Phlorotannin protein precipitation

Very little information exists on the phenolic protein-conplexing resins, except for that on creosote bush and sane arctic plants. In contrast to condensed tannins and hydrolyzable tannins, these are typically ether-soluble compounds this may allow their entry into the body across cell membranes, and thios give them the potential for action outside the gut lumen. Reports for animals consuming seaweed indicate that astringent protein-precipitating substances (presumably phlorotannins), are potentially important in marine plant-herbivore interactions. 

In vitro studies by Stem and co-workers124164 have attempted to further define the parameters that control precipitation of phlorotannins by proteins. In general, they found that pH, redox condition, and solution composition influenced phlorotannin-protein interactions. Unlike terrestrial tannins, they found that phlorotannins from marine algae spontaneously oxidized and reacted with... 

Covalent bonds between oxidized phenolics and proteins were shown to be more likely to form at high pH since phenolics are more readily oxidized at high pH. This was particularly true with basic proteins and less so with acidic proteins.124163164 Because precipitation of phlorotannin-protein complexes was independent of temperature, hydrophobic forces were not considered likely to be important in their formation.124 164 These studies suggest that, although phlorotannin structure is important, at least part of the variation in sensitivity to dietary tannins is due to variation in herbivore gut chemistry. 

Tannins are polyphenolic compounds of high molecular weight that occur naturally and react with proteins. They can form insoluble complexes with proteins, which are responsible for the taste known as astringency that is caused by precipitation of mouth proteins. Tannins are typically classified into three groups (1) the condensed tannins, (2) the hydrolyzable tannins, and (3) the phlorotannins (Figure 11.3.10). 

In ex vivo experiments, Stem124 also showed that phlorotannins precipitated protein from unaltered gut fluids obtained from both Australian and Californian invertebrate herbivores. Although the results showed no difference in precipitation with gut fluids from different regions, the analysis did indicate that phlorotannins from different seaweeds precipitated at different levels and that this effect depended on the herbivore gut fluid used. 

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