Ryan J. Elias

Antioxidant Activity of Proteins and Peptides

Proteins can inhibit lipid oxidation by biologically designed mechanisms (e.g. antioxidant enzymes and iron-binding proteins) or by nonspecific mechanisms. Both of these types of antioxidative proteins contribute to the endogenous antioxidant capacity of foods. Proteins also have excellent potential as antioxidant additives in foods because they can inhibit lipid oxidation through multiple pathways including inactivation of reactive oxygen species, scavenging free radicals, chelation of prooxidative transition metals, reduction of hydroperoxides, and alteration of the physical properties of food systems. A proteins overall antioxidant activity can be increased by disruption of its tertiary structure to increase the solvent accessibility of amino acid residues that can scavenge free radicals and chelate prooxidative metals. The production of peptides through hydrolytic reactions seems to be the most promising technique to form proteinaceous antioxidants since peptides have substantially higher antioxidant activity than intact proteins. While proteins and peptides have excellent potential as food antioxidants, issues such as allergenicity and bitter off-flavors as well as their ability to alter food texture and color need to be addressed.

The antioxidant and pro-oxidant activities of green tea polyphenols: a role in cancer prevention.

Green tea (Camellia sinensis) is rich in catechins, of which (-)-epigallocatechin-3-gallate (EGCG) is the most abundant. Studies in animal models of carcinogenesis have shown that green tea and EGCG can inhibit tumorigenesis during the initiation, promotion and progression stages. Many potential mechanisms have been proposed including both antioxidant and pro-oxidant effects, but questions remain regarding the relevance of these mechanisms to cancer prevention. In the present review, we will discuss the redox chemistry of the tea catechins and the current literature on the antioxidant and pro-oxidative effects of the green tea polyphenols as they relate to cancer prevention. We report that although the catechins are chemical antioxidants which can quench free radical species and chelate transition metals, there is evidence that some of the effects of these compounds may be related to induction of oxidative stress. Such pro-oxidant effects appear to be responsible for the induction of apoptosis in tumor cells. These pro-oxidant effects may also induce endogenous antioxidant systems in normal tissues that offer protection against carcinogenic insult. This review is meant point out understudied areas and stimulate research on the topic with the hope that insights into the mechanisms of cancer preventive activity of tea polyphenols will result.

Role of Physical Structures in Bulk Oils on Lipid Oxidation

Lipid oxidation is important to food manufacturers especially when they increase unsaturated lipids in their products to improve nutritional profiles. Unfortunately, the number of antioxidants available to food manufacturers to control oxidative rancidity is limited and the approval of new antioxidants is unlikely due to economic barriers in obtaining government approval for new food additives. Therefore, new antioxidant technologies are needed for food oils. This paper reviews the current knowledge of lipid oxidation in foods with emphasis on how physical properties of food systems impact oxidation chemistry. In particular, the role of association colloids in bulk oils on lipid oxidation chemistry is discussed in an attempt to understand mechanisms of oxidation. Increasing the understanding of how physical properties impact lipid oxidation could lead to the development of novel antioxidant technologies that not only protect the oil against oxidation and increase shelf-life but also allow food manufacturers to include more nutritionally beneficial fatty acids in their products.

Controlling the Fenton reaction in wine.

The fate of hydrogen peroxide in a model wine system was studied under a competitive scenario in the presence of ferrous ions and sulfur dioxide. The metal-catalyzed reduction of hydrogen peroxide (H(2)O(2)), referred to as the Fenton reaction, yields hydroxyl radicals capable of oxidizing ethanol to acetaldehyde and is now thought to be a key step in nonenzymatic wine oxidation. It appears that sulfur dioxide (SO(2)) exerts its protective function in wine by scavenging hydrogen peroxide in oxidizing wine, thereby diverting peroxide from the Fenton route. In this study, the factors affecting the rate and outcome of hydroxyl radical-mediated ethanol oxidation were examined under wine conditions. The exclusion of oxygen in the model wine led to conditions wherein ferric ions (50 microM) were rapidly reduced, presumably by 1-hydroxyethyl radicals. This resulted in the complete stoichiometric conversion of H(2)O(2) (300 microM) to hydroxyl radicals, giving an equimolar concentration of acetaldehyde ( approximately 300 microM). Surprisingly, the yield of acetaldehyde was markedly depressed in the presence of oxygen. The addition of a model phenol, 4-methylcatechol (4-MeC; 12 mM), did not protect the ethanol from hydroxyl radical-mediated oxidation under the conditions tested but rather appeared to slightly increase the rate of the Fenton reaction, perhaps by forming a complex with the added iron. The competition for H(2)O(2) in the presence of Fe(II) ions and SO(2) was also examined, and the effect of added 4-MeC, as well as dissolved oxygen, was investigated. Higher concentrations of 1-hydroxyethyl radicals, which were trapped by N-tert-butyl-alpha-phenylnitrone (PBN) and detected by electron paramagnetic resonance spectroscopy, were observed when oxygen was excluded and when 4-MeC was included.

