IsoLife - Stable Isotope Labelled Plant Products for the Life Sciences

Applications  |  Authentication: Organic versus Conventional Beef


Authenticity of beef: differentiating between organic and conventional farming systems.

Introduction

'You are what you eat' is the title of a Science paper by Kohn (1999) in which he describes how the isotopic composition of our food (a natural fingerprint) is reflected in our tissues. This phenomenon was earlier observed by DeNiro and Epstein (1978) and can be extremely useful in a world where global food transportation is common business. In the food chain from farmer to consumer counterfeiting indeed occurs for many food products and methods have to be further developed for authentication purposes.

Stable Isotope Solution: Use the isotopic composition as a natural fingerprint

Most temperate grasses and herbs use the C3 pathway of photosynthesis. The C4 pathway, employed by many (sub)tropical plant species, results in less 13C-depleted plant biomass. The carbon isotope composition (d13C) of C3 plants (e.g. ryegrass) varies from about -21 to -34‰ with an average of about -27‰ (Figure 1). The carbon isotope composition of C4 plants (e.g. maize) is higher and d13C values range from about -10 to -18‰, with an average of -13‰ (Cerling et al, 1997).

Figure 1. Delta values of C3 and C4 plants (adapted after Cerling et al, 1997).

Where paper documents or plastic labels ultimately fail to indisputable ascertain the authenticity of food, counterfeiting natural fingerprints like isotopic composition is virtually impossible. They can therefore often be used for authentication of food products.

Typical Result

The 13C/12C ratio of a product may yield information about the farming system of e.g. beef production. Fodder used by organic farms in Western and Central Europe mainly consists of C3 plants like ryegrass, whereas conventional farms often use maize, a C4 plant. Boner and Förstel (2004) showed that by analysing the 13C/12C ratios of raw beef protein it is possible to differentiate between organic and conventional cattle farming system origins (Figure 2).

Figure 2. Delta values of organic and conventional beef proteins (adapted after Boner & Förstel, 2004).

The authors concluded that the complete analysis of the stable isotopes of the five biologically most abundant elements (H, C, N, O, and S) is a powerful tool for testing the authenticity and for tracing the origin of a product independently from its certificate. For organic farming, a 13C/12C ratio of -20‰ appeared to be the upper limit for organic farming.

References

Boner M, H Förstel. 2004.
Stable isotope variation as a tool to trace the authenticity of beef.
Analytical and Bioanalytical Chemistry 378: 301-310.

Cerling TE, JM Harris, BJ MacFadden, MJ Leakey, J Quadek, V Eisenmann, JR Ehleringer. 1997.
Global vegetation change through the Miocene/Pliocene boundary.
Nature 389: 153-158.

DeNiro MJ, S Epstein. 1978.
Influence of diet on the distribution of carbon isotopes in animals.
Geochimica et Cosmochimica Acta 42: 495-506.

Kohn MJ. 1999.
You are what you eat.
Science 283: 335-336.

 

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