Improved method for measuring hydrolyzable tannins using potassium iodate

Abstract

Until now, the recommended procedure for measuring hydrolyzable tannins has been to mix the reagent and sample, subject the mixture to a certain amount of chill, allow the reaction to continue for some time at a higher temperature and then measure the absorbance of the colored solution. The effect of different chill conditions has been studied by many workers but the effect of conditions after the chill period has not been studied. In this work, the effects of changing certain reaction variables during the increased temperature time period were examined and it was found that small changes in the reaction conditions resulted in large changes in the reaction process. Additionally, the behavior of the reaction depended on the variety of plant from which the hydrolyzable tannins were extracted and the time of the season when the leaves were collected. It is recommended that no chill be used in the colorimetric procedure but, instead, the following procedure should be used: extract the plant material with 70% acetone and take 1 ml of the extract plus 5 ml of 2.5% potassium iodate and place in a test-tube. Vortex mix the mixture and immediately place the test-tube in a 25 °C water bath. When the optimum length of time has passed (which should be determined for each type of plant material and must be precisely measured), remove the sample from the water-bath and measure the absorbance at 550 nm.