Food analysis isotope ratios

Stable isotope studies usually involve administration of the enriched stable isotope in or with a meal. The method of labeling depends on the type of study undertaken. For elements such as selenium, where absorption and metabolism are highly dependent on chemical form, it is usually necessary to use an intrinsic label (i.e., one that is biosynthetically incorporated into the food). Conversely, minerals believed to form a common pool in the digestive system may be mixed directly with the food (extrinsic labeling). In some cases a second isotope is injected or infused intravenously to correct for endogenous losses. Samples of breath, blood, urine, saliva, or feces are then collected for an appropriate period and subjected to isotopic analysis. Isotope ratio measurement often requires specialized instrumentation such as... 

In recent years, together with enantioselective analysis, the determination of the natural abundance of stable isotopes by means of stable isotope ratio mass spectrometry (TRMS) can be very useful for the assignment of the origin of foods and food ingredients, and of authenticity evaluation (24). 

Marino, B.D. and DeNiro, M.J. 1987 Isotopic analysis of archaeobotanicals to reconstruct past climates Effects of activities associated with food preparation on carbon, hydrogen and oxygen isotope ratios of plant cellulose. Journal of Archaeological Science 14 537-548. 

Herbach, K.M. et al.. Isotope ratio mass spectrometrical analysis of betanin and isobetanin isolates for authenticity evaluation of purple pitaya-based products. Food Chem., 99, 204, 2006. 

Fingerprinting of Foods by Trace Analysis and Isotope Ratio Measurements... 

More recently, enantiomer ratios have been used as evidence of adulteration in natural foods and essential oils. If the enantiomer distribution of achiral component of a natural food does not agree with that of a questionable sample, then adulteration can be suspected. Chiral GC analysis alone may not provide adequate evidence of adulteration, so it is often used in conjunction with other instrumental methods to completely authenticate the source of a natural food. These methods include isotope ratio mass spectrometry (IRMS), which determines an overall 13C/12C ratio (Mosandl, 1995), and site-specific natural isotope fractionation measured by nuclear magnetic resonance spectroscopy (SNIF-NMR), which determines a 2H/ H ratio at different sites in a molecule (Martin et al 1993), which have largely replaced more traditional analytical methods using GC, GC-MS, and HPLC. 

Fingerprinting methods such as the anthocyanin methods and the Kirksey method for polyphenols (Kirksey el al., 1995) offer good ways to check for the addition of other fruits in a product. As the adulterators have become more sophisticated in the approaches that they use to extend juices, there has been a need for more complex methods of analysis. This means that it is now not uncommon to have to use fingerprinting techniques and isotopic methods to detect the most sophisticated forms of adulteration. These sophisticated analytical methods can even involve detection of the isotope ratios within a class of compounds such as sugars (Hammond el al., 1998). Using the RSSL 13C-IRIS approach, which was developed with financial support from the UK Food Standards Agency, it was possible to reduce the detection limit for the addition of C4-derived sugars to juices by about a factor of two. 

Lamprecht, G., Pichlmayer, F. and Schmid, E.R. (1994) Determination of the authenticity of vanilla extracts by stable isotope ratio analysis and component analysis by HPLC. Journal of Agricultural and Food Chemistry 42, 1722-1 72 7. 

Lee, K., Gillatt, P. and Rossell, J.B. (1993) Authenticity of edible vegetable oils and fats, Part XX determination of maize oil purity by stable carbon isotope ratio analysis (SCIRA). Leatherhead Food RA Research Reports No. 719. Leatherhead Food RA, UK. 

TABLE 5.1. An Overview of the Use of Heavy Isotopic Ratio Analysis in Studies to Determine the Geographical Origin of Foods... 

J. R. Dean, L. Ebdon, R. C. Massey, Isotope ratio and isotope dilution analysis of lead in wine by inductively coupled plasma-mass spectrometry, Food Addit. Contam., 7 (1990), 109-116. 

Schmidt, O., Quilter, J.M., Bahar, B., Moloney, A.P., Scrimgeour, C.M., Begley, I.S., Monahan, F.J. Inferring the origin and dietary history of heef from C, N and S stable isotope ratio analysis. Food Chem. 91, 545-549 (2005)... 

Analysis of herbage (of forage) has sometimes been used to detect and identify radionuclides deposited from the atmosphere (Jackson et al., 1981). However, the problem arises that when the deposition rate is low, large areas of vegetation need to be sampled for detection. In the case of plutonium, an alternative is to collect the faeces of grazing animals such as cows, sheep and rabbits. Plutonium is very poorly absorbed by the mammalian gut and so virtually all that is ingested by an animal will appear in its faeces. Also, if the species selected obtains its food entirely by grazing, then the isotopic ratio Pu will be the same in the faeces as deposited on the... 

F. Camin, K. Wietzerbin, A. Blanch Cordes, G. Haberhauer, M. Lees, G. Versini (2004) Application of multi-element stable isotope ratio analysis for the characterisation of French, Italian and Spanish cheese. J. Agric. Food Chem. 52, 6592-6601... 

M. Butzenlechner, A. RoBmann, H.-L. Schmidt (1989) Assignment of bitter almond oil to natural and synthetic sources by stable isotope ratio analysis. J. Agric. Food Chem. 22, 410-412... 

Over the years, Site-Specific Natural Isotope Fractionation (SNIF) NMR has been used extensively in food analysis. Deuterium ( H) is widely dispersed in the whole solar system and so it is as well on earth. Actually, the deuterium isotope ratio in water, usually expressed in parts per milhon (ppm - just... 

Schwab W. (1998) Application of stable isotope ratio analysis explaining the bioformation of 2,5-dimethyl-4-hydroxy-3(2//)-furanone in plants by a biological Maillard reaction. (Furaneol). J. Agric. Food Chem. 46, 2266-9. 

Hoffman, P. Salb, M. Isolation and stable isotope ratio analysis of vanillin. J. Agric. Food Ghent. 1979, 27, 352- 355. 

Faulharber et al (5,6) and other researchers (7-9) have described how the determination of the isotope values of constituents is of increasing importance, especially in view of the demand for authenticity control and origin determination of essential oils and foods. To determine isotope values, g chromatography-isotope ratio mass spectrometry (GC-IRMS) has been used, although not widely. The present authors (70) have studied the possibility of a more convenient and common means of analysis of isotope values, based on the isotope peak in the mass spectrum of a compound. The present study focuses on the development of a new analytical method for the differentiation of quality in commercial citrus oils of various origins. 

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