Exploring blueberry aroma complexity by chromatographic and direct-injection spectrometric techniques

Blueberry (Vaccinium spp.) fruit consumption has increased over the last 5 years, becoming the second most important soft fruit species after strawberry. Despite the possible economic and sensory impact, the blueberry volatile organic compound (VOC) composition has been poorly investigated. Thus, the great impact of the aroma on fruit marketability stimulates the need to step forward in the understanding of this quality trait. Beside the strong effect of ripening, blueberry aroma profile also varies due to the broad genetic differences among Vaccinium species that have been differently introgressed in modern commercial cultivars through breeding activity. In the present study, divided into two different activities, the complexity of blueberry aroma was explored by an exhaustive untargeted VOC analysis, performed by two complementary methods: SPME-GC-MS (solid phase microextraction-gas chromatography-mass spectrometry) and PTR-ToF-MS (proton transfer reaction-time of flight-mass spectrometry). The first experiment was aimed at determining the VOC modifications during blueberry ripening for five commercially representative cultivars ("Biloxi," "Brigitta Blue," "Centurion," "Chandler," and "Ozark Blue") harvested at four ripening stages (green, pink, ripe, and over-ripe) to outline VOCs dynamic during fruit development. The objective of the second experiment was to confirm the analytical capability of PTR-ToF-MS to profile blueberry genotypes and to identify the most characterizing VOCs. In this case, 11 accessions belonging to different Vaccinium species were employed: V. corymbosum L. ("Brigitta," "Chandler," "Liberty," and "Ozark Blue"), V. virgatum Aiton ("Centurion," "Powder Blue," and "Sky Blue"), V. myrtillus L. (three wild genotypes of different mountain locations), and one accession of V. cylindraceum Smith. This comprehensive characterization of blueberry aroma allowed the identification of a wide pull of VOCs, for the most aldehydes, alcohols, terpenoids, and esters that can be used as putative biomarkers to rapidly evaluate the blueberry aroma variations related to ripening and/or senescence as well as to genetic background differences. Moreover, the obtained results demonstrated the complementarity between chromatographic and direct-injection mass spectrometric techniques to study the blueberry aroma

Quantifying lycopene synthesis and chlorophyll breakdown in tomato fruit using remittance VIS spectroscopy

The aim of this study was to increase the understanding of chlorophyll breakdown and lycopene synthesis at a quantitative level in Solanum lycopersicum fruit. To accomplish this, a kinetic model is proposed describing the transition from chloro- to chromoplast. Remittance VIS spectroscopy was used to assess chlorophyll and lycopene levels non-destructively in cocktail and round type tomatoes. Tomatoes were stored at constant temperatures between 4 and 24 °C, or at a stepwise changing temperature between 4 and 16 °C. Chlorophyll and lycopene levels were measured repeatedly over time and used to calibrate a kinetic model that describes how an autocatalytic enzyme system links chlorophyll breakdown to lycopene synthesis, including breakdown of lycopene precursor and lycopene itself. Increasing storage temperatures increased the reaction constant for lycopene synthesis more than that of chlorophyll breakdown for both tomato types. The reaction constants describing chlorophyll breakdown and lycopene synthesis were considerably larger, and the estimated enzyme levels lower for the round type. This allows round tomatoes to quickly resume lycopene synthesis after a cold storage period when enzyme levels are low. Lycopene breakdown was established for the round type while the cocktail type showed lycopene precursor breakdown. Chlorophyll breakdown and lycopene synthesis, as affected by storage temperature and tomato type, is covered well by the model for both tomato types. We hypothesise that the postulated enzyme system, responsible for the direct link between chlorophyll breakdown and lycopene synthesis, is due to STAY-GREEN proteins. Remittance VIS spectroscopy is, in combination with a parameter estimation tool, suited to screen tomato genotypes for intended colour transformation performance, or as tool in chloroplast to chromoplast transition studies

Tracking of hop-derived compounds in beer during fermentation with PTR-TOF-MS

The craft beer market is experiencing a rapid increase in growth. To help brewers optimise hop character, and to make beer with distinctive hop profiles, a better understanding of the role that yeast play in the development of hop character is required. Beyond anecdotal evidence, a paucity of published data exists on the interactions between hop varieties and different yeasts and the resulting effect on beer flavour. In the current study, proton transfer reaction-time of flight-mass spectrometry (PTR-TOF-MS) was used as a novel, direct and real-time analytical method to monitor small-scale fermentations carried out in 20 mL vials (3 mL sample volume) at 20 ◦C with repeated measurements of the headspace VOCs every six hours for four days. A design matrix of two yeast strains (California Ale and Edinburgh Scottish Ale) and two New Zealand aroma hop varieties (Motueka and Nelson Sauvin), together with their respective no addition controls, were used to investigate yeasthop interactions. VOCs that showed evidence of hop-yeast interactions were identified. Differentiation between isomeric compounds was achieved through separation with fastGC and identification of compounds was supported by GC-MS and scientific literature. The results highlighted the advantages of using online analytical measurements, such as PTR-TOF-MS, to understand temporal changes that occurred in VOCs during fermentation. For example masses such as ms145.121 (2-nonanol, or ethyl hexanoate), ms105.068 (pentanethiol, or 3-methyl-1-butanethiol) and ms173.153 (isoamyl isovalerate, or octyl acetate) initially increased during the fermentation process and then decreased towards its end due to competing reactions. Distinct differences were observed in the VOCs profile of the different beers based on combinations of yeast strain and hop type; e.g. samples with Motueka and California Ale were associated with higher levels of ms75.077 (2-methyl- 1-propanol), while samples with Motueka and Scottish Ale had higher concentrations of ms137.132 (pinene, or myrcene) and ms89.057 (3-methyl-1-butanol). A better understanding of how hop-derived compounds in beer are influenced during fermentation by yeast will improve our understanding of the generation of the hop aroma of beer and will give insight on how to achieve a desired hop character by selecting yeast strains and modifying fermentation parameter

Can strawberry volatile emissions influence Botrytis cinerea growth?

