric on SDS-PAGE. pH optimum of the enzyme was found to be in the range of 5.0–5.5. The activation energy was 25 kJmol⁻¹. Xylanase showed maximum stability at 35 °C in a pH range of 5.0–6.0. K _m and V _max of purified xylanase were found to be 0.2% and 4.5 μmol min⁻¹, respectively. Metal ions such as Ca²⁺, Mg²⁺, Mn²⁺, Cu²⁺, Fe²⁺, Ag²⁺ and Ni²⁺ enhanced xylanase activity at 5 mM concentration. p-chloromercuribenzoate, citric, oxalic and boric acids inhibited the enzyme in concentration dependent manner. The mode of action of xylanase was found to be “endo” as determined by the analysis of products liberated from larchwood xylan by ESI-MS and H¹NMR. In vitro studies using Bifidobacterium and Lactobacillus sp. confirmed the prebiotic activity of the xylo-oligosaccharides.     

Pomological features, nutritional quality, polyphenol content analysis, and antioxidant properties of domesticated and 3 wild ecotype forms of raspberries (Rubus idaeus L.)

Abstract: The raspberry (Rubus idaeus L.) is an economically important berry crop that contains many phenolic compounds with potential health benefits. In this study, important pomological features, including nutrient content and antioxidant properties, of a domesticated and 3 wild (Yayla, Yavuzlar, and Yedigöl) raspberry fruits were evaluated. Also, the amount of total phenolics and flavonoids in lyophilized aqueous extracts of domesticated and wild ecotypes of raspberry fruits were calculated as gallic acid equivalents (GAEs) and quercetin equivalents (QE). The highest phenolic compounds were found in wild Yayla ecotype (26.66 ± 3.26 GAE/mg extract). Whilst, the highest flavonoids were determined in wild Yedigöl ecotype (6.09 ± 1.21 QA/mg extract). The antioxidant activity of lyophilized aqueous extracts of domesticated and wild ecotypes of raspberry fruits were investigated as trolox equivalents using different in vitro assays including DPPH^?, ABTS^?+, DMPD^?+, and O^??₂ radical scavenging activities, H₂O₂ scavenging activity, ferric (Fe³⁺) and cupric ions (Cu²⁺) reducing abilities, ferrous ions (Fe²⁺) chelating activity. In addition, quantitative amounts of caffeic acid, ferulic acid, syringic acid, ellagic acid, quercetin, α‐tocopherol, pyrogallol, p‐hydroxybenzoic acid, vanillin, p‐coumaric acid, gallic acid, and ascorbic acid in lyophilized aqueous extracts of domesticated and wild ecotypes of raspberry fruits were detected by high‐performance liquid chromatography and tandem mass spectrometry (LC‐MS‐MS). The results clearly show that p‐coumaric acid is the main phenolic acid responsible for the antioxidant and radical scavenging activity of lyophilized aqueous extracts of domesticated and wild ecotypes of raspberry fruits.     

Analysis of tryptophan oxidation by fluorescence spectroscopy: Effect of metal-catalyzed oxidation and selected phenolic compounds

The suitability of using fluorescence spectroscopy to assess tryptophan (TRYP) depletion by quantifying the loss of natural TRYP fluorescence during metal-catalyzed oxidation (MCO) was assessed. To analyze the effect of the oxidation conditions, N-acetyl-l-tryptophanamide (NATA) solutions were oxidized in the presence of Cu²⁺ and Fe²⁺ (40 and 80 μM), with and without 0.8 mM H₂O₂. Also, the effect of selected phenolic compounds (PhC), namely, catechin, genistein, quercetin, rutin, gallic acid and chlorogenic acid (0.08, 0.8 and 8.0 μM), on TRYP MCO was studied. Oxidation systems catalyzed by Fe²⁺ had a major oxidative potential as a result of a higher amount of free radicals formed through the Fenton reaction. PhC could exert both antioxidant and pro-oxidant effects depending on their concentration, chemical structure of the PhC and the oxidation system. In general, all PhC acted as pro-oxidant agents at the highest dose. The major pro-oxidant effect was displayed by gallic and chlorogenic acid in the presence of Fe²⁺, Cu²⁺ or Cu²⁺/H₂O₂. Quercetin, rutin and gallic acid showed antioxidant effect against TRYP oxidation at low concentrations in Fe²⁺/H₂O₂ systems. Plausible mechanisms for the antioxidant and pro-oxidant effects of PhC on TRYP oxidation are discussed in the present article. The antioxidant efficiency of PhC or PhC-rich extracts must be studied before being used as functional food ingredients.     

Purification and Characterization of Polyphenol Oxidase from Hemşin Apple (Malus communis L.)

