GC-IRMS analysis of black Ceylon, Assam and Darjeeling teas

 The δ¹³C_PDB values of characteristic flavour compounds of black Ceylon, Darjeeling and Assam teas were determined using gas chromatography-isotope ratio mass spectrometry. The influence of different harvest times, years and various cultivation regions on the δ¹³C_PDB and the δ¹³C _{cis linalool oxide (fur.)} values were investigated. By comparison with suitable internal isotopic standards, adulterations with methyl salicylate were detectable.     

Reductive ester cleavage of acyl glycerides–GC-C/P-IRMS measurements of glycerol and fatty alcohols

By reductive glyceride cleavage food fats of different origin, converted to free glycerol and to fatty alcohols of the corresponding fatty acids, were investigated. Multielement IRMS-analysis (δ¹³C, δ¹⁸O) of the decomposition products was performed in order to develop GC-IRMS methods to the authenticity assessment of food fats. For this reason glycerol from olive oils of definite origin, as well as glycerol of commercially available edible fats and oils, was analysed. Furthermore, the determination of ¹⁸O/¹⁶O and ¹³C/¹²C isotope ratios of commercial glycerols from different origins was achieved. In addition, δ¹³C_V‐PDB values of fatty alcohols corresponding to genuine fatty acid moieties were measured and their usability in view of fat authenticity assessment is discussed.     

Progress in wine authentication: GC–C/P–IRMS measurements of glycerol and GC analysis of 2,3-butanediol stereoisomers

The determination of glycerol and 2,3-butanediol by photometric or enzymatic methods is well established. This paper reports on the direct assessment of glycerol and stereoselective analysis of 2,3-butanediol isomers in wine using capillary GC without any derivatisation. A “model wine” and commercially available wines, as well as wines of definite origin were investigated. The contents of glycerol and 2,3-butanediol and the ratio of (R,R)- and meso-2,3-butanediol were determined. Capillary GC has proved to be a reliable alternative in glycerol assessment from wine, thus a GC-IRMS method for authenticity assessment of glycerol was developed.δ¹³C_V‐PDB and δ¹⁸O_V‐SMOW multi-element IRMS-analysis of glycerol, an important by-product of wine fermentation, is reported. For that reason glycerol, extracted from a self-prepared “model wine”, from wines of definite origin, as well as commercially available wines, was investigated. Furthermore, the ¹⁸O/¹⁶O and ¹³C/¹²C isotope ratios of commercial glycerols from different origins were determined. In addition fermentation experiments with beet and cane sugar, and with grape juices were carried out. In order to check the influence of water on the oxygen isotope ratios, water from different places in Germany was used in the fermentation experiments with cane and beet sugar.     

Bestimmung der Fols?ure-Gehalte von Gemüse und Obst mit Hilfe der Hochleistungsflüssigchromatographie (HPLC)

Summary The ¹³C_PDB values of nine flavour compounds from five different lemon oils were determined using gas chromatography-isotope ratio mass spectrometry. By definition of a suitable internal isotopic standard (i-IST), the influence of CO₂ fixation during photosynthesis is eliminated. The isotopic effects among genuine monoterpenes are, therefore, limited to the influence of enzymatic reactions during secondary biogenetic pathways. Calculating versus nerylacetate as an i-IST yields fruit-specific ( ¹³C values for neral and geranial with low standard deviation and seems to be suitable for authenticity control of lemon oils.

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cGC-IRMS-Analyse in der Echtheitskontrolle von Aromen und etherischen Ölen. Teil I: Zitronenöl

Zusammenfassung Die ¹³C_PDB-Werte von neun Aromakomponenten aus fünf unterschiedlichen Zitronenölen werden mittels GC-IRMS bestimmt. Durch die Wahl eines internen Isotopenstandards (i-IST) werden Isotopeneffekte während der CO₂-Fixierung (in der Photosynthese) eliminiert und die zwischen den einzelnen Substanzen auftretenden Unterschiede im¹³C/¹²C-Verhältnis auf enzymatische Einflüsse des Sekundärstoffwechsels begrenzt. Mit Nerylacetat als i-IST lassen sich fruchtspezifische ¹³C-Werte von Neral bzw. Geranial mit hoher Genauigkeit bestimmen und zur Authentizitätskontrolle von Zitronenölen heranziehen.

