ESR and NMR spectroscopy studies on protein oxidation and formation of dityrosine in emulsions containing oxidised methyl linoleate

• Published in: Food and chemical toxicology Vol. 44; no. 8; pp. 1385 - 1392
• Main Authors: Saeed, Suhur, Gillies, Duncan, Wagner, Gabriele, Howell, Nazlin K.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.08.2006; New York, NY Elsevier Science
• Subjects: amino acids; Biological and medical sciences; dietary protein; Dityrosine; Electron Spin Resonance Spectroscopy; Emulsions - chemistry; ESR spectroscopy; Free radical; free radical scavengers; free radicals; Free Radicals - chemistry; Humans; lactoglobulins; Lactoglobulins - chemistry; Lactoglobulins - metabolism; Linoleic Acids - chemistry; Linoleic Acids - metabolism; lipid peroxidation; Medical sciences; NMR; nuclear magnetic resonance spectroscopy; Nuclear Magnetic Resonance, Biomolecular; oxidation; Oxidation-Reduction; oxidative stress; protein degradation; Protein oxidation; Toxicology; Tyrosine - analogs & derivatives; Tyrosine - chemistry; Tyrosine - metabolism; Tyrosyl radical; ESR spectroscopy; NMR; Protein oxidation; Dityrosine; Tyrosyl radical; Free radical; EPR spectrometry; Oxidation; Nuclear magnetic resonance; Protein
• ISSN: 0278-6915; 1873-6351
• DOI: 10.1016/j.fct.2006.03.005

Oxidised lipids are reported to interact with proteins causing undesirable changes in nutritional and functional properties including a loss of amino acids, cross-linking and damage to proteins and DNA. ESR spectroscopy with spin trapping was used to study the type of radical species generated in methyl linoleate and the transfer of the radical to protein β-lactoglobulin. Antioxidants vitamins C and E reduced lipid oxidation and subsequent transfer of the radical to the protein as shown by the shape and size of the radical adduct. Changes to protein molecular structure due to oxidation were investigated by multidimensional NMR spectroscopy and liquid chromatography. NMR spectra indicated that as a result of oxidation and protein denaturation, there was an increase in structural flexibility and some initially protected backbone amide groups were exposed as they become sharper and easily identifiable. Dityrosine was detected in all samples tested which is indicative of oxidative damage to proteins. Monitoring tyrosyl radicals and formation of dityrosine is of practical value in order to enhance the acceptability, nutritional and safety aspects of proteins.