Dear Nobosse,

In my opinion, in vitro antioxidant assays are easy, cheap but have no meaning when relating to health effects. In addition, many people ignore the facts behind antioxidant assays (a common example is that Folin-Ciocalteu is per se an antioxidant assay, definitely not specific for polyphenols, and I have seen countless articles with correlations to DPPH for example). Many antioxydants further are not at all bioavailable (a typical example being the proanthocyanidins, the main polyphneol class in beverages and fruits) and when bioavailable the circulating forms are metabolites.

To advance on this topic in my opinion we MUST understand the specific activities of metabolites (which are not related to the antioxidan tpropoerties) and the metabolisation of polyphenols in the gut and by the microbiota.

Cordially

Catherine

Dear Nobosse

We can not ignore  importance of antioxidant just on the basis that it is not established as a effective during in vivo clinical trails. Most of the plant phenolics are considered as an anti oxidant at the same time said phytochemicals have good  antioxidant efficacy. 

Dear Nobosse,

you posed very important trends on antioxidants. In addition I would add some more questions:

Starting from its uptake from the diet, how do they act on (our) microbiom and what are bacteria doing with phytochemicals? Regarding the importance of the microbiom on our health, this question needs to be answered.

Enterocytes have the first contact with phytochemicals. Here, the decission is made if and how the antioxidants will enter the lymph stream. This is still unknown for most compounds.

You correctly mentioned the fact that after the first passage through the liver, metabolites of the phytochemicals will act in cells.

Another important trend might be the the fact that antioxidants act as pro-oxidants, thereby inducing an adaptive response that induces antixodant enzymes within the cell. This phenomenon is also called "antioxidant paradoxon". This is a very different view on the topic and questioned all in vitro antioxidant assays.

Many questions on researchgate deal with this kind of "test tube" assays. From my point of view, they are useless since the results do not correlate with the situation in living organisms.

Finally, the view on reactive oxygen species (ROS) changed since the act as important signalling molecules. Scavenging all ROS by AO might influence the adaptive response of the organism. Of course, too much ROS will kill the cells.

Thanks again to Nobosse starting this discussion. I hope it will continue...

Best

Marc

Dear Nobosse,

In my opinion, in vitro antioxidant assays are easy, cheap but have no meaning when relating to health effects. In addition, many people ignore the facts behind antioxidant assays (a common example is that Folin-Ciocalteu is per se an antioxidant assay, definitely not specific for polyphenols, and I have seen countless articles with correlations to DPPH for example). Many antioxydants further are not at all bioavailable (a typical example being the proanthocyanidins, the main polyphneol class in beverages and fruits) and when bioavailable the circulating forms are metabolites.

To advance on this topic in my opinion we MUST understand the specific activities of metabolites (which are not related to the antioxidan tpropoerties) and the metabolisation of polyphenols in the gut and by the microbiota.

Cordially

Catherine

There are a lot of good points in all the answers. On my side, I would like to highlight the points raised by Catherine.

The bioavailability is the key issue, with the parent compounds and/or the metabolites. These studies are also important to support the efficacy in a scientific and/or normative field (e.g. nutrition and health claims)

http://www.efsa.europa.eu/en/topics/topic/nutrition