Understanding the bioactivity of plant tannins

MSc Marica Engström from the Natural Chemistry Research Group (https://naturalchemistry.utu.fi) defended her doctoral thesis on June 17. The method developments and findings included in the thesis will have a significant impact on all fields of science dealing with tannin chemical analysis.

New tools for rapid tannin fingerprinting by UPLC-MS/MS

Prof. Emeritus Daneel Ferreira (2nd right, from University of Mississippi, USA) was the opponent to MSc Marica Engström (2nd left), prof. Juha-Pekka Salminen was the custos and Dr. Maarit Karonen and Dr. Petri Tähtinen the other supervisors.

Prof. Emeritus Daneel Ferreira (2nd right, from University of Mississippi, USA) was the opponent to MSc Marica Engström (2nd left), prof. Juha-Pekka Salminen was the custos and Dr. Maarit Karonen and Dr. Petri Tähtinen the other supervisors.

The most significant results of the thesis by Marica Engström are certainly related to the method developments in tannin analysis by clever utilization of tannin dissociation in the ion source region of the XEVO TQ mass spectrometer. The group-specific methods thus created for proanthocyanidins that contain procyanidin and/or prodelphinidin subunits together with hydrolysable tannins that contain galloyl and/or HHDP subunits arguably change the way we think of accurate tannin analysis. The so-called fingerprints that are automatically produced by these methods are of tremendous use for many fields of science interested in utilizing plant tannins or plants containing tannins. As a bonus, the developed methods also enable qualititative and quantitative analysis of the most common groups of plant flavonol derivatives together with one of the most common group of plant phenolics, i.e. the quinic acid derivatives.

Links to the methods development papers:


Better understanding of tannins’ structure-activity relationships

There is a lot of non-sense speculations of tannins’ structure activity relationships related to many types of bioactivities to be found in the scientific literature. Much of the speculative nature of these findings comes from the fact that the scientific community just does not fully appreciate the complex nature of tannin structures found in plants. Only too often structure-activity relationships are elucidated by using mixtures of semi-purified mixtures of tens or hundreds of tannins that have not been properly characterized for their individual structures. The conclusions of these studies are often too general, stating e.g. that tannins had no effect on… or that hydrolysable tannins were proven to be efficient against… The two papers by Marica Engström clearly show once more how tannins should be looked at individually and no general conclusions are warranted even within one group of tannins. Both the anthelmintic activities of the tested 33 hydrolysable tannins – which is a huge number of purified tannins to be used in one study – and the covalent and non-covalent interactions of a more limited set of tannins showed clear structure-activity patterns. Both of these papers enable us to predict the measured bioactivities on the basis of either tannin structure or chemical property. This is a significant finding that clearly enables us to build more comprehensive understanding of the bioactivities also with other types of tannins not included in these papers.

Link to the bioactivity paper: http://dx.doi.org/10.1021/acs.jafc.5b05691
The other bioactivity paper is currently pending revision and it will appear later at https://naturalchemistry.utu.fi/publications/2016-publications/

The dissertation and evening party

Prof. Emeritus Ferreira is a true tannin chemistry expert and performed excellently as the opponent by letting Marica explain all the details from stereochemistry of D- and L-glucoses to the formation of HHDP-moieties of ellagitannins via oxidative coupling reactions and further to the biosynthesis of simple galloyl derivatives, gallo- and ellagitannins. The whole dissertation event had a very good spirit and long-lasting discussions, and at times, according to Marica, it felt like there were no other people present in the lecture hall but the opponent and the PhD candidate. Very well done, this is the way dissertations should be like.

After the dissertation, Marica’s thesis was accepted with honors, which is very rare. This was also the first time that the PhD work was done in less than four years in our group, which set the bar quite high for other PhD candidates. It also must be noted that all the endlessly positive feedback Marica and the whole group got from prof. Ferreira in his final statement and during the evening party leaves us with a humble feeling that we must have been doing something right during the years. To receive this feedback from true tannin chemist with massive expertise in the field feels even better, since not too many chemists know or understand what tannin chemists are doing and that is sometimes reflected in their opinions.

This was one of those days when we were again able to witness the truly magnificent team spirit of our research group. Especially the evening party left us with many good memories and some excellent photos :). We can be very proud of Marica and of the whole group.

Juha-Pekka Salminen

The thesis has been published in electronic format at https://www.doria.fi/handle/10024/123586