nmr (16)

Rapid NMR Test to Authenticate Olive Oil

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In 2019, a Europol-coordinated operation resulted in the seizure of 150,000 litres of low-quality oils that had been adulterated with colourants to make them appear like extra virgin olive oils, with 20 arrest made. There are recommended methods to authenticate olive oils using different test procedures applied one after the other, which is time-consuming and expensive. German researchers have developed a rapid NMR (nuclear magnetic resonance) that gives a  profile based on the identification of constituents such as fatty acids and polyphenols in one hour. A database of profiles has been built up with extra virgin olive oil produced in Greece, Italy and Spain permitting the country of origin to be checked as well.

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NMR has been used for the authenticity of wines for over 30 years, but has evolved significantly in the last two decades. It was developed as the official method for added water and sugar to wine, but its use in metabolomics gives a lot of information on grape varieties, cultivation techniques and vintage. NMR can also yield information on geographic origin.

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Herbs and spices have been shown to be the group of foods most susceptible to adulteration. This extensive review by Polish researchers examines the application of different types of NMR (nuclear magnetic resonance) combined with chemometrics to characterise and distinguish authentic and adulterated spice samples.

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Maple syrup, the concentrated sap of Acer saccharum March, is sought after for its unique flavour and taste. As a popular and high value product, it is increasingly susceptible to adulteration by other sugar syrups. This review looks at most recent advances in the analytical methods used for detecting the different types of maple syrup adulteration.It concludes that SpectrAcer and nuclear magnetic resonance (NMR) are the most efficient methods for detection of maple syrup adulteration. SpectrAcer, an automated spectroscopy sytem developed by the Canadian company Acer, based reflected light at different wavelengths using the syrup's fluorescence properties with UV, and sugar composition at other wavelengths.

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Using NMR to Authenticate Spanish Wine

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This article reports a recent webinar to discuss the role of NMR in the non-targeted authenticity analysis of wine, and in particular Spanish wine. The NMR analysis is able to identify and quantify several hundred compounds present in the wine. Reference databases have been built up of these compound profiles using authentic wine, and these are used on wine samples to verify whether they are authentic or not. The method has been adopted by the  Estación Enológica de Haro (EEH) part of the Institute of Vine and Wines Sciences in La Rioja, which serves the wine industry across Spain, and analyses 25,000 samples annually and conducts around 263,000 analyses every year from private clients.  

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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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The Canadian Food Inspection Agency (CFIA) conducted targeted surveillance between 2019 and 2020 as part of ongoing efforts to detect honey adulteration with exogenous sugars in both domestic and imported honey sold in Canada. A total of 275 samples were collected across Canada and analysed using Stable Isotope Ratio Analysis (SIRA) and Nuclear Magnetic Resonance (NMR). Two types of honey samples were collected. One group of 127 samples, consisted of single-ingredient honey products such as bulk and honey for further processing from importers and a small proportion from domestic establishments. These were collected from suppliers where the chance of non-compliance was higher, based on risk-factors such as a history of non-compliance, gaps in preventive controls, or unusual trading patterns. The other 148 samples of honey were collected by an independent third party at retailers in various cities across Canada as part of CFIA's compliance monitoring of the marketplace, to gauge overall compliance. Of the targeted samples 17(13%) were considered unsatisfactory from the analytical results of which only 1 was Canadian honey. Of the retail samples, only 3 were considered unsatisfactory, and all of these were imported. As a result of CFIA's actions, an estimated 83,461 kg of adulterated honey was prevented from being sold in the Canadian marketplace between April 1, 2019 and March 31, 2020.

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Prof. Chris Elliott gives a reasoned response to two reports about widespread honey fraud on the UK and Indian markets. In both cases, the analysis of the honey samples was by NMR (nuclear magnetic resonance), and although the method is soundly based, issues have been raised around the databases used to verify adulteration or authenticity of honey from different countries, and this was discussd in a UK Government sponsored workshop organised by LGC on the technique last year: Honey authenticity: determination of exogenous sugars by NMR Seminar (2019) Report

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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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The Government Chemist, the Department for Environment Food and Rural Affairs (Defra), the Food Standards Agency (FSA) and Food Standards Scotland (FSS) held a UK seminar on honey authenticity: determination of exogenous sugars by nuclear magnetic resonance (NMR) on 13 November 2019, which was attended by 57 people representing stakeholder organisations.

