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Summary: In food technology, the term 'fermentation' encompasses a spectrum of microbial‐driven bioprocesses that preserve and improve the quality of raw materials, transforming them into new fermented products with minimal resource consumption. Furthermore, fermentation plays a crucial role in driving the eco‐friendly transformation of the agricultural industry. Within this domain, the fermented beverage sector stands out due to its consumer‐friendly appeal. To promote innovation in this field, there is a need for cost‐effective, versatile and sustainable techniques that can accelerate research and development activities. In the bioprocess sector, innovation management requires consideration of an array of variables, including diverse raw materials, various microorganisms and different fermentation parameters. Direct injection mass spectrometry (DIMS) technologies offer solutions for bioprocess monitoring, particularly in the analysis of volatile organic compounds (VOCs) and are constantly improving their performance in terms of sensitivity and specificity. Among the DIMS methods, proton transfer reaction‐mass spectrometry (PTR‐MS), when coupled with autosampling and customised data handling and analysis, has demonstrated its efficiency in studying VOCs associated with fermentation. This approach brings automation to data production and management, offers exceptional versatility akin to a sensor and aligns closely with the principles of green chemistry. In this perspective paper, after reviewing key aspects of modern fermentation practice, we showcase the application of PTR‐MS as a model to demonstrate its potential as sensor‐like approach to drive innovation within the fermented beverage sector. This approach enables swift, large‐scale assessments of multiple variables while providing comprehensive insights into the quality and safety of the final products. [ABSTRACT FROM AUTHOR]

Higher alcohols and esters are among the predominant classes of volatile organic compounds (VOCs) that influence the quality of beer. The concentrations of these compounds are determined through a specific yeast strain selection and fermentation conditions. The effect of yeast strains on the formation of higher alcohols and esters throughout fermentations (at 20°C) was investigated. Flavour‐relevant esters (ethyl acetate, isoamyl acetate, ethyl hexanoate and ethyl octanoate) and higher alcohols (isoamyl alcohol, isobutyl alcohol and phenylethyl alcohol) were monitored throughout the fermentation using proton transfer reaction–time of flight–mass spectrometry (PTR‐ToF‐MS) coupled with an automated sampling system for continuous measurements. Compound identification was confirmed by analysis of samples using gas chromatography–mass spectrometry (GC–MS). Results demonstrated the specific time points where variation in higher alcohol and ester generation between yeast strains occurred. In particular, the concentrations of isoamyl acetate, ethyl octanoate and isoamyl alcohol between yeast strains were significantly different over the first 2 days of fermentation; whereas, after Day 3, no significant differences were observed. The two Saccharomyces pastorianus strains produced comparable concentrations of the key higher alcohols and esters. However, the key higher alcohol and ester concentrations varied greatly between the two S. cerevisiae strains. The use of PTR–ToF–MS to rapidly measure multiple yeast strains provides new insights on fermentation for brewers to modify the sensory profile and optimise quality. [ABSTRACT FROM AUTHOR]

Isoprene synthase (IspS) is the sole enzyme in plants responsible for the yearly emission in the atmosphere of thousands of tonnes of the natural hydrocarbon isoprene worldwide. Species of the monocotyledonous family Arecaceae (palms) are among the highest plant emitters, but to date no IspS gene from this family has been identified. Here, we screened with PTR‐ToF‐MS 18 genera of the Arecaceae for isoprene emission and found that the majority of the sampled species emits isoprene. Putative IspS genes from six different genera were sequenced and three of them were functionally characterized by heterologous overexpression in Arabidopsis thaliana, demonstrating that they encode functional IspS genes. Site‐directed mutagenesis and expression in Arabidopsis demonstrated the functional relevance of a novel IspS diagnostic tetrad from Arecaceae, whose most variable amino acids could not preserve catalytic function when substituted by a putatively dicotyledonous‐specific tetrad. In particular, mutation of threonine 479 likely impairs the open–closed transition of the enzyme by altering the network of hydrogen bonds between helices H1α, H, and I. These results shed new light on the evolution of IspS in monocots, suggesting that isoprene emission is an ancestral trait within the Arecaceae family. The identification of IspS from Arecaceae provides promising novel enzymes for the production of isoprene in heterologous systems and allows the screening and selection of commercially relevant palm varieties with lower environmental impact. [ABSTRACT FROM AUTHOR]

