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Wageningen University, 2003
Foods have two main functions, i.e. they provide nutrition and an occasion for a pleasurable social event. Both functions are fulfilled only if a food is actually consumed. A food composed of the nutritional elements required for an optimal diet that is unattractive and thus not consumed provides no nutrition. Flavouring systems are of vital importance in savoury food manufacturing. Many industrially prepared foods are particularly attractive to potential consumers primarily because of their typical flavours. Therefore it's no surprise that the food industry dealing with these product segments shows great interest in the use of food or food ingredients carrying the typical umami taste and flavour enhancement systems. Flavourings can play an important nutritional role, particularly in foods that are not very flavourful, by providing the needed appeal (Löliger, 2000).
Monsodium glutamate also known as MSG, Ve-tsin or E621 is a frequently used flavour enhancer in foods. Originally it comes from the Far East, but nowadays it is used in many products. Monosodium glutamate is a controversial additive. Many people claim health problems after eating MSG, on the other hand clinical studies give no reason for concern.
The aim of this report is to give an accurate overview of the knowledge on monosodium glutamate examining scientific literature and reviewing MSG claims on the internet.
In chapter 2 a general explanation on monosodium glutamates will be given, describing what monosodium glutamate is and the function and use of monosodium glutamate in food. In chapter 3 a safety evaluation of monosodium glutamate will be made as reported in scientific literature.
In chapter 4 the influence of MSG labelling on consumer ratings will be described and consumer claims as found on the internet will be described. In the conclusion a balance of the perceptions found in the previous chapters will be summarised.
Monosodium glutamate (MSG) is the sodium salt of the amino acid glutamic acid (Figure 1, Löliger, 2000). Glutamic acid or glutamate is one of the most common amino acids found in nature. It is the main component of many proteins and peptides, and is present in most tissues. It is made commercially by the fermentation of molasses, but exists in many products made from fermented proteins, such as soy sauce and hydrolysed vegetable protein. Glutamate is also produced in the body and plays an essential role in human metabolism (IFIC, 1994) .
Figure 1. Chemical structure of Monosodium Glutamate (Löliger, 2000).
Virtually every food contains glutamate. It is a major component of many protein-rich food products such as meat, fish, milk and some vegetables. However, only the free form of glutamic acid or glutamates has an effect on the glutamate receptors. When bound to other amino acids in a protein, it does not stimulate glutamate receptors. They become partially free during processing, thereby accentuating their characteristic flavour properties (Löliger, 2000).
The level of glutamates and free amino acids increases considerably after ripening or seasoning of certain foods. Especially certain cheeses (such as Parmesan cheese) due their taste and texture to long ripening, which increases the presence of amino acids (among which glutamate). Free glutamates exist in certain cheeses, in tomato products, and in soy sauce. These products are often used to enhance the flavour of meat dishes. Proteins can be hydrolysed by heat, releasing free glutamates. Cooked meats, especially grilled meats, get some of their taste from free glutamates. In table 1 an overview is given of the natural glutamate content of fresh food (mg/100g food), present in the bound form to a protein (Institute of Food Technologists, 1987).
Table 1 . Natural glutamate content of fresh food. The values are expressed in mg/100g food (Institute of food technologists, 1987)
The tongue is sensitive to five flavours -- salt, sweet, bitter, sour, and " umami ” in the Japanese language, the taste of MSG. There is no analogous word to describe this taste quality in the English language. “Umami” is used by the Japanese to describe the taste of MSG as well as the meaty taste of certain fish and broth (Schiffman, 2000). The substances which constitute the umami taste can be divided in two main groups: one is the a-amino acid group, represented by monosodium glutamate and the other is the 5'-nucleotid group, represented by inosine 5'-monophosphate (IMP) and guanosine mono phosphate (GMP) and their derivatives (Papi, 2003).
Food palatability increases with appropriate concentrations of MSG (Halpern, 2000).
The basic sensory function of MSG is attributed to its ability to enhance the presence of other taste-active compounds. Foods containing MSG have a typical salty taste, because it contains 12.3 % sodium (e.g. one third of table salt). The detection threshold for MSG is 6.25 x 10 -4 mol/L, which interestingly is higher than for bitterness or sourness, and lower than that for sweetness and about equal to that for saltiness. In general, the usage level of MSG in savoury foods is approximately one tenth that of salt; thus the sodium contribution of MSG is roughly one thirtieth of the total added sodium. By adding MSG appropriately, the sodium chloride addition could be reduced by 30-40 % while maintaining the same perception of saltiness. Results of taste panel studies on processed foods indicate that an MSG level of 0.2-0.8 % of food by weight optimally enhances the natural food flavour (Löliger, 2000).
