Pyrrolizidine Alkaloids in Culinary Herbs – Take Caution with Borage-Containing Herbal Mixes

Report from a day in the lab

Thomas Kapp

 

Reports of findings of liver-damaging pyrrolizidine alkaloids (PAs), especially in herbal and rooibos teas, have become commonplace. With this in mind, in 2015 and 2016 CVUA Stuttgart analyzed a total of 62 samples of culinary herbs for the presence of these unwanted, harmful substances, sometimes with surprising results.

 

Which samples were investigated?

The focus of the investigations was chopped herb mixes, from which it is difficult for the consumer to recognize and remove any foreign plant parts. There were three categories of herb samples analyzed: 5 samples of fresh, chopped herbs, 13 samples of dried herbs, and 44 samples of frozen herbs. While the fresh, chopped herbs contained a single herb, such as chives or parsley, most of the dried and frozen herbs were mixes of different salad herbs or Mediterranean herbs.

 

Illustration: Fresh plus dried and finely chopped oregano leaves. Source: Pixabay, CC0 Public Domain.

Fresh herbs with intact structures can easily be identified by their leaves (here, oregano). With finely chopped herbs, however, it is difficult to ascertain whether foreign plant parts are present. Foto: ariesa66/Pixabay, CC0 Public Domain.

 

Info Box

Pyrrolizidine Alkaloids

Pyrrolizidine alkaloids (PAs) are a group of several hundred structurally closely related individual compounds. They occur naturally in more than 6,000 different plant species, and serve to protect the plants from pests. These species can be divided into three main families:

  • Composite plants (Asteraceae),
  • Leguminous plants (Fabaceae or Leguminosae), and
  • Borage plants (Boraginaceae).

PAs are problematic and, therefore, unwanted in foods because they cause chronic liver damage. The sub-group of unsaturated PAs is especially problematic, in that they are suspected of causing genetic damage, and have been proven in animal studies to be carcinogenic.

The Federal Institute for Risk Assessment (BfR) recommends, therefore, not to exceed a daily dose of 0.007 µg unsaturated PAs/kg bodyweight [1]. For an adult weighing 60 kg this would mean the extremely low amount of just 0.42 µg PAs per day. For children or babies, the corresponding amount is even lower.

Currently, the investigatory spectrum at CVUA Stuttgart covers 30 toxic individual compounds. In order to better present and compare the level of PA contamination in the analyzed samples, the measured individual values were summarized as totals.

PA-forming plants, with the exception of borage, are not usually consumed as food. Higher PA levels are therefore an indication that foreign plants were also harvested and processed together with the plants of intention. Due to its marked toxicity, efforts should be undertaken to avoid as much contamination with PAs as possible.

 

Research Results

Fresh and dried herbs

Among the fresh, chopped herbs, only one sample contained minute traces of PAs, whereas the dried herb samples showed significantly more diversity. One sample of dried parsley was conspicuous for containing 200 µg/kg of PAs, above the average amount. The highest quantity by far, however, was in a sample of „Italian Mixed Herbs“, which contained, in addition to oregano, rosemary, basil and marjoram, other herbs that were, unfortunately, toxic. The PAs contained therein amounted to 6,200 µg/kg and was judged, therefore, as unsafe to eat. Even the consumption of just one gram of this dried herb mix would have resulted in the exceedance of the safe daily maximum dose for an adult by a factor of 14 (see Info Box).

 

Frozen Herbs

Of the 44 samples of frozen herbs, 16 consisted of single herbs such as chives, parsley, basil or dill. Fortunately, there were no PAs detected in the vast majority of these samples (14 of 16 samples). Low-level traces of PA contamination were detected in just two of the single herb samples.

 

Overview of the research results.

