Characterization of major radical scavenger species in bovine milk through size exclusion chromatography and functional assays

Contribution of the interfacial layer to the protection of emulsified lipids against oxidation

The oxidative stability of oil-in-water (O/W) emulsions is highly dependent on the type of emulsifier. The purpose of this work was to investigate the specific role of the adsorbed emulsifiers on lipid oxidation of O/W emulsions. Emulsions of similar droplet size distribution stabilized by minimum amounts of proteins or surfactants were oxidized at 25 °C in the presence of equimolar iron-EDTA complex. The pH and the amount of emulsifier in the aqueous phase were also varied to investigate the role of the droplet charge and the emulsifier in the aqueous phase. Oxygen uptake, conjugated dienes (CD), and volatile compound formation demonstrated that the protein-stabilized interfaces are less efficient at protecting emulsified lipids against oxidation than surfactant-stabilized interfaces. The antioxidant effect of unadsorbed proteins was also confirmed.

Damage to amino acid-nucleotide pairs induced by 1 eV electrons

We have investigated the role of two selected amino acids, glycine and arginine, on damage induced to a short chain of single stranded DNA, the tetramer GCAT, during 1 eV electron exposure. At this energy, DNA has a high cross section for DNA damage via exclusively dissociative electron attachment. Surprisingly, at low ratios of glycine:GCAT, an increase in the total fragmentation yield is observed, whilst at higher ratios, glycine and arginine appear to protect DNA from the direct action of electrons. In addition, binding energies were calculated by molecular modelling of the interactions between these amino acids and either nucleobases or nucleotides. These binding energies appear to be related to the ability of amino acids to protect DNA against low energy electron damage.

Lipid oxidation in algae oil-in-water emulsions stabilized by bovine and caprine caseins

Caseins (alpha(s1)-, alpha(s2)-, and beta-casein) are phosphoproteins that are capable of binding transition metals and scavenging free radicals; this property makes them good candidates to be used as natural antioxidants in oil-in-water emulsions. Caprine casein exhibits variability in alpha(s1)-casein content generated by genetic polymorphism. This variability in composition could lead to altered antioxidant properties. Thus, the ability of two caprine caseins differing in alpha(s1)-casein content to inhibit lipid oxidation in algae oil-in-water emulsions at 5% oil was investigated and compared to bovine caseinate. All caseins inhibited the formation of lipid oxidation at pH 7.0 as determined by lipid hydroperoxides and thiobarbituric acid reactive substances (TBARS). However, caprine caseins were in general more effective inhibitors of lipid oxidation than the bovine caseins, which may be attributed to their altered casein amino acid content and/or metal binding capabilities. The combination of the carotenoids with bovine and caprine caseins was highly effective at repressing oxidation leading to the speculation that the caseins may inhibit the loss of the carotenoids and/or react with and enhance the carotenoid activity; again some differences between bovine and caprine caseins were observed with caprine caseins being slightly more effective in the presence of carotenoids.

Characterization of peroxides formed by riboflavin and light exposure of milk. Detection of urate hydroperoxide as a novel oxidation product

Characterization of peroxides by size exclusion chromatography (SEC) of milk following exposure to riboflavin and light showed that hydrogen peroxide was the most abundant peroxide formed since it could be removed by catalase. Formation of peroxides after separation by SEC showed that hydrogen peroxide formation was primarily increased in the presence of caseins and ascorbate, although whey proteins also were found to contribute. Caseins and beta-lactoglobulin also formed catalase-resistant peroxides, presumably protein hydroperoxides. A catalase-resistant and unstable peroxide was observed in fractions containing urate. Experiments performed with pure urate suggested that urate radicals reacted further with superoxide leading to a urate hydroperoxide. Electron paramagnetic resonance spectroscopy using spin-traps showed that the presence of oxygen was required for urate radical formation, which could be assigned as nitrogen-centered radicals. These results suggest a new route during light-induced oxidation sensitized by flavins, in effect making urate pro-oxidative.