We compute the proton transfer rates to a range of volatile organic compounds (VOCs) related to cork taint in wine. These rates are useful to support quantification in proton‐transfer‐reaction mass spectrometry (PTR‐MS) and in selected‐ion flow‐tube mass spectrometry (SIFT‐MS). We apply the average dipole orientation theory and the parameterized trajectory method to evaluate the rate coefficients for proton transfer occurring in ion–molecule collision, from both H3O+ and NH 4+ to the VOCs. The main input ingredients for these methods are the electric dipole moment and polarizability of the VOC molecules, which we evaluate by means of quantum chemical calculations based on density functional theory. We provide new data for proton transfer rate coefficients of compounds responsible for cork taint and off‐flavor in wine such as chloroanisoles, bromoanisoles, methylisoborneol, guaiacol, and terpenes. [ABSTRACT FROM AUTHOR]

Lactose‐free dairy products undergo several chemical modifications during shelf life because of the reactivity of glucose and galactose produced by the lactose enzymatic hydrolysis. In this study, proton transfer reaction‐mass spectrometry (PTR‐MS), coupled with a time‐of‐flight (TOF) mass analyzer, was applied to get an insight on the phenomena occurring during the shelf life of ultrahigh‐temperature (UHT) lactose‐free milk (LFM). UHT LFMs produced by three different commercial lactase preparations were evaluated during storage at 20°C over a 150 days period, sampling the milk every 30 days. Production was repeated three times, on three consecutive weeks, in order to take milk variability into consideration. Principal component analysis applied to the whole “volatilome” data demonstrated the capability of PTR‐TOF‐MS in detecting the milk batch‐to‐batch variability: Freshly produced milk samples were distinguished based on the week of production at the beginning of shelf life. Additionally, a clear evolution of the volatiles organic compounds (VOCs) profiling during storage was highlighted. Further statistical analysis confirmed VOCs temporal evolution, mostly because of changes in methyl ketones concentration. Differences caused by the commercial lactases did not emerged, except for benzaldehyde. Altogether, data demonstrated PTR‐TOF‐MS analysis as a valuable and rapid method for the detection of changes in the VOCs profiling of UHT LFM. [ABSTRACT FROM AUTHOR]

Changes in the headspace volatile profile of tea infusion during brewing were determined by analysing the aliquots taken every 30 s using proton transfer reaction time‐of‐flight mass spectrometry in conjunction with principal component analysis and hierarchical cluster analysis. The effect of three different brewing temperatures (60, 70 and 80°C), two leaf sizes (broken and full leaves) and two water mineralizations (soft and hard), on the concentration of volatile compounds in the headspace of tea, was studied as a function of infusion time. An increase in brewing temperature resulted in increased volatile content in the headspace, reflecting an increase in extraction efficiency. Such differences on extraction efficiency were more pronounced with increasing brewing times. Leaf size had also a big impact on the extraction of volatile compounds, but mainly during the early phase of brewing. Water mineralization had a low but noticeable impact on the volatile content. Furthermore, clusters of samples prepared with different combinations of brewing parameters but resulting in analogous volatile profiles could be identified using hierarchical clustering analysis. [ABSTRACT FROM AUTHOR]