Many fungal pathogens that infect fruit in the field cause symptomatic disease during storage and marketing as ripening progresses. The development of some diseases is also enhanced by the occurrence of mechanical injuries. As an increase in volatile emissions generally occurs during fruit ripening and following wounding, we hypothesized that volatile organic compounds (VOCs) could be involved in disease development, and have tested this hypothesis in the strawberry-Botrytis cinerea interaction. Thirty-five strawberry VOCs were tested on B. cinerea in vitro and fruit volatile emissions were analyzed in ‘Monterey’ strawberries harvested at four ripening stages by headspace solid-phase microextraction/gas chromatography-mass spectrometry and proton transfer reaction – time of flight – mass spectrometry Results showed that key strawberry aroma compounds stimulated B. cinerea conidial germination at concentrations naturally detected in ripe strawberry, and that some ‘green leaf volatiles’ emitted from wounded fruit also stimulated pathogen’ conidial germination or mycelial growth. These results suggest that B. cinerea may exploit some strawberry volatiles as chemical signals to: i) recognize the ripening stage of the fruit host and resume its growth from the latent phase, and ii) recognize the presence of damaged tissues in the host and increase their colonization by increasing conidial germination or mycelial growth in response to specific VOCs

Role of strawberry volatile organic compounds in the development of Botrytis cinerea infection

Botrytis cinerea, the main pathogen of strawberry, has the ability to remain quiescent in unripe tissue and develop disease symptoms in ripe fruit. As strawberry ripening is characterized by an increase of aroma compounds, the role of volatile emission in the development of infection was investigated. Thirty-five strawberry volatile organic compounds (VOCs) were tested on B. cinerea in vitro and volatile emission was analysed in strawberry harvested at four ripening stages by headspace solid-phase microextraction/gas chromatography–mass spectrometry and proton transfer reaction– time of flight–mass spectrometry. The coupling of such data sets made it possible to conclude that key strawberry aroma compounds stimulate B. cinerea conidial germination and some typical wound-volatiles stimulate pathogen conidial germination or mycelial growth. This study is the first report of fungal stimulation by some VOCs naturally occurring in strawberry: the esters ethyl butanoate, cis-3-hexenyl acetate, trans-2-hexenyl acetate, methyl butanoate and hexyl butanoate, the furanones furaneol and mesifurane, and the alcohol trans-2-hexenol. The results of this work provide advances in understanding the functional role of fruit VOCs and suggest, for the first time, that fruit VOCs may influence the development of B. cinerea from the latent phase and that they could favour the invasive growth of B. cinerea after wounding. In particular, ethyl butanoate and furaneol could signal strawberry ripening, and the green leaf volatiles trans-2-hexenol, trans-2-hexenyl acetate and cis-3-hexenyl acetate could signal the presence of damaged tissues that are easier sites for penetration by B. cinere

Analysis of flavor generation in beer by PTR-ToF-MS

The online studies of beer aroma generation by PTR-ToF-MS help to unravel the role of yeast and hope on the final product qualit

Profiling of volatile sesquiterpenes and monoterpenes in grapevine genotypes after Plasmopara viticola inoculation by PTR-ToF-MS analysis

none8noneAlgarra Alarcon, Alberto; Lazazzara, Valentina; Cappellin, Luca; Bianchedi, Pierluigi; Wohlfahrt, G.; Pertot, Ilaria; Biasioli, Franco; Perazzolli, Michel

Effect of hot water treatment on peach volatile emission and Monilinia fructicola development

The effect of hot water treatment (HWT) to control peach brown rot was investigated. Peaches were dipped in water at 60\ub0C for 60 s and artificially inoculated with Monilinia fructicola conidia. HWT failed to control brown rot if applied before inoculation and microscopic observations revealed a stimulatory effect on germ tube elongation of M. fructicola conidia placed immediately after HWT on the fruit surface, compared to the control. The influence of fruit volatile emission due to HWT was performed on the pathogen conidia exposed to the headspace surrounding peaches. The results showed an increase of M. fructicola conidial germination ranging from 33 to 64% for cultivars Lucie Tardibelle and Red Haven heat-treated peaches, respectively, compared to the control. The volatile blend emitted from heat-treated fruit was analysed by solid-phase microextraction/gas chromatography-mass spectrometry (SPME/GC-MS) and proton transfer reaction-time of flight-mass spectrometry (PTR-ToF-MS). Fifty compounds were detected by SPME/GC-MS in volatile blends of cv. Lucie Tardibelle peaches and significant differences in volatile emission were observed among heated and control fruit. Using PTR-ToF-MS analysis, acetaldehyde and ethanol were detected at levels 15- and 28-fold higher in heated fruit compared to unheated ones, respectively. In vitro assays confirmed the stimulatory effect (60 and 15%) of acetaldehyde (0\ub76 \u3bcL L-1) and ethanol (0\ub72 \u3bcL L-1) on M. fructicola conidial germination and mycelial growth, respectively. The results showed that volatile organic compounds (VOCs) emitted from heat-treated peaches could stimulate M. fructicola conidial germination, increasing brown rot incidence in treated peaches when the inoculation occurs immediately after HW