     

Resolution of racemic δ-lactone flavors on Chiralcel OB by packed column super critical fluid chromatography

Six racemic δ-lactone (C₇–C₁₂) flavors were successfully resolved in less than 14 min each by packed column super critical CO₂ fluid chromatography (pSFC). Baseline resolution was achieved for δ-C₇–δ-C_10. Chiralcel OB column and modifier isopropanol were selected. The chromatographic conditions including column temperature, column pressure, content of isopropanol in mobile phase and flow rate of mobile phase were optimized while their influences on capacity factor (k), enantioselectivity factor (α) and resolution factor (R _s ) were discussed. The present work indicated that preparative resolution of the δ-lactone racemates by the pSFC method was potential.     

Determination of the 13C/12C ratios of ethanol and higher alcohols in wine by GC-C-IRMS analysis

More than 50 authentic EU data bank wines from Germany (vintages: 2003, 2004 and 2006) have been extracted by liquid–liquid extraction with a mixture of cyclohexane and 2-methyl-2-propanol. The δ¹³C values of the extracted wine ethanol and other co-extracted higher alcohols have been determined by gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS). The stable isotope ratios of wine ethanol obtained by liquid–liquid extraction were compared with those obtained after distillation according to the official EU method. No significant differences of the isotope ratios of ethanol measured by the two compared methods were found (R ² = 0.972), thus it was concluded that no significant isotope effect during sample preparation occurred. Additionally, the ¹³C/¹²C isotope ratios of the major co-extracted alcohols, e.g. 2-methylpropan-1-ol, 2- and 3-methylbutan-1-ol, butan-2,3-diol and 2-phenyl-1-ethanol were determined and set in relation to the δ¹³C values of the corresponding extracted wine ethanol. Also, high correlations between their isotope ratios (e.g. 2,3-methylbutan-1-ol R ² = 0.829) were found. The key benefits of the introduced liquid–liquid extraction are the time- and cost-saving determination of δ¹³C values of wine ethanol, the small amount of sample needed for the extraction and additionally the potential analysis of the co-extracted higher alcohols which could be valuable for the detection of fraud.     

Bioactive lipids and fatty acids profile of Cistanche phelypaea

Oil extracted from the wild plant of Cistanche phelypaea was analyzed for its fatty acid, sterol, hydrocarbon and tocopherol contents. Total lipids (TL) content was 10 g/kg (on dry weight basis). The majority of fatty acids were of the unsaturated type (50.4 % of total fatty acids), while the saturated (mainly palmitic acid) were about 43.2 % of the total fatty acids. Oleic acid was the dominating fatty acid followed by palmitic and linoleic acids. High amounts of sterols were found in the oil with the main component β-sitosterol. Other phytosterols (e.g. stigmasterol, ∆⁷-avenasterol and ∆⁵-avenasterol) were present at approximately equal amounts (6–9 % of total sterols). The main identified hydrocarbon compounds were C₂₁, C₂₆ and C₃₂ constituting about 61.2 % of total hydrocarbons. Small amounts of C₁₂, C₁₈ and C₂₂, however, were also detected. Tocopherol levels were high in the oil (3.36 g/kg oil), wherein β-tocopherol was the main component followed by α-isomer. Both tocopherol components comprised more than 87 % of total vitamin E content in the oil. Furthermore, γ- and δ-tocopherols were detected in small amounts in the oil accounting for 14–16 % of the total vitamin E content. Information provided by the present work will be of importance for food applications and chemotaxonomy of Cistanche phelypaea.     

Food authenticity using natural carbon isotopes (12C, 13C, 14C) in grass-fed and grain-fed beef

Natural carbon isotopes, ¹²C, ¹³C, and ¹⁴C, help to authenticate/trace foods and beverages. Levels of total carbon (TC), ¹³C (δ¹³C), and ¹⁴C in muscle and lipid tissues from grass-fed versus grain-fed steers are reported. The δ¹³C in muscle versus lipid of steaks were around 5‰ higher in grain over grass-fed (p<0.05). The δ¹³C and ¹⁴C levels were higher in muscle over lipid tissues while the opposite was true for TC (p<0.05). TC content was around 20% higher in lipid over muscle due to different elemental compositions, lipid versus muscle, not carbon isotopes discrimination.     

