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Pyrrolizidine alkaloids in herbs and spices: why sampling matters as much as analysis

Pyrrolizidine alkaloids (PAs) are naturally occurring toxins that have gained increasing attention in recent years, particularly within the herbs and spices sector. Produced by plants as a defense mechanism against herbivores, these compounds are widespread in nature, occurring in thousands of plant species. 

Their presence in food is not without concern. Certain PAs, especially the 1,2-unsaturated forms, are known to be hepatotoxic, genotoxic and carcinogenic, making long-term dietary exposure a relevant food safety issue. 

Where does the contamination come from?

Contamination through co-harvested weeds

In herbs and spices, PAs are rarely intrinsic to the crop itself. Instead, contamination typically originates from PA-producing weeds that are co-harvested along with the main crop. This makes their occurrence highly dependent on agricultural practices, environmental conditions and the effectiveness of weed control measures. 

Products such as oregano, thyme, basil and mixed herbs are particularly susceptible. Similarly, teas, herbal infusions and plant-based food supplements are known risk categories. 

Why dried herbs are particularly sensitive 

European legislation has placed a strong focus on dried herbs, and for good reason. 

During the drying process, water is removed while contaminants such as PAs remain, leading to a concentration effect. As a result, even low-level contamination in the field can translate into higher concentrations in the final product. 

Once plant material is dried, cut or ground, the visual identification and removal of contaminating weeds become significantly more difficult. This further increases the risk of unnoticed contamination entering the food chain. 

For spices, regulatory limits remain more limited, with a specific maximum level currently established only for cumin. 

Why reliable analysis is so demanding

A challenge of heterogeneity 

One of the defining characteristics of PA contamination is its heterogeneous nature. 

Rather than being evenly distributed, PAs are often localized in small fragments of contaminating plant material. This leads to significant variability within a batch and can result in different analytical outcomes depending on the sub-sample tested. 

This behaviour closely resembles that of mycotoxins and has important implications for both sampling and analysis. 

Sampling: the most critical step 

The importance of representative sampling is explicitly recognized in European legislation. 

Regulation (EU) 2023/2783, which addresses plant toxins, aligns with the sampling principles defined for mycotoxins in Regulation (EU) 2023/2782. This alignment reflects the similar challenges posed by heterogeneous contaminants. 

For operators, this means that sampling protocols must be carefully designed. In the case of large lots of dried herbs and spices, aggregate samples can reach up to 2 kg in order to adequately capture variability within the batch. 

How we approach it at Primoris

Beyond detection: the importance of homogenization 

While advanced analytical techniques such as UPLC-MS/MS enable the detection of multiple PAs at low levels, the reliability of the final result depends heavily on sample preparation. 

Given the heterogeneous distribution of PAs, proper homogenization is essential. 

At Primoris, particular attention is paid to the grinding and blending process. Ensuring sufficient free space in the blender allows for optimal turbulence, which is crucial to achieve a uniform distribution of contaminants within the laboratory sample.  

Since the analysis of certain matrices remains complex, we continuously evaluate new analytical techniques to refine our approach and keep pace with evolving science and regulatory requirements.

This significantly reduces the risk of non-representative results and strengthens the reliability of analytical data used for compliance and risk assessment.

What this means for you as a QA professional 

PA contamination can't be fully eliminated. But it can be managed through a combination of good agricultural practices, effective supply chain control and an analytical partner who understands the full picture.

Questions about PA testing in your herbs or spices? Get in touch.