Methionine and riboflavin have been identified as key reactants in the development of off‐flavours induced by light exposure. However, the mechanism behind the production of volatiles organic compounds (VOCs) that are generated during the early stages of light exposure is still unclear. To provide new insights into the development of light‐induced off‐flavours, fluorescent light was applied for up to 6 hours to model solutions of methionine and riboflavin and the released VOCs were continuously monitored by proton‐transfer‐reaction mass spectrometry (PTR‐MS). Upon light exposure, methanethiol was rapidly generated, with methional not being released until about 3 minutes later. 2‐Propenal and formic acid, which are methanethiol coproducts from oxidation of methional, were not released until after approximately 22 and 29 min exposure, respectively. These observations coupled with the results from the methional reductive amination blocking experiment suggest that methanethiol could be formed directly from methionine rather than only via the methional intermediate. This means that the light‐induced oxidation of methionine can undergo, at least, two parallel pathways, both leading to the formation of methanethiol. The finding was confirmed in semi‐skimmed milk subjected to similar fluorescence light exposures where consistent changes in VOC signal intensities were observed. The results from these trials demonstrate the advantages of direct injection mass spectrometry techniques like PTR‐MS which enable reactions to be followed in real time and offer the potential to uncover new insights into reaction pathways. [ABSTRACT FROM AUTHOR]

This work proposes a novel method for the direct flow injection profiling of acylglycerols in edible oils and fats without preliminary extraction and consequent reconstitution in the injection solvent. The work exploits the outstanding performance of high-resolution mass spectrometry to target unique elemental compositions even in the most complex matrices. The performance of isopropanol as the unique solvent for both the solubilization and analysis of acylglycerols was investigated in comparison with other classical methods involving preliminary extractions, sample recovery, and analysis. The calibrations of two triglyceride standards (triolein and trilinolenin) were successfully performed in presence and absence of oil matrix. As final application, the effects on the acylglycerol fraction of a heat treatment on three different fat samples (extra virgin olive oil, lard oil, and fat from dry cured ham--speck) were monitored. The proposed method is therefore suitable for a rapid evaluation of acylglycerol fractions in food lipid samples. [ABSTRACT FROM AUTHOR]

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Rationale: The processing of retinyl acetate, a vitamin and biomarker, at high temperatures causes significant decomposition of the compound and thus loss of its activity. The rate of mass loss can be conveniently studied by thermogravimetry (TG). However, this technique generally fails to reveal which compounds have evolved from the compound. In this work we propose a new hyphenation approach to continuously monitor the thermal decomposition of retinyl acetate and follow the evolution of specific volatile organic compounds (VOCs). Methods: Thermal degradation of retinyl acetate was followed by TG coupled to a direct injection mass spectrometer based on proton transfer reaction mass spectrometry (PTR-MS) to follow continuously the thermal decomposition of retinyl acetate. The results were also compared with those obtained by a second evolved gas analysis system based on the coupling of TG with FTIR. Results: The TG results showed two main mass losses, at 180°C and 350°C. When the PTR-MS instrument was connected to the outlet of the TG instrument, specific fragment ions (m/z 43, 61, 75, 85 and 97) showed characteristic evolution profiles. The first mass loss was mainly associated with the release of acetic acid (m/z 43 and 61), whereas the second mass loss was connected with the degradation of the molecule backbone (m/z 43, 61, 75, 85 and 97). These results were substantially correlated with those achieved by TG coupled with FTIR, although PTR-MS showed superior performance in terms of the qualitative identification of specific fragments and better sensitivity toward complex organic VOCs. Conclusions: The proposed TG-PTR-MS technique shows a great potential for following in real time the thermal degradation of ingredients such as retinyl acetate and identifying compounds evolved at specific temperatures. [ABSTRACT FROM AUTHOR]

Apple ( Malus x domestica Borkh.) is a model species for studying the metabolic changes that occur at the onset of ripening in fruit crops, and the physiological mechanisms that are governed by the hormone ethylene. In this study, to dissect the climacteric interplay in apple, a multidisciplinary approach was employed. To this end, a comprehensive analysis of gene expression together with the investigation of several physiological entities (texture, volatilome and content of polyphenolic compounds) was performed throughout fruit development and ripening. The transcriptomic profiling was conducted with two microarray platforms: a dedicated custom array ( iRIPE) and a whole genome array specifically enriched with ripening-related genes for apple ( WGAA). The transcriptomic and phenotypic changes following the application of 1-methylcyclopropene (1- MCP), an ethylene inhibitor leading to important modifications in overall fruit physiology, were also highlighted. The integrative comparative network analysis showed both negative and positive correlations between ripening-related transcripts and the accumulation of specific metabolites or texture components. The ripening distortion caused by the inhibition of ethylene perception, in addition to affecting the ethylene pathway, stimulated the de-repression of auxin-related genes, transcription factors and photosynthetic genes. Overall, the comprehensive repertoire of results obtained here advances the elucidation of the multi-layered climacteric mechanism of fruit ripening, thus suggesting a possible transcriptional circuit governed by hormones and transcription factors. [ABSTRACT FROM AUTHOR]

