Research reviewGlutamate. Its applications in food and contribution to health
Introduction
For many years, food additives have been used for flavoring, coloring and extension of the useful shelf-life of food, as well as the promotion of food safety (Rangan & Barceloux, 2009). Flavoring systems are very important in savory food manufacturing. Flavorings can play an important nutritional role, particularly in foods that are not very flavorful, by providing the needed appeal (Löliger, 2000). Foods and ingredients high in free amino acids or made up of protein hydrolysates have been used in cooking for many centuries, in many cultures, in order to enhance the sensory qualities of various foods (Bellisle, 1999). Umami taste helps improve flavor in foods, by giving meaty and savory flavors. The most closely studied flavor enhancer is monosodium glutamate, the sodium salt of glutamic acid. Glutamate is a frequently used flavor enhancer in foods, enhances the savory flavors imparted by glutamic acid, which occurs naturally in proteinaceous foods e.g. meats, seafood, stews, soups, sauces (Rangan & Barceloux, 2009). There is no precise definition for basic tastes; however they are defined by prototypical stimuli. The four traditional basic tastes are sweet, sour, salty, and bitter, and the fifth widely accepted basic taste is umami.
The natural occurring glutamate is in the form of l-glutamic acid, firstly discovered in 1866 by Karl Ritthausen, a German scientist, who isolated it from the acid hydrolysate of wheat gluten (Ritthausen, 1913). Salts of glutamic acid were first discovered in 1908 when Professor Kikunae Ikeda, a Japanese scientist identified the unique taste of umami attributed by glutamic acid; he identified umami as fifth basic taste after sweet, sour, salty and bitter in the tongue, where umami receptor taste located. Professor Ikeda, also has extracted and identified glutamic acid from soup stock prepared from konbu seaweed as the source of the umami taste, which from then, umami is described as savory, or meat or broth-like taste means delicious in Japanese (Ikeda, 1909, Ninomiya, 2001). In 1913, Kodama, isolated 5′-inosinic acid from dried skipjack as another key component of the konbu seaweed stock. In 1957, Kinoshita explored a bacterial strain Micrococcus glutamicus (later changed to Corynebacterium glutamicus) which could produce and accumulate large amounts of l-glutamic acid (Kinoshita, Udaka, & Shimeno, 1957). In 1960, Kuninaka isolated 5′-guanylate and recognized its role as key component of umami taste in the broth of dried shiitake mushroom (Kuninaka, 1960).
There have been numerous studies on umami taste and glutamate and their relation to food palatability and flavor acceptance (Baryłko-Pikielna and Kostyra, 2007, Bellisle, 1999, Bellisle, 2008, Fuke and Shimizu, 1993, Gould et al., 2008, Yeomans et al., 2008), nutritional considerations (Bellisle, 1999), presence in foodstuffs (Daniels et al., 1995, Khairunnisak et al., 2009, Mau, 2005, Nicholas and Jones, 1991, Populin et al., 2007, Skurray and Pucar, 1988), sensing in the oral cavity and gut (Burrin et al., 2008, Kurihara and Kashiwayanagi, 2000), physiological role in the food digestion (Uneyama, Gabriel, Kawai, Tomoe, & Torii, 2008), safety (Mallick, 2007, Simon, 2000, Walker and Lupien, 2000), and adverse effects (Diniz et al., 2005, Freeman, 2006, Ortiz et al., 2006). This review focuses on applications of glutamate as a food additive in food and its contribution to health.
Section snippets
Glutamate natural occurrence
Glutamate, one of the most common amino acids found in nature, is present in many proteins and peptides and most tissues. Glutamate is also produced in the body and binds with other amino acids to form a structural protein (Filer & Stegink, 1994). When glutamate bounds to protein molecule, it is tasteless and does not provide umami taste to food. However, protein hydrolysis during fermentation, aging, ripening and heat cooking process will liberate free glutamate (Yoshida, 1998). Glutamate is a
Glutamate as a food additive
Although glutamate is naturally occurring in many foods, it is frequently added as a flavor enhancer. Foods containing large amounts of free glutamate, such as tomatoes, mushrooms and cheese are traditionally used to obtain savory dishes (Giacometti, 1979, Yamaguchi and Ninomiya, 2000). When glutamate is added to foods, it provides a flavoring function similar to naturally occurring free glutamate (Yamaguchi & Ninomiya, 2000). Therefore, it is used to enhance the natural flavors of meats,
Metabolism in human body
Glutamate and disodium 5′-monoisinate (IMP) are the two amino acids that have received attention as oral stimulators of appetite and metabolism. Study by Lenjeune and Smeets (2007) showed that the addition of glutamate and IMP to a high-protein diet has a significant effect on desire to eat and no effect on energy metabolism. Adding glutamate to foods increases their umami taste quality, their acceptability and their consumption (Prescott, 2004). Study on novel savory flavors with glutamate has
Nutritional aspects
l-glutamate is a multifunctional amino acid involved in taste perception, intermediary metabolism, and excitatory neurotransmission (Kondoh, Mallick, & Torii, 2009). The oral stimulation by glutamate solution (umami taste) increases secretion of saliva and promotes mastication, and activation of the efferent pathways of the gastric and pancreatic vagal rami to facilitate gastric and pancreatic functions and to increase gastric endocrine and pancreatic exocrine and endocrine secretions
Safety evaluation and regulations
In 1958 the U.S. Food and Drug Administration (FDA) designated glutamate as a Generally Recognized As Safe (GRAS) ingredient, along with many other common food ingredients such as salt, vinegar and baking powder (USDHHS, 1958). There was general consensus in the scientific community, based on numerous biochemical, toxicological and medical studies conducted over four decades, that glutamate is safe for the general population, including pregnant and lactating women, and children (IFIC, 2003).
Safety concern
Worldwide glutamate consumption has increased dramatically in recent decades (He et al., 2008, Hermanussen et al., 2006). There was a safety concern of glutamate with respect to epidemic overweight or obesity. While there are not much published studies on glutamate intake in relation to obesity or overweight in human, a single study by He et al. (2008) from China provided human data that glutamate intake may be associated with increased risk of overweight independent of physical activity and
Conclusions
The main goal of this article was to review the benefits and role of glutamate as one of the common food ingredients used all over the world. Glutamate is one of the most common amino acids and present in many proteins and peptides and most tissues. It is a crucial component of the taste of umami or savory which contained abundantly in various foods, including vegetables, seafood, meat and cheese, and contributes greatly to the characteristic tastes of these foods. Although glutamate is
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