[Luchner2012] "Implementation of proton transfer reaction-mass spectrometry (PTR-MS) for advanced bioprocess monitoring.",
, vol. 109, no. 12: ACIB GmbH, Muthgasse 11, A-1190 Vienna, Austria., pp. 3059–3069, Dec, 2012.
We report on the implementation of proton transfer reaction-mass spectrometry (PTR-MS) technology for on-line monitoring of volatile organic compounds (VOCs) in the off-gas of bioreactors. The main part of the work was focused on the development of an interface between the bioreactor and an analyzer suitable for continuous sampling of VOCs emanating from the bioprocess. The permanently heated sampling line with an inert surface avoids condensation and interaction of volatiles during transfer to the PTR-MS. The interface is equipped with a sterile sinter filter unit directly connected to the bioreactor headspace, a condensate trap, and a series of valves allowing for dilution of the headspace gas, in-process calibration, and multiport operation. To assess the aptitude of the entire system, a case study was conducted comprising three identical cultivations with a recombinant E. coli strain, and the volatiles produced in the course of the experiments were monitored with the PTR-MS. The high reproducibility of the measurements proved that the established sampling interface allows for reproducible transfer of volatiles from the headspace to the PTR-MS analyzer. The set of volatile compounds monitored comprises metabolites of different pathways with diverse functions in cell physiology but also volatiles from the process matrix. The trends of individual compounds showed diverse patterns. The recorded signal levels covered a dynamic range of more than five orders of magnitude. It was possible to assign specific volatile compounds to distinctive events in the bioprocess. The presented results clearly show that PTR-MS was successfully implemented as a powerful bioprocess-monitoring tool and that access to volatiles emitted by the cells opens promising perspectives in terms of advanced process control.
[Ting2012] "In vitro and in vivo flavor release from intact and fresh-cut apple in relation with genetic, textural, and physicochemical parameters.",
J Food Sci
, vol. 77, no. 11: Research and Innovation Centre, Foundation Edmund Mach, via Mach 1, San Michele all' Adige, (TN), Italy., pp. C1226–C1233, Nov, 2012.
Flavor release from 6 commercial apple cultivars (Fuji, Granny Smith, Golden Delicious, Jonagold, Morgen Dallago, and Red Delicious) under static conditions (intact or fresh-cut samples) and during consumption of fresh-cut samples (nosespace) was determined by proton transfer reaction mass spectrometry. Textural (firmness, fracturability, flesh elasticity, and rupture) and physicochemical (pH, acidity, and water content) properties of the apples were also measured. Static headspace analysis of intact fruits revealed Fuji and Granny Smith apples had the lowest concentration for all measured flavor compounds (esters, aldehydes, alcohols, and terpenes), whereas Red Delicious apples had the highest. Fresh-cut samples generally showed a significant increase in total volatile compounds with acetaldehyde being most abundant. However, compared to intact fruits, cut Golden and Red Delicious apples had a lower intensity for ester related peaks. Five parameters were extracted from the nosespace data of peaks related to esters (m/z 43, 61), acetaldehyde (m/z 45), and ethanol (m/z 47): 2 associated with mastication (duration of mastication-t(con); time required for first swallowing event-t(swal)), and 3 related with in-nose volatile compound concentration (area under the curve-AUC; maximum intensity-I(max); time for achieving I(max)-t(max)). Three different behaviors were identified in the nosespace data: a) firm samples with low AUC and t(swal) values (Granny Smith, Fuji), b) mealy samples with high AUC, I(max), t(swal) values, and low t(con) (Morgen Dallago, Golden Delicious), and c) firm samples with high AUC and I(max) values (Red Delicious). Strengths and limitations of the methodology are discussed. PRACTICAL APPLICATION: Volatile compounds play a fundamental role in the perceived quality of food. Using apple cultivars, this research showed that in vivo proton transfer reaction mass spectrometry (PTR-MS) could be used to determine the relationship between the release of volatile flavor compounds and the physicochemical parameters of a real food matrix. This finding suggests that in vivo PTR-MS coupled with traditional physicochemical measurements could be used to yield information on flavor release from a wide range of food matrices and help in the development of strategies to enhance food flavor and quality.
[JLTing2012] "In Vitro and In Vivo Flavor Release from Intact and Fresh-Cut Apple in Relation with Genetic, Textural, and Physicochemical Parameters",
Journal of food science
, vol. 77, no. 11: Wiley Online Library, pp. C1226–C1233, 2012.
Flavor release from 6 commercial apple cultivars (Fuji, Granny Smith, Golden Delicious, Jonagold, Morgen Dallago, and Red Delicious) under static conditions (intact or fresh-cut samples) and during consumption of fresh-cut samples (nosespace) was determined by proton transfer reaction mass spectrometry. Textural (firmness, fracturability, flesh elasticity, and rupture) and physicochemical (pH, acidity, and water content) properties of the apples were also measured. Static headspace analysis of intact fruits revealed Fuji and Granny Smith apples had the lowest concentration for all measured flavor compounds (esters, aldehydes, alcohols, and terpenes), whereas Red Delicious apples had the highest. Fresh-cut samples generally showed a significant increase in total volatile compounds with acetaldehyde being most abundant. However, compared to intact fruits, cut Golden and Red Delicious apples had a lower intensity for ester related peaks. Five parameters were extracted from the nosespace data of peaks related to esters (m/z 43, 61), acetaldehyde (m/z 45), and ethanol (m/z 47): 2 associated with mastication (duration of mastication–tcon; time required for first swallowing event–tswal), and 3 related with in-nose volatile compound concentration (area under the curve–AUC; maximum intensity–Imax; time for achieving Imax–tmax). Three different behaviors were identified in the nosespace data: a) firm samples with low AUC and tswal values (Granny Smith, Fuji), b) mealy samples with high AUC, Imax, tswal values, and low tcon (Morgen Dallago, Golden Delicious), and c) firm samples with high AUC and Imax values (Red Delicious). Strengths and limitations of the methodology are discussed.
