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.

Thesis: M.S., Massachusetts Institute of Technology, Department of Food Technology, 1960 / Includes bibliographical references (leaves 97-99). / by Arthur E. Humphrey. / M.S. / M.S. Massachusetts Institute of Technology, Department of Food Technology

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.

The purpose of this study was to study the changes which occur in fish lipids with emphasis on cholesterol during processing. Frying, drying, and UV, solar and gamma-irradiation were selected as means of processing at different conditions. Cholesterol, cholesterol oxides, fatty acids, and volatiles were analyzed qualitatively and quantitatively to monitor the fish lipid changes during processing. The omega-3 fatty acids in mackerel were not significantly reduced by pan-frying. However, major amounts of the fish oil were physically lost during frying. The concentration of the omega-3 fatty acids in the oil released was significantly reduced, demonstrating the possible sensitivity to oxidation once the oil is removed from its natural state. When pollock was deep fat fried without batter, extensive absorption of the frying oil occurred. Batter coating appeared to protect the fillets against loss of moisture, absorption of cooking oil and dilution or loss of flavor volatiles. Oxidative interactions of cholesterol with other compounds were studied at 180 C for one hour. When triacylglycerols were added to cholesterol before heating at 180 C, the latter oxidized faster than cholesterol heated alone, and a relatively high amount of oxides was found. Dipalmitoylphosphatidylethanolamine and all the amino acids tested showed a protective effect, with cysteine and alanine being the most effective. When pure cholesterol, cholesterol in aqueous system, and cholesterol-containing squid were exposed under the UV radiation, cholesterol was destroyed in varying degrees depending on the wavelength, radiation time, and the state of cholesterol. Pure cholesterol and cholesterol in aqueous system were destroyed much faster than that in squid fish indicating some physical and chemical protection in fish muscle. Cholesterol in aqueous system produced higher amount of oxides suggesting different oxidative pathways when water is present. In all cases, the fastest and most severe destruction resulted from exposure at 312 nm. Solar radiation also resulted in certain degrees of cholesterol oxidation in squid. Gamma-irradiation induced cholesterol oxidation when exposed to high energy radiation. Cholesterol in aqueous system was destroyed faster than pure cholesterol and than the cholesterol in squid. (Abstract shortened with permission of author.)

Thesis: B.S., Massachusetts Institute of Technology, Department of Food Technology, 1951 / Bibliography: leaves 41-43. / by Aaron L. Brody. / B.S. / B.S. Massachusetts Institute of Technology, Department of Food Technology