Effects of food structure and ingredient interactions on antioxidant capacity

Foods are complex biological materials, and the lipids within the food are susceptible to lipid oxidation, which is retarded by antioxidants. The precise structure and composition of the food may affect the antioxidant activity quite strongly in some cases. Solubility of the antioxidant in the phases present is one of the main parameters that affects the variation in antioxidant activity with phase composition of food. Polar antioxidants are more effective in oils, whereas non-polar antioxidants are more effective in oil-in-water emulsions. Antioxidant activity has been reported in a range of different media, including oils, emulsions, liposomes, microemulsions, fish and meat muscles, and the antioxidant activity may vary from one medium to another. Synergy between antioxidants may also vary from one medium to another. Interactions with metals and with proteins affect antioxidant activity and these interactions are also dependent on the phases present.

Synthesis, X-ray crystal structure and catalytic activity of the manganese(II) complex [Mn(bdoa)(H2O)3](bdoaH2 =benzene-1,2-dioxyacetic acid)

Benzene-1,2-dioxyacetic acid (bdoaH2) reacts with Mn(CH3CO2)2·4H2O in an ethanol-water mixture to give the manganese(II) complex [Mn(bdoa)(H2O)3]. The X-ray crystal structure of the complex shows the metal to be pseudo seven-coordinate. The quadridentate bdoa2− dicar☐ylate ligand forms an essentially planar girdle around the metal, being strongly bondedtransoid by a car☐ylate oxygen atom from each of the two car☐ylate moieties (mean MnO 2.199A˚) and also weakly chelated by the two internal ether oxygen atoms (mean MnO 2.413A˚). The coordination sphere about the manganese is completed by three water molecules (mean MnO 2.146A˚) lying in a meridional plane orthogonal to that of the bdoa2− ligand. Magnetic, conductivity and voltammetry data for the complex are given, and its use as a catalyst for the disproportionisation of H2O2 is described.

Synthesis and reactions of [Et3NH]4[Mo8O6]: X-ray crystal structure of [Et3NH]3[NaMo8O26]

[Et3NH]4[Mo8O26] (1) was prepared by reacting triethylamine with either molybdenum trioxide dihydrate or with a solution of ammonium molybdate in aqueous HCl. An aqueous solution of complex 1 reacted with an excess of sodium chloride to give a mixture of [Et3NH]3[NaMo8O26] (2) and [Et3NH]2[Mo6O19] (3). Complex 2 was also formed on reacting sodium molybdate with triethylamine in aqueous HCl. In the reaction of 1 with potassium chloride the nature of the product obtained was critically dependent upon reaction time. After a 5.5 h reflux period a mixture of [Et3NH]3[KMo8O26] (4) and 3 was obtained, whereas upon prolonged reflux (24 h) only K4Mo8O26 · H2O (5) was precipitated. The X-ray crystal structure of 2 shows it to be polymeric, with each Na+ ion sandwiched between two β[Mo8O26]4− ions. Four oxygen atoms on one face of each β[Mo8O26]4− ion are coordinated to a Na+ ion, and four oxygens from the opposite face are bonded to the next Na+ ion in the polymer chain. This produces a zig-zag arrangement of Na+ ions throughout the molecular structure. Spectral, conductivity and voltammetry data are given.

Effects of inulin on lipid parameters in humans

Convincing lipid-lowering effects of the fructooligosaccharide inulin have been demonstrated in animals, yet attempts to reproduce similar effects in humans have generated conflicting results. This may be because of the much lower doses used in humans as a result of the adverse gastrointestinal symptoms exhibited by most subjects consuming daily doses in excess of 30 g. Two studies that fed either oligofructose (20 g/d) or inulin (14 g/d) observed no effect on fasting total, LDL or HDL cholesterol, or serum triglycerides. Two other studies that fed inulin either in a breakfast cereal (9 g/d) or as a powdered addition to beverages and meals (10 g/d) reported similar reductions in fasting triglycerides (227 and 219%, respectively). In one of these studies, total and LDL cholesterol concentrations were also modestly reduced (5 and 7%, respectively). Because animal studies have identified inhibition of hepatic fatty acid synthesis as the major site of action for the triglyceride-lowering effects of inulin, and because this pathway is relatively inactive in humans unless a high carbohydrate diet is fed, future attempts to demonstrate lipid-lowering effects of inulin should consider the nature of the background diet as a determinant of response.

