MARIA BIKAKI

• Proteins, one of the most vital classes of food components, play an important role in the human diet providing the essential amino acids required for tissue maintenance and growth. In many food processes, however, the structure of food proteins might change as a result of various externally applied conditions. Heat treatment, for instance, performed either at a household level or at an industrial scale, may cause alterations in food proteins chemically converting proteins to new products thus altering their property causing desirable or undesirable characteristics. Due to the complexity of the food matrix, very little is known yet regarding the products of the thermal degradation of food proteins. In this thesis, both intact and digested food proteins derived from bovine milk and hen eggs, have been thermally treated at temperatures ranging from 150 ºC till 250 ºC. The thermal decomposition products have been investigated using LC-MS and a combination of further analytical techniques. Exhaustive chemical conversion of model food proteins has been successfully demonstrated and analytical data generated that describe such changes. However, limitations in high resolution mass spectrometry data of the generated thermal decomposition products did not allow an unambiguous determination of the chemical structures and hence these results remained inconclusive. In order to elucidate the structures of the thermal degradation products of proteins and the underlying mechanisms that govern their formations, 15 custom pentapeptides were selected and were thermally treated at optimised heating conditions. In total, more than 300 thermal degradation products have been detected and around 200 have been identified. Three representative examples including amide cleavage and DKP formation reaction, oxidation of tryptophan residue, C-terminal decarboxylation and formation of N-terminal dicarbonyls by two distinct reaction pathways have been identified in this thesis and are discussed.