Application of PTR-MS to the Fast Characterisation of Volatile Organic Compounds in Cheese = FT L'applicazione di una tecnica innovativa di spettrometria di massa per la caratterizzazione rapida della componente volatile dei formaggi

Proton Transfer Reaction Mass Spectrometry (PTR-MS) is a direct injection mass spectrometry technique which is based on the efficient implementation of efficient chemical ionization, and allows for the fast monitoring of volatile organic compounds (VOCs) at high-sensitivity. The first implementation of the Proton Transfer Reaction (PTR), was based on a quadrupole mass analyzer (PTR-Quad-MS), and provides only the nominal mass of the ions measured and thus limited chemical information. In order to partially overcome these limitations and in order to improve the analytical potential of this technique, recently, a new version has been developed and commercialized which couples PTR to a time-of-flight detector (PTR-TOF-MS). Here we present the application of this innovative technique to dairy science. Primarily, the aim was to study the effects of collection and storage modalities of milk used for Trentingrana cheese manufacturing on the final quality of cheese. Four different milk storage conditions were tested: two refer to the traditional double milk collection (churn - room temperature - and 18°C) and two to the single milk collection (12°C and 8°C). The complete experiment was repeated in two different seasons: winter and summer time. We show that coupling fast PTR-ToF-MS fingerprinting with advanced data-mining methods can quickly verify that production conditions, such as the storage conditions of the milk, have an effect on the VOCs profile of Trentingrana cheese. We show that the peaks used for the statistical discrimination of summer sample are different from the ones used in the case of winter samples. Notably, all peaks related to esters are used for summer samples, while peaks related to aldehydes and ketones are used for winter samples. A crucial advantage of PTR-ToF-MS is that the improved mass resolution and mass accuracy allow for the separation and quantification of important classes of compounds, e.g. sulphur compounds. In summary, PTR-TOF-MS presents itself as a sensitive and versatile analytical technique for quality control of agricultural food products.