Overview of the research results. No pyrrolizidine alkaloids, or only traces thereof, were detected in about two-thirds of all samples. Considerable amounts of PAs were found especially in borage-containing frozen herb mixtures. (LOQ = Limit of Quantitation)

 

The remaining frozen herb mixes showed a different picture; mainly the 15 samples that contained borage were noteworthy. These mixes are often sold with a combination of 6, 7, or 8 herbs, and it is only with an attentive look at the ingredient label on which borage is listed, that the presence of PAs will be evident. The amount of borage depends on the particular combination of herbs, but usually comprises 10 % or less of the total weight. As is typical for borage PAs, all of the borage-containing herbal mixtures were detected with pronounced levels of lycopsamine N-oxide. In addition to the PAs stemming from borage, six of the 15 samples also showed signs of contamination from poisonous ragwort. The frozen sample with the highest level of PA contamination contained 770 µg/kg, only 10 % of which could be attributed to the borage listed on the ingredients label. The remaining alkaloids exhibited characteristics typical of ragwort, resulting in the determination that this sample was unsafe to eat, due to its contamination from PA-containing foreign plants.

 

What does this mean for the consumer?

In contrast to the situation for other foods, the positive finding of PAs in borage-containing herb mixtures doesn’t necessarily mean that the sample was contaminated by the presence of unwanted foreign plant parts, but rather, that the mixture consisted of PA-containing ingredients. The obvious advantage for the consumer is that, with an interested glance at the ingredients list, he or she can see that PA-containing herbs are included in the mixture and react accordingly.

Borage fans should be aware that this plant forms substances that, when consumed in excessive amounts, appear to be toxicologically harmful. On average, the herb mixtures containing borage had a PA amount of about 200 µg/kg. The daily consumption of about two grams of such herb mixtures would not be harmful for an adult. However, larger amounts shouldn’t be consumed regularly. This is especially so, given that the additional exposure to PAs through other foods such as herbal tea and honey can raise the daily total intake.

The results also show that one should be careful when eating borage alone, e.g. from one‘s own garden. Scientifically reliable data on PA amounts in borage are not yet available; at CVUA Stuttgart, however, such data are currently being collected and analyzed within the realm of an ongoing monitoring project. In the meantime, to be absolutely sure, one would be advised to avoid borage completely.

 

Info Box

Borage

This plant, which actually comes from the Mediterranean region but has been cultivated north of the alps since the middle ages, is used, among others, as a culinary herb. Given that this plant contains liver-damaging PAs and that therapeutic claims have been unsubstantiated, its use as a medicinal plant has not been supported since 1991 [2]. Meanwhile, there are no limitations in Germany for its use as a food. The situation is different in other countries such as Belgium, however; due to the presence of PAs, borage has not been authorized for consumption since 1997 [3].

In Germany borage is mainly used as a culinary herb, due to its fresh, cucumber-like taste. In some regions, it is very popular as an addition to salads, soups or herbal sauces. In Hesse, for example, borage is traditionally part of the much loved Frankfurt green sauce.

Botanically, borage (Borago officinalis L.) belongs to the family of Boraginaceae and is visually characterized by its vivid, blue petals. The sepals, stems and leaves have bristly hairs. The large, pointy-oval and slightly fleshy leaves give the plant a fairly rough appearance, in contrast to the delicate petals. All of the plant parts that are above ground contain pyrrolizidine alkaloids, especially the leaves that are used in cooking.

 

Illustration: blooming borage, Source: Pixabay, CC0 Public Domain.

Borage (Borago officinalis L.) should not be consumed in larger quantities, due to its naturally occurring pyrrolizidine alkaloids. Foto: Fablegros/Pixabay, CC0 Public Domain.

 

Sources:

[1] Stellungnahme Nr. 030/2016 des BfR vom 28. September 2016: „Pyrrolizidinalkaloide: Gehalte in Lebensmitteln sollen nach wie vor so weit wie möglich gesenkt werden

[2] Monographie des BGA/BfArM (Kommission E): "Borago / Boretsch", erschienen im Bundesanzeiger Nr. 127 vom 12.7.1991

[3] Koninklijk Besluit van 29 Augustus 1997 betreffende de fabricage van en de handel in voedingsmiddelen die uit planten of uit plantenbereidingen samengesteld zijn of deze bevatten (B.S. 21.XI.1997)

 

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Report published on 22.05.2017 10:53:50