Proton-transfer reaction mass spectrometry (PTR-MS) for the authentication of regionally unique South African lamb

Molecular insights into quality and authentication of sheep meat from proteomics and metabolomics

Sheep meat (encompassing lamb, hogget and mutton) is an important source of animal protein in many countries, with a unique flavour and sensory profile compared to other red meats. Flavour, colour and texture are the key quality attributes contributing to consumer liking of sheep meat. Over the last decades, various factors from 'farm to fork', including production system (e.g., age, breed, feeding regimes, sex, pre-slaughter stress, and carcass suspension), post-mortem manipulation and processing (e.g., electrical stimulation, ageing, packaging types, and chilled and frozen storage) have been identified as influencing different aspects of sheep meat quality. However conventional meat-quality assessment tools are not able to elucidate the underlying mechanisms and pathways for quality variations. Advances in broad-based analytical techniques have offered opportunities to obtain deeper insights into the molecular changes of sheep meat which may become biomarkers for specific variations in quality traits and meat authenticity. This review provides an overview on how omics techniques, especially proteomics (including peptidomics) and metabolomics (including lipidomics and volatilomics) are applied to elucidate the variations in sheep meat quality, mainly in loin muscles, focusing on colour, texture and flavour, and as tools for authentication. SIGNIFICANCE: From this review, we observed that attempts have been made to utilise proteomics and metabolomics techniques on sheep meat products for elucidating pathways of quality variations due to various factors. For instance, the improvement of colour stability and tenderness could be associated with the changes to glycolysis, energy metabolism and endogenous antioxidant capacity. Several studies identify proteolysis as being important, but potentially conflicting for quality as the enhanced proteolysis improves tenderness and flavour, while reducing colour stability. The use of multiple analytical methods e.g., lipidomics, metabolomics, and volatilomics, detects a wider range of flavour precursors (including both water and lipid soluble compounds) that underlie the possible pathways for sheep meat flavour evolution. The technological advancement in omics (e.g., direct analysis-mass spectrometry) could make analysis of the proteins, lipids and metabolites in sheep meat routine, as well as enhance the confidence in quality determination and molecular-based assurance of meat authenticity.

Bibliometric Review on the Volatile Organic Compounds in Meat

Meat flavor is an important aspect of meat quality that also influences consumer demand, and is therefore very important for the meat industry. Volatile organic compounds (VOCs) contribute in large part to the flavor of meat, and while increasing numbers of articles are published on this topic, reviews of these articles are very scarce. Therefore, our aim was to perform a bibliometric analysis of the scientific publications on VOCs in meat over the period 2000-2020. We selected 611 scientific sources from the Scopus database related to VOCs in meat (seafood excluded). The bibliometric information retrieved included journals, authors, countries, institutions, keywords, and citations. From this analysis, we drew up a list of the most important journals, authors, countries, and institutions, and the trends in VOC research on meat. We conducted a social network analysis (SNA) to identify the collaborations among the many authors and countries, and a keyword analysis to generate a network map of the authors' keywords. We also determined which meat species were most frequently chosen as research subjects, traced the evolution of the various methods/instruments used, and explored the research tendencies. Finally, we point out the need for further research in defining meat quality, improving meat flavor, identifying adulterants, and certifying the authenticity of meat.

Direct analysis in real time high-resolution mass spectrometry for authenticity assessment of lamb

In comparison to more traditional methods of determining food authenticity, such as gas chromatography analysis, the primary advantages of DART-HRMS include its high speed and throughput of analysis. This study used a non-targeted metabolomics method based on real-time high-resolution mass spectrometry combined with chemometric analysis to distinguish lamb samples from four regions. Orthogonal least squares-discriminant analysis revealed a distinct difference between these four lamb regions. The potential markers were chosen based on the variable's importance in projection values, variance, and fold change. A total of 79 markers were identified using the matching chemistry database. These markers differed significantly between lambs in four regions according to heatmap analysis. The linear discriminatory analysis model had an initial classification rate of 100.0% and a cross-validation accuracy of 82.50% on the identified markers. The research demonstrates that DART-HRMS can perform a rapid authentication evaluation of lamb samples.

In vivo and in vitro aroma release in surimi gel with different cross-linking degrees by proton transfer reaction-mass spectrometry

Transglutaminase-induced cross-linking has been suggested as a strategy to govern surimi gels' texture. To achieve the aroma regulation of surimi gels by cross-links, surimi gels were treated with microbial transglutaminase to get different cross-linking degrees, and in vivo and in vitro aroma releases were investigated by a proton transfer reaction-mass spectrometry (PTR-MS). Seventeen compounds in surimi gels were detected by PTR-MS. The in vitro release curves of odorants were fitted by a pseudo-first-order kinetics model. As the cross-links increased, most aroma compounds' released concentrations and release rates decreased first, and then increased significantly (P < 0.05) when the cross-linking degree exceed around 35.4%, negatively related to the springiness and the gel strength of surimi gels. However, the in vivo aroma release results showed that the harder surimi gel released fewer aroma compounds. In conclusion, texture affected by cross-links could be a strategy to control the aroma release of surimi gels.

Sensory Characteristics of Male Impala (Aepyceros melampus) Meat, Produced under Varying Production Systems and Nutrition

The objective of this study was to determine the influence of three production systems (intensive, semi-extensive and extensive) with differing nutrition on the descriptive sensory and fatty acid profiles of sub-adult (±15-18 months old) male impala longissimus thoracis et lumborum (LTL) muscles. The discriminant analysis plot showed that extensively produced impala had a sensory profile distinct from the intensive and semi-extensive system impala. Extensively produced impala had the highest sensory ratings for overall intensity, gamey, beef-like, herbaceous, and sweet-associated aroma and flavor of their meat. The intensive and semi-extensive system impala did not differ for most of the sensory attributes, except for higher ratings for gamey flavor, liver-like flavor, tenderness and mealiness, and lower ratings for residue found in semi-extensive system impala. The overall aroma and flavor intensities of impala meat in general had strong positive correlations with gamey, beef-like, herbaceous, and sweet-associated aromas and flavors; however, marketing should be adjusted depending on the nutrition received by the impala, to allow consumers to select their preferential sensory profile. Impala meat from all three production systems had low fat contents (<2%), and desirable fatty acid profiles.

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.

Rapid and non-invasive multivariate approach for the quality control of raw milk from mountain areas based on proton transfer reaction mass spectrometry data

RATIONALE

A rapid and non-invasive method for the control of milk by proton transfer reaction mass spectrometry was developed. The approach has the potential to verify the geographic origin and altitude of dairy farms, provided that the cows have been extensively grazed with forage that reflects the botanical composition of the mountain environment.

METHODS

Over a 1-month period, a total of 116 samples were analysed by proton transfer reaction mass spectrometry (PTRMS). A multivariate control chart based on the Hotelling T² statistic was built with PTRMS data and, for comparison, with the chemical parameters obtained by infrared spectroscopy (FTIR, MilkoScan).

RESULTS

The headspace analysis of the samples led to characteristic volatile profiles. Farms located in different mountain areas were discriminated by the protonated molecules m/z 45 (acetaldehyde), 59 (acetone), 73 (2-butanone) and 89 (butyric acid, ethyl acetate, pentanol). Milk samples were also discriminated according to the altitude of the farms according to m/z 45, 59, 63 (dimethyl sulfide), 73 (propionic acid, methyl acetate) and 81 (terpenes).

CONCLUSIONS

A multivariate control chart based on PTRMS data was used for the quality control of milk. Milk samples from farms located at different mountain areas and altitudes were successfully discriminated.