Metallic Sensation-Just an Off-Flavor or a Biologically Relevant Sensing Pathway?

Metallic off-flavors are a frequent theme in discussions of food product quality, with publications dating back over 90 years. The causes of this unpleasant perception are diverse, ranging from unfavorable concentrations of micronutrients, the use of artificial sweeteners, processing, packaging, and storage, to side effects of pharmaceutical or chemotherapeutic agents. However, the mechanisms behind metallic sensing and its contributions to taste, smell, and trigeminal nerve sensations are still poorly understood. Although even defining oral/nasal metallic sensation has proven difficult, thought should also be given to possible biological activities of food constituents eliciting a metallic sensation though activation of ectopically expressed chemoreceptors. This perspective seeks to summarize and connect research conducted on different food-borne stimuli of metallic sensation, their sensory evaluations up to more recent contributions addressing the mechanistic approaches to identify chemosensory-active food constituents, and their biological effects mediated by ectopically expressed chemosensory receptors. With this perspective, we hope to spark interest in fully characterizing the mostly unwanted metal off-flavor, thereby laying grounds for increased product quality on one hand and providing novel insights into chemosensory-associated biological functions of metallic sensation on the other hand, which might help to understand and combat these sensations experienced in various diseases and therapies, e.g., platinum-based chemotherapy.