Study Of Maillard Reaction During Dry Heating Process For Gel Properties Of Hen Ovalbumin

The gel strength of egg white powder which is widely used in food industry for its high-gelation character depends on the property of ovalbumin which is major ingredient of egg white protein. In our study, we modified ovalbumin with low-mass reducing sugar with the purpose of researching the different effects between glucose, maltose and maltotriose on modification with ovalbumin.In our study we firstly observed the relationship between grafting percentage of ovalbumin with reducing sugars and fluorescence intensity of their products by which represented the primary and advanced stage of the maillard reaction. The result showed that advanced maillard reaction goes synchronic with primary maillard reaction. With the mass of reducing increased, the advanced maillard reaction was greatly restrained.Since we got the rough information on the process during maillard reaction, some details on secondary structure during maillard reaction was needed to investigate. The results showed thatα+βstructure (tight and order structure) of ovalbumin was significant reduced during incubation. Especially the ones modified by maltose and maltotrioes reduced faster than the one modified by glucose. T-structure (loose and order structure) were greatly increasing during incubation, following order: maltotrioes > maltose > glucose. We can conclude that the reducing sugar contributes to changing protein structure to a"molten"status. And maltose and maltotrioes are more contributed than glucose.Base the knowledge of modified ovalbumin on secondary structure, further investigations on solubility, hydrophobic, surface SH group content and gelation properties of modified ovalbumin were required. We found that the solubility of modified ovalbumin was much higher than unmodified one at early stage of maillard reaction. But at the later stage, the solubility of modified ovalbumin was lower than unmodified one and the reducing speed was decreased with increasing reducing sugar mass. Hydrophobicity of unmodified ovalbumin was increasing with incubation time at early stage of incubation. At later stage of incubation the trend on hydrophobicity of unmodified ovalbumin turns to decreased. This is because the hydrophobic groups which were buried internal of protein molecular were exposed onto the surface of molecular during incubation. The exposed hydrophobic groups were recombined at the later stage of incubation. Hydrophobicity of modified ovalbumin was increased at the early stage of incubation but remain stable at the later stage. This may be related to the change of protein secondary structure which was induced by reducing sugar. Because there were more hydrophobic groups exposed when protein secondary structure changed. The content of surface SH groups of modified ovalbumin were increased at the early stage of incubation and decreased at the later stage which may be related to combined action of structure changes and sulfhydryl-disulfide exchange reaction. The strength of modified ovalbumin heat-induced gel was higher than the one which was unmodified. The gel strength of ovalbumin modified with maltotriose was increasing with incubation time, but the ones modified with maltose and glucose were increased at early stage of incubation and decreased at later stage.Finally, we attempted to find the glycated sites on ovalbumin by using LC/MS technic. Glycated ovalbumin was digested by trypsase. Throughout analysis, we found 15 peptides were connected by reducing sugar. But the sequence of glycated peptides were not detected until LC/MS optimization condition figured out.