Lipid oxidation leads to quality deterioration of foods high in unsaturated fatty acids. Edible oils contain surface active compounds and water that can form physical structures known as association colloids. To better understand the influence of physical structures on the oxidative stability of bulk oils the role of association colloids on lipid oxidation was investigated. The effectiveness of chain-breaking antioxidants at retarding lipid oxidation depends on their chemical properties and physical location within a food. The first study showed that the surface activity and/or polarity of lipid-soluble antioxidant were not the only determinant of their effectiveness in food lipids. In the second study of model association colloids in oils, we found that the size of the reverse micelles increased with increased water or phosphatidylcholine concentration, but decreased upon addition of cumene hydroperoxide or oleic acid. Iron catalyzed oxidation of methyl linolenate in the reverse micelle system decreased with increasing water concentration. Phosphatidylcholine decreased methyl linolenate oxidation compared to control and reverse micelles with added oleic acid. These results indicate that water, cumene hydroperoxide, oleic acid, and phosphatidylcholine can alter reverse micelle size and lipid oxidation rates. The influence of these compounds on physical structures of bulk oil was also confirmed in a study using surface active fluorescence probe. The fluorescence intensity of 5-dodecanoylaminofluorescein (DAF) increased with increasing water concentration in the edible oil. Addition of oleic acid decreased DAF fluorescence due to the ability of the free fatty acid to decrease the pH of the aqueous phase of the bulk oil. Phosphatidylcholine increased DAF fluorescence due to its ability to increase DAF exposure to the aqueous phase. Oleic acid had no impact in the interactions between DAF and water soluble peroxyl radicals while phosphatidylcholine decreased peroxyl radical degradation of DAF. This research established the significance of physical structures of bulk oils on lipid oxidation. Understanding how the physical properties of bulk oils impact lipid oxidation could lead to development of novel antioxidant technologies that help improve the oxidative stability of oils containing increased concentrations of polyunsaturated fatty acids.

Phytophenols are antimicrobials that may inhibit the growth of foodborne pathogens. However, their antimicrobial activity is low because of low water solubility. The objective of this study was to formulate emulsion and microemulsion and test their efficacy as antimicrobial delivery systems. Eugenol was solubilized into cationic-nonionic (Mirenat-N® -T-Maz®80K or LAE-TM) and nonionic surfactant mixtures (T-Maz®80K-Surfynol®485W or TM-S485). Formulation of emulsions using eugenol is challenging due to Ostwald ripening. Eugenol was mixed with hydrocarbons to decrease Ostwald ripening rate using compositional ripening. Physicochemical characterization included surface tension, particle size, charge and solubilization capacity. Antimicrobial efficiency was tested using spot inoculation against four strains of Listeria monocytogenes and Escherichia coli O157:H7. The antimicrobial activity of eugenol micelles in ultra-high temperature pasteurized milk containing different percentages of milk fat was investigated. Nonionic mixed surfactant micelles showed no inhibition against both pathogens but the individual surfactants showed inhibition with 8mM of eugenol. The antimicrobial efficiency of cationic-non-ionic micelles was high since LAE alone inhibited the growth of E. coli O157:H7 and Listeria. Micelles inhibited all microbial the growth with exception of the TM:LAE (5:1) ratio. Addition of eugenol at 3mM inhibited the growth of Listeria and 7 mM inhibited the growth of E. coli O157:H7. When microemulsions were tested in a food system (milk), the antimicrobial efficiency varied depending on the fat level. Microemulsions completely prevented growth of Listeria and E. coli O157:H7 in skim and 2% milk but not in 4% fat in milk. Therefore, food composition, especially fat level, may affect the efficiency of targeting of foodborne pathogens by surfactant-encapsulated antimicrobials. The stability and antimicrobial efficacy of 5% oil-in-water emulsions formulated with eugenol and hydrocarbons was evaluated. Eugenol and lipids were mixed at different eugenol:lipid ratios. Corn-oil emulsions loaded with eugenol were the most stable and inhibited the growth against E. coli O157:H7 strains depending on loading ratio but failed to inhibit growth of Listeria strains. When surfactants are used as transport vehicles, selection of surfactant and mixing ratios is of crucial importance. Microemulsion and emulsions have substantial potential as new preservation systems for foods since they were completely composed of GRAS compounds.

