EFFECTS OF HERBIVORE GUT SURFACTANTS ON KELP POLYPHENOL DEFENSES

The idea that plant polyphenols act as digestibility-reducing compounds is well entrenched. This hypothesis has recently been countered with the proposal that the presence of surfactants in the gut fluids of herbivores may preclude the digestibility-reducing effects of plant polyphenols. We examined three marine isopods, three limpets, and a rock lobster, and established that surfactants are present in the digestive fluids of all of these organisms. However, further determinations of the efficacy with which these surfactants can prevent the complexation of proteins by brown-algal polyphenols in vitro revealed substantial differences between species. Moreover, in cases where the surfactants were ineffective, polyphenols reduced in vitro digestibility in a dose-dependent manner. We therefore conclude that the presence of gut surfactants does not necessarily preclude protein precipitation by polyphenols in vivo. Thus polyphenols might still be regarded as digestibility-reducing compounds, since gut surfactants only counter these effects in some cases.