Where is your food from? Strontium isotopes trace the origin of cereals

• Many people are becoming increasingly interested in where their food has come from.
• Most of the existing analytical methods of food tracing are prone to variability across seasons.
• Fortunately, strontium isotope analysis provides a robust alternative.
• The research group of Dr Felix Bacher from the Laimburg Research Centre, Italy, have proven its ability to locate cereals specifically to the South Tyrol region of Italy.

In South Tyrol, a region of northern Italy, there is a need for ways to prove where cereals like spelt and rye have been grown. The research group of Dr Felix Bacher from the Laimburg Research Centre in collaboration with Eco Research and the Free University of Bozen-Bolzano, Italy, are looking at new ways of determining this, using strontium isotope analysis.

Many foods have protected statuses if produced in certain areas. Champagne is a famous example, only coming from certain parts of France. These statuses are then used to justify an increased price for the consumer. Without a way to prove the geographical origins, this could be open to fraud.

Concerns over sustainability and climate change are also leading more and more people to seek out food items that have been produced either locally or using specific farming practices. Again, without proper tracing, this could be used to mislead consumers into buying a product that isn’t what they think it is.

There is now a clear and growing need for food researchers to develop robust methods of food tracing. An excellent example of this can be seen in South Tyrol.

Strontium isotope analysis produces consistent results and is not as affected by climate or pollution.

What’s so special about South Tyrol?

South Tyrol has historically been an important producer of cereals, but this has changed over the decades. In 1900, the region contained 30,000 hectares of cereal fields; in 2000, this had dropped to just 243 hectares. To combat this, the European Social Fund funded the Regiokorn project. Farmers are rewarded considerably above the market value for cereals, as long as they abide by certain farming practices, such as avoiding mineral fertilisers, and grow their cereals in South Tyrol.

To avoid fraud, an accurate food tracing system needs to be in place. If grain grown elsewhere is allowed to benefit, the initiative won’t necessarily succeed in its original goal of bringing farming back to the region. Many methods exist for geographical food tracing, but they are often quite variable and prone to changes between seasons. One of the most robust methods is strontium isotope analysis. It produces consistent results and is not as affected by climate or pollution.

It’s all about mass

Strontium is an element found consistently throughout the Earth’s crust. It has four distinct isotopes – variants of the same element with a slightly different mass – known as ⁸⁸Sr, ⁸⁷Sr, ⁸⁶Sr and ⁸⁴Sr. The ratio between ⁸⁷Sr and ⁸⁶Sr (known as ⁸⁷Sr/⁸⁶Sr) can vary considerably based on local geology and can be used to trace samples to their origin. The growing areas of South Tyrol have a very different bedrock – composed of much more silicates such as gneiss and granite – compared to the surrounding areas. It is therefore quite likely that the ⁸⁷Sr/⁸⁶Sr ratio will be different and could be used to trace the cereals specifically to South Tyrol.

Bacher’s group collected soil samples from fields throughout South Tyrol, and the neighbouring regions Trentino (Italy), East Tryol, and North Tyrol (both Austria), along with grains grown in those same fields. The researchers then isolated the strontium and analysed it by mass spectrometry. This is a process that separates and measures all the analytes present in a sample in their ionic form by their mass to charge ratio. By doing so, the instrument is capable of determining the makeup of a sample down to picking out different isotopes of the same element. Through this, the ⁸⁷Sr/⁸⁶Sr ratio can then be calculated for every sample.

Pinpointing the region of growth

As expected, the soil samples from South Tyrol showed a significant difference in ⁸⁷Sr/⁸⁶Sr compared to other regions. Importantly, the research group also saw this difference in the grain, proving that strontium isotope analysis is capable of tracing cereal grains specifically to the region of South Tyrol.

The study also showed very little variability between the years, with no significant difference in the overall results between 2019 and 2020. Additionally, there was also very little difference between all the various species tested – barley, oat, rye, and spelt. Overall, this demonstrates that the strontium isotope-based analysis is a very robust method for tracing grains grown specifically in the South Tyrol region.

Cereals from South Tyrol showed a significant difference in ⁸⁷Sr/⁸⁶Sr compared to the other regions.

These very promising results are at least in part due to the large geological diversity of the area. Specifically, South Tyrol is very different from the surrounding regions, and this method is much less effective in separating any of the other regions investigated from each other.

Still, there are many cases where this method could prove to be very effective. The researchers note that existing data from other groups show that cereals from South Tyrol can be separated from several other countries by their Sr isotope ratio. Cereals from the US, Canada, China, Argentina, and Japan showed significantly lower Sr-isotopic ratios than cereals from South Tyrol, while values from Australia were in part overlapping because also there exist cereal production areas based on old primitive rocks like granite.

Strontium isotope analysis has already shown promising signs of being a useful method for determining grain origins in this region. The researchers now plan to expand their research to assess whether these ratios persist into processed forms, such as bread baked from these grains, which would allow the specifically marketed food products themselves, such as the artisanal breads from the Regiokorn project, to be tested.