This study applies proton transfer reaction time-of-flightmass spectrometry for the rapid analysis of volatile compounds released from single coffee beans. The headspace volatile profiles of single coffee beans (Coffeea arabica) from different geographical origins (Brazil, Guatemala and Ethiopia) were analyzed via offline profiling at different stages of roasting. The effect of coffee geographical origin was reflected on volatile compound formation that was supported by one-way ANOVA. Clear origin signatures were observed in the formation of different coffee odorants. [ABSTRACT FROM AUTHOR]

Instant coffee is awidespread product, generally related to a high consumer acceptability, also because of its ease of preparation. The present work addresses the characterization of the headspace of freshly brewed instant coffees resulting from different blends, during and immediately after preparation. The sample set consisted of 10 coffees, obtained by mixing three different blends in different proportions. The employment of Proton Transfer Reaction-Mass Spectrometry (PTR-MS) allowed for direct and real-time sampling from the headspace, under conditions that mimic those that are encountered above the cup during and right after brewing. Different coffee brews were separated on the basis of the respective volatile profiles, and data showed good consistency with the respective blend compositions. When the headspace evolution was monitored during preparation, similar results were obtained in terms of blend separation;moreover, different blends displayed different and reproducible 'signatures' in terms of time evolution. A straightforwardmethod for the prediction of headspace composition is proposed, allowing to predict the volatile profiles of two-component and three-component blends on the basis of the respective parent components. Overall, the results constitute a successful example of the applicability of PTR-MS as a tool for product development in food science. [ABSTRACT FROM AUTHOR]

The grapevine (Vitis vinifera) is one of the most widely cultivated fruit crops globally, and one of its most important diseases in terms of economic losses is downy mildew, caused by Plasmopara viticola. Several wild Vitis species have been found to be resistant to this pathogen and have been used in breeding programs to introduce resistance traits to susceptible cultivars. Plant defense is based on different mechanisms, and volatile organic compounds (VOCs) play a major role in the response to insects and pathogens. Although grapevine resistance mechanisms and the production of secondary metabolites have been widely characterized in resistant genotypes, the emission of VOCs has not yet been investigated following P. viticola inoculation. A Proton Transfer Reaction-Time of Flight-Mass Spectrometer (PTR-ToF-MS) was used to analyze the VOCs emitted by in vitro-grown plants of grapevine genotypes with different levels of resistance. Downy mildew inoculation significantly increased the emission of monoterpenes and sesquiterpenes by the resistant SO4 and Kober 5BB genotypes, but not by the susceptible V. vinifera Pinot noir. Volatile terpenes were implicated in plant defense responses against pathogens, suggesting that they could play a major role in the resistance against downy mildew by direct toxicity or by inducing grapevine resistance. The grapevine genotypes differed in terms of the VOC emission pattern of both inoculated and uninoculated plants, indicating that PTR-ToF-MS could be used to screen hybrids with different levels of downy mildew resistance. [ABSTRACT FROM AUTHOR]