Online determination of <Superscript>2</Superscript>H/<Superscript>1</Superscript>H and <Superscript>13</Superscript>C/<Superscript>12</Superscript>C isotope ratios of cinnamaldehyde from different sources using gas chromatography isotope ratio mass spectrometry

The combination of gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS) and gas chromatography-pyrolysis-isotope ratio mass spectrometry (GC-P-IRMS) is applied to the authenticity assessment of cinnamaldehyde from various sources. For that reason, cinnamon oils were self-prepared by steam distillation from three different varieties of cinnamon bark on the market, C. ceylanicum (ceylon), C. cassia (cassia) and C. burmanii (cassia vera). Furthermore, the so-called wood cinnamon was investigated, which is produced from the outer bark of older branches of cinnamon of minor quality. Self-prepared oils were analysed from commercial cinnamon powder. In addition several commercial samples of cinnamon oil and cinnamaldehyde, some of them declared to be natural, were investigated. ²_V-SMOW and ¹³C_V-PDB values of cinnamaldehyde were determined and characteristic authenticity ranges were deduced, allowing the differentiation between synthetic and natural samples. By correlation of both the ²_V-SMOW and ¹³C_V-PDB values, characteristic authenticity ranges were defined for ceylon, cassia and wood cinnamon. The ²_V-SMOW and ¹³C_V-PDB values of cassia vera samples are in the range of cassia. By comparing the ²_V-SMOW values of different self-prepared samples (ground bark, distillate) of cinnamon determined by TC/EA-IRMS with the corresponding GC-IRMS values, online GC-IRMS methods are proved to be essential in the authentication of complex natural products.     

M?glichkeiten und Ergebnisse der Kombination von Messungen der Verh?ltnisse stabiler Wasserstoff-und Kohlenstoff-Isotope mit Resultaten konventioneller Analysen (RSK-Werte) zum Nachweis des Zuckerzusatzes zu Fruchts?ften

Zusammenfassung Die D- und die ¹³C-Werte der Zuk-ker und die ¹³C-Werte fester Bestandteile (Pulpe; bei Citrussäften) aus einer größeren Anzahl von naturbelassenen Apfel-, Grapefruit-, Orangen- und Zitronen-Säften sowie die D- und ₁₃C-Werte von Glucose aus Maisund Kartoffelstärkehydrolysaten sowie von Rübenzuk-ker wurden bestimmt. Die Resultate zeigen pflanzen- und klimatypische Bereiche, die trotz einiger Überschneidungen Verfälschungen (Zuckerung) in unbekannten Proben zu erkennen erlauben. Ein Vergleich der Ergebnisse mit Resultaten konventioneller Analysen (Bestimmung der RSK-Parameter) führt zu sehr guten Übereinstimmungen, so daß aus der Kombination dieser konventionellen Untersuchungsmethoden mit der Isotopen-Verhältnismessung ein zuverlässiger Nachweis des unerlaubten Zuckerzusatzes von Zucker aus C₃- oder C₄-Pflanzen zu Säften resultiert. Als weiterer Ausbau des Verfahrens wird der Einbezug von ¹⁸O-Bestimmungen empfohlen.

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Possibilities and results of the combination of hydrogen and carbon stable isotope ratio determination with results of conventional analyses (RSK-values) for the proof of sugar addition to fruit juices

Summary The D and ¹³C values of the sugars and the ¹³C values of the solid ingredients (pulp; in citrus juices) of a larger number of natural apple, grapefruit, orange and lemon juices, as well as the D and ¹³C values of glucose from corn and potato starch hydrolysates and from beet sugar, have been determined. The values cover plant and climate typical areas which permit, in spite of some overlap, the recognition of the addition of sugar to the juices. A comparison of the results with those of conventional analyses (determination of RSK parameters) agree satisfactorily, thus demonstrating that a combination of these classical criteria together with the isotope ratio determination prove that sugars form C₃-or C₄-plants are illegally added to the juices. With respect to further development of the method future integration of ¹⁸O measurements is recommended.

     

Isotopic composition of dissolved inorganic carbon in bottled waters on the Slovene market

This study investigates the stable isotopic composition of dissolved inorganic carbon (DIC), expressed as δ¹³C_DIC, in domestic and foreign bottled waters randomly collected on the Slovene market. All together 58 brands and 16 replicates were analysed. The δ¹³C_DIC values varied between −63.1‰ and +1.0‰ with an average of −12.3‰. Average δ¹³C_DIC values for naturally sparkling, artificially sparkling, still and flavoured waters were −3.3‰, −36.5‰, −10.0‰ and −11.0‰, respectively. The lowest values are characteristic of artificial sparkling waters (minimum −63.1‰) and can be attributed to injection of industrial CO₂ during bottled water production. Therefore, determination of the isotopic composition of DIC can represent a useful analytical tool to distinguish between natural and artificially sparkling waters. Furthermore, the method used enabled determination of the various origins of still waters. From the bottled waters sampled it was possible to discern waters that originate from deeper aquifers, from aquifers in equilibrium with soil CO₂, or from aquifers with their recharge in a mountainous area. Finally, δ¹³C_DIC values of flavoured waters illustrate that isotopic fractionation occurs during the production process and that δ¹³C_DIC values in products of some producers have a large variation.     

