味精对身体是否有伤害

Is Monosodium Glutamate a Harmful Substance to the Human Body?Liu BoyuanEAPVI/CProfessor HalioJune 7, 2011AbstractMSG is widely accepted and used food enhancer; it have been discovered for over hundreds of years, and marketed all over the world. However Americans are extremely afraid of umami (MSG), even though the governments issued restrict regulations on this food additive. With the curiosity of the reason of the behavior of Americans about this additive, the harmfulness of MSG have been investigated thoroughly from the aspects of animal tests, which included tests on mice, monkeys, and pigs. In each test, there is no obvious evidence that can prove whether it is harmful or not. Also the investigation on the contaminated crystals found that which might have too many possibilities to endanger people’s lives. The basic instructions of usage had also been involved, and the illustrations of reasons of why it cannot be banned are involved.I.Basic information about MSGFor the past hundred years, people have used monosodium glutamate (MSG) for enhancing the flavor of food. However, at the same time, people have never stopped complaining and arguing about whether it is a good thing or a harmful invention. Monosodium glutamate, which is one of the most famous food additives, consists of “78.2% glutamate, 12.2% sodium, and 9.6% of water” (Myers, 2007, p. 181). The first sample of monosodium glutamate was invented by the Japanese professor, Kikunae Ikeda, of Tokyo University in 1908 (Sano, 2009). At the beginning, it was treated as a rare flavor enhancer; even someone said that it was a new flavor, besides sour, spicy, sweet, salty and bitter (Myers, 2007). The cost of manufacturing MSG was extremely expensive until 1956, when Japanese engineers found that producing MSG by bacterial fermentation would definitely save money and raise product yield (Myers, 2007). Once it reached the factory manufacturing scale, the production of MSG rose up to millions of tons a year; since that time, MSG has become a world-wide consumed, multi-functional product. The product comes mainly from the combination of pyroglutamic acid and the sodium salts of optical isomers of L-glutamic acid and D-glutamic acid (Myers, 2007). The former isomer is one of the non-essential amino acids which can be found in human body; the latter isomer does not appear in mammals’ bodies (Myers, 2007). As an essential flavor enhancer, the mixture has a unique taste that Ikeda called umami, which means delicious (Sano, 2009). The taste of umami is a little bit salty, and when it dissolves in saliva it forms a special good smell. The saltiness of umami may be due to deionized sodium ions. Pure monosodium glutamate is considerably stable at room temperature, and has a melting point at 232 degrees Celsius (Myers, 2007). However, MSG can be decomposed and reformed to pyroglutamic acid and salt under a thermo-conditionwhich is around 200 degrees Celsius (Airaudo, 1987). The reformed compound may cause some toxic effects on the human body.In 1908, Ikeda decided to figure out what is in the umami; “Within a year, he had succeeded in isolating, purifying, and identifying the principal component of umami and quickly obtained a production patent” (Sano, 2009). After that, he established a company named Ajinomoto, which aimed to manufacture MSG on a mass scale. The biggest problem was how to industrialize three processes: extraction, isolation and purification. “Because this was the first attempt to produce amino acids on an industrial scale, the absence of experience made the development process very challenging” (Sano, 2009). So Ikeda made the processes into three phases, one after the other. He started by extracting L-glutamine, which can form essential components of umami, from white gluten, which is considered full of L-glutamine, that can be hydrolyzed to L-glutamic acid (Sano, 2009). After hydrolysis, the liquid was allowed to react with hydrochloric acid to form L-glutamic hydrochloride salt, and then the salt solution took some time to crystallize (Sano, 2009). The next step was called isolation: crystals were washed with extra water until the recrystallized salts had a PH value of 3.2 (Sano, 2009). The final step was purification: the new crystals were dissolved in water and filtered; the filtered and solidified MSG was regarded as the first packaged commercial monosodium glutamate, which has a purity of roughly 85% (Sano, 2009). These kinds of processes of producing MSG were used for almost half of a century; in the mid-1950s, manufacture of MSG by bacterial fermentation was discovered by Japanese engineers. According to Myers, “In this process bacteria strains, such as Micrococcus glutamicus or Corynebacterium glutamicus, that synthesize relatively large quantities of glutamic acid are cultivated in an aerobic broth containing a carbon source, such as ammonia, ammonium salt, or urea” (2007, p. 182).Since then, MSG has become a universally produced food additive; especially in Asia, where almost every food contains this substance. According to Sona, “In 2007 the world production of MSG was estimated to be ≈2 million tons (2 billion kg), with demand continuing to increase ≈3%/y, notably in developing countries” (2009). Not only the production of MSG has been developing, but also the profit of umami has been rising. “Ajinomoto discovered MSG a century ago and last year sold $980 million worth of the flavor-enhancing white crystals, 9% of its total revenue” (Schoenberger, 2008, p. 66). However, in the U.S., the white crystals are highly unacceptable. Why are Americans so afraid of MSG? The reason is that there is a disease called ‘Chinese restaurant syndrome’. This disease causes numbness of back, neck and heart palpitations; also it causes thirst and the feeling of being hot (Myers, 2007). However, there is no conclusive evidence that can prove sickness is closely related to umami in Chinese foods (Schoenberger. 