Verifying organic produce with isotopes

Organic food testing with SIRA

Using stable isotopes to protect standards

With the increase in organic food on shelves, it’s important to protect your brand and support your customers when it comes to ensuring organic reliability.

Organic products are often sold at a premium, which furthers the risk of substitution food fraud – selling conventionally-grown produce as organic and increasing profits.

From apples to zucchini, Agroisolab are experts in using stable isotope technology to verify the status in organic products.

Tracing problems back to the root

Stable isotope testing has an advantage over other methods of testing organic verification due to the opportunity it offers – to trace problems back to their roots in a range of products, from fruit to meat.

Using the stable isotope method exploits the fact that bioelements (hydrogen, carbon, nitrogen, oxygen and sulphur) have heavier ‘versions’ of themselves – stable isotopes. For example, in addition to a ‘normal’ nitrogen, there also exists a heavier version (1 additional neutron).

This subtle, but profound difference gives us the opportunity to track produce.

Organic fertilisers (such as composts, manures and green manures) show greater enrichment of heavy nitrogen (15N) than conventional mineral fertilisers (used to grow non-organic produce).

Organic fertilisers typically have nitrogen ratios of +10‰ +/- 4 in comparison to mineral fertiliser, which has nitrogen ratios of roughly 0 ‰ (Shearer 1974) (see image).

The science behind using 15N/14N for checking fertilisation sources

Want to know more about the scientific difference between organic and conventional produce?

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The enrichment of heavy nitrogen in biomass-derived fertilisers (organic), such as compost, manure, bonemeal, is the product of metabolism – the chemical reactions that take place in living organisms in order to keep them alive.

Transaminase, an enzyme that exists in all organisms and is involved in protein/urea metabolism, prefers heavy nitrogen (15N) as opposed to normal nitrogen (14N). Further heavy nitrogen enrichment in manure-based fertilisers is attributed to the preferential volatilisation of ammonia – a process where ammonia from urea fertilisers is converted to ammonia gas at the soil surface (Sturm et al. 2011).

As a result, biomass-derived fertilisers are enriched in heavy nitrogen and can be easily differentiated from mineral fertilisers.

Nitrogen ratios from the fertilisers are reflected in crops grown in the fertilised soil. If the soil was fertilised with organic (biomass-derived) fertilisers which show the enriched heavy nitrogen signature, this will show in the crop.

The opposite is also true – if the crop is fertilised with mineral (non-organic) fertiliser, the nitrogen ratio of the crop will also reflect this in the signature.

As the use of mineral fertiliser is prohibited in organic farming, the use of isotope testing offers a valuable service in terms of authentication, surveillance and the detection of product mislabelling in products declared as organic.

To this date, there is a wealth of peer-reviewed scientific literature (Choi, 2003, Nakano 2003, Bateman 2007, Rogers 2008, Sturm 2011) demonstrating and supporting the evidence that analysing nitrogen ratios (15N/14N) in agricultural produce offers excellent opportunity to determine organic provenance in many products.

How can organic isotope testing be employed?

The stable isotope method as an authentication/surveillance tool is most powerful when supplied with the declared fertilisation method – for example, “This carrot was grown using organic fertiliser.”

The best products that show the greatest differentiation between organic and conventional varieties are the shallow root plants that have a high demand for fertilisation. However, when used appropriately, this technique can be used in finished products such as eggs and meat.

The use of reference databases to authenticate products

Agroisolab GmbH prefers to establish databases for each agricultural product to get the best overview which ratios of nitrogen are expected to be observed in organic and conventional produce.

Furthermore, any information about the fertiliser used to cultivate the test sample is to helpful draw accurate conclusions from the report.

Testing products without a reference database

If there is no direct database of organic/conventional products available to compare a test sample to, it is only possible to evaluate whether the product was produced using organic (biomass-derived) fertilisers, leguminous plants/nitrogen fixing cultures, or mineral fertiliser.

What happens if a sample has abnormal ratios?

If a sample is discovered to have abnormal nitrogen ratios after isotope testing, Agroisolab recommends following up the investigation with further tests to determine the source of the issue.

Origin testing – In the case of mislabelled and abnormal samples, there is a high risk that the sample does not originate from its declared origin. Therefore, it is recommended to check the origin of the sample as well.

For origin testing, the following isotopes are normally used:

Hydrogen D/H (regional parameter of water)
Carbon 13C/12C (climate parameter)
Sulphur 34S/32S (geological parameter)

GMO testing – Where the risk of GMO adulteration is high, further evidence of non-organic status should be sought from GMO analysis. For example, if corn was discovered to have nitrogen ratios more negative than 0 ‰, it is possible the product has been diluted/substituted with GMO corn.

Agroisolab GmbH works closely with a network of labs that can be recommended to carry out this test.

Pesticide/residue analysis - Where applicable, Agroisolab recommends that further evidence of non-organic status is also gathered from pesticide/residue analysis. It is possible for mislabelled organic products to be fertilised with mineral fertiliser, and not have non-compliant pesticide residues.

Agroisolab is able to recommend a lab, from our close network, to carry out this test.

Further product/ingredient testing - When finished products such as eggs, labelled as organic, are discovered to have abnormal nitrogen signatures, there may be several reasons for this:

This is a non-organic product mislabelled as organic
This product is from an organic production system where non-organic feed is being fed to the animals
This product is from an organic production system that is being diluted with conventional products

In these cases, further investigation is required to reach the root of the problem, we are happy to offer advice about how best to investigate and resolve the issue.