Expanding solid-state phosphorus nuclear magnetic resonance insights into Mozzarella cheese ageing

Abstract

With the addition of reference spectra and 1H31P cross-polarisation kinetics we have increased the analysis available by 31P NMR of the cheese ageing process. A previous study demonstrated that solid-state 31P NMR can be used to monitor the state of phosphorus in ageing cheeses. It is possible to differentiate between the mobile and immobile phosphorus species present in the cheese casein micelles. In this work, proton to phosphorus cross polarisation (CP) kinetic experiments (1H31P CP-MAS) (where MAS = magic angle spinning) enable the observation of the state of the colloidal calcium phosphate (CCP) and phosphoserine (PSer) separately in the casein micelles. Also, 1H31P CP-MAS spectra can be used to indirectly monitor the levels of micellar calcium. From the data gathered, we were able to conclude these points about the ageing process of Mozzarella cheese; in the first 20 days the cheese texture is dependent on the dynamics of free water and immobile calcium and phosphate, the CCP phosphate is mobilised at an exponential rate with the majority mobilised within the first 20 days, the driving force for CCP mobilisation is possibly the migration of water from the cheese serum into the casein proteins and CCP phosphorus is preferentially mobilised while immobile phosphoserine levels remains relatively unchanged during the early (40 days) of Mozzarella cheese ageing.