Sensitive Determination of Decoquinate in Milk by High-Performance Liquid Chromatographic Coupled to Laser-Induced Fluorescence Detection

A new and sensitive method based on high performance liquid chromatography with laser-induced fluorescence detection has been developed for the determination of decoquinate in milk. Laser source was obtained with a He–Cd laser using a continuous excitation wavelength at 325 nm. Decoquinate exhibits moderate fluorescence, but it is increased using Ca(NO₃)₂ in the mobile phase. The chromatographic separation was performed on a Luna C₁₈ 5-mm reversed phase column, which solves the broadening of peaks and peak tailing compared with other columns tested. The mobile phase, delivered at 1 ml min⁻¹, consisted of methanol–calcium nitrate (0.025 M)–acetonitrile (83/13/4 v/v/v). Decoquinate was successfully cleaned up from milk by solid-phase extraction using C₁₈ cartridges. The method was found to be linear between 0.16 and 16.33 ng ml⁻¹. The results of recovery studies were found to be satisfactory; an average recovery rate of 88.7% was obtained. The LOQ of decoquinate in milk was 0.16 ng ml⁻¹. The intraday relative standard deviation (RSD) was 4%, and interday assay gave an RSD of 4.4%.     

Simultaneous on-line analysis of 18O/16O and 13C/12C ratios of organic compounds using GC-pyrolysis-IRMS

 The on-line coupling of gas chromatography and isotope ratio mass spectrometry via a pyrolysis interface (GC-pyrolysis-IRMS, GC-P-IRMS) allows the simultaneous determination of δ¹³C and δ¹⁸O values for organic compounds. On the basis of illustrative investigations of vanillin from different origins, the scope and limitations of the new method are discussed. Received: 18 October 1997 / Revised version: 18 December 1997     

Simultaneous on-line analysis of 18O/16O and 13C/12C ratios of organic compounds using GC-pyrolysis-IRMS

 The on-line coupling of gas chromatography and isotope ratio mass spectrometry via a pyrolysis interface (GC-pyrolysis-IRMS, GC-P-IRMS) allows the simultaneous determination of δ¹³C and δ¹⁸O values for organic compounds. On the basis of illustrative investigations of vanillin from different origins, the scope and limitations of the new method are discussed. Received: 18 October 1997 / Revised version: 18 December 1997     

Kinetics of green asparagus ascorbic acid heated in a high-temperature thermoresistometer

 Thermal degradation of green asparagus ascorbic acid in high-temperature short-time conditions was studied by heating in a five-channel computer-controlled thermoresistometer. Ascorbic acid was heated to between 110  °C and 140  °C and the degradation kinetics were analyzed assuming that two different inactivation mechanisms were occurring, one aerobic and the other anaerobic. The two reactions followed first-order kinetics, with E _a=12.3(2.0) kcal/mol and k _125  °C=47.0(3.0)×10^–3 s^–1 for the aerobic oxidation, and E _a=6.1(1.4) kcal/mol and k _125  °C=4.1(0.2)×10^–3 s^–1 for the anaerobic degradation. Received: 30 January 1998 / Revised version: 11 June 1998     

Worldwide stable carbon and nitrogen isotopes of Big Mac® patties: An example of a truly “glocal” food

The Big Mac®, McDonald’s® signature burger, is a global food served in over 100 countries. We measured carbon (δ¹³C) and nitrogen (δ¹⁵N) stable isotope ratios of Big Macs® from twenty-six countries. The δ¹³C values varied from −25.4‰ to −11.1‰, representing cattle-rearing systems based exclusively on C₃ plants, exclusively on C₄ plants, or both C₃ and C₄ plants. Median δ¹⁵N value was 6.6‰; the 25th and 75th percentile were 5.9‰ and 7.3‰, respectively. Calculated percentages of imported beef were consistent with the δ¹³C values of purchased Big Macs®. Japanese patties had higher δ¹³C values than expected based on that country’s C₃ agriculture, however Japan imports beef from Australia, where C₄ plants are prevalent. Lower latitude countries generally had higher δ¹³C values than higher latitude countries, reflecting the larger distribution of C₄ plants in warm regions. Although Big Macs® are a global food, we conclude they also contain local components.     

