Comparison of glycation in conventionally and microwave-heated ovalbumin by high resolution mass spectrometry.

The glycation extent of ovalbumin under two heating conditions, conventional and microwave heating was monitored by high resolution mass spectrometry, following pepsin digestion. The sequence coverage of the unglycated and glycated ovalbumin was 100% and 95%, respectively. About 35.2% of the lysines after microwave heating and 40.8% of the lysines after conventional heating were modified by d-glucose. The glycation content increased quickly when ovalbumin-glucose mixture was incubated for 15min, under both processing conditions. These modifications were slowed down after 30min of heating and no obvious advanced stage products were observed. The glycated peptides exhibited varying degrees of glycation, under both conventional and microwave heating, suggesting that glycation is strongly relevant to the protein structure. The fact that some peptides showed a lower level of glycation when heated by microwave indicated that microwave radiation might be a non-thermal process. In addition, the lack of browning after microwave heating emphasised the difference between microwave and conventional heating.