Rethinking the Iodine Reaction Methodology in the Classic Starch Degradation Experiment

High Resolution Image Download MS PowerPoint Slide In 2021, amid the COVID-19 pandemic, the Journal of Chemical Education published a study by Vargas-Oviedo, Morantes, and Diaz-Báez on a home experiment involving the degradation of starch by salivary amylase, using iodine to indicate starch presence. We replicated their experiment, reducing the total volume from 20 to 5 mL and added heated saliva as a negative control. This was to account for potential interference from crude enzymatic sources in the iodine-based methodology. Undergraduate chemistry students conducted the activity at home, and some noticed discrepancies between expected and observed results. These discrepancies, specifically the apparent hydrolysis of starch by heat-denatured saliva, may be related to the interaction of iodine with salivary proteins. This indicates that proteins can compete with starch for iodine binding, potentially leading to misleading results. Given the common use of this experiment in chemistry and biochemistry courses, we stress the importance of including appropriate controls, such as heat-denatured saliva, to avoid false detection of starch hydrolysis in cases with limited iodine concentration.