Testing for Gums, Starches, and Mucilages in Artifacts with O-toluidine

The o-toluidine test for complex carbohydrates was first developed for the identification of gums, mucilages, and starches using small samples from artifacts. This test as described for the analysis of museum collections was revised by systematically testing reference materials. This paper reports on the color reactions obtained on treating reference materials with the o-toluidine reagent to better understand the resultant color reactions of various gums, mucilages, and starches. The green color reaction commonly reported in the literature was found to be only partially accurate. This test will yield a green color for polysaccharides that yield only aldohexoses upon hydrolysis, such as starches and certain mucilages. Gum exudates and mucilages that are polysaccharides of both aldohexoses and aldopentoses yield a brown color reaction. Also discussed are the classification, sources, and uses of various plant polysaccharides and where this microchemical test was useful in understanding the collections at the Arizona State Museum.