Electrochemical characterisation and anodic stripping voltammetry at mesoporous platinum rotating disc electrodes

Using the technique of liquid crystal templating a rotating disc electrode (RDE) was modified with a high surface area mesoporous platinum film. The surface area of the electrode was characterised by acid voltammetry, and found to be very high (ca. 86 cm(2)). Acid characterisation of the electrode produced distorted voltammograms was interpreted as being due to the extremely large surface area which produced a combination of effects such as localised pH change within the pore environment and also ohmic drop effects. Acid voltammetry in the presence of two different types of surfactant, namely Tween 20 and Triton X-100, suggested antifouling properties associated with the mesoporous deposit. Further analysis of the modified electrode using a redox couple in solution showed typical RDE behaviour although extra capacitive currents were observed due to the large surface area of the electrode. The phenomenon of underpotential deposition was exploited for the purpose of anodic stripping voltammetry and results were compared with data collected for microelectrodes. Underpotential deposition of metal ions at the mesoporous RDE was found to be similar to that at conventional platinum electrodes and mesoporous microelectrodes although the rate of surface coverage was found to be slower at a mesoporous RDE. It was found that a mesoporous RDE forms a suitable system for quantification of silver ions in solution.

Underpotential deposition and anodic stripping voltammetry at mesoporous microelectrodes

Using the technique of liquid crystal templating a series of high surface area mesoporous platinum microelectrodes was fabricated. The underpotential deposition of metal ions at such electrodes was found to be similar to that at conventional platinum electrodes. The phenomena of underpotential deposition, in combination with the intrinsic properties of mesoporous microelectrodes (i.e. a high surface area and efficient mass transport) was exploited for the purpose of anodic stripping voltammetry. In particular the underpotential deposition of Ag+, Pb2+ and Cu2+ ions was investigated and it was found that mesoporous microelectrodes were able to quantify the concentration of ions in solution down to the ppb range. The overall behaviour of the mesoporous electrodes was found to be superior to that of conventional microelectrodes and the effects of interference by surfactants were minimal.

Supplementation with fruit and vegetable soups and beverages increases plasma carotenoid concentrations but does not alter markers of oxidative stress or cardiovascular risk factors

This study was aimed at determining whether an increase of 5 portions of fruits and vegetables in the form of soups and beverages has a beneficial effect on markers of oxidative stress and cardiovascular disease risk factors. The study was a single blind, randomized, controlled, crossover dietary intervention study. After a 2-wk run-in period with fish oil supplementation, which continued throughout the dietary intervention to increase oxidative stress, the volunteers consumed carotenoid-rich or control vegetable soups and beverages for 4 wk. After a 10-wk wash-out period, the volunteers repeated the above protocol, consuming the other intervention foods. Both test and control interventions significantly increased the % energy from carbohydrates and decreased dietary protein and vitamin B-12 intakes. Compared with the control treatment, consumption of the carotenoid-rich soups and beverages increased dietary carotenoids, vitamin C, alpha-tocopherol, potassium, and folate, and the plasma concentrations of alpha-carotene (362%), beta-carotene (250%) and lycopene (31%) (P < 0.01) and decreased the plasma homocysteine concentration by 8.8% (P < 0.01). The reduction in plasma homocysteine correlated weakly with the increase in dietary folate during the test intervention (r = -0.35, P = 0.04). The plasma antioxidant status and markers of oxidative stress were not affected by treatment. Consumption of fruit and vegetable soups and beverages makes a useful contribution to meeting dietary recommendations for fruit and vegetable consumption.

Perception of thickness, mouth-coating and mouth-drying of dairy beverages by younger and older volunteer

Sensory perception has been found to change during ageing. The perception of mouth feel by older adults, and the role of ageing on the sensory perception of texture attributes is uncertain. . This study investigated perception of the textural attributes of thickness, mouth-coating and mouth-drying, in the context of dairy beverages, by older and younger adults. Just noticeable differences (JND) of a starch thickener and for cream concentration within milk were established for thickness and mouth-coating perception, finding no age-related differences between participant groups. Mouth-drying was assessed through the directional paired comparison of a mouth-drying milk beverage to a skimmed milk sample. The older adults were found to be more sensitive to mouth-drying (p=0.03) than the younger adults. This study found no age-related decline in texture perception with older adults finding perception of some attributes such as mouth-drying enhanced by ageing.

