Researchers at the University of Southern California reported evidence that the human tongue can detect a sixth basic taste. The findings, published in Nature Communications, challenge the long-held view that the tongue recognizes only five tastes: sweet, sour, salty, bitter, and umami. The newly identified flavor has a profile reminiscent of Scandinavian desserts and evokes the sharp, mineral-like note of salty licorice.
Central to the discovery is the OTOP1 receptor, known for its role in sour taste by guiding hydrogen ions into cells. The USC team proposed that ammonium chloride, which also alters hydrogen ion concentration within cells, interacts with this receptor. In chemical terms, ammonium chloride is commonly referred to as hydrochloric ammonia, a mineral often formed when coal gases condense during coal burning processes.
In their experiments, scientists cultured human cells and exposed them to ammonium chloride. The results indicated that ammonium chloride potently activates the OTOP1 receptor. To explore the perceptual outcome, researchers then used a mouse model. In one group, mice displayed a taste response to ammonium chloride and showed aversion to water containing the substance. A second cohort did not exhibit a reaction even at higher concentrations.
These observations led the authors to suggest that the ability to taste ammonium chloride may have evolved as a protective mechanism to prevent the consumption of potentially poisonous foods.
In a broader context, the study highlights how taste perception can involve specialized cellular receptors that respond to specific chemical cues. While the exact sensory experience of ammonium chloride in humans warrants further study, this line of work contributes to a more nuanced map of how the tongue detects a wider range of chemical stimuli than previously recognized. Researchers emphasize that taste is a complex system influenced by receptors, ion channels, and neural processing that work together to shape what people perceive as flavor. Future investigations may reveal additional compounds that engage the same receptor and help clarify how these signals translate into conscious taste experiences, preferences, and dietary choices.
Past discussions about sexual development and aging have varied widely across cultures and scientific disciplines. This study, however, remains focused on gustatory biology and the molecular basis by which new tastes may be perceived and differentiated by humans and animals. The researchers acknowledge that more work is needed to determine how common or rare this sixth taste might be across populations, and how it could influence nutrition and health in everyday life. Further experiments will seek to confirm these findings in diverse models and human participants, while exploring the potential implications for food science and sensory research [Citation: Nature Communications, 2024].