2008). In fact, it is unusual that people get into trouble with MSG. According to Myers, “FASEB concluded that only a small population of MSG-intolerant individuals and people with severe, poorly controlled asthma suffer MSG symptom complex when MSG is ingested in relatively high quantities” (2007, p. 183). The FDA still forces factories to label their products with the sign of ‘No MSG’ or ‘No Added MSG’ (Myers, 2007). Is there any relation between monosodium glutamate and adverse reactions on the human body? It is hard to say, but in Japan, even patients who have some sensitivity to umami eat more food when MSG is added (Schoenberger. 2008). In contrast, MSG might have some benefits on controlling obesity by fooling the brain, and making a wrong judgment on fullness. In 2008, Schoenberger said that “Maybe inserting glutamate into a head of broccoli would make kids think they were eating a cheeseburger” (p. 66).II.Investigations on harmfulness effectsIn order to find out the relationship between MSG and its harmfulness on the human body, scientists have been conducting lots of tests and experiments on animals which include mice, monkeys and pigs; these animals give a kind of reference on humankind. According to Filer (1997), in two years, a mouse treated with the white crystals that weighed four percent ofits total mass per day, compared with one that was fed 1-2% w/w a day, showed no abnormalities. In addition, there were no significant mass differences between the two (Filer, 1997). So these finds may indicate that under a normal intake conditions, umami is not harmful to the body and it will not cause weight gain. However, what will happen if monosodium glutamate intake exceeds safe condition? According to Filer (1997), a baby mouse fed superfluous MSG became fatty, and when the mouse reached its adulthood, it had some sorts of malfunctions in its body. “Pizzi et al.(31) gave MSG at dose levels of 2.2 to 4.2 g/kg on days 2 to 11 after birth. When these animals became adults, reproductive dysfunction was seen in both sexes” (Filer, 1997, p. 205). “RECENT reports have implicated monosodium glutamate (MSG) in neuronal damage of the central nervous system [12, 19, 20, 21, 22, 23, 24]” (Pizzi, 1975, p. 1). Serious damage to the brain, such as nervous system desensitization, which induces a delay of response in its limbs, was seen in mice that consumed MSG as mentioned by Onley (1969). Such evidence may arouse public attention about the amount of white crystals in the food for infants which can potentially cause damage in babies. However, some studies on monkeys, which have a relatively closer relationship with humankind, for the same issue, show a totally reversed situation compared with mice. It might be a good thing to know that the monkey is quite tolerable of monosodium glutamate, because such species are highly genetically comparable to humankind.In the monkey’s situation, baby monkeys fed with an enormous amount of MSG for two months and a week, showed no differences compared with monkeys that were not fed MSG (Filer, 1997). “feeding 9.1% MSG formula for 1 year to an infant cynamolgus and an infant bush-baby monkey had no effect when compared with two control infant monkeys” (Filer, 1997, p. 205). This probably shows that having monosodium glutamates in the body reasonable conditions would not have any bad effects. However this does not mean that accumulated glutamates in body will not induce damage to the brain and tissues in the long term. According to Filer (1997), infusion of a great amount of concentrated MSG solution into a monkey will cause death within three hours. In this experiment, the decomposition ability of the body failed to protect from the excessive umami; therefore, accumulated white crystals in the body highly challenge the metabolism of human organisms.When it comes to pigs, scientists try to figure out the neural taxability by mixing MSG into pig foods with a ratio of one gram to one kilogram of its mass. (Stegink, n.d). In this experiment, they found out that a relatively smaller amount of umami is likely to be converted into other amino acids like alanine, which is one of the most commonly recognized amino acids in the human body; finally, these amino acids are either used as ATP-energy for cells or disposed in urea. (Stegink, n.d). “This observation indicates that the liver normally converts glutamate into other metabolites” (Stegink, n.d, p. 1151). Therefore, it can be concluded that using umami as a food enhancer, under a tolerable range for humans, in a non-successive way, will definitely reduce the harmfulness of the body to the minimal amount, which would be considered as a safety and healthy choice; in such conditions, the user will be able to avoid the cumulative effects of monosodium glutamates, which include lesions of the brain, central nervous system,tissues and reproductive organs. At the same time, people would be pleased by the mild flavor of MSG.It seems that umami has many potential bad effects on the human body. Why do governments around the world do not ban it? The reasons are that there are no obvious connections between MSG and sickness of the body, and the great amount of consumption also makes it such a world-wide famous food additive that the political officials are so afraid that publicity of uncertain information would induce a panic among monosodium glutamate users. Besides the fear of the panic, there is also a large amount of tax money coming from the producers of MSG. It is acknowledged that there are more than 6 billion people on the earth and the majority of the population is occupied by Asians, who regard MSG as an essential food additive. They use umami every day when they are trying to prepare most foods. The great consumption power brings numerous amounts of taxes to the government.There are purchases, so there are usages. Sometime consumers buy the MSG, but they do not know how to use it. The cautions of utilizing the white crystals include the amounts per dish and the time to add. Usually it is regarded that the concentration of monosodium glutamate aqueous solution, which has flavor properties, varies from 4 × 10-5 to 4 × 10-3 M (Filer, 1997). This means that even 1g of umami dissolves in roughly 1.5 cubic meter of water would