Proton transfer reaction time-of-flight mass spectrometry: A highthroughput and innovative method to study the influence of dairy system and cow characteristics on the volatile compound fingerprint of cheeses

The aim of this work was to study the effect of dairysystem and individual cow-related factors on the volatilefingerprint of a large number of individual modelcheeses analyzed by proton transfer reaction time-offlightmass spectrometry (PTR-ToF-MS). A total of1,075 model cheeses were produced using milk samplescollected from individual Brown Swiss cows rearedin 72 herds located in mountainous areas of Trentoprovince (Italy). The herds belonged to 5 main dairysystems ranging from traditional to modern and thecows presented different daily milk yields (24.6 ± 7.9kg × d−1), stages of lactation (199 ± 138 d in milk),and parities (2.7 ± 1.8). The PTR-ToF-MS revealed619 peaks, of which the 240 most intense were analyzed,and 61 of these were tentatively attributed torelevant volatile organic compounds on the basis oftheir fragmentation patterns and data from the literature.Principal component analysis was used to convertthe multiple responses characterizing the PTR-ToF-MSspectra into 5 synthetic variables representing 62% ofthe total information. These principal components wererelated to groups of volatile compounds tentatively attributedto different peaks and used to investigate therelationship of the volatile compound profile obtainedby PTR-ToF-MS to animal and farm characteristics.Lactation stage is related to 4 principal componentswhich brought together 52.9% of the total variance and57.9% of the area of analyzed peaks. In particular, 2principal components were positively related to peakstentatively attributed to aldehydes and ketones andnegatively related to alcohols, esters, and acids, whichdisplayed a linear increase during lactation. The thirdprincipal component was affected by dairy system; itwas lower in the modern system in which cows receivedtotal mixed rations. The third principal componentwas positively related to daily milk production. In summary,we report the first application of this innovative,high-throughput technique to study the effects of dairysystem and individual animal factors on volatile organiccompounds of model cheeses. Individual cheesemakingprocedures together with this spectrometric techniqueopen new avenues for genetic selection of dairy specieswith respect to both milk and cheese quality.