Identification of Free Radical Intermediates in Oxidized Wine Using Electron Paramagnetic Resonance Spin Trapping

Free radicals are thought to be key intermediates in the oxidation of wine, but their nature has not been established. Electron paramagnetic resonance spectroscopy was used to detect and identify several free radical species in wine under oxidative conditions with the aid of spin traps. The 1-hydroxylethyl radical was the sole radical species observed when α-(4-pyridyl-1-oxide)-N-tert-butylnitrone was used as a spin trap in a heated (55 °C), low-sulfite (15 mg L(-1)) red wine. This radical appears to arise from ethanol oxidation via the hydroxyl radical, and this latter species was confirmed by using a high concentration (1.5 M) of the 5,5-dimethylpyrroline-N-oxide spin trap, thus providing the first direct evidence of the Fenton reaction in wine. Hydroxyl radical formation in wine was corroborated by converting hydroxyl radicals to methyl radicals by its reaction with dimethyl sulfoxide. The novel spin trap 5-tert-butoxycarbonyl 5-methyl-1-pyrroline N-oxide was also used in this study to identify sulfite radicals in wine for the first time. This spin trap has also been shown to trap hydroperoxyl radicals, the generation of which is predicted in wine; however, no evidence of this species was observed.

Effects of Postharvest Pulsed UV Light Treatment of White Button Mushrooms (Agaricus bisporus) on Vitamin D2 Content and Quality Attributes

Pulsed UV light (PUV) was investigated as a means to rapidly increase vitamin D(2) (D(2)) content in fresh button mushrooms (Agaricus bisporus). D(2) was found to increase to over 100% RDA/serving following 3 pulses (1 s). Following 12 pulses, D(2) began to approach a maximum concentration of 27 μg/g DW. The D(2) produced with 3 pulses decreased from 11.9 to 9.05 μg/g DW after 3 days of storage; however, D(2) levels remained nearly constant after this point throughout an 11-day shelf life study. PUV treated sliced mushrooms produced significantly more D(2) than whole mushrooms, and it was also observed that brown buttons generated significantly less D(2) than white buttons. Several quality attributes were assessed, and no significant differences between control and PUV treated mushrooms were observed. These findings suggest that PUV treatment is a viable method for rapidly increasing the D(2) content of fresh mushrooms without adversely affecting quality parameters.

Reaction Mechanisms of Metals with Hydrogen Sulfide and Thiols in Model Wine. Part 1: Copper-Catalyzed Oxidation

Sulfidic off-odors as a result of hydrogen sulfide (H2S) and low-molecular-weight thiols are commonly encountered in wine production. These odors are usually removed by the process of Cu(II) fining, a process that remains poorly understood. The present study aims to elucidate the underlying mechanisms by which Cu(II) interacts with H2S and thiol compounds (RSH) under wine-like conditions. Copper complex formation was monitored along with H2S, thiol, oxygen, and acetaldehyde concentrations after the addition of Cu(II) (50 or 100 μM) to air-saturated model wine solutions containing H2S, cysteine, 6-sulfanylhexan-1-ol, or 3-sulfanylhexan-1-ol (300 μM each). The presence of H2S and thiols in excess to Cu(II) led to the rapid formation of ∼1.4:1 H2S/Cu and ∼2:1 thiol/Cu complexes, resulting in the oxidation of H2S and thiols and reduction of Cu(II) to Cu(I), which reacted with oxygen. H2S was observed to initially oxidize rather than form insoluble copper sulfide. The proposed reaction mechanisms provide insight into the extent to which H2S can be selectively removed in the presence of thiols in wine.