Potential sources of mouth drying in beverages fortified with dairy proteins: a comparison of casein and whey-rich ingredients

Oral nutritional supplement drinks (ONS) are beverages high in dairy proteins that are prescribed to individuals at risk of malnutrition. Consumption of ONS is poor in elderly care facilities, with patients commenting that the sensory attributes of these drinks reduce their enjoyment and willingness to consume. Mouth drying is an attribute of ONS found to build with repeated consumption, which may further limit liking of these products. This study investigated the sources of drying sensations by sequential profiling, with a trained sensory panel rating a range of model milk systems and ONS over repeated sips and during after-effects. Sequential profiling found that fortification of milk with both caseinate and whey protein concentrate significantly increased the perception of mouth drying over repeated consumption, increasing by between 35 and 85% over consumption of 40mL. Enrichment of ONS with either whey protein concentrate or milk protein concentrate to a total protein content of 8.7% (wt/wt) resulted in whey and casein levels of 4.3:4.4% and 1.7:7.0% respectively. The product higher in whey protein was substantially more mouth drying, implying that whey proteins may be the most important contributor to mouth drying in ONS. However, efforts to mask mouth drying of protein-fortified milk by increasing sweetness or fat level were unsuccessful at the levels tested. Increasing the viscosity of protein-fortified milk led to a small but significant reduction in mouth drying. However, this approach was not successful when tested within complete ONS. Further analysis is required into the mechanism of protein-derived mouth drying to mask negative sensations and improve the enjoyment and consumption of protein-rich ONS.

Does speciation impact on Cu uptake by, and toxicity to, the earthworm Eisenia fetida?

Eisenia fetida were exposed to different concentrations (0.009, 0.049 and 0. 125 mg L-1) of Cu in an aqueous medium. Cu speciation was manipulated through the addition of different concentrations (0. 15, 0.35 and 50 mg L-1) of EDTA. Cu speciation (as labile and non-labile pools) was determined using Differential Pulse Anodic Stripping Voltammetry. Labile Cu includes free Cu ions together with weak inorganic Cu complexes and a small fraction of easily dissociable organic complexes. Metal uptake and earthworm mortality increased with total Cu concentration in the EDTA free solutions. In the presence of EDTA both metal uptake and mortality decreased. These experiments demonstrate that Cu speciation governs uptake and consequent toxicity of Cu to E. fetida. (c) 2007 Elsevier Masson SAS. All rights reserved.

Electrochemical and sonoelectrochemical monitoring of indigo reduction by glucose

The reduction of indigo (dispersed in water) to leuco-indigo (dissolved in water) is an important industrial process and investigated here for the case of glucose as an environmentally benign reducing agent. In order to quantitatively follow the formation of leuco-indigo two approaches based on (i) rotating disk voltammetry and (ii) sonovoltammetry are developed. Leuco-indigo, once formed in alkaline solution, is readily monitored at a glassy carbon electrode in the mass transport limit employing hydrodynamic voltammetry. The presence of power ultrasound further improves the leuco-indigo determination due to additional agitation and homogenization effects. While inactive at room temperature, glucose readily reduces indigo in alkaline media at 65 degrees C. In the presence of excess glucose, a surface dissolution kinetics limited process is proposed following the rate law d eta(leuco-indigo)/dt = k x c(OH-) x S-indigo where eta(leuco-indigo) is the amount of leuco-indigo formed, k = 4.1 x 10(-9) m s(-1) (at 65 degrees C, assuming spherical particles of I gm diameter) is the heterogeneous dissolution rate constant,c(OH-) is the concentration of hydroxide, and Sindigo is the reactive surface area. The activation energy for this process in aqueous 0.2 M NaOH is E-A = 64 U mol(-1) consistent with a considerable temperature effects. The redox mediator 1,8-dihydroxyanthraquinone is shown to significantly enhance the reaction rate by catalysing the electron transfer between glucose and solid indigo particles. (c) 2006 Elsevier Ltd. All fights reserved.

