Kevin M. Williams

Effects of xanthan–locust bean gum mixtures on the physicochemical properties and oxidative stability of whey protein stabilised oil-in-water emulsions

The effects of xanthan gum (XG)-locust bean gum (LBG) mixtures (0.05, 0.1, 0.15, 0.2 and 0.5 wt%) on the physicochemical properties of whey protein isolate (WPI) stabilised oil-in-water (O/W) emulsions containing 20% v/v menhaden oil was investigated. At higher concentrations, the apparent viscosity of the emulsions containing XG/LBG mixtures was significantly higher (p<0.05) than the emulsions containing either XG or LBG alone. Locust bean gum showed the greatest phase separation, followed by XG. Microstructure images showed depletion flocculation at lower biopolymer concentrations, and thus led to an increase in creaming instability and apparent viscosity of the emulsions. Addition of 0.15, 0.2 and 0.5 wt% XG/LBG mixtures greatly decreased the creaming of the emulsions. The rate of lipid oxidation for 8-week storage was significantly lower (p<0.05) in emulsions containing XG/LBG mixtures than in emulsions containing either of the biopolymer alone.

Paradoxical enhancement of the toxicity of 1,2-dibromoethane by O6-alkylguanine-DNA alkyltransferase.

The presence of the DNA repair proteinO 6-alkylguanine-DNA alkyltransferase (AGT) paradoxically increases the mutagenicity and cytotoxicity of 1,2-dibromoethane (DBE) in Escherichia coli. This enhancement of genotoxicity did not occur when the inactive C145A mutant of human AGT (hAGT) was used. Also, hAGT did not enhance the genotoxicity of S-(2-haloethyl)glutathiones that mimic the reactive product of the reaction of DBE with glutathione, which is catalyzed by glutathione S-transferase. These experiments support a mechanism by which hAGT activates DBE. Studies in vitro showed a direct reaction between purified recombinant hAGT and DBE resulting in a loss of AGT repair activity and a formation of an hAGT-DBE conjugate at Cys145. A 2-hydroxyethyl adduct was found by mass spectrometry to be present in the Gly136-Arg147 peptide from tryptic digests of AGT reacted with DBE. Incubation of AGT with DBE and oligodeoxyribonucleotides led to the formation of covalent AGT-oligonucleotide complexes. These results indicate that DBE reacts at the active site of AGT to generate an S-(2-bromoethyl) intermediate, which forms a highly reactive half-mustard at Cys145. In the presence of DNA, the DNA-binding function of AGT facilitates formation of DNA adducts. In the absence of DNA, the intermediate undergoes hydrolytic decomposition to form AGT-Cys145-SCH2CH2OH.

Effect of xanthan/enzyme-modified guar gum mixtures on the stability of whey protein isolate stabilized fish oil-in-water emulsions.

The effect of xanthan gum (XG) and enzyme-modified guar (EMG) gum mixtures on the physicochemical properties and oxidative stability of 2wt% whey protein isolate (WPI) stabilized oil-in-water (O/W) emulsions containing 20%v/v fish oil was investigated. EMG was obtained by hydrolyzing native guar gum using α-galactosidase enzyme. At higher gum concentrations (0.2 and 0.3wt%), the viscosity of the emulsions containing XG/EMG gum mixtures was significantly higher (P<0.05) of all emulsions. Increasing concentrations (0-0.3wt%) of XG/EMG gum mixtures did not affect the droplet size of emulsions. Microstructure images revealed decreased flocculation at higher concentrations. Primary and secondary lipid oxidation measurements indicated a slower rate of oxidation in emulsions containing XG/EMG gum mixtures, compared to XG, guar (GG), and XG/GG gum mixtures. These results indicate that XG/EMG gum mixtures can be used in O/W emulsions to increase physical and oxidative stabilities of polyunsaturated fatty acids in foods.

Creaming and oxidative stability of fish oil-in-water emulsions stabilized by whey protein-xanthan-locust bean complexes: Impact of pH

The impact of pH on the physicochemical properties of 10% menhaden oil-in-water (O/W) emulsions containing 2% whey protein isolate (WPI) and 0.1% xanthan (XG)-locust bean gum (LBG) mixtures was investigated. The O/W emulsions containing 0.1% XG-LBG mixtures were compared to emulsions with 0.1% XG and 0.1% LBG. The results indicated that stability is dependent on pH and biopolymer type. At both pH 3 and 5, emulsions containing either XG or XG-LBG mixtures had large particle sizes, viscosity, droplet aggregation, and creaming index, resulting in poor physical stability which can be related to the adsorbed protein-polysaccharide interactions. At pH7, the XG-LBG emulsions showed the greatest resistance to phase separation and resulted in stable emulsions. Lipid oxidation measurements also indicated that XG-LBG mixtures can be used to form stable emulsions at pH 3 and pH 7. These results have significant implications for the development of novel structures containing lipid phases susceptible to lipid oxidation.

Thermal and Oxidative Properties of Physiologically Relevant Free Fatty Acids by Dielectric Analysis and Differential Scanning Calorimetry

Physiologically relevant fatty acids and related organic acids are basic for human life. The essential fatty acids, linoleic, linolenic, and arachidonic acids, are sourced from vegetable seed oils (corn, sunflower, safflower), and margarines blended with vegetable oils. The functions of these special acids are in the synthesis of prostaglandins and membrane structures. Growth cessation and dermatitis occurs with a deficiency of the fatty acids. A typical therapeutic dosage of the essential fatty acids is up to 10 g per day. The polyunsaturated fatty acids. linoleic (9,12-octadecaidienoic), linolenic (9,12,15-octadecatrienoic), and arachidonic (5,8,11,14-eicosatetraenoic) are referred to as essential fatty acids. They unlike other lipids must be provided by diet. Arachidonic acid can be produced in the body by linoleic acid. This thermal analytical study is to determine fatty acids’ physical transitions [melting] by DSC at low temperatures and their surface properties by low frequency dielectric analysis and relate those properties to the inherent amount of unsaturation in the fatty acids. It is our premise that the degree of unsaturation will affect low temperature melt temperature and electrical properties, e.g., electrical conductivity and complex permittivity. We have observed that the DEA properties of the air-aged liquid fatty acids indicate that the electrical conductivity and complex permittivity can be correlated with the degree of unsaturation. It is our objective to establish a relationship between the amount of unsaturation, number of double bond sites and the electrical properties, complex permittivity, and electrical conductivity.