Modification of ovalbumin with a rare ketohexose through the Maillard reaction: effect on protein structure and gel properties.

The effect of nonenzymatic glycation on the structural changes and gelling properties of hen ovalbumin (OVA) through the Maillard reaction was studied. OVA was incubated at the dry state with a rare ketohexose (D-psicose, Psi) and two alimentary sugars (D-fructose, Fru; D-glucose, Glc) at 55 degrees C and 65% relative humidity. To evaluate the modification of OVA by different reducing sugars during the glycation process, the extent of the Maillard reaction, aggregation processes, structural changes, and gelling behaviors were investigated. Reactivity of Psi with the protein amino groups was much lower than that of both Fru and Glc, whereas Psi induced production of browning and fluorescent substances more strongly than the two alimentary sugars did. Furthermore, OVA showed an increased tendency toward multimeric aggregation upon modifying with Psi through covalent bond. The modified OVAs with reducing sugar were similar to nonglycated control sample in Fourier transform infrared (FT-IR) characteristics, but significantly decreased in intensity of tryptophan-related fluorescence. The results indicate that although glycation brought about similar changes in the secondary structure without great disruption of native structure, its influence on the side chains of protein in tertiary structure could be different. Breaking strength of heat-induced glycated OVA gels with Psi was markedly enhanced by the Maillard reaction. These results suggest that Psi had a strong cross-linking activity with OVA; consequently, the glycated OVA with Psi could improve gelling properties under certain controlled conditions.