Iuliia Khomenko

Comprehensive VOC profiling of an apple germplasm collection by PTR-ToF-MS

Fruit quality is generally represented by several components, among which aroma plays a fundamental role in determining the overall appreciation. To generate a comprehensive data inventory of aroma compounds in apple, a large collection represented by 190 apple accessions was characterized by a proton transfer reaction-time of flight-mass spectrometry (PTR-ToF-MS) instrument, a valid alternative to a gas chromatography-mass spectrometry (GS-MS) apparatus. The analytical performance of this instrument allowed to profile volatile organic compound (VOC) spectra of a portion of apple fruit flesh in a short time and efficient manner. Based on the VOC composition, the collection resulted grouped into six main clusters, mainly determined by ester and alcohols. These two VOC categories were also further exploited for the definition of an Alcohols/Esters index, which can be considered as a novel fruit quality descriptor useful for a further and more exhaustive characterization of several apple accessions. The distribution of these compounds and the possible further use of these information are discussed.

Untargeted metabolomics investigation of volatile compounds involved in the development of apple superficial scald by PTR-ToF-MS

The superficial scald is an important physiological disorder affecting apple fruit during postharvest storage. To date, the accumulation, and further oxidation, of α-farnesene was considered as the most probable cause for the development of this physiopathy. In order to perform a more broad investigation, a PTR-ToF–MS (proton transfer reaction—time of flight—mass spectrometry) was employed to monitor the volatile organic compounds (VOCs) production along with the progression of this disorder in fruit of “Granny Smith”, an apple variety known to be highly susceptible to scald. The untargeted metabolite investigation was performed on both skin and pulp, as well as comparing control versus treated tissues with 1-methylcyclopropene (1-MCP), an ethylene competitor widely used to prevent the development of this phenomenon. The rapid and non-destructive analysis of the VOC array carried out by PTR-ToF–MS identified three specific groups of metabolites in the skin, among which the 6-methyl-5-hepten-2-one (MHO) resulted significantly associated with the development of the superficial scald in apple. The results proposed in this work suggest the use of this novel equipment for an on-line monitoring of the VOCs released by the apple during the postharvest storage, as well as to use MHO as a possible biochemical marker for an early detection of the superficial scald symptoms.

QTL analysis coupled with PTR-ToF-MS and candidate gene-based association mapping validate the role of Md-AAT1 as a major gene in the control of flavor in apple fruit

Volatile organic compounds (VOCs) are fundamental elements of flavor, one of the most important fruit-quality traits. Despite its importance, this aspect is still poorly considered in assisted breeding programs, due to the lack of suitable and fast detection systems as well as validated functional markers. In this work, a full-sib parental mapping population (‘Fuji × Delearly’) was initially employed to perform a comprehensive quantitative trait locus (QTL) survey, to assess the VOC segregation detected by a novel proton-transfer-reaction time-of-flight mass spectrometry (PTR-ToF-MS) on fruit collected after a 2-month period of postharvest storage. Among this set of genomic regions, on chromosome 2 was also verified the coincident location between a group of QTLs, mainly associated to esters and alcohols, with a functional marker designed for Md-AAT1, a gene involved in the last step of the ester biosynthetic pathway. The allelic effect of this marker (here named Md-AAT1SSR) was further validated by candidate gene association mapping approach in a collection of 124 apple accessions. In this case, the volatile profiling was performed on peeled fruit flesh, as an important fraction of the aromatic blend of apple is released only after cutting. This work proposed a new and fast method for aroma phenotyping as well as a novel marker for an easy and widely applicable apple fruit quality advanced selection.

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.

Genome-wide association study unravels the genetic control of the apple volatilome and its interplay with fruit texture

Highlight VOC production and fruit texture, assessed by multiple factor analysis, showed a contrasting behavior in apple. A GWAS approach dissected regulation of the volatilome and identified QTLs co-locating with important candidate genes.

PTR-ToF-MS Coupled with an Automated Sampling System and Tailored Data Analysis for Food Studies: Bioprocess Monitoring, Screening and Nose-space Analysis