In apples, consumers predominantly use visual, auditory and texture cues as quality/preference indicators and struggle to describe complex olfactory sensations. This study investigated apple cultivar differentiation using analytical and sensory techniques with the goal of achieving more relevant instrumental characterization. Sensory flavor/odor data were compared with volatile organic compounds (VOCs) measured using proton transfer reaction time-of-flight mass spectrometer (PTR-ToF-MS) and sensory texture data were compared with mechanical-acoustic textural parameters obtained using a texture analyzer. Both techniques separated cultivars similarly. PTR-ToF-MS data separated cultivars into VOC families that correlated to specific sensory attributes (e.g., butanoate esters to lemon flavor/odor). Analytical and sensory firmness were positively correlated where the former differentiated crunchy from hard-not crunchy cultivars. Sweet taste did not correlate to soluble solids content but was positively correlated to fruity esters which could indicate a taste-aroma interaction. This study demonstrates the potential to predict sensory attributes of apples using analytical techniques. Practical Application The description of apple flavor is challenging for both trained panelists and consumers to describe due to the complexity of the multimodal stimulations that occur within the oral and ortho/retro nasal cavity during consumption that induce odor, taste, flavor and sound perception. Therefore, this study looks at objectively characterizing apple cultivars based solely on instrumental techniques that reflect attributes attained from a descriptive sensory analysis of the same cultivars. The current study found apple cultivars were separated into similar groups when sensory and instrumental texture, physicochemical and VOC data were compared. Specific analytical properties that correlated strongly to sensory attributes could be used as predictors of important sensory attributes that differentiated the samples. Hence, the use of these instrumental techniques to characterize apples could be an option to increase throughput. [ABSTRACT FROM AUTHOR]

Drying process is commonly used to allow long time storage of valuable porcini mushrooms ( Boletus edulis). Although considered a stable product dried porcini flavour changes during storage. Monitoring of volatile compounds during shelf life may help to understand the nature of the observed changes. In the present work two mass spectrometric techniques were used to monitor the evolution of volatile compounds during commercial shelf life of dried porcini. Solid phase microextraction (SPME) coupled to gas chromatography - mass spectrometry (GC-MS) allowed the identification of 66 volatile compounds, 36 of which reported for the first time, monitored during the commercial shelf life of dried porcini. Proton transfer reaction - time of flight - mass spectrometry (PTR-ToF-MS) , a direct injection mass spectrometric technique, was shown to be a fast and sensitive instrument for the general monitoring of volatile compound evolution during storage of dried porcini. Furthermore, PTR-ToF-MS grants access to compounds whose determination would otherwise require lengthy pre-concentration and/or derivatization steps such as ammonia and small volatile amines. The two techniques, both used for the first time to study dried porcini, provided detailed description of time evolution of volatile compounds during shelf life. Alcohols, aldehydes, ketones and monoterpenes diminish during the storage while carboxylic acids, pyrazines, lactones and amines increase. The storage temperature modifies the rate of the observed changes influencing the final quality of the dried porcini. We showed the advantages of both techniques, suggesting a strategy to be adopted to follow time evolution of volatile compounds in food products during shelf life, based on the identification of compounds by GC-MS and the rapid time monitoring by PTR-ToF-MS measurements in order to maximize the advantages of both techniques. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

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. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