A rotating disc voltammetry study of the 1,8-dihydroxyanthraquinone mediated reduction of colloidal indigo

Colloidal indigo is reduced to an aqueous solution of leuco-indigo in a mediated two-electron process converting the water-insoluble dye into the water-soluble leuco form. The colloidal dye does not interact directly with the electrode surface, and to employ an electrochemical process for this reduction, the redox mediator 1,8-dihydroxyanthraquinone (1,8-DHAQ) is used to transfer electrons from the electrode to the dye. The mediated reduction process is investigated at a (500-kHz ultrasound-assisted) rotating disc electrode, and the quantitative analysis of voltammetric data is attempted employing the Digisim numerical simulation software package. At the most effective temperature, 353 K, the diffusion coefficient for 1,8-DHAQ is (0.84 +/- 0.08)x10(-9) m(2) s(-1), and it is shown that an apparently kinetically controlled reaction between the reduced form of the mediator and the colloidal indigo occurs within the diffusion layer at the electrode surface. The apparent bimolecular rate constant k (app)=3 mol m(-3) s(-1) for the rate law d[leuco-indigo]/dt = k(app) x [mediator] x [indigo] is determined and attributed to a mediator diffusion controlled dissolution of the colloid particles. The average particle size and the number of molecules per particles are estimated from the apparent bimolecular rate constant and confirmed by scanning electron microscopy.

Interaction of 2-(arylazo)phenols with rhodium. Usual coordination vs. C-H and C-C activation

Reaction of 2-(2'-hydroxyphenylazo)phenol with [Rh(PPh3)(3)Cl] in refluxing benzene in presence of triethylamine afforded a red complex in which the ligand is coordinated to rhodium as a tridentate O,N,O-donor. However, similar reaction of [Rh(PPh3)(3)Cl] with 2-(2'carboxyphenylazo)-4-methylphenol yielded two complexes, viz. a blue one and a green one. In both the complexes the ligand is coordinated as C,N,O-donor. However, in the blue complex orthometallation takes place from the ortho-carbon atom, which bears -COOH group via decarboxylation and in green one orthometallation occurs from the other ortho-carbon. Structures of all the three complexes were determined by X-ray crystallography. In all the three complexes rhodium is sharing the equatorial plane with the tridentate ligand and a chloride, and the two triphenylphosphines are axially disposed. All of the complexes show intense MLCT transitions in the visible region. Cyclic voltammetry on these complexes shows a Rh(III)-Rh(IV) oxidation on the positive side of SCE and a reduction of the coordinated azophenolate ligand on the negative side. (c) 2006 Elsevier B.V. All rights reserved.

Dinuclear complexes of M-II thiocyanate (M = Ni and Cu) containing a tridentate Schiff-base ligand: synthesis, structural diversity and magnetic properties

A dinuclear Ni-II complex, [Ni-2(L)(2)(H2O)(NCS)(2)]center dot 3H(2)O (1) in which the metal atoms are bridged by one water molecule and two mu(2)-phenolate ions, and a thiocyanato-bridged dimeric Cull complex, [Cu(L)NCS](2) (2) [L = tridentate Schiff-base ligand, N-(3-aminopropyl)salicylaldimine, derived from 1:1 condensation of salicylaldehyde and 1,3-diaminopropane], have been synthesized and characterized by IR and UV/Vis spectroscopy, cyclic voltammetry and single-crystal X-ray diffraction studies. The structure of 1 consists of dinuclear units with crystallographic C-2 symmetry in which each Ni-II atom is in a distorted octahedral environment. The Ni-O distance and the Ni-O-Ni angle, through the bridged water molecule, are 2.240(11) angstrom and 82.5(5)degrees, respectively. The structure of 2 consists of dinuclear units bridged asymmetrically by di-mu(1,3)-NCS ions; each Cull ion is in a square-pyramidal environment with tau = 0.25. Variable-temperature magnetic susceptibility studies indicate the presence of dominant ferromagnetic exchange coupling in complex 1 with J = 3.1 cm(-1), whereas complex 2 exhibits weak antiferromagnetic coupling between the Cu-II centers with J = -1.7 cm(-1). ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)