Carbon isotope ratios of selected volatiles in Citrus sinensis and in orange-flavoured food

A review of recent compound-specific isotope analysis studies applied to food authentication

Compound-specific stable isotope analysis (CSIA) of food products is a relatively new and novel technique used to authenticate food and detect adulteration. This paper provides a review of recent on-line and off-line CSIA applications of plant and animal origin foods, essential oils and plant extracts. Different food discrimination techniques, applications, scope, and recent studies are discussed. CSIA δ13C values are widely used to verify geographical origin, organic production, and adulteration. The δ15N values of individual amino acids and nitrate fertilizers have proven effective to authenticate organic foods, while δ2H and δ18O values are useful to link food products with local precipitation for geographical origin verification. Most CSIA techniques focus on fatty acids, amino acids, monosaccharides, disaccharides, organic acids, and volatile compounds enabling more selective and detailed origin and authentication information than bulk isotope analyses.. In conclusion, CSIA has a stronger analytical advantage for the authentication of food compared to bulk stable isotope analysis, especially for honey, beverages, essential oils, and processed foods.

Construction of IsoVoc Database for the Authentication of Natural Flavours

Flavour is an important quality trait of food and beverages. As the demand for natural aromas increases and the cost of raw materials go up, so does the potential for economically motivated adulteration. In this study, gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS) analysis of volatile fruit compounds, sampled using headspace-solid phase microextraction (HS-SPME), is used as a tool to differentiate between synthetic and naturally produced volatile aroma compounds (VOCs). The result is an extensive stable isotope database (IsoVoc—Isotope Volatile organic compounds) consisting of 39 authentic flavour compounds with well-defined origin: apple (148), strawberry (33), raspberry (12), pear (9), blueberry (7), and sour cherry (4) samples. Synthetically derived VOCs (48) were also characterised. Comparing isotope ratios of volatile compounds between distillates and fresh apples and strawberries proved the suitability of using fresh samples to create a database covering the natural variability in δ¹³C values and range of VOCs. In total, 25 aroma compounds were identified and used to test 33 flavoured commercial products to evaluate the usefulness of the IsoVoc database for fruit flavour authenticity studies. The results revealed the possible falsification for several fruit aroma compounds.

Trace Element Concentration and Stable Isotope Ratio Analysis in Blueberries and Bilberries: A Tool for Quality and Authenticity Control

Vaccinium genus berries—wild bilberries (Vaccinium myrtillus L.) and cultivated highbush blueberries (Vaccinium corymbosum L.)—are consumed worldwide, and their consumption has a trend of stable increase. Thus, considering their wide use in ethnomedicine, for juice and jam production, as functional food, as well as their use in preparations of extracts which have application potential in pharmaceutical and cosmetics industries, studies regarding the composition of these berries are of special importance. The aim of this study is to characterise the elemental and isotopic composition, as well as variation in element concentration in bilberries gathered from different sites in Northern Europe and in commercially available blueberry samples from across the World. Furthermore, our aim was to develop tools for authenticity and quality control of these berries. The elemental composition of berries was analysed using inductively coupled plasma with optical emission detection (ICP-OED), while isotope ratio mass spectrometry (IRMS) was used for the determination of isotope ratio values. The results demonstrated detectable differences between macro- and microelement values in bilberries. IRMS analysis of blueberries revealed significant differences in isotope ratios based on the place of origin, indicating the possibility to use this analytical method for authenticity testing. In none of the samples, pollution was detected, even though there were indications of different growth conditions and geochemical differences affecting bilberry composition.

Compound-specific carbon and hydrogen isotope analysis of volatile organic compounds using headspace solid-phase microextraction

Natural flavouring materials are in high demand, and a premium price is paid for all-natural flavourings, making them vulnerable to fraud. At present, compound-specific isotope analysis (CSIA) is perhaps the most sophisticated tool for determining flavour authenticity. Despite promising results, the method is not widely used, and the results are limited to the most common volatile organic compounds (VOCs). This paper describes a robust protocol for on-line measurements of δ¹³C and δ²H using HS-SPME coupled with GC-C-IRMS and GC-HTC-IRMS for common fruit VOCs. To achieve reproducible and accurate results, a combination of a peak size/linearity correction with drift correction were used. Finally, the results were normalised by multiple point linear regression using the known and measured values of reference materials. Special care was taken to avoid irreproducible isotopic fractionation and the effects of equilibration, adsorption, desorption times and temperatures on δ¹³C or δ²H values were examined. Method validation was performed, and the average combined measurement uncertainty (MU) was 0.42‰. All the δ¹³C_VPDB values were below ±3*MU, regardless of analytical conditions. In contrast, for δ²H_VSMOW-SLAP values, only low temperature (30 °C) with equilibration time (15 min) and shorter adsorption time (between 10 and 20 min) can produce an isotopic difference of <10‰. Therefore, method optimisation can minimise MU, and data normalisation and method validation are essential for obtaining meaningful data for use in flavour authenticity studies.