PTR‐TOF‐MS and data‐mining methods for rapid characterisation of agro‐industrial samples: influence of milk storage conditions on the volatile compounds profile of Trentingrana cheese

Abstract

Proton transfer reaction-mass spectrometry (PTR-MS), a direct injection mass spectrometric technique based on an efficient implementation of chemical ionisation, allows for fast and high-sensitivity monitoring of volatile organic compounds (VOCs). The first implementations of PTR-MS, based on quadrupole mass analyzers (PTR-Quad-MS), provided only the nominal mass of the ions measured and thus little chemical information. To partially overcome these limitations and improve the analytical capability of this technique, the coupling of proton transfer reaction ionisation with a time-of-flight mass analyser has been recently realised and commercialised (PTR-TOF-MS). Here we discuss the very first application of this new instrument to agro-industrial problems and dairy science in particular. As a case study, we show here that the rapid PTR-TOF-MS fingerprinting coupled with data-mining methods can quickly verify whether the storage condition of the milk affects the final quality of cheese and we provide relevant examples of better compound identification in comparison with the previous PTR-MS implementations. In particular, 'Trentingrana' cheese produced by four different procedures for milk storage are compared both in the case of winter and summer production. It is indeed possible to set classification models with low prediction errors and to identify the chemical formula of the ion peaks used for classification, providing evidence of the role that this novel spectrometric technique can play for fundamental and applied agro-industrial themes.

The effect of milk collection and storage conditions on the final quality of Trentingrana cheese: Sensory and instrumental evaluation

“…Findings on volatile compounds were compatible with previous work by Fabris et al (2010) conducted on a similar sample set but analyzed with a direct head-space analysis based on the new proton transfer reaction time of flight mass spectrometry (PTReTOFeMS) technique, only recently applied to food investigations (Soukoulis et al, 2010). Rapid PTReTOFeMS fingerprinting coupled with data mining methods gave results that were in quantitative and qualitative agreement with the GC/MS analysis presented here.…”

Effect of the pig rearing system on the final volatile profile of Iberian dry-cured ham as detected by PTR-ToF-MS

“…Principal component (PCA) and discriminant analysis were also performed. A simplified version of the methods used in Fabris et al (2010) was used for discriminant analysis on PTR-ToF-MS data, using Penalized Discriminant Analysis (PDA) (Granitto et al, 2007) as classifier. To evaluate the results of the classification method a leavegroup-out (LGO) method was used: the process of leaving a group out as test set and using the rest of the data set to fit the models was iterated.…”

The role of direct high-resolution mass spectrometry in foodomics

“…Since then, improvements in mass resolution, mass range, and LOD have been achieved [43]. Since the pioneering works in 2010 involving the analysis of VOCs by PTR-TOF MS to study the effect of storage conditions of milk on the final quality of cheese [44] and for monitoring of lactic acid fermentation of milk [45,46], a variety of applications have demonstrated the great potential of this approach in the field of food science and technology. Analysis of VOCs by PRT-TOF MS permitted the discrimination among different olive varieties and stage of ripeness [47], as well as the monitoring of VOC release during post-harvest ripening of different apple cultivars [48].…”