Fast field cycling NMR relaxometry as a tool to monitor Parmigiano Reggiano cheese ripening

It is widely recognized that the longer the ageing, the more valuable Parmigiano Reggiano (PR) cheese becomes, due to the improvement of its sensorial and nutritional properties. Up to now, the evaluation of PR properties has been performed on samples mainly aged up to 40 months. For this reason, this study was aimed at collecting information about the chemical-physical characteristics of PR cheeses after ageing at 24, 48 and 84 months. The basic analyses on water amount, protein content and volatile organic compounds (VOC) revealed that PR ageing is associated to the decomposition of the organic components into smaller units. This drives water molecules closer to the aforementioned units, thereby leading to a reduction of water activity. Moreover, it appears, from VOC investigation, that either the total amount of long chain fatty acids (LCFA) or the sole 9Z-octadecenoic acid considerably increased with PR aging, thereby making these molecular systems good fingerprint to monitor PR ripening. Fast field cycling (FFC) NMR relaxometry revealed different components of the molecular dynamics in the complex PR cheese samples, which were attributed to water trapped in casein micelles, water bound to polar groups in organic components, proteins, and fats. In particular, the reduction of the correlation times associated to the organic components was explained by the molecular size decrement following degradation processes. The ageing-independent component of the motion was assigned to water molecules bound to polar groups in organic moieties. Finally, the ageing-independent contribution to the overall relaxation rate was assigned to water molecules in casein micelles. This study revealed that FFC NMR relaxometry can be a promising technique to monitor the chemical physical changes during Parmigiano Reggiano cheese ripening.