Healthy eating is essential for maintaining a good quality of life, especially in an ageing population.
Amplification of flavour and taste with MSG can improve food palatability and acceptance, increase salivary flow and immunity, and reduce oral complaints in both sick and healthy elderly. Flavours increase the number of molecules that interact with receptors and compensate for chemosensory losses. MSG adds an additional taste but does not enhance any other tastes (Schiffman, 2000).
Bellisle et al. (1996) suggest that adding MSG (at some optimal dose) to nutritionally valuable foods would represent a means that everyone could use in order to selectively develop a preference for this food or to enhance its intake of other foods (that is without increasing total energy intake). Individuals as well as the food industry might want to use this effect of MSG in order to selectively orient food choices toward nutritionally rich foods (Bellisle et al ., 1996).
MSG is used to give a "meaty", "savoury", or "brothy" taste to foods by stimulating the glutamate receptors on the tongue. There are glutamate receptors in other parts of the body, notably the brain, where glutamate is a neurotransmitter.
Flavours probably exert their effect by increasing the number of molecules that interact with receptors on chemosensory membranes in the nose and oral cavity. This intensification of chemosensory stimulation induces more salivation, produces greater stimulation of the olfactory and limbic system of the brain and promotes immune function (Schiffman, 2000).
MSG (with or without 5'-ribonucleotides) likely exerts its effect by adding another taste quality to the food, i.e. umami, which improves palatability (Bellisle et al ., 1991). Neither MSG nor 5'-ribonucleotides appear to exert their effect by altering the perceived intensity of other components of food or altered the intensities of salts, sweeteners, amino acids or bitter compounds (Schiffman, 2000).
However, free glutamate, as found in soy sauce or prepared foods, enters the bloodstream much faster than the glutamates bound in proteins, where they are released slowly during digestion.
In table 2 the average daily intake of monosodium glutamate (g/d) is reported for several countries. The average consumption of MSG in the diet is highest for Korea of all reported counties at 1.57 g/d.
In general the consumption is higher in the oriental countries than in the western countries. This is due to traditional oriental cooking which uses a lot of condiments to supplement, enhance of round-off the flavours of many savoury-based processed foods, with for example soy sauce (Löliger, 2000).
Table 2 . Daily intake of monosodium glutamate (Institute of Food Technologists, 1987)
Knowing the beneficial contribution of glutamate to many savoury flavours, it is not at all surprising that industrial processes take advantage of the rather high natural glutamate concentrations of some vegetables in the production of vegetable protein hydrolysates. These hydrolysates contain considerable amounts of free glutamic acid (sodium glutamate), e.g. traditional soy sauce (Löliger, 2000). Today's soy sauce is the product of thousands of years of development. This age-old discovery is understood today and it is used to enhance the pleasure of eating industrially processed food (Löliger, 2000).
In 1958 the U.S. Food and Drug Administration (FDA) designated MSG as a Generally Recognised As Safe (GRAS) substance, along with many other common food ingredients such as salt, vinegar and baking powder.
Consumers continue to have questions regarding MSG's safety and efficacy. However, there is general agreement in the scientific community, based on numerous biochemical, toxicological and medical studies over the last twenty years, that MSG is safe for the general population, including pregnant and lactating women, and children (IFIC, 1994).
The Joint FAO/WHO Expert Committee on Food Additives (JECFA), was established in the mid-1950s by the Food and Agricultural Organisation of the United Nations (FAO) and the World Health Organisation (WHO) to assess the safety of chemical additives in food on an international basis.
The JECFA studies put their attention to a possible neurotoxicity of MSG, especially in children and to the pathology called the Chinese Restaurant Syndrome. In relation to neurotoxicity, the Committee considered reports of 59 studies conducted in mice, rats, hamsters and other animals. Lesions in the arcuate nucleus of the hypothalamus were observed reproducibly in rodents and rabbits after intravenous or subcutaneous administration of MSG. These neural lesions were observable within hours of administration. Notably most studies in primates were negative with regard to hypothalamic lesions. The oral doses required to produce the lesions were on the order of 1000-mg/kg-body weight, and in only one study were lesions seen after "voluntary" ingestion of MSG. In that case, the mice were deprived of food and water overnight, and then given solutions containing 5 or 10 % of MSG as the sole drinking fluid. No such lesions were seen when MSG was given at 10 % of the diet even though plasma glutamate levels were doubled, nor after administration at high concentrations in drinking water ad libitum (Walker and Lupien, 2000).