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Abstract not available

Even though edible oils undergo refining processes to remove undesirable components, commercial oils still contain small amounts of minor components that can contribute to either prooxidant and antioxidant pathways which ultimately affect the quality of the oils. The objective of this research was to determine the role of free fatty acids and mono- and diacylglycerols on the oxidative stability of oil-in-water emulsions. Free fatty acids acted as a strong prooxidants in stripped soybean oil-in-water emulsions. Concentrations as low as 0.1% of the lipid accelerated lipid oxidation rate by both shortening the lag phase of lipid hydroperoxide and hexanal formation. The results showed that the most likely mechanisms for the prooxidant activity of free fatty acids is through their ability to increase the negatively charge on emulsion droplets that in turn could attract the cationic transition metals to the emulsion droplet surface where they can interact with lipid and thus promote oxidation. The prooxidant activity of free fatty acids was dependent on fatty acid type with lipid oxidation rates being in the order of linolenic < linoleic < oleic. Surprisingly, an increase in the degree of unsaturation of the free fatty acids lowered the ability of the free fatty acids to promote oxidation which may be due to their differences in geometric shape thus influencing their ability to access the emulsion droplet interface and increase the negative charge. Overall, free fatty acids are strong prooxidants in oil-in-water emulsions. This prooxidant activity is dependent not only on their concentration but also on the molecular structure of the fatty acid. Addition of mono- and diacylglycerols in oil-in-water emulsions showed an antioxidative effect in both non-stripped and stripped soybean oil. Addition of 1-monooleoylglycerol only had a small impact on the oxidative stability of non-stripped soybean oil-in-water emulsions but did inhibit lipid oxidation in emulsions prepared with stripped soybean. Much stronger antioxidant activity was observed upon the addition of 1,2-dioleoyl-sn-glycerol to both non-stripped and stripped soybean oil-in-water emulsions. Both lipid hydroperoxide and hexanal formation decreased with increasing 1,2-dioleoyl- sn-glycerol concentrations with 2.5% 1,2-dioleoyl-sn-glycerol almost completely preventing hydroperoxide and hexanal production over the course of the study. Overall, these results suggest that diacylglycerols could be an effective antioxidant in oil-in-water emulsions which possibility due to their ability to form a liquid crystal phase which could form a physical barrier that decreases interactions between unsaturated fatty acids in the emulsion droplet core and prooxidants or oxygen in the aqueous phase of the emulsion. However, the antioxidant mechanism of diacylglycerols is not currently understood and needs further investigation.

No description available.

No description available.

No description available.

The fat globules in milk are surrounded by a membrane, approximately 7.6 nm in thickness, which contains proteins, lipids and other minor components. Although the total amount of the fat globule membrane is very small, it plays an important role in the quality of milk and dairy products. The purpose of this study was to examine the role of the components of the membrane, separately and in combination, on the oxidation of milk and milk fat. Such examinations were carried out by measuring atmospheric oxygen consumption and the disappearance of unsaturated fatty acids. In general, the results indicate that the milk fat globule membrane contains both antioxidative and oxidative components. The influence of the membrane on the oxidation of milk and dairy products depends largely on a delicate balance between two opposing factors. Such balance is governed by a number of parameters including the composition of the membrane, temperature, the presence or absence of water, pH, metal ions, and other minor components. Effects of individual phospholipids and amino acids on the milk fat oxidation were also conducted. At 50$\sp\circ$C, dipalmitoyl phosphatidyl ethanolamine (DPE) and dipalmitoyl phosphatidyl choline (DPC) inhibited milk fat oxidation in the dry system while accelerating it in the aqueous system. DPE was more effective than DPC. All amino acids tested protected milk fat against oxidation. Amino, sulfhydryl, phenol indole groups in the side chain were found to be responsible for the antioxidative activity of amino acids and proteins. The freeze-dried lysine. HCL and alanine.HCL promoted milk fat oxidation while the corresponding control amino acids inhibited it. An understanding of the mechanisms involved, and the processing conditions which influence inhibition and/or acceleration, would be of significant value in the control of oxidative reactions in milk, dairy products and other food systems.

In the study of bread staling, progress is limited due to its complex system. Two primary wheat constituents, gluten and starch, and the major bread ingredients water and sucrose were used for molecular interaction studies in model systems. Starch retrogradation in breads and their microstructures were examined to observe the effects of ingredients in practical system. Sorption isotherms and $\sp2$H, $\sp{13}$C, and $\sp{17}$O NMR were used to examine molecular interactions and study water mobility in model systems. DSC was used for thermal transition studies. Light and polarized light microscopies were used for microstructure and starch crystal observations. Sucrose and gluten, and sucrose and starch "interacted" in the model systems. The "interacted" sucrose-gluten or sucrose-starch mixtures showed water absorption behaviors intermediate between that of pure sucrose and gluten or starch. The water mobility of sucrose-gluten mixtures was decreased with the increase of sucrose concentration, while for that of sucrose-starch mixtures it was increased with the increase of sucrose concentration. Water plasticized gluten more effectively than starch perhaps because gluten is complete amorphous while starch contains about 40% amorphous regions. Sucrose also plasticized gluten or starch. However, in sucrose-water-gluten or starch mixture, sucrose showed less plasticization effect (antiplasticizer). Sucrose had a strong antiplasticization effect in the gluten mixtures but not in the starch mixtures. Starch gelatinization endothermic energy increased with the increase of moisture content indicating that gelatinization is dependent on availability of water. With constant moisture content, both salt and sucrose increased gelatinization peak temperatures and endothermic energies. However, salt had greater retarding effect on gelatinization than did sucrose. Bread was sealed in cans and kept at room temperature for 4 days. Bread made from hard wheat flour had more intact microstructure and low starch crystalline melting endothermic energy than bread made from soft wheat or all-purpose flour. Among 3 types of surfactants added to bread doughs, sodium stearoyl lactylate produced bread with the most highly homogeneous distribution of medium sized air cells and intact cell walls. Sucrose ester (HLB 16)-added bread had the lowest starch crystalline melting endothermic energy, and thus would decrease retrogradation more than the other surfactants.