As far as I know, the clinical relevance of some phenolic substances is limited by their low (water) solubility, which in the specific case of phenolics is defined by the presence and distribution of hydrophobic/"hydrophilic" functional gropus, which in turn greatly affect their antioxidant capacity.
On the other hand, the affinity of polyphenols for proteins, amongst other characteristics that are relevant for their actual (in-vivo) bioactivity (oxygen radical-scavenging capacity included), are rarely mirrored in laboratory conditions.
Then can one say in broad terms that, considering only these factors, antioxidant capacity/bioavailability/bioactivity of polyphenols are at least somewhat directly correlated to their water solubility? No? What would be an accurate way of posing this relationship? Thanks to all those who will read this question.
I think such correlation is possible but only within narrow range of compounds which are very similar in structure and the quality of such correlation may be not so good. The reason to be careful in predicting of mentioned correlation is the very complex nature of solubility parameter which depends on a number of solute and solvent properties. For example, the water solubility for particular substance is hard to predict despite one can see the chemical formula.
There is an inverse relationship of phenolics in medium due to low solubility that distorts or lower down its free radical scavenging activity. Bioactivity is directly proportional to utilization of substrates and conversion factor at a definite temperature as well as photomeric condition. Phenolics in medium are also sensitive to light. Bbioactivity depends on free ion availability while anti-oxidant activity utilizes free ions. Bioavailability depends on radiation spectrum used, temperature and photopigments in plants.
Dear Carlos,
I suggest you to read the following article: Nutrients and phytochemicals: from bioavailability to bioefficacy beyond antioxidants.
There are other mechanism apart from antioxidant activity by which polyphenols are bioactive. In fact, it is already accepted that the bioactivity of polyphenols in terms of their antioxidant activity could be significant only at the gastrointestinal level where their concentration can reach the mM range.
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