The aim of the seminar was to bring together stakeholders involved in honey production and analysis to discuss this topic and ideally come to an agreed position. It was anticipated that the output of this seminar would help inform future UK government policy on the use of NMR for honey authenticity.

The seminar consisted of a series of presentations from invited experts that set the scene for the workshop part of the day, which involved participants splitting into four representative groups to discuss the suitability of NMR for enforcement purposes and to identify gaps and priorities to assessing the use of NMR for the appraisal of honey authenticity.

The report details the aims and outputs of the seminar.Honey authenticity: determination of exogenous sugars by NMR Seminar Report (PDF, 913KB, 19 pages)

Presentations are also available

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Tesco's withdrawal of its own-label honey comes after an investigation by Richmond Council  Trading Standards. Honey was sent for analysis by NMR,which gave results that it was adulterated with exogenous sugar syrups. Tesco has temporarily taken the honey off the shelves for further examination, but insists the product is "100% pure, natural and can be directly traced back to the beekeeper".

3742110317?profile=RESIZE_710x Read the BBC article

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This review by Polish researchers reviews the use of spectroscopic methods in testing the authenticity of some selected herbs and spices. The review covers the spectroscopic techniques - IR, NMR, UV in combination with advanced statistical methods (PCA, CA) to confirm either the origin of the product or  distinguishes the herbs or spices from any adulterating ingredients. 

3686348872?profile=RESIZE_710x Read the abstract here

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Nuclear magnetic resonance (NMR) spectroscopy has increasingly been applied in the field of food authenticitation. Its instrumental variability is very low so that it is possible to compile large databases of authentic spectra. This review discusses the application of NMR for authenticating honey, beer and spices. For honey, it is possible to verify the botanical origin and exclude adulteration with sugars. In beer analysis, it is possible to distinguish between major beer types and to detect the geographical origin of beer. In spice analysis, NMR allows to detect crude adulterations (e.g. of saffron) or quantify marker ingredients such as essential oils.

                 Read the full review at: NMR authentication

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16-O-methylcafestol (16-OMC)  is used as a marker for non-Arabica coffees (Robusta coffee). UK researchers have analysed lipophilic extracts from 30 authentic roasted Arabica coffees by high-field and low-field proton NMR spectroscopy, and found a small marker peak, which has subsequently been identified as 16-OMC and 16-O-methylkahweol.  This is the first time these markers have been found in Arabica coffee, and previously thought to only exist in non-Arabica coffee. However, the level of 16-OMC in Arabica coffee is very low and much higher in Robusta coffee. Therefore, using low-field NMR, Robusta in Arabica could be detected at levels of the order of 1–2% w/w. A surveillance study of retail purchased “100% Arabica” coffees found that 6 out of 60 samples displayed the marker signal to a degree commensurate with adulteration at levels of 3–30% w/w. 

Read the full article at: Arabica coffee authenticity

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Researchers applying a multi-step approach using HPLC, UV–Vis, FT-IR and NMR analyses, uncovered a new type of adulteration of a commercial product labelled as “saffron”, and sold packed in powder form in a major consuming country.  Applying the four methods and NMR data from in-house databases, they uncovered a  “tailor-made” case of 100% substitution of saffron by a mixture of exogenous chemical compounds in such a way that the commercial product would approximately mimic not only the appearance of saffron but also its UV–Vis spectrum and specific absorbance values. The findings indicated a sophisticated practice, including total substitution of saffron constituents by tartrazine and sunset yellow along with propane-1,2-diol, propan-2-ol and acylglycerols, probably as emulsifier agents. 

Read the abstract at: Multi-step approach uncovers saffron fraud

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