The Fifth Taste: Discovering Umami

Research from the International Food Information Council Foundation  on consumer perceptions of food and nutrition issues has consistently shown that taste is the primary driver of food purchasing decisions among US adults (International Food Information Council Foundation, 2010). The discovery of “umami” in foods (also known as our fifth taste) has led to the development of many products and ingredients that offer a savory and appealing taste, providing a broader range of options for consumers to enjoy.
 
Although umami has long been a natural component of foods, and “umami” flavor additives were first developed nearly a century ago, the full story is only more recently being told. In 2009, The American Journal of Clinical Nutrition highlighted monosodium glutamate (MSG) as the compound responsible for umami in a special supplement titled, “100th Anniversary Symposium of Umami Discovery.” MSG has been the subject of ongoing debate regarding its safety and alleged role in food sensitivities although authorities declared the safety of MSG from a scientific perspective. The supplement reviews the scientific advances and evolution of umami and MSG research from its initial discovery and demonstrated safety to taste mechanisms and their role in health.
 
A common flavoring ingredient that imparts an umami taste to foods, MSG was introduced as an ingredient to the United States in 1917.  Effective in small amounts, it has been widely used for years for its ability to improve palatability of foods by balancing and enhancing other flavors (e.g., sugar seems sweeter; sodium seems saltier). It is often added to soups, gravies, bouillon flavoring, and sauces. Natural glutamate, found in foods such as tomatoes and Parmesan cheese, functions similarly.
 
Although valued in ancient world cuisine for more than 2,000 years, the rich, satisfying taste of umami was not identified until about 100 years ago (Curtis, 2009, and Kurihara, 2009).  In 1908, Professor Kikunae Ikeda of Tokyo Imperial University uncovered the distinctive savory taste he found to be common to asparagus,  tomatoes, cheese, and meat, clearly different from sweet, sour, bitter and salty (Kurihara, 2009).
 
While working with a seaweed broth called kombu, a traditional food in Japanese cuisine, he identified glutamate (or glutamic acid), one of the most common amino acids in nature, as the compound responsible for umami. Amino acids are the building blocks of proteins. Thus, significant levels of glutamate are found in many plant and animal protein sources.  Examples include tomato, Chinese cabbage, walnuts, Parmesan cheese, sardines, and clams (Kurihara, 2009).  It is also found in hydrolyzed protein products such as soy sauce, and autolyzed yeast extracts. When glutamate is bound to protein, it does not produce the umami taste.  Processes like aging, drying, roasting, fermentation, toasting, or ripening foods, however, unbind the glutamate, causing the deliciousness in foods known as umami to be brought out (Red Herring, 2001).
 
Just as a sweet taste may signal the need for energy, it has been speculated that the umami taste may signal the presence of protein in food, but this idea has proven to be complex and requires additional supportive research (Beauchamp, 2009).  
 
In the human body, whether consumed naturally from foods or in the form of MSG added to foods, glutamate is absorbed and metabolized exactly the same. Further, glutamate is produced by the body, is found in high levels in breast milk, and is vital to metabolism and brain function as a neurotransmitter.  While sodium is a component of MSG, MSG contains only about one-third of the amount of sodium found in table salt on a volume-to-volume basis.  In fact, chefs, food scientists, and food manufacturers are recognizing that MSG can play a large role in reduced-sodium applications (Marcus, 2009).
 
With the safety of food ingredients in the spotlight in recent years, debate surrounding the use of MSG in foods has arisen from time to time. The scientific community and major health organizations, however, have continued to reaffirm the safe use of MSG in foods. In 1958, the U.S. Food and Drug Administration (FDA) declared MSG a Generally Recognized As Safe (GRAS) ingredient (U.S. Department of Health and Human Services, 2009). In addition, in 1987 the Joint Expert Committee on Food Additives (JECFA) of the United Nations Food and Agriculture Organization (FAO) and the World Health Organization (WHO) confirmed that MSG is safe, and the European Commission's Scientific Committee for Food agreed with this in 1991, indicating that it was unnecessary to set an Acceptable Daily Intake (ADI) level for MSG (JECFA, 1988; Commission of the European Communities, 1991). Upon reviewing the literature, the safe use of MSG in foods was again confirmed in a 1995 report to the FDA by the Federation of American Societies for Experimental Biology (FASEB, 1995).
 
