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Mechanism Of Soybean Protein Aggregation Induced By Lipoxygenase-Catalyzed Linoleic Acid

Posted on:2007-04-27Degree:DoctorType:Dissertation
Country:ChinaCandidate:Y R HuangFull Text:PDF
GTID:1101360185995783Subject:Food, grease and vegetable protein engineering
Abstract/Summary:PDF Full Text Request
Soybean proteins in food industry are prepared from defatted soybean flour, but the oxidation of lipids remained in defatted soybean flour can be catalyzed by lipoxygenases during the preparation of soybean proteins, and oxidized lipids in lipid-protein systems are considered to induce polymerization and aggregation of proteins, causing undesirable changes in the nutritional and functional properties of the proteins. Since a lot of research contents are involved in the aggregation of soybean proteins, this dissertation focuses on the mechanism of soybean protein aggregation induced by lipoxygenase catalyzed linoleic acid.Aggregation of soybean proteins induced by lipoxygenase catalyzed linoleic acid was investigated by chemical analysis, electrophoresis, high performance size exclusion chromatography (SEC-HPLC) and laser light scattering (LLS). Soybean proteins obtained from the model systems consisting of lipid-reduced soybean proteins and different levels of linoleic acid and lipoxygenase showed increased turbidity and surface hydrophobicity but decreased sulfhydryl and disulfide contents. SDS-PAGE of reacted samples showed that subunits of proteins were all involved in the reaction, especially 7S fractions, and suggested other covalent linkages than disulfide bonds formed during the formation of aggregates. Native-PAGE, SEC-HPLC and LLS indicated that aggregates with high molecular weight and large particle size existed in reacted samples.The interactions of soybean proteins and oxidizing linoleic acid catalyzed by lipoxygenase were investigated by fluorescence spectroscopy, protein oxidation, amino acid analysis, thiobarbituric acid (TBA) value, gas chromatography-mass spectrometry (GC-MS) and soluble protein hydrophobicity. The fluorescence of the oxidized samples showed excitation and emission maxima at 350 and 440 nm respectively. The fluorescent compounds were partially soluble in the organic layer of the chloroform-methanol (2:1,v/v). The solution fluorescence showed an excitation maximum at 350 nm and an emission maximum at 430 nm, and the intensity increased with reaction time. The interactions of soybean proteins and oxidizing linoleic acid catalyzed by lipoxygenase also resulted in increases of protein oxidation, but decreases of soluble protein hydrophobicity, and the contents of tryptophan, histidine, arginine, lysine, tyrosine and cysteine/cystine. C-C or C-N linkages were formed between protein molecules and polymerization was promoted in the reacted samples.Free radical species and transfer from oxidizing linoleic acid catalyzed by lipoxygenase to soybean proteins in different model systems were evaluated by electron spin resonance (ESR) in the presence or absence of antioxidants. A strong central singlet signal was detected by ESR spectroscopy and identified as the carbon radical (g value range 2.0041 to 2.0054). A...
Keywords/Search Tags:soybean proteins, aggregation, mechanism, lipoxygenase, linoleic acid, lipid oxidation, free radicals, fluorescence
PDF Full Text Request
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