Identification of organically farmed Atlantic salmon by analysis of stable isotopes and fatty acids

Using isotope ratio mass spectrometry (IRMS), the ratios of carbon (δ ¹³C) and nitrogen (δ ¹⁵N) stable isotopes were investigated in raw fillets of differently grown Atlantic salmon (Salmo salar) in order to develop a method for the identification of organically farmed salmon. IRMS allowed to distinguish organically farmed salmon (OS) from wild salmon (WS), with δ ¹⁵N-values being higher in OS, but not from conventionally farmed salmon (CS). The gas chromatographic analysis of fatty acids differentiated WS from CS by stearic acid as well as WS from CS and OS by either linoleic acid or α-linolenic acid, but not OS from CS. The combined data were subjected to analysis using an artificial neural network (ANN). The ANN yielded several combinations of input data that allowed to assign all 100 samples from Ireland and Norway correctly to the three different classes. Although the complete assignment could already be achieved using fatty acid data only, it appeared to be more robust with a combination of fatty acid and IRMS data, i.e. with two independent analytical methods. This is also favourable with respect to a possible manipulation using suitable feed components. A good differentiation was established even without an ANN by the δ ¹⁵N-value and the content of linoleic acid. The general applicability in the context of consumer protection should be checked with further samples, particularly regarding the variability of feed composition and possible changes in smoked salmon.     

Determination of CO2 origin (natural or industrial) in sparkling bottled waters by 13C/12C isotope ratio analysis

This paper describes an isotope control method designed to identify the origin of CO₂ in sparkling bottled waters. The method is based on the analysis of the ¹³C/¹²C ratio in the dissolved inorganic carbon (DIC) of carbonated bottled water. Natural carbonated natural water has δ¹³C_PDB (DIC) values between −8‰ and +7‰. Generally, the industrial carbon dioxide injected into mineral bottled water is produced from hydrocarbons by burning or chemical processing. Hydrocarbons, and their derived CO₂, are characterised by a low ¹³C/¹²C ratio. Thus, a single analysis distinguishes the carbon dioxide in the bottled water (i.e. either from a natural source or added exogenous CO₂ of industrial origin). Rarely, CO₂ can be obtained from other industrial sources, mainly as a by-product of fermentation plants. Nevertheless, the carbon isotope fingerprint allows detection of the industrial gas injected in most of these cases.     

Engineering Properties of Edible Transglutaminase Cross-Linked Caseinate-Based Films

In this work, the effect of the weight ratio (Y _E/C) between transglutaminase (TGase) and sodium caseinate on the main engineering properties and microstructure of maltodextrin/caseinate/glycerol-based films, as well as cross-linking kinetics of the corresponding film-forming mixtures, was assessed. In the absence of TGase, the film forming solution did not jelly at all even after a 20-h gel cure experiment at 30 °C. As Y _E/C was increased from 0.5 to 8.3 mg/g, the gel point time exhibited quite a hyperbolic dependence on Y _E/C, whereas the pseudo-first order reversible kinetic constant rate of casein reticulation linearly increased with the enzyme concentration. Despite a certain data scattering, the initial and equilibrium complex shear moduli appeared to be practically constant and independent of Y _E/C. This finding was also extended to the mechanical and water barrier properties of the films under study. This was also indirectly confirmed by scanning electron microscopy, the film structure being quite compact, dense, and about free of air bubbles. In particular, their complex tensile modulus (E*) resulted to be not only independent of the cross-linking agent dosage but also interconvertible with the elastic modulus (E) determined in the quasi-static mode at an initial strain rate equal to the angular frequency. The water vapor permeability (WVP) for all the films examined was found to be extremely dependent on the water, desiccant, or Permatran-W standard methods used as well as on the difference in water activity (a _W) at the inside (a _Wi = 1.0 or 0) and outside (a _Woi = 0 or ∼0.5) of the test cup. By maintaining a _Wi = 0 and a _Woi = 0.5, the Permatran-W method yielded practically constant WVP values (30 ± 4 pg m⁻¹ s⁻¹ Pa⁻¹) whatever the enzyme/caseinate ratio used. Nevertheless, TGase appeared to decrease the water vapor permeability of not cross-linked maltodextrin–caseinate films.