We report the energy-dependent fragmentation patterns upon protonation of eight sulfides (organosulfur compounds) in Proton Transfer Reaction-Mass Spectrometry (PTR-MS). Studies were carried out, both, experimentally with PTR-MS, and with theoretical quantum-chemical methods. Charge retention usually occurred at the sulfur-containing fragment for short chain sulfides. An exception to this is found in the unsaturated monosulfide allylmethyl sulfide (AMS), which preferentially fragmented to a carbo-cation at m/z 41, C3H5+. Quantum chemical calculations (DFT with the M062X functional 6-31G(d,p) basis sets) for the fragmentation reaction pathways of AMS indicated that the most stable protonated AMS cation at m/z 89 is a protonated (cyclic) thiirane, and that the fragmentation reaction pathways of AMS in the drift tube are kinetically controlled. The protonated parent ion MH+ is the predominant product in PTR-MS, except for diethyl disulfide at high collisional energies. The saturated monosulfides R-S-R' (with R+ fragment. The saturated disulfides R-S-S-R display more fragmentation than the saturated monosulfides, the most common fragments are disulfide containing fragments or long-chain carbo-cations. The results rationalize fragmentation data for saturated monosulfides and disulfides and represent a detailed analysis of the fragmentation of an unsaturated sulfide. Apart from the theoretical interest, the results are in support of the quantitative analysis of sulfides with PTR-MS, all the more so as PTR-MS is one of a few techniques that allow for ultra-low quantitative analysis of sulfides. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Breath testing has been largely used as a diagnostic tool, but the difficulties in data interpretation and sample collection have limited its application. We developed a fast (< 20 s), on-line, non-invasive method for the collection and analysis of exhaled breath in awake rats based on proton transfer reaction time of flight mass spectrometry (PTR-ToF-MS) and applied it to investigate possible relationships between pathologies induced by dietary regime and breath composition. As a case study, we investigated rats with dietary induced non-alcoholic steatohepatitis (NASH) and modifications induced by coffee addition to the diet. We considered two different diets (standard and high fat) complemented with two different drinking possibilities (water or decaffeinated coffee) for a total of four groups with four rats each. Several spectrometric peaks were reliable markers for both dietary fat content and coffee supplementation. The high resolution and accuracy of PTR-ToF-MS allowed the identification of related compounds such as methanol, dimethyl sulphide, dimethyl sulphone and ammonia. In conclusion, the rapid and minimally invasive breath analysis of awake rats permitted the identification of markers related to diet and specific pathologic conditions and provided a useful tool for broader metabolic investigations. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Hail climatology is usually weakly known and unsatisfactorily standardised in measurement techniques. Trentino, in the Italian Alps, boasts a 271-hailpad network operated since 1974, covering nearly the whole of the regional agricultural area. Many hail indices, concerning both extensive and energetic features of hailstorms, were investigated in a 35-year period, seeking for climatic trends. The results show that, despite a slight, non-significant trend of decrease in the number of events and in the hit surfaces, most energetic indices, which are directly correlated to the damage to crops, have increased in the period, some at considerable rates. Particularly, indices referring to extreme values show the clearest trends. The correlation with atmospheric variables from ECMWF's reanalysis (ERA-40) was considered. Data were processed at six gridpoints, to calculate three instability-related indices. Other ten variables were considered, either integrated over the atmospheric column or at separate atmospheric levels. Correlations between seasonally averaged single atmospheric predictors and hail indices show a varied record of cases, where only some pairs of atmospheric predictors and hail indices give positive results. Statistical links were also sought using a multivariate method involving principal component regression (PCR) and partial least square regression (PSLR) techniques. Despite the more general approach allowed by these methods, only some hail indices respond to the attempt of setting up satisfactory statistical models. The principal-component predictors are built with many atmospheric variables, warning against a simplified use of correlations of some hail indices with few atmospheric predictors. Particularly, it is shown that the number of events is not a useful index for assessing general climatic features of hailstorms, and that the use of one instability index alone-like convective available potential energy ( CAPE)-does not allow a thorough description of the links between atmospheric precursors of hail and its real occurrence. Copyright © 2010 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

The interaction of oral processing protocols and food texture on in vivo flavour release was evaluated by nose-space analysis. Nose-space analysis was carried out by proton transfer reaction mass spectrometry, and strawberry-flavoured custards were prepared with 0.1% (w/w) and 1.0% (w/w) carboxymethyl cellulose to modify the texture. Two oral processing protocols were adopted during the study; a free-chewing protocol and an imposed protocol. Twenty-one subjects participated in the study. Significant effects on in-nose flavour release were observed for the type of compound, the custard's texture, the oral processing protocol and the subjects. When people were allowed to eat as they normally do, individuals could be divided into three groups on the basis of swallowing time: first group, swallowing time <4 s; second group, swallowing time >6 s; intermediate group, t(swallow) varying (4-6 s). Within each group, different effects of the texture of the custards on in-nose flavour concentrations were observed, indicating that individual behaviour plays a considerable role in determining texture effects on flavour perception. Copyright © 2006 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]