Tracing hazelnuts geographical origin: Isotopic markers

Food fraud can have many implications. Ranging from ‘counterfeit’ parmesan cheese​ to contaminated pork​ – fraud is a constant presence within the food industry.

Hazelnuts are not immune. The commodity, despite not being deforestation-linked by the EUDR​, is coming under scrutiny​ due to its links to bonded labour and child labour amongst its farmers, many of whom are seasonal workers.

The level of food fraud in hazelnuts, largely consisting of misleading consumers on their geographical origin, is difficult to quantify, but its effect on the sector is profound. With a diverse origin, hazelnut prices vary, and food fraud particularly impacts local producers with a protected geographical origin (PDO or PGI). Furthermore, prevalent food fraud generates consumer distrust in the sector. Now a new study has developed a way to link hazelnuts to their origin.

Isotopic markers as tracers​

The study has developed methods of tracking the origin of hazelnuts, using isotopic markers to do so. The composition of isotopes, which are forms of atom that have different weights but the same chemical structure, depend heavily on their geographical locations. Isotopes are affected by factors like the geology of the ground and the type of agricultural practices that are applied on the soil, and thus isotopes can be considered ‘markers’ of a certain environment.

However, ascertaining the level of insight sufficient to ascertain a geographical location is often, from a single isotopic marker, difficult.

One of the major difficulties is that in addition to factors influenced by the climate in the hazelnuts’ geographical origin, there are agricultural factors to contend with. Some fertilisers, for instance, can influence isotopic markers. Others do not provide this issue.

In the study, the researchers were able to evaluate a range of isotopic markers and identify which ones were affected by environmental factors alone, rather than the less location-specific factors contingent on human intervention.

Once the right isotopic markers are found, the research suggests, the information can be used to identify the geographical origin of hazelnuts more easily, therefore providing the industry with a way to better locate food fraud.

A multitude of isotopes​

In order to understand which isotopic markers enabled the geographic origin of hazelnuts to be traced, the researchers analysed the elemental isotopic profile of the hazelnut oil of 40 different samples of hazelnuts from four geographic regions (Chile, Georgia, Italy, Spain).

The researchers found that samples were indistinguishable in regards to their geographic origin when tested by the isotopic marker of sulphur. Affected by fertilisers, these markers have had their geographic origins masked by the diverse range of agronomic practices used within their respective plantations.

Some isotopic markers proved complex. One, nitrogen, was able to differentiate between the geographies. However, it was affected significantly by the use of fertilisers. Researchers were able to identify the isotopic markers of the Chile and Italy samples with the expected effect of the fertilisers used in those regions. However, the fertilisation affects on the Spanish samples did not align with the current fertilisation practices in Spain. Thus the researchers concluded that the presence of factors such as plant physiology and climate and soil characteristics made this isotopic marker a less-than-perfect geographical indicator.

Several others, oxygen, carbon and hydrogen, appeared to be relevant, as they are minimally influenced by factors such as fertilisation. Their combined use was determined to be a good way towards geographical classification.

The isotopic marker of the element strontium made geographical origins very clear. The strontium isotopic markers in each sample aligned with the geogenic factors (relating to the soil they originated from) of each of the areas that the samples had come from. While fertilisers can affect these isotopic markers, the researchers found that this affect was too negligible to prevent the geographical area being discovered. However, distinguishing geographical origin from this marker was shown to be more labour intensive than others, and required higher operating costs.

Overall, the researchers decided that the isotopic markers of oxygen, carbon and hydrogen were the most reliable tools to ascertain geographical origin, with strontium useful as a confirmatory tool.

Sourced From: Food Chemistry
'Investigating isotopic markers for hazelnut geographical authentication: Promising variables and potential applications'
Published on: 5 April 2024
Doi: https://doi.org/10.1016/j.foodchem.2024.139083
Authors: B. Torres-Cobos, M. Rosell, A. Soler, M. Rovira, A. Romero, F. Guardiola, S. Vichi, A. Tres