Conformational alteration and the glycated sites in ovalbumin during vacuum freeze-drying induced glycation: A study using conventional spectrometry and liquid chromatography-high resolution mass spectrometry

Ovalbumin (Oval)-ribose glycation induced by vacuum freeze-drying (VFD) was studied. The protein conformational changes based on fluorescence, ultraviolet and circular dichroism spectra were evident with the increase in VFD time. The glycated sites and the average degree of substitution per peptide molecule (DSP) were determined using LC-HRMS. Lysine was shown to be the sole glycated site. Two glycated sites and the minimum DSP values were found during the first 6 h of VFD and increased to nine and the maximum DSP values after 48 h of VFD. The glycated sites located on the protein surface were mostly more active than those in the folded or helical regions, and the hydrophilic/hydrophobic environment could also influence DSP values. This study gave relationships between VFD time and the conformational structure and glycated sites of VFD-treated Oval-ribose system, providing a theoretical basis for VFD technique-based protein food and drug industries.