Rapid non-invasive quality control of semi-finished products for the food industry by direct injection mass spectrometry headspace analysis: the case of milk powder, whey powder and anhydrous milk fat.

In this study, we demonstrated the suitability of direct injection mass spectrometry headspace analysis for rapid non-invasive quality control of semi-finished dairy ingredients, such as skim milk powder (SMP), whole milk powder (WMP), whey powder (WP) and anhydrous milk fat (AMF), which are widely used as ingredients in the food industry. In this work, for the first time, we applied proton transfer reaction-mass spectrometry (PTR-MS) with a time-of-flight (ToF) analyzer for the rapid and non-invasive analysis of volatile compounds in different samples of SMP, WMP, WP and AMF. We selected different dairy ingredients in various concrete situations (e.g. same producer and different expiration times, different producers and same days of storage, different producers) based on their sensory evaluation. PTR-ToF-MS allowed the separation and characterization of different samples based on the volatile organic compound (VOC) profiles. Statistically significant differences in VOC content were generally coherent with differences in sensory evaluation, particularly for SMP, WMP and WP. The good separation of SMP samples from WMP samples suggested the possible application of PTR-ToF-MS to detect possible cases of adulteration of dairy ingredients for the food industry. Our findings demonstrate the efficient and rapid differentiation of dairy ingredients on the basis of the released VOCs via PTR-ToF-MS analysis and suggest this method as a versatile tool (1) for the facilitation/optimization of the selection of dairy ingredients in the food industry and (2) and for the prompt innovation in the production of dairy ingredients. Copyright © 2016 John Wiley & Sons, Ltd.

PTR-MS Characterization of VOCs Associated with Commercial Aromatic Bakery Yeasts of Wine and Beer Origin.

In light of the increasing attention towards "green" solutions to improve food quality, the use of aromatic-enhancing microorganisms offers the advantage to be a natural and sustainable solution that did not negatively influence the list of ingredients. In this study, we characterize, for the first time, volatile organic compounds (VOCs) associated with aromatic bakery yeasts. Three commercial bakery starter cultures, respectively formulated with three Saccharomyces cerevisiae strains, isolated from white wine, red wine, and beer, were monitored by a proton-transfer-reaction time-of-flight mass spectrometer (PTR-ToF-MS), a direct injection analytical technique for detecting volatile organic compounds with high sensitivity (VOCs). Two ethanol-related peaks (m/z 65.059 and 75.080) described qualitative differences in fermentative performances. The release of compounds associated to the peaks at m/z 89.059, m/z 103.075, and m/z 117.093, tentatively identified as acetoin and esters, are coherent with claimed flavor properties of the investigated strains. We propose these mass peaks and their related fragments as biomarkers to optimize the aromatic performances of commercial preparations and for the rapid massive screening of yeast collections.

Monitoring of lactic fermentation driven by different starter cultures via direct injection mass spectrometric analysis of flavour-related volatile compounds.

In this work, we used Proton Transfer Reaction-Mass Spectrometry (PTR-ToF-MS), coupled with an automated sampling system, to monitor lactic fermentation driven by different yogurt commercial starter cultures via direct injection mass spectrometric analysis of flavour-related volatile compounds. The aim is the identification of markers for real-time and non-invasive bioprocess control and optimisation as an industrial driver of innovation in food technology and biotechnology. We detected more than 300 mass peaks, tentatively identifying all major yogurt aroma volatiles. Thirteen mass peaks showed statistically significant differences among the four commercial starters. Among these are acetaldehyde, methanethiol, butanoic acid, 2-butanone, diacetyl, acetoin, 2-hydroxy-3-pentanone/pentanoic acid, heptanoic acid and benzaldehyde which play a key role in yogurt flavour. These volatile described the diverse flavour properties claimed by food biotechnological companies and, considering the possible contribution to yogurt flavour, are potential markers for the rapid screening of starter cultures and for the quality design in this fermentation-driven production. The strength of our approach lies in the identification, for the first time, of specific depletion kinetics of four sulphur containing compounds occurring during fermentation (hydrogen sulphide, methanethiol, S-methyl thioacetate/S-ethyl thioformate, pentane-thiol), which suggest a new possible protechnological feature of yogurt starter cultures.

Proton-transfer-reaction mass spectrometry for the study of the production of volatile compounds by bakery yeast starters.

The aromatic impact of bakery yeast starters is currently receiving considerable attention. The flavor characteristics of the dough and the finished products are usually evaluated by gas chromatography and sensory analysis. The limit of both techniques resides in their low-throughput character. In the present work, proton-transfer-reaction mass spectrometry (PTR-MS), coupled to a time-of-flight mass analyzer, was employed, for the first time, to measure the volatile fractions of dough and bread, and to monitor Saccharomyces cerevisiae volatile production in a fermented food matrix. Leavening was performed on small-scale (1 g) dough samples inoculated with different commercial yeast strains. The leavened doughs were then baked, and volatile profiles were determined during leavening and after baking. The experimental setup included a multifunctional autosampler, which permitted the follow-up of the leavening process on a small scale with a typical throughput of 500 distinct data points in 16 h. The system allowed to pinpoint differences between starter yeast strains in terms of volatile emission kinetics, with repercussions on the final product (i.e. the corresponding micro-loaves). This work demonstrates the applicability of PTR-MS for the study of volatile organic compound production during bread-making, for the automated and online real-time monitoring of the leavening process, and for the characterization and selection of bakery yeast starters in view of their production of volatile compounds.