The "Chinese Restaurants syndrome" takes its name because it generally occurs after ingestion of Chinese foods. As responsible of this illness glutamate has always been indicated, because of its frequent use in Chinese cuisine and it was suggested that there might be idiosyncratic intolerance in some individuals. Symptoms include broncho-constriction in asthmatics. However, controlled double -blind crossover studies have failed to establish a relationship between Chinese Restaurant Syndrome and ingestion of MSG, even in individuals reportedly sensitive to Chinese meals and asthmatics (Walker 1999). Stevenson (2000) concluded from several studies that no MSG-induced asthma, even in history positive patients has been established.
Geha et al . (2000) conducted a double blind placebo controlled study in 130 subjects to analyse the response of subjects who report symptoms from ingesting MSG. The results suggested that a large dose of MSG given without food might elicit more symptoms than a placebo in individuals who believe that they react adversely to MSG. However, the frequency of the responses was low and the responses reported were inconsistent and were not reproducible. The responses were not observed when MSG was given with food (Geha et al ., 2000).
After many years of evaluations and meetings the JECFA decided in 1987 that monosodium glutamate (MSG) was allocated with an "ADI not specified". This indicates that no toxicological concerns arise associated with its use as a food additive in accordance with good manufacturing practice (GMP). For that reason it is not necessary to allocate a numerical ADI (Walker, 1999). In 1991 the European Community's Scientific Committee for Food (SCF) confirmed the safety of MSG and came to the same conclusion that specification of an ADI was unnecessary (IFIC, 1994).
A subsequent review by the Federation of American Societies for Experimental Biology (FASEB) and the federal Drug Administration (FDA) came to the same safety conclusions as the JEFCA (Walker and Lupien, 2000).
During the past three decades, there has been substantial controversy regarding the use of MSG in foods, at least in Western countries. The original source of this controversy appears to be a letter to the New England Journal of Medicine (Kwok, 1968) in which it was speculated that MSG (as one alternative among several other ingredients) could be the cause of adverse reactions following consumption of Chinese restaurant food. This article and subsequent publicity about MSG seems to have tapped into more general consumer concerns regarding food additives, resulting in an increasingly widespread belief among consumers that MSG is responsible for allergic reactions, variously asthma or "Chinese restaurant syndrome" of numbness, weakness, headaches and palpitations (Prescott and Young, 2002). However, as discussed in the previous chapter, no evidence in studies is found implicating MSG as a cause of these or other adverse reactions (Geha et al ., 2000).
Nevertheless, and despite the fact MSG is often required to be included among the list of food ingredients, many food manufacturers have increasingly adopted a strategy of placing additional prominent messages regarding MSG on food labels. As a result, food labels advertising "No added MSG" have become commonplace. One possible consequence of such labels is that they generate and reinforce beliefs that MSG is harmful and/or an unsafe ingredient. Recent research on the effects of different types of label information suggests the possibility that these messages may also influence the acceptability of products containing added MSG. Prescott and Young (2002) examined the impact of information specifying the addition of MSG to foods or not on ratings of the hedonic and sensory properties of soups. In addition they measured the beliefs and attitudes towards MSG in foods with a view to provide a context within which any effects could be interpreted. The attitudes towards MSG were evaluated and found to be generally negative. To assess the impact of information about MSG content, subjects evaluated saltiness, richness, natural taste of and liking for, vegetable soups with (MSG +) and without (MSG -) added MSG. Subjects tasted both soups under three information conditions, presented as an ingredient list: contains added MSG, or not, or no mention. The expected changes in liking and sensory properties due to MSG were found, but there were no effects of information. This suggests that sensory properties are weighted more than information when products are evaluated during tasting, even when the information is highly relevant (Prescott and Young, 2002).
The aim of literature research was to give an overview of the current knowledge of MSG, and evaluate its danger and consumer attitudes.
Monosodium glutamate is the sodium salt of the amino acid glutamic acid. It is a major component of many protein-rich foods such as meat, fish, cheese, milk and some vegetables. However, only the free form of glutamic acid of glutamates has an effect on the glutamate receptors.
