Measuring antioxidant effectiveness in food     

Decker EA  Warner K  Richards MP  Shahidi F 《Journal of agricultural and food chemistry》2005,53(10):4303-4310

Many new in vitro methods have been developed to evaluate antioxidant activity. Unfortunately, these in vitro methods often correlate poorly with the ability of compounds to inhibit oxidative deterioration of foods because the in vitro assays do not account for factors such as the physical location of the antioxidant, its interaction with other food components, and environmental conditions. To accurately evaluate the potential of antioxidants in foods, models must be developed that have the chemical, physical, and environmental conditions expected in food products. This paper outlines model systems of the evaluation of antioxidants in three types of foods: bulk oil, oil-in-water emulsions, and muscle foods. These model systems are not intended to be inclusive of all possible methods to measure lipid oxidation and antioxidant activity. However, use of these models would allow researchers to more easily compare research results from one paper to another.  相似文献   

beta-glucosidases from five black Aspergillus species: study of their physico-chemical and biocatalytic properties     

Decker CH  Visser J  Schreier P 《Journal of agricultural and food chemistry》2000,48(10):4929-4936

Five black Aspergillus strains (A. aculeatus, A. foetidus, A. japonicus, A. niger, and A. tubingensis) were cultivated on crude wheat arabinoxylan as the carbon source under defined pH, temperature, and oxygen conditions. Protein and beta-glucosidase content differed remarkably within the obtained culture filtrates, of which eleven beta-glucosidases were isolated. Seven beta-glucosidases were purified to apparent electrophoretic homogeneity using anion-exchange and gel-permeation chromatography. They were found to be acidic proteins and most of them appeared to be glycoproteins with a molecular mass between 93 and 142 kDa. Classification of the beta-glucosidases into four groups (I-A, I-B, II, and III) is suggested according to their physicochemical and biocatalytic properties. The major beta-glucosidases were assigned to groups I-A and I-B, the minor beta-glucosidases to groups II and III, comprising acid-tolerant and glucose-tolerant enzymes, respectively.  相似文献   

Voyager 1 in the foreshock, termination shock, and heliosheath     

Decker RB  Krimigis SM  Roelof EC  Hill ME  Armstrong TP  Gloeckler G  Hamilton DC  Lanzerotti LJ 《Science (New York, N.Y.)》2005,309(5743):2020-2024

Voyager 1 (V1) began measuring precursor energetic ions and electrons from the heliospheric termination shock (TS) in July 2002. During the ensuing 2.5 years, average particle intensities rose as V1 penetrated deeper into the energetic particle foreshock of the TS. Throughout 2004, V1 observed even larger, fluctuating intensities of ions from 40 kiloelectron volts (keV) to >/=50 megaelectron volts per nucleon and of electrons from >26 keV to >/=350 keV. On day 350 of 2004 (2004/350), V1 observed an intensity spike of ions and electrons that was followed by a sustained factor of 10 increase at the lowest energies and lesser increases at higher energies, larger than any intensities since V1 was at 15 astronomical units in 1982. The estimated solar wind radial flow speed was positive (outward) at approximately +100 kilometers per second (km s(-1)) from 2004/352 until 2005/018, when the radial flows became predominantly negative (sunward) and fluctuated between approximately -50 and 0 km s(-1) until about 2005/110; they then became more positive, with recent values (2005/179) of approximately +50 km s(-1). The energetic proton spectrum averaged over the postshock period is apparently dominated by strongly heated interstellar pickup ions. We interpret these observations as evidence that V1 was crossed by the TS on 2004/351 (during a tracking gap) at 94.0 astronomical units, evidently as the shock was moving radially inward in response to decreasing solar wind ram pressure, and that V1 has remained in the heliosheath until at least mid-2005.  相似文献   

DNA Replication and Recombination     

EA Adelberg 《Science (New York, N.Y.)》1964,146(3648):1193-1195

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Scientific Communications Should Be Improved     

Decker FW 《Science (New York, N.Y.)》1957,125(3238):101-105

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Ability of lipid hydroperoxides to partition into surfactant micelles and alter lipid oxidation rates in emulsions     

Nuchi CD  Hernandez P  McClements DJ  Decker EA 《Journal of agricultural and food chemistry》2002,50(19):5445-5449

Lipid hydroperoxides are important factors in lipid oxidation due to their ability to decompose into free radicals. In oil-in-water emulsions, the physical location of lipid hydroperoxides could impact their ability to interact with prooxidants such as iron. Interfacial tension measurements show that linoleic acid, methyl linoleate, and trilinolein hydroperoxides are more surface-active than their non-peroxidized counterparts. In oil-in-water emulsion containing surfactant (Brij 76) micelles in the continuous phase, linoleic acid, methyl linoleate, and trilinolein hydroperoxides were solubilized out of the lipid droplets into the aqueous phase. Brij 76 solubilization of the different hydroperoxides was in the order of linoleic acid > trilinolein > or = methyl linoleate. Brij 76 micelles inhibited lipid oxidation of corn oil-in-water emulsions with greater inhibition of oxidation occurring in emulsions containing linoleic acid hydroperoxides. Surfactant solubilization of lipid hydroperoxides could be responsible for the ability of surfactant micelles to inhibit lipid oxidation in oil-in-water emulsions.  相似文献   

Impact of lipid physical state on the oxidation of methyl linolenate in oil-in-water emulsions   总被引：1，自引：0，他引：1  

Okuda S  McClements DJ  Decker EA 《Journal of agricultural and food chemistry》2005,53(24):9624-9628

