Beyond the Big Five: Emerging Candidates for the Sixth Taste
While sweet, sour, salty, bitter, and umami have long been accepted as the five basic tastes, modern sensory science has revealed that our gustatory system is far more complex. Recent research has put forth several strong contenders for the title of the sixth taste, challenging long-held assumptions and offering new insights into how we perceive flavor. These emerging candidates include fat, kokumi, and starchy flavors, each with unique properties and underlying biological mechanisms.
Oleogustus: The Taste of Fat
One of the most compelling candidates for the sixth taste is the sensation of fat, officially named 'oleogustus'. While fat has long been known to influence food texture and aroma, researchers at Purdue University demonstrated that humans possess a specific taste sensation for fatty acids. This distinct taste, often described as pungent, rancid, or bitter in higher concentrations, is separate from other known tastes. This discovery supports the idea that the tongue can detect fats chemically, not just through their physical properties. The body's ability to taste fat is thought to be a survival mechanism, as it helps us identify nutrient-rich, high-energy foods, though it can also signal that a food is spoiled. For the food industry, understanding oleogustus offers opportunities to develop healthier products by manipulating fat perception without relying on high-fat ingredients.
Kokumi: The Taste of Richness
Another contender is 'kokumi,' a Japanese term for a sensation that enhances and deepens other flavors. Kokumi is not a standalone taste like umami but rather a mouthfeel of richness, complexity, and lingering satisfaction. Substances that produce kokumi, such as specific peptides found in aged cheeses, garlic, and yeast extracts, interact with calcium-sensing receptors on the tongue to create this effect. Unlike umami, which adds a savory flavor, kokumi amplifies and prolongs the taste of other elements without contributing a flavor of its own at certain concentrations. This makes it a valuable tool for food manufacturers seeking to reduce fat, salt, or sugar content without sacrificing the overall taste profile and satisfaction. The Ajinomoto Group, who first identified kokumi, continues to research its potential benefits for developing healthier, more flavorful food options.
Starch: The Taste of Carbohydrates
Recent studies have also suggested that humans can taste starch, adding another dimension to our understanding of carbohydrate perception. Previously, it was believed that we could only taste the sweet sugars that carbohydrates break down into. However, research from Oregon State University demonstrated that people can detect the flavor of starchy carbohydrates, even with their sweet receptors blocked. This taste, described as 'starchy,' 'bread-like,' or 'rice-like,' is linked to the body's recognition of energy sources and may have driven our evolutionary preference for carb-heavy foods. While further research is needed to identify the specific receptors responsible, the discovery suggests that the human taste system evolved to detect complex carbohydrates, not just simple sugars.
Ammonium Chloride: The Survival Taste
In 2023, scientists at USC Dornsife discovered evidence of a receptor on the tongue that responds to ammonium chloride, a compound used in some Scandinavian candies. This sensation, often described as a mix of bitter, salty, and a little sour, may also be a survival mechanism. The ability to taste ammonium chloride could help organisms avoid decaying or toxic substances, such as spoiled meat, which often contain ammonia. This potential sixth taste, detected by the OTOP1 protein receptor, reinforces the evolutionary purpose of taste perception.
Comparison of Potential Sixth Tastes
| Candidate Taste | Stimulus | Associated Foods | Key Characteristic | Receptors Involved |
|---|---|---|---|---|
| Oleogustus (Fat) | Non-esterified fatty acids (NEFA) | Oils, aged cheese, meat | Distinctive, often unpleasant in isolation | CD36, GPR120 |
| Kokumi | Glutamyl peptides, glutathione | Aged cheeses, yeast extracts, garlic | Enhances and deepens existing flavors | Calcium-sensing receptors (CaSR) |
| Starch | Glucose oligomers from starch breakdown | Pasta, bread, rice, cereals | Starchy, bread-like flavor | Currently unknown |
| Ammonium Chloride | Ammonium chloride | Salty licorice, decaying organic matter | Pungent, salty, bitter, sour mix | OTOP1 protein |
Scientific Significance and Health Implications
The identification of new taste categories has significant implications for both scientific research and public health. For centuries, the understanding of taste was limited, but these discoveries reveal the intricate and still largely unknown processes governing our perception of flavor. For researchers, identifying the receptors for these potential new tastes opens new avenues for studying human ingestive behavior, food preferences, and metabolism.
From a health perspective, these findings could lead to breakthroughs in managing obesity and other diet-related conditions. For example, understanding oleogustus could help develop foods that trigger the rewarding sensation of fat without the associated calories. Similarly, leveraging kokumi could enable manufacturers to reduce high-calorie or high-sodium ingredients while maintaining product palatability and consumer satisfaction. Furthermore, individual differences in fat taste perception have been linked to dietary intake and body mass index, suggesting a personalized approach to nutrition might be necessary. Our evolved ability to detect starchy flavors and ammonium chloride also underscores the fundamental role of taste in survival, guiding us toward beneficial nutrients and away from harmful substances.
Conclusion: The Expanding World of Taste
While the concept of the "sixth taste" is still debated, the compelling evidence for oleogustus, kokumi, starchy flavors, and ammonium chloride demonstrates that the human taste system is more nuanced than previously thought. These discoveries move us beyond the traditional five categories, revealing new layers of complexity in our relationship with food. From the distinct perception of fat to the flavor-enhancing properties of kokumi, these emerging tastes are expanding the culinary landscape and offering new tools for scientists and food technologists alike. The ultimate classification of a new basic taste will depend on fulfilling specific scientific criteria, but the ongoing research is already transforming our understanding of nutrition, evolution, and the pure enjoyment of eating. More information on the evolutionary aspects of taste is available in the article "An Evolutionary Perspective on Food Review and Human Taste".
