Psychophysics of Divalent Salts and Metallic Taste

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DESCRIPTION (provided by applicant): Sensory properties of divalent salts such as those of calcium and iron have received scant attention in the literature on the chemical senses. Given the aging of the US population and the prevalence of osteoporosis, dietary calcium insufficiency is a growing concern and is being addressed by an increasing number of calcium fortified food products. Iron deficiency is a continuing problem in the third world, affecting billions of people worldwide. Understanding the sensory properties of divalent salts such as those of calcium and iron will add to the knowledge base in the senses of taste and smell and may help the engineering of foods and supplements with acceptable sensory properties. A program of research is proposed here in two main sections. First, psychophysical characterization of divalent salts will address the qualitative and intensive properties of Group II of the period table including calcium, an active participant in various steps of taste transduction, as well as magnesium and barium. In preliminary research with calcium and magnesium, a frequent taste descriptor was the term "metallic." This property of multivalent halides has received little attention but qualitative work suggests that it results from the production of a volatile substance that is perceived retronasally. That is, metallic taste may be a smell and not a true taste. This is consistent with literature from food chemistry suggesting that metallic ions such as iron and copper can catalyze the production of very potent odor compounds from oxidation of lipids. The second program of research aims to characterize the sensory properties of iron and copper salts, which produce complex sensations in the oral cavity. Instrumental-sensory correlations will be brought to bear on the identification and characterization of volatile compounds produced from mixing ferrous sulfate with human saliva, and comparison of these compounds to known lipid oxidation products known to smell "metallic" as identified in the food chemistry literature. A parallel to the reports of metallic sensations from electric taste will be investigated. A primary question of interest is whether metallic taste is olfactory, gustatory or tactile in nature or some combination of the three.