Protein-lipid complexes are known to result from complex molecular interactions which contribute to physiochemical and functional properties of foods. To identify the interactions of food proteins with lipids and the associated changes in properties, the following factors were investigated: incubation temperature, pH, type of lipids (phospholipid, triglyceride and fatty acids) and different proteins (ovalbumin and soybean glycinin). The effects of lipids on physiochemical and functional characteristics of ovalbumin and glycinin were investigated using polyacrylamide gel electrophoresis (PAGE), fluorescence, differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, and emulsification and gelation properties. / The results showed that pH, temperature and the type of lipids affected both ovalbumin-lipid interactions and physiochemical properties of ovalbumin. Changes in the electrophoretic behavior of ovalbumin were related to the presence of lipids, and the relative fluorescence of ovalbumin decreased in the presence of lipids at different pH values. In addition, lipids increased the stability of ovalbumin as revealed by the thermal denaturation (Td) and by the enthalpy transition (DeltaH). FTIR spectra in the amide I absorption region revealed that lipids affected the secondary structure of ovalbumin. Changes in the integrated intensity of the amide II band between (1520--1555) cm -1 in the presence of D2O showed that H-D exchange of ovalbumin decreased in the presence of lipids. Emulsifying properties, gel strength and water holding capacity (WHC) of ovalbumin increased significantly (P < 0.05) in the presence of lipids. Scanning electron microscopy (SEM) showed difference in the microstructure of ovalbumin gel in the presence of different lipids. The more pronounced effect of lipids was observed with lecithin and the lowest was with stearic acid. The order of magnitude for the effects of lipids on physiochemical and functional properties of ovalbumin was: lecithin > cocoa butter > oleic acid > linoleic acid > linolenic acid > stearic acid. It is likely that the degree of polarity of lipids play an important role in protein-lipid interactions and in the enhancement of the functional properties of ovalbumin. / The effects of soybean oil (SO), soybean lecithin (SL) and a mixture of both (SOL) on physiochemical and functional properties of soybean glycinin were studied at pH 8.0, with incubation at 40°C. Changes in the electrophoretic behavior were related to the presence of lipids. Relative fluorescence of glycinin decreased in the presence of lipids. Lipids increased the thermal stability (Td) of glycinin from 89.7°C to 92.0°C, 94.3°C and 93.4°C with SO, SL and SOL respectively. FTIR spectra indicated changes in both; the secondary structure and H-D exchange of glycinin in the presence of lipids. Gel strength, WHC and emulsifying properties of glycinin increased significantly (P < 0.05) in the presence of lipids; the order of consequence increase was: SL > SOL > SO. SEM showed difference in the microstructure of glycinin gels with the different lipids used. Overall, the results demonstrate both quantitative and qualitative effects on the physiochemical and functional properties of ovalbumin and glycinin as a result of protein-lipid interactions.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.38144 |
| Date | January 2002 |
| Creators | Alzagtat, Ahmeda A. |
| Contributors | Alli, I. (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Food Science and Agricultural Chemistry.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001872198, proquestno: NQ78638, Theses scanned by UMI/ProQuest. |
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