Ipomeamarone in blemished and diseased sweet potatoes (Ipomea batatas)

A simple and efficient procedure is described for the quantitative determination of ipomeamarone in sweet potato products. The method is rapid and sensitive to 1 ppm. Sweet potato shreds or mash are comminuted and extracted in a blender with a mixture of chloroform, methanol, and water. After filtering the homogenate, the chloroform layer is dried and evaporated under vacuum. The residual oily material is dissolved in a known volume of chloroform and analyzed quantitatively by gas chromatography. The method was applied to blemished and diseased sweet potatoes before and after processing. Although the method indicates that blemished and diseased sweet potatoes have a relatively high concentration of ipomeamarone, it also reveals that peeling and trimming raw, baked, or boiled sweet potatoes leaves healthy tissue with little or no detectable ipomeamarone. Neither baking nor boiling appears to promote diffusion of ipomeamarone into the healthy tissue; however, baking appears to reduce the concentration of this hepatotoxin. American and Japanese investigators have isolated several furanoterpenoid toxins from blemished and diseased sweet potatoes and have shown that ipomeamarone, the most common of these metabolites, produces liver necrosis in mice and other animals (Wilson and Hayes, 1973). Since most sweet potatoes are consumed as human food or animal feed, it is essential to determine the presence of this hepatotoxin in sweet potato products. Although several procedures are available for the determination of ipomeamarone (Boyd and Wilson, 1971; Wood and Huang, 1975; Coxon et al., 1975), we needed more practical methodology for our survey. A modified method of analysis was developed that permits rapid and efficient quantitative determination of ipomeamarone in sweet potato products. This procedure also indicates that ipomeamarone is concentrated primarily in the blemished and diseased tissue of the sweet potatoes. MATERIALS AND METHODS Sweet Potato Samples. Blemished and diseased sweet potatoes were selected either from discarded potatoes at the grading line of packing sheds or from washed potatoes that became blemished and diseased in storage.