Adsorption of oak tannins to compounds of carbohydrates

The tannins are phenolic compounds which are repellants to predators, animal or microbial. They are of relatively high molecular weight and have the ability to complex strongly with carbohydrates and proteins. It has to be suggested that the effective concentration of the tannins decreases if they come into contact with carbohydrates within the gut of an insect (e.g. starch of the leafs pr chitin of the peritrophic membrane). In this presentation the adsorption of tannins derived from oak leaves to carbohydrates like starch, chitin and compounds which contain carbohydrates (peritrophic membrane of Lymantria dispar and tannin free powder of leafs) were investigated. The concentrations of single tannins were measured by HPLC and compared with an external standard. After incubation with the tannins they were extracted out of the carbohydrates with 70% acetone to proove the strength of the bondings. The degree of adsorbtion of tannins depends on the type of carbohydrate. Highest amount of tannins were bonded by the oak leaf powder. Starch could catch only catechine. Chitin and the peritrophic membrane adsorbed mostly the same amount of tannins. The bonding at the peritrophic membranes was the strongest; none of the adsorbed phenolics could be extracted from the membranes. We conclude that carbohydrates can decrease the effective amount of the tannins within the gut of an phytophagous insect. Since the adsorption to the peritrophic membranes is very strong, the insects possess a potential mechanism against the tannins.