The polyphenol oxidase (PPO) enzyme was purified and characterized from Hem?in Apple (Malus communis L.), which was organically grown in Hem?in, in the Rize province of Turkey. Enzyme (PPO) activation was determined with catechol substrate. Apples were homogenized with homogenate buffer (pH 8.5). This process was followed by precipitation with (20–80%) saturated solid (NH₄)₂SO₄ and dialysis. Finally, purification with DE52-Cellulose ion-exchange and Sephadex G-25 columns was performed. Experiments were performed at an optimum pH (5.5) and optimum temperature (30–40°C). The kinetic and thermal parameters Km (3.40 mM), Vmax (333.3 EU/mL.min), Ea (3.57 kcal), ?H (2.968 kcal/mol), Q₁₀ (1.33), k_cat (24.57 min^?1) and V₀ (7.2x10³ mM^?1.min^?1) were assessed. Additionally, the effects of Mg²⁺, Pb ²⁺, Fe²⁺, Fe³⁺, Cd²⁺, Cu²⁺, Zn²⁺, Co²⁺, Al³⁺, Mn²⁺ and Na⁺ on enzyme activity was recorded, and the IC₅₀ values, K_? values and inhibition types were determined.     

Pea mitochondrial lipids and their oxidation during mitochondria swelling

The composition and oxidation of lipids in pea mitochondria induced by swelling in presence of some transitional metal ions and ascorbic acid has been studied. Among the major mitochondrial lipids found were phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol and diphosphatidylglycerol. The major fatty acids present in these lipids were linoleic, oleic and palmitic acids. The average unsaturation for mitochondria total fatty acids, expressed as Double Bond Index was 1.44, while the unsaturation for fatty acids of individual lipids varied between 1.02 and 1.73 being highest for an unidentified phospholipid and 1.44 for phosphatidylcholine present in mitochondria as the major lipid. Mitochondria isolated from pea seeds germinated for 4 days were found to be tightly coupled and to have an ADP/O ratio of 1.3. The swelling assay in 0.1 M-KCl for 1-day-old mitochondria has shown a swelling ability matching those of 4 and up to 8 days of age. Isolated mitochondria aged for 24 h at 2–4º C showed a swelling comparable to that of the fresh preparation. Swelling in the presence of ascorbic acid did not induce mitochondrial lipid oxidation. However, this was brought about in the presence of Cu²⁺ ions. The presence of Fe²⁺ ions induced the highest degree of oxidation, and instead of a concurrent swelling, it induced contraction. At the same level of ions, Fe²⁺ was more effective than Fe³⁺. Contrary to iron used at 4% of its physiological level, Mn²⁺ and Co²⁺ used at 12 to 24% of their levels found in pea seeds were ineffective in inducing oxidation. Nevertheless, the degree of mitochondrial swelling was highest in the medium containing KCl, lower in the presence of Co²⁺ and ascorbic acid and lowest in the presence of Fe³⁺. These results suggested that mitochondrial lipid oxidation does not depend on the degree of swelling. The lipid peroxides formed within mitochondria, up to 8 mg of mitochondrial protein, could not be detected by dropping mercury electrode polarography but were readily determined colorimetrically using thiobarbituric acid reagent.     

Influence of dietary phenolic acids on redox status of iron: Ferrous iron autoxidation and ferric iron reduction

We investigated the effect of dietary phenolic acids on the oxidation of Fe²⁺ caused by molecular oxygen. All phenolic acids bearing 3,4-dihydroxy (catechol) or 3,4,5-trihydroxy (galloyl) moiety formed chelates with ferric iron and significantly increased the rate of Fe²⁺ autoxidation. The carboxylate group and catechol substitution instead of galloyl moiety facilitated the ferrous ion oxidation more effectively. Caffeic acid and protocatechuic acid, the strongest accelerators of Fe²⁺ autoxidation, were able to facilitate autoxidation at concentrations lower than 1% of the initial amount of Fe²⁺. Therefore chelates of these catecholic acids with iron displayed ferroxidase-like activity. Conversely, when we started from ferric ions, catechols partially formed ferrous ions in the presence of ferrozine. Thus, catecholic acids formed stable chelates with iron, in which ferric ion is the dominant species, but the redox cycling of iron between Fe²⁺ and Fe³⁺ in chelates probably plays a crucial role in the catalysis of ferrous iron autoxidation. Interestingly, 3-hydroxybenzoic acid, 4-hydroxybenzoic acid and vanillic (4-hydroxy-3-methoxybenzoic) acid protected ferrous ions from autoxidation as effectively as ascorbic acid and cysteine. These monophenolic acids, differently from ascorbic acid and cysteine, were not able to reduce ferric ions. Syringic (3,5-dimethoxy-4-hydroxybenzoic) acid did not alter the redox state of iron, only in a large excess over metal, syringic acid slightly inhibited ferrous ions autoxidation and partially reduced ferric ions. Therefore, the effects of syringic acid at high concentration were similar but much lower to those of ascorbic acid and cysteine. The biological importance of ferroxidase-like activity of polyphenols, especially the influence on iron absorption, is also discussed.