The taste quality of MSG is described as umami and is considered as the fifth flavour after salt, sweet, bitter and sour. Food palatability increases with appropriate concentrations of MSG, but MSG is also able to enhance the presence of other taste-active compounds. This amplification of flavour and taste with MSG can improve food palatability and acceptance among elderly and sick people, thus contributing to a healthy diet.
MSG gives its meaty/savoury/brothy taste to foods by stimulating the glutamate receptors on the tongue and other parts of the body.
In general consumption of glutamates is higher in oriental countries than in western countries due to the traditional oriental cuisine which uses a lot of condiments as soy sauces. Today the use of glutamates is also used to enhance the flavours of industrially processed foods.
In the western countries there has been a lot of concern about possible adverse reactions towards monosodium glutamates. Adverse reactions would include the Chinese Restaurant Syndrome (broncho-constriction in asthmatics), taking its name because it occurs often after eating Chinese, and neurotoxicity in children. Therefore monosodium glutamate has become one of the most intensively studied food ingredients. After intensive studies, the JECFA (Joint Expert Committee on Food Additives of the United Nations) placed it in the safest category of food additives. Later both the SCF (Scientific Committee for Food) and the FASEB (Federation of American Societies for Experimental Biology) came to the same conclusions. Therefore MSG does not have an ADI.
Despite the proved safety of MSG consumer attitudes towards MSG are found negative generally. While tasting products with the knowledge they contain MSG, the sensory properties did not change.
Looking on the internet many claims against MSG can be found, varying from cardiac, neurological to respiratory complaints.
It can be concluded that MSG can be considered as a safe food enhancer, but more should be done to inform consumers.
Bellisle, F., Monneuse, M.O., Chabert, M., Laure-Achagiotis, C., Lantaume, M.T., Louis-Sylvestre, J. Monosodium glutamate as a palatability enhancer in the European diet. Physiology and Behaviour 1991 , 49 , 869-874.
Bellisle, F., Dalix, A.M., Chappuis, A.S., Rossi, F., Fiquet, P., Gaudin, V., Assoun, M., Slama, G. Monosodium glutamate affects mealtime food selection in diabetic patients. Appetite 1996 , 26 , 267-276.
Geha, R.S., Beiser, A., Ren, C., Patterson, R., Greenberger, P.A., Grammer, L.C., Ditto, A.M., Harris, K.E., Shaughnessy, M.A., Yarnold, P.R., Corren, J., Saxon, A. Review of alleged reaction to monosodium glutamate and outcome of a multicenter double-blind placebo-controlled study. Journal of Nutrition 2000 , 130 , 1058S-1062S.
Halpern, B.P. Glutamate and the flavour of food. Journal of Nutrition 2000 , 130 , 910S-914S.
IFIC. Review on Monosodium Glutamate:Examining the Myths 1994
Website: http://www.geocities.com/HotSprings/2455/ir-msg.html visited 4 March 2004
Institute of Food Technologists' Expert Panel on Food Safety and Nutrition. Monosodium Glutamate. Food Technology 1987 , 41 , 143-145.
Kwok, R.H.M. Chinese-restaurant syndrome. New England Journal of Medicine 1968 , 278, 796.
Löliger, J. Function and importance of glutamate for savory foods. Journal of Nutrition 2000 , 130 , 915S-920S.
Papi, T. sostanze umami: il glutammato monosodico chapter 3 of thesis: Umami il quinto gusto e prodotti ittici.
Website: http://xoomer.virgilio.it/giancarlo.papi/sostanze_MSG.pdf visited 4 March 2004.
Prescott, J., Young, A. Does information about MSG (monosodium glutamate) content influence consumer ratings of soups with and without added MSG? Appetite 2002 , 39 , 25-33.
Schiffman, S.S. Sensory enhancement of foods for the elderly with monosodium glutamate and flavors. Food Reviews International 1998 , 14 , 321-333.
Schiffman, S.S. Intensification of sensory properties of foods for the elderly. Journal of Nutrition 2000 , 130 , 927S-930S.
Stevenson, D.D. Monosodium glutamate and asthma. Journal of Nutrition 2000 , 130 , 1067S-1073S.
Walker, R., Lupien, J.R. The safety evaluation of monosodium glutamate.
Journal of Nutrition 2000 , 130 , 1049S-1052S.
Walker, R. The significance of excursions above the ADI Case Study: Monosodium Glutamate. Regulatory Toxicology and Pharmacology 1999 , 30 , S119-S121.
Websites with internet claims against MSG:
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