Proton Transfer Reaction (PTR), combined with a Time-of-Flight (ToF) Mass Spectrometer (MS) is an analytical approach based on chemical ionization that belongs to the Direct-Injection Mass Spectrometric (DIMS) technologies. These techniques allow the rapid determination of volatile organic compounds (VOCs), assuring high sensitivity and accuracy. In general, PTR-MS requires neither sample preparation nor sample destruction, allowing real time and non-invasive analysis of samples. PTR-MS are exploited in many fields, from environmental and atmospheric chemistry to medical and biological sciences. More recently, we developed a methodology based on coupling PTR-ToF-MS with an automated sampler and tailored data analysis tools, to increase the degree of automation and, consequently, to enhance the potential of the technique. This approach allowed us to monitor bioprocesses (e.g. enzymatic oxidation, alcoholic fermentation), to screen large sample sets (e.g. different origins, entire germoplasms) and to analyze several experimental modes (e.g. different concentrations of a given ingredient, different intensities of a specific technological parameter) in terms of VOC content. Here, we report the experimental protocols exemplifying different possible applications of our methodology: i.e. the detection of VOCs released during lactic acid fermentation of yogurt (on-line bioprocess monitoring), the monitoring of VOCs associated with different apple cultivars (large-scale screening), and the in vivo study of retronasal VOC release during coffee drinking (nosespace analysis).

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

In situ riboflavin fortification of different kefir-like cereal-based beverages using selected Andean LAB strains

Cereal-based functional beverages represent social, economic, and environmental sustainable opportunities to cope with emerging trends in food consumption and global nutrition. Here we report, for the first time, the polyphasic characterization of three cereal-based kefir-like riboflavin-enriched beverages, obtained from oat, maize and barley flours, and their comparison with classical milk-based kefir. The four matrices were successfully fermented with commercial starters: i) milk-kefir and ii) water-kefir, proving the potential of cereal ingredients in the formulation of dairy-like fermented beverages with milk-kefir starter behavior better in these matrices. In the light of their potentiality, seven riboflavin-producing Andean Lactic Acid Bacteria (LAB) were tested for tolerance to food stresses commonly encountered during food fermentation. Moreover, the LAB strains investigated were screened for spontaneous riboflavin overproducing derivatives. Lactobacillus plantarum M5MA1-B2 with outstanding response to stress, was selected to improve riboflavin content in an in situ fortification approach. The combination of L. plantarum M5MA1-B2 riboflavin overproducing strain with milk kefir starter in oat, lead to cover, for one serving of 100 g, 11.4% of Recommended Dietary Allowance (RDA). Besides, addition of L. plantarum M5MA1-B2 improved performance of water kefir in oat and maize matrices. Proton Transfer Reaction Time-of-Flight Mass Spectrometry (PTR-ToF-MS) analysis provided the on-line Volatile Organic Compounds profiles supporting the best combination of starter, LAB and cereal matrix for novel functional foods development.

Analysis of volatile organic compounds in crumb and crust of different baked and toasted gluten-free breads by direct PTR-ToF-MS and fast-GC-PTR-ToF-MS

PTR-ToF-MS has been recently employed as a quick, easy and sensitive alternative to GC-MS for the analysis of volatile compounds in food. In the present work, PTR-ToF-MS was applied to the characterisation of the volatile profiles of the baked and toasted crumbs and crusts of five gluten-free breads elaborated with quinoa, teff and rice flours as well as corn and wheat starches and wheat bread as a control samples. 259 peaks (m/z) were detected, 86 peaks were tentatively identified and 56 volatile compounds were selected as important contributors to bread aroma. Fast-GC- PTR-ToF-MS analyses were performed with 42 standards in order to identify them in the baked crumbs and crusts, 18 of them being present in all the samples. From the baked samples it was concluded that quinoa crust was the one with higher volatile compound in high abundance, characterised by volatile compounds from fermentation, lipids oxidation, 2-acetyl-1-pyrroline and diethyl-pyrazines, while wheat crust was characterised by the highest content in furan derivatives. The toasting time led to crust samples with an increased content in all the volatile compounds: quinoa crust was now characterised by the highest content in all the pyrazines and furan derivatives, while starches were distinguished by the highest abundance in 2-acetyl-1-pyrroline and diethyl-pyrazines. Neither the baked crumbs nor the toasted crumbs presented the highest content in none of the volatile compounds. Therefore, it was concluded that quinoa flour can be a suitable alternative for the elaboration of baked and toasted breads due to the high content of pleasant volatile compounds from fermentation, the key volatile in crust 2-acetyl-1-pyrroline (baked sample) as well as pleasant pyrazines and toasted-like furan derivatives (baked and toasted samples); however, the off-flavours volatile compounds from lipids oxidation as well as the bitter saponins present in quinoa bread should be taken into account.

The Application of Proton Transfer Reaction Mass Spectrometry to the Analysis of Foods

The instrumental characterization of volatile organic compounds (VOCs) is essential to have a precise, reliable, and reproducible estimation of food aroma and, therefore, of the overall product quality. In this article we will list the main characteristics of PTR-MS (proton transfer reaction mass spectrometry) and its application in the agri-food chain research. The high time resolution brought by this technology allows real-time monitoring of fast food processes and rapid and noninvasive VOC fingerprinting.