Real Time Detection of Aroma Compounds in Meat and Meat Products by SIFT-MS and Comparison to Conventional Techniques (SPME-GC-MS)

Dissecting grilled red and white meat flavor: Its characteristics, production mechanisms, influencing factors and chemical hazards

Meat flavor is composed of a complex mixture of volatile compounds developed as a result of heat driven multi-directional reactions. Typical reactions include Maillard reaction, lipid oxidation, as well as nitrogenous compounds degradation. Such complex flavor is characterized by a rich variety of volatile species, and to strongly influence consumer's preference. The objective of this review is to holistically dissect the flavor characteristic for cooked meat products with special emphasis on grilling and the factors that affect their production to ensure best quality and or safety levels. The review also highlights different analytical techniques used for the detection of flavor compounds in grilled meat. This comprehensive literature research critically analyze grilled flavor derived from heat mediated reactions, with a special emphasis on key flavors or hazard chemicals and their production mechanism. The various influencing factors i.e., grilling temperature, meat, food components, animal ante-mortem factors and food additives are summarized.

The application of selected ion flow tube-mass spectrometry to follow volatile formation in modified-atmosphere-packaged cooked ham

Cooked pork products, i.e., sliced cooked hams maintained under modified-atmosphere-packaging (MAP), were analysed both microbiologically and with respect to volatile levels during storage. Three storage temperature ranges were compared (4-6 °C, 7-9 °C, and 11-13 °C), representing different refrigeration conditions at household level. The microbial loads were determined by plating samples on six different agar media, followed by (GTG)₅-PCR fingerprinting of genomic DNA of selected isolates, and identification of representative isolates by 16S rRNA, pheS, and rpoA gene sequencing. Carnobacterium maltaromaticum, Lactobacillus sakei, and Serratia proteamaculans were the major bacterial species found among the 619 isolates identified. The volatiles produced during storage were followed by selected ion flow tube-mass spectrometry (SIFT-MS) and the identity of the volatiles was confirmed by headspace solid-phase microextraction combined with gas chromatography and time-of-flight mass spectrometry (HS-SPME-GC-TOF-MS). SIFT-MS analysis showed that volatiles, such as 2,3-butanediol, acetoin, and ethanol, may serve as potential markers for spoilage development. Differences in volatile production between samples were likely due to discrepancies in the initial microbial load and the effect of storage conditions. In conclusion, this study combines the use of new mass spectrometric techniques to examine volatile production during spoilage as an additional source of information during microbiological community analysis.

Volatile compounds profiling by using proton transfer reaction-time of flight-mass spectrometry (PTR-ToF-MS). The case study of dark chocolates organoleptic differences

Direct-injection mass spectrometry (DIMS) techniques have evolved into powerful methods to analyse volatile organic compounds (VOCs) without the need of chromatographic separation. Combined to chemometrics, they have been used in many domains to solve sample categorization issues based on volatilome determination. In this paper, different DIMS methods that have largely outperformed conventional electronic noses (e-noses) in classification tasks are briefly reviewed, with an emphasis on food-related applications. A particular attention is paid to proton transfer reaction mass spectrometry (PTR-MS), and many results obtained using the powerful PTR-time of flight-MS (PTR-ToF-MS) instrument are reviewed. Data analysis and feature selection issues are also summarized and discussed. As a case study, a challenging problem of classification of dark chocolates that has been previously assessed by sensory evaluation in four distinct categories is presented. The VOC profiles of a set of 206 chocolate samples classified in the four sensory categories were analysed by PTR-ToF-MS. A supervised multivariate data analysis based on partial least squares regression-discriminant analysis allowed the construction of a classification model that showed excellent prediction capability: 97% of a test set of 62 samples were correctly predicted in the sensory categories. Tentative identification of ions aided characterisation of chocolate classes. Variable selection using dedicated methods pinpointed some volatile compounds important for the discrimination of the chocolates. Among them, the CovSel method was used for the first time on PTR-MS data resulting in a selection of 10 features that allowed a good prediction to be achieved. Finally, challenges and future needs in the field are discussed.

Gas-phase chemical ionization of 4-alkyl branched-chain carboxylic acids and 3-methylindole using H3 O+ , NO+ , and O2+ ions

RATIONALE

4-Methyloctanoic acid, 4-ethyloctanoic acid, 4-methylnonanoic acid, and 3-methylindole are primary contributors to the distinctive aroma and flavor of lamb meat. The reactions of H₃ O⁺ , NO⁺ , and O₂⁺ with these compounds, and identification of the product ions and their distribution, are fundamental to their characterization and rapid, real-time trace analysis using selected ion flow tube mass spectrometry (SIFT-MS).

