Text

theses

ETD_4254

M.S.

Includes bibliographical references

by Lisa Hayley Schultz

Although lipid oxidation is recognized as a major chemical reaction limiting shelf life of foods, its role in degrading food quality and the mechanisms involved remain incompletely elucidated. Interactions of oxidizing lipids with other food molecules have been largely ignored, even though these reactions can have dramatic impact on food properties. Lipid co-oxidation of proteins occurs extensively in nearly all processed foods and degrades textures, flavors, color, and nutritional value. It is important to measure both lipid and protein co-oxidation products to understand the full extent of oxidative deterioration during food storage. This thesis is part of a larger project examining baked and fried tortilla chips to differentiate thermal damage to proteins from lipid co-oxidation during processing and storage. In a previous study, gel electrophoresis revealed modification of protein surfaces that affected dye binding, as well as formation of sizeable protein aggregates too large to enter normal gels involving disulfide, free radical, and other crosslinks. As an alternative to polyacrylamide gels, capillary electrophoresis can separate peptides without molecular weight limits, by modes that may be more sensitive to side chain modifications, and requires only a few nanoliters of sample. Thus, this study investigated the use of capillary electrophoresis for tracking fragmentation and crosslinking in co-oxidized proteins. Results corroborated observations that fried tortilla chip samples had greater changes than baked tortilla chip samples and higher incubation temperature resulted in more protein damage, most notably in fried reducing fractions. In addition, surface modifications altered protein charge, which interfered with migration in capillary electrophoresis. Peptide detection was limited to zeins of about 50 kDa because the sample filtration step intended to prevent capillary blockage also removed higher molecular weight fractions, including glutelins. However, fragmentation products not distinguishable in gel electrophoresis were detected. Overall, results of this study suggest that capillary electrophoresis has intriguing possibilities for supplementing SDS-PAGE and other protein analyses, particularly in verifying the presence of surface modifications. However, significant hurdles—such as reasons for lack of high molecular weight peptide loading and migration—remain to be overcome before capillary electrophoresis can become a primary method for analysis of modified proteins.

http://hdl.rutgers.edu/1782.1/rucore10001600001.ETD.000066967

doi:10.7282/T3VD6X7K

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