[Frank2012] "In vitro measurement of volatile release in model lipid emulsions using proton transfer reaction mass spectrometry.",
J Agric Food Chem
, vol. 60, no. 9: Food Futures Flagship, CSIRO Food, Nutritional Sciences, North Ryde, New South Wales, Australia. email@example.com, pp. 2264–2273, Mar, 2012.
The presence of fat in food plays an important role in the way aroma is released during consumption and in the creation of the overall sensory impression. Fat acts as a reservoir for lipophilic volatile compounds and modulates the timing and delivery of aroma compounds in a unique manner. Despite considerable research, reproducible in vitro methods for measuring the effect of fat on volatile release are lacking. An open in vitro cell was used to simulate the open human naso-oropharygeal system and was interfaced with a proton transfer reaction mass spectrometer (PTR-MS) to examine some of the fundamental effects of fat on dynamic volatile release in liquid fat emulsions. Lipid emulsions with various fat contents (0-20%) and droplet sizes (0.25, 0.5, and 5.0 ?M) were spiked with flavor volatiles representing a range of lipophilicity (K(o/w) = 1-1380). Preloaded syringes of spiked emulsion were injected into the cell, and temporal changes in release were measured under dynamic conditions. Significant differences in release curves were measured according to the lipid content of emulsions, the vapor pressure, and K(o/w) values of the volatile compounds. With increasing addition of fat, the critical volatile release parameters, maximum concentration (I(max)), time to maximum concentration (T(max)), and the integrated area under the concentration curve (AUC), were affected. The in vitro curves were reproducible and in agreement with theory and correlated with the preswallow phase of in vivo release data. An exponential model was used to calculate changes in mass transfer rates with increased fat addition.
[Dunne2012] "Interference in the PTR-MS measurement of acetonitrile at m/ z 42 in polluted urban air�A study using switchable reagent ion PTR-MS",
International Journal of Mass Spectrometry
, vol. 319: Elsevier, pp. 40–47, 2012.
In Proton Transfer Reaction Mass Spectrometer (PTR-MS) measurements of the atmosphere, the signal at m/z 42 is commonly regarded as a unique measure of acetonitrile. However, two other ions potentially contribute to the signal at m/z 42. These are 13C isotopologues of C3H5+ and the product ion C3H6+ produced by reaction of NO+ and O2+ (present in trace amounts in the H3O+ reagent gas), with a number of volatile organic compounds. Thus, there is the possibility of interference in the measurement of acetonitrile at m/z 42 by PTR-MS. Interference in the measurement of acetonitrile at m/z 42 was quantified in urban air over 17 days in Sydney, Australia, in summer. A PTR-MS with Switchable Reagent Ion capability was used for measurements at m/z 41 and 42 in three different primary reagent ion modes, O2+, NO+ and H3O+, to quantify the contribution of non-acetonitrile compounds to the signal at m/z 42 when the PTR-MS was operating in H3O+ reagent ion mode. Acetonitrile dominated the ion signal at m/z 42; however non-acetonitrile ions contributed 5–41% of the total ion signal at m/z 42. The average corrected and uncorrected acetonitrile concentrations were 120 pptv and 148 pptv respectively. The interference in the m/z 42 signal was calculated from known or interpolated concentrations of compounds identified as potential interferrants. Overall the isotopologue correction is due to alkenes including isoprene with probable contributions from other compounds not measured in this study. The other component of the interference, produced by reactions of O2+, is due to alkanes and alkenes. Levoglucosan, a biomass burning tracer in atmospheric particulate matter was more highly correlated with the corrected acetonitrile signal than the uncorrected acetonitrile signal. Measurements of acetonitrile by PTR-MS at m/z 42 in urban air will frequently require correction because of the non-trivial concentrations of alkanes and alkenes commonly observed in urban air.
[Loekke2012] "Investigation of Volatiles Emitted from Freshly Cut Onions (Allium cepa L.) by Real Time Proton-Transfer Reaction-Mass Spectrometry (PTR-MS).",
, vol. 12, no. 12: Department of Engineering, Aarhus University, Blichers AllÃ© 20, P.O. Box 50, Tjele DK-8830, Denmark. Anders.Feilberg@agrsci.dk., pp. 16060–16076, 2012.
Volatile organic compounds (VOCs) in cut onions (Allium cepa L.) were continuously measured by PTR-MS during the first 120 min after cutting. The headspace composition changed rapidly due to the very reactive volatile sulfurous compounds emitted from onion tissue after cell disruption. Mass spectral signals corresponding to propanethial S-oxide (the lachrymatory factor) and breakdown products of this compound dominated 0-10 min after cutting. Subsequently, propanethiol and dipropyl disulfide predominantly appeared, together with traces of thiosulfinates. The concentrations of these compounds reached a maximum at 60 min after cutting. Propanethiol was present in highest concentrations and had an odor activity value 20 times higher than dipropyl disulfide. Thus, propanethiol is suggested to be the main source of the characteristic onion odor. Monitoring the rapid changes of VOCs in the headspace of cut onion necessitates a high time resolution, and PTR-MS is demonstrated to be a very suitable method for monitoring the headspace of freshly cut onions directly after cutting without extraction or pre-concentration.