Hannah McKerchar

PhD Student

Thesis Title: Detecting crosslinks in milk using mass spectrometry.

During food processing and storage, crosslinks can form between proteins, which profoundly influence the nutritional value and properties of food. One crosslink that can form with heating and basic pH, two typical food processing procedures used in milk products, is lysinoalanine. This crosslink is interesting because it has been shown to decrease essential amino acid availability (particularly lysine) and protein digestibility, protein quality and mineral bioavailability. Despite the potential shortcomings of lysinoalanine, its formation and biological fate is not well understood.

 Harnessing the highly accurate analysis of small quantities of analytes afforded by mass spectrometry provides a means to detect and characterise lysinoalanine in milk proteins. The typically low relative abundance of crosslinked peptides compared to linear peptides and the complex fragmentation pattern produced by crosslinks compared to linear peptides, together with several other factors, makes investigating crosslinked peptides in food challenging.

 My PhD project looks to address these challenges by building a model crosslink that minimises or negates some the complexities of endogenous or insulti-induced crosslinks. We are subjecting two short bespoke peptides to heat and alkaline treatment and form a lysinoalanine crosslink of between the peptides. By characterising the fragmentation pattern, this simple model can be used as a diagnostic tool for identifying lysinoalanine crosslinks in larger protein complexes and enable us to untangle the many unknowns of crosslinks in food proteins.