METHODS

The chemical ionization of pure standards of 4-ethyloctanoic acid, 4-methyloctanoic acid, 4-ethylnonanoic acid, and 3-methylindole was carried out using the H₃ O⁺ , NO⁺ , and O₂⁺ reagent ions of a V200™ SIFT mass spectrometer. Kinetic data were calculated using the Langevin collision rate with parameterized trajectory equations. Identification of product ions, distribution, and interferences was performed by further evaluation of the pertinent ion-molecule reaction mechanisms, careful spectral analyses, and molecular mass-molecular structure pairing.

RESULTS

The collisional capture rate constants of the reaction of the precursor ions H₃ O⁺ , NO⁺ , and O₂⁺ , their extended hydrates and the analytes, which were assumed to occur at or near the collisional rate, were all of the order of 10^-9  cm³ molecule s^-1 - typical for bimolecular ion-molecule reactions. Positive identification of the primary and secondary product ions, fragmented ionic species, and potential ion conflicts and interferences, from each reagent ion channel, was determined for each compound.

CONCLUSIONS

We have established the ion chemistry involved in the ionization of the 4-alkyl branched-chain fatty acids and 3-methylindole using the precursor ions, H₃ O⁺ , NO⁺ , and O₂⁺ in SIFT-MS. The ion-molecular chemistry and the associated kinetics serve as a fundamental basis for the accurate characterization of these compounds by SIFT-MS.

Ion chemistry at elevated ion–molecule interaction energies in a selected ion flow-drift tube: reactions of H3O+, NO+ and O2+ with saturated aliphatic ketones

Rate coefficients and product ion branching ratios determined for proton transfer, association and charge transfer reactions provide insight into reaction mechanisms.

Status of selected ion flow tube MS: accomplishments and challenges in breath analysis and other areas

This article reflects our observations of recent accomplishments made using selected ion flow tube MS (SIFT-MS). Only brief descriptions are given of SIFT-MS as an analytical method and of the recent extensions to the underpinning analytical ion chemistry required to realize more robust analyses. The challenge of breath analysis is given special attention because, when achieved, it renders analysis of other air media relatively straightforward. Brief overviews are given of recent SIFT-MS breath analyses by leading research groups, noting the desirability of detection and quantification of single volatile biomarkers rather than reliance on statistical analyses, if breath analysis is to be accepted into clinical practice. A 'strengths, weaknesses, opportunities and threats' analysis of SIFT-MS is made, which should help to increase its utility for trace gas analysis.

Reactions of the selected ion flow tube mass spectrometry reagent ions H3O(+) and NO(+) with a series of volatile aldehydes of biogenic significance

RATIONALE

It has been shown that aldehydes are often present in biogenic media. For their analysis by selected ion flow tube mass spectrometry (SIFT-MS), the rate coefficients and the product ion distributions for the reactions of the analyte ions H3O(+) and NO(+) with volatile aldehydes in the presence of water vapour are required.

METHODS

The reactions of H3O(+) and NO(+) ions have been studied with a series of n-aldehydes ranging from acetaldehyde (designated as C2), through undecanal (C11) under the conditions used for SIFT-MS analyses (1 Torr He, 0.1 Torr air sample, 300 K) and over a range of sample gas absolute humidity from 1% to 7%. For comparison, the C5 pentanal isomer 3-methyl butanal, the unsaturated trans-2-pentenal and trans-2-octenal and the aromatic benzaldehyde were also included in the study.

RESULTS

The H3O(+) reactions led to the formation of protonated molecules MH(+) and their hydrates MH(+)(H2O)0,1,2,3 , and (MH(+)-H2O). The NO(+) reactions resulted in the production of NO(+)M adduct ions and of [M-H](+) fragment ions. The percentages of the different product ions for each aldehyde are seen to be dependent on the air sample humidity. Kinetic modelling was used to quantitatively explain these observations and to obtain rate coefficients for the association reactions producing NO(+) M adduct ions.

CONCLUSIONS

This detailed study has provided the kinetics data, in particular the product ion distributions, for the reactions of a number of volatile aldehydes, which allows their analyses by SIFT-MS in humid air, including exhaled breath, food emanations and other biogenic media.