A literature review conducted in 2006 reconsidered the effects of MSG and concluded that there is not consistent evidence to suggest that individuals are sensitive to MSG (Freeman, 2006).   New research published in the journal Appetite acknowledges glutamate as one of the most intensely studied food ingredients in the food supply. The authors state, “There are no consistent clinical data” to support the claim that glutamate can elicit asthma, migraine headaches, and Chinese Restaurant Syndrome (a term given to a collection of symptoms that some people experience after eating Chinese food) (Jinap and Hajeb, 2010).  Additional evidence shows that there is no link between MSG and the development of allergies, and, according to the American College of Allergy, Asthma and Immunology, MSG is not considered an allergen (Williams and Woessner, 2009; ACAAI, 1991).  Anecdotally, some individuals claim to experience sensitivities such as lethargy or headaches after consuming MSG, although studies have failed to consistently document such symptoms. Nevertheless, as with all ingredients, FDA requires MSG to be listed in the ingredients list of food products containing it (Geha et al., 2000).  Those wishing to limit MSG consumption may do so by reading food labels, although it should be noted that naturally occurring glutamate in foods does not have to be labeled.

Years of debate as to whether umami was a separate unique taste or if it simply intensified one or more of the other four tastes led to research that has clearly defined it as an independent taste phenomenon (Kurihara, 2009; Yamaguchi, 1987).  Advances in the past decades have shown that multiple taste receptors are implicated in the mechanism of umami taste perception (FASEB, 1995).  Additionally, biochemical studies have led to the identification of additional taste-active components of umami that have been shown to act synergistically with glutamate (Marcus, 2009; Kuninka, 1960; Yamaguchi, 1967; Torii & Cagan, 1980). These compounds (5’-inosinate and 5’-guanylate) are ribonucleotides that create amplified, long-lasting, dimensional taste upon interaction with glutamate. Inosinate, originally identified in fish flakes known as bonito flakes, is found only in animal food products (Yamaguchi and Ninomiya, 2000).  Guanylate occurs only in foods of plant origin (Yamaguchi, 1967). An example of umami synergy in Western cuisine is combining onions, carrots and celery (glutamate) with beef (inosinate), such as in a stew.
 
The science on umami remains cutting-edge and demonstrates implications in human health.  Researchers question whether in addition to taste, umami may also have a so-called “feeling component” often described as “fullness” (Beauchamp, 2009).   Since there are similarities between endocrine cells of the gut and taste cells of the mouth, researchers are exploring unknowns about the role of umami receptors throughout the digestive system (Beauchamp, 2009). Attempts are also being made to clarify relationships between savory taste perception, MSG, body weight, appetite regulation, and eating behavior (Donaldson, 2009; Shi et al., 2010; He et al., 2008; Maffeis et al., 2008; Kondoh and Torii, 2008). As an umami signaling factor, glutamate could be an important signaling factor between gut and brain (Uneyama, 2006; Tsukugitawa, 2009).
 
Few molecules of biological importance appear to have as many roles as glutamate does in the body. From discovering umami, our fifth taste, in the early twentieth century, to understanding how umami sensory mechanisms and physiologic pathways may have significant implications for human health, it is evident that umami will remain an integral part of cuisines around the world, promoting a rich, delicious flavor in food.
 
For a full list of the references used in this article, view the online article at FoodInsight.org.
 
For more about MSG, view the IFIC Foundation brochure Everything You Need To Know About Glutamate And Monosodium Glutamate.