Antioxidant and pro-oxidant activity of (-)-epigallocatechin-3-gallate in food emulsions: Influence of pH and phenolic concentration.

Polyphenols have been observed to exert both antioxidant and pro-oxidant activity in lipid foods, and factors that influence that net effect include both polyphenol concentration and matrix pH. In this study, the effects of concentration (1-500 μM) of a model polyphenol, (-)-epigallocatechin-3-gallate (EGCG), and matrix pH (2-7) on the net anti-/pro-oxidant activity of EGCG in flaxseed oil-in-water (o/w) emulsions were systematically evaluated. After 24h, EGCG (5-100 μM) was observed to exhibit pro-oxidant activity in low pH (pH 2-4) emulsions, as determined by conjugated dienes (CDs) and thiobarbituric acid reactive substances (TBARSs) production. At the higher pH values studied (pH 5-7), lower CD and TBARS concentrations were detected in samples with 25-500 μM EGCG at 24h. Overall, EGCG concentration and pH both played significant roles in determining net antioxidant or pro-oxidant effects, with the largest antioxidant and pro-oxidant effects observed at the higher EGCG concentrations (100-500 μM) tested.

Solute distribution and stability in emulsion-based delivery systems: An EPR study

Oil-in-water emulsions and related systems are often used to deliver hydrophobic solutes in foods, personal care products, and pharmaceuticals. Recent work has considered the use of crystalline lipid carrier particles (i.e., solid lipid nanoparticles, SLN) to control the availability of the solute; however, there is little direct evidence for the localization of small molecules in these systems. Alkanes (10 wt.% tetradecane or eicosane) containing the spin probe 4-phenyl-2,2,5,5-tetramethyl-3-imidazoline-1-oxyl (PTMIO, 200 ppm) were homogenized into sodium caseinate solution (1 wt.%) to produce fine or coarse droplets (0.2 μm or 1.3 μm, respectively) and cooled to 21.5 °C where eicosane is crystalline and tetradecane is liquid. Analysis of the resulting EPR spectra revealed populations of probe in two discrete environments (i.e., aqueous and lipid). PTMIO is largely hydrophobic with 77% and 70% present in the coarse and fine liquid lipid droplets (i.e., tetradecane droplets), respectively. In the solid droplets (i.e., eicosane), all of the probe was excluded from the droplets into the aqueous environment. In all cases, the mobility of the probe in both lipid and aqueous environments was affected by the droplet surface; thus, we hypothesize that the majority of the probe molecules are associated with the droplet interface. The PTMIO was reduced to an EPR-silent form by the addition of iron/ascorbate to the aqueous phase, and the apparent rate constant of the reaction was proportional to the fraction of the spin probe in the aqueous phase. Based on these findings, we propose that droplet crystallization excludes solute molecules from the droplet core to the aqueous environment where they interact with the droplet surface.

Investigation of Ethyl Radical Quenching by Phenolics and Thiols in Model Wine

In the present study, the reaction between 1-hydroxyethyl radicals (1-HER) and various wine-related phenolics and thiols, including gallic acid, caffeic acid, ferulic acid, 3-mercaptohexan-1-ol (3MH), cysteine (Cys), and glutathione (GSH), was studied using competitive spin trapping with electron paramagnetic resonance (EPR) and mass spectrometry. Previous studies have reported several important reactions occurring between quinones and other wine components, but the fate of 1-HER within the context of wine oxidation is less understood. Furthermore, the ability of these compounds to prevent formation of acetaldehyde, a known nonenzymatic oxidation product of ethanol, was measured. The hydroxycinnamic acids and thiol compounds tested at 5 mM concentrations significantly inhibited spin adduct formation, indicating their reactivity toward 1-HER. In addition, we confirm that loss of 3MH under model wine conditions is due to quinone trapping as well as 1-HER-induced oxidation.