The purpose of this research was to examine the influence of the physical state of lipids on iron-promoted oxidation of methyl linolenate in octadecane oil-in-water emulsions. Octadecane and methyl linolenate oil-in-water emulsions were prepared that contained droplets having the octadecane as either liquid or solid. The physical state of the octadecane was confirmed by a differential scanning calorimeter (DSC). The effect of the physical state of the lipid on oxidation rates was determined as a function of iron concentration (80 and 160 microM), pH (3.0 or 7.0), emulsifier type, and cooling rate. Oxidation of methyl linolenate was determined by lipid hydroperoxides and thiobarbituric acid reactive substances (TBARS). Emulsions containing solid octadecane had higher rates of lipid hydroperoxide and TBARS formation than those containing liquid octadecane. The rate at which the emulsions were cooled had no influence on oxidation rates. Oxidation rates in both emulsions increased with increasing iron concentration and decreasing pH. Oxidation rates were lowest in emulsions with cationic droplet membranes (dodecyl trimethylammonium bromide-stabilized), presumably due to the repulsion of iron from the oxidizable methyl linolenate in the emulsion droplet core. These results suggest that upon crystallization of octadecane, the liquid methyl linolenate migrated to the emulsion droplet surface, where it was more prone to oxidation because it was in closer contact with the iron ions in the aqueous phase.  相似文献   

Production and characterization of O/W emulsions containing cationic droplets stabilized by lecithin-chitosan membranes     

Ogawa S  Decker EA  McClements DJ 《Journal of agricultural and food chemistry》2003,51(9):2806-2812

Oil-in-water emulsions containing cationic droplets stabilized by lecithin-chitosan membranes were produced using a two-stage process. A primary emulsion was prepared by homogenizing 5 wt % corn oil with 95 wt % aqueous solution (1 wt % lecithin, 100 mM acetic acid, pH 3.0) using a high-pressure valve homogenizer. This emulsion was diluted with aqueous chitosan solutions to form secondary emulsions with varying compositions: 1 wt % corn oil, 0.2 wt % lecithin, 100 mM acetic acid, and 0-0.04 wt % chitosan (pH 3.0). The particle size distribution, particle charge, and creaming stability of the primary and secondary emulsions were measured. The electrical charge on the droplets increased from -49 to +54 mV as the chitosan concentration was increased from 0 to 0.04 wt %, which indicated that chitosan adsorbed to the droplet surfaces. The mean particle diameter of the emulsions increased dramatically and the emulsions became unstable to creaming when the chitosan concentration exceeded 0.008 wt %, which was attributed to charge neutralization and bridging flocculation effects. Sonication, blending, or homogenization could be used to disrupt flocs formed in secondary emulsions containing droplets with high positive charges, leading to the production of emulsions with relatively small particle diameters (approximately 1 microm). These emulsions had good stability to droplet aggregation at low pH (< or =5) and ionic strengths (<500 mM). The interfacial engineering technology utilized in this study could lead to the creation of food emulsions with improved stability to environmental stresses.  相似文献   

Impact of dietary conjugated linoleic acid on the oxidative stability of rat liver microsomes and skeletal muscle homogenates     

Livisay SA  Zhou S  Ip C  Decker EA 《Journal of agricultural and food chemistry》2000,48(9):4162-4167

Dietary conjugated linoleic acid (CLA; 0-2.0%) increased CLA concentrations in liver microsomes and skeletal muscle homogenates from rats. Dietary CLA decreased oleic and arachadonic acid concentrations in both liver microsomes and skeletal muscle. The presence of CLA in liver microsomes had no impact on linoleic acid, arachadonic acid, and alpha-tocopherol oxidation rates. Dietary CLA (2.0%) also did not alter alpha-tocopherol oxidation rates in liver microsomes or muscle homogenates. Formation of malonaldehyde (MDA) in oxidizing liver microsomes decreased with increasing CLA concentration as determined by measurement of thiobarbituric acid-MDA complexes by HPLC. The ability of CLA to decrease MDA formation without impacting other lipid oxidation markers such as the disappearance of fatty acid and alpha-tocopherol suggests that decreased MDA concentration was the result of CLA's ability to lower polyenoic fatty acids such as arachadonic acid. While CLA does not appear to act as an antioxidant, its ability to decrease polyenoic fatty acid concentrations could decrease the formation of highly cytotoxic lipid oxidation products such as MDA.  相似文献   

Role of continuous phase protein on the oxidative stability of fish oil-in-water emulsions   总被引：4，自引：0，他引：4  

Faraji H  McClements DJ  Decker EA 《Journal of agricultural and food chemistry》2004,52(14):4558-4564

Whey protein isolate (WPI), soy protein isolate (SPI), and sodium caseinate (CAS) can inhibit lipid oxidation when they produce a positive charge at the interface of emulsion droplets. However, when proteins are used to stabilize oil-in-water emulsions, only a fraction of them actually absorb to the emulsion droplets, with the rest remaining in the continuous phase. The impact of these continuous phase proteins on the oxidative stability of protein-stabilized emulsions is not well understood. WPI-stabilized menhaden oil-in-water emulsions were prepared by high-pressure homogenization. In some experiments WPI was removed from the continuous phase of the emulsions through repeated centrifugation and resuspension of the emulsion droplets (washed emulsion). Unwashed emulsions were more oxidatively stable than washed emulsions at pH 7.0, suggesting that continuous phase proteins were antioxidative. The oxidative stability of emulsions containing different kinds of protein in the continuous phase decreased in the order SPI > CAS > WPI, as determined by both hydroperoxide and headspace propanal formation. Iron-binding studies showed that the chelating ability of the proteins decreased in the order CAS > SPI > WPI. The free sulfhydryls of both WPI and SPI were involved in their antioxidant activity. This research shows that continuous phase proteins could be an effective means of protecting omega-3 fatty acids from oxidative deterioration.  相似文献