metabolomics (8)

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Polyphenols are a diverse group of natural compounds contributing to the organoleptic properties of wine. Their distribution and content in wines is dependent on grape variety, where the grapes are grown, oenological practices, and storage conditions and time. Hence they are good markers for wine authenticity. This review examines the analytical methods to determine polyphenols especially the metabolomic studies using NMR (nuclear magnetic resonance) or MS (mass spectrometry) combined with chemometrics, and previous studies utilising polyphenols for wine authenticity.

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There has been a large increase in the sale of craft beers, which pride themselves as having distinctive flavours and colour by using proprietary recipes of cereals and flavourings. As craft beers sell for a premium price over large scale produced beers, having a method to distinguish the two types is important to prevent fraud. The use of 1H NMR and chemometrics to identify metabolites in craft beers, which are absent in large scale produced beers has been used by various researchers around the world. In a recent paper, Italian researchers developed a protocol for NMR anlaysis with chemometrics enabling the automatic identification and quantification of metabolites in approximately thirty seconds per spectrum. Craft beers possessed lower concentrations of adenosine/inosine and trehalose and higher levels of trigonelline, asparagine, acetate, lactate, and succinate when compared with large scale produced beers. These results give a starting point for the development of a standardised protocol to distinguish between the two types of beers.

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Labelling rules require that if raw fish has been previously frozen and sold as chilled/fresh, then it must be labelled as previously frozen or defosted. Norwegian researchers have developed a method based on D/H-NMR analysis to look at certain metabolites, which change concentration when Atlantic salmon is frozen and thawed, then stored chilled. Of the metabolites studied, aspartate concentration was considered the best marker for previously frozen salmon, as it formed in the thawed fish only after the second day of storage at 4 °C, reaching a maximum after 3-5 days then declining. 

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This method has been developed so that it can differentiate between a slaughtering method that conforms with Islamic rights, and therefore can be certified as Halal, and one which does not.. Kosher slaughter and Islamic rights, Zabiha (ZA) slaughtering procedure involves the severing of the poultry's throat with a single stroke of a sharp knife thus cutting a carotid artery, jugular vein, windpipe, and esophagus without injuring the spinal cord. Non-Zabiha (NZ) slaughter may involve completely cutting off the neck of the animal during slaughter, and hence detaching the spinal cord. Liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) based non-targeted metabolomics of chicken meat samples were evaluated to differentiate meat samples based on slaughtering methods. Forty samples were grouped into equal numbers of Zabiha (cutting neck without detaching spinal cord) and Non-Zabiha (completely detaching neck). A volcano plot revealed at least 150 features found significantly different between the two groups having ≥ 2-fold changes in intensities with p-values ≤ 0.05. Among them 5 identified metabolites and 25 unidentified metabolites have clear differences in peak intensities. After chemometric analysis, the 5 metabolites were considered as potentially significant markers to differentiate between the two methods of slaughter.

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6201677901?profile=RESIZE_400x Organic milk attracts a premium over conventionally produced milk. Reading University and other consortium partners have completed a European Horizon 2020 project using metabolomics and NMR technology on 1,900 samples of organic milk collected on farms and at retail in the UK and Finland, to develop a test to authenticate organic milk.  

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3925480647?profile=RESIZE_710xThe assessment of durum wheat geographical origin is an important and emerging challenge, due to the added value that a claim of origin could provide to the raw material itself, and subsequently to the final products (i.e. pasta). As an alternative to the use of stable isotopes and trace elements to determine geographic origin, Italian researchers used non-targeted high resolution mass spectrometry (LC-HRMS) to select chemical markers related to the geographical origin of durum wheat. Durum wheat samples from the 2016 wheat harvest were used to set up the model and to select the markers, while samples from the 2018 harvest were used for model and metabolomic markers validation. Different geographies across different continents were used in the sample set, so that it is now possible to discriminate between Italian, European and Non-European durum wheat samples.

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The assessment of egg freshness is still challenging, due to the lack of robust chemical markers.  Freshness is a crucial parameter for ensuring the production of safe and high‐quality foods. Italian researchers have selected 31 marker compounds based on a metabolomic approach related to the freshness of egg products used as ingredients for compound foods. They were selected from samples of egg products, which were extracted after delivery to the production plant, and after 24 and 48 hours at room temperature. The extracts were analysed by ultrahigh‐pressure liquid chromatography–high‐resolution mass spectrometry (UHPLC‐HRMS), and different chemometric models were created to select those compounds that changed during the storage period, and hence are related to freshness. Furthermore, this UHPLC‐HRMS metabolomic approach allows for the detection of a larger set of metabolites clearly related to possible microbial growth over time, which is a relevant point for also ensuring food safety.

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In this review by Spanish researchers, an updated, comprehensive and balanced overview of the recent studies (2015-2018) that have applied omics-based technologies for the authentication of food is given. The omics-based molecular tools discussed in the review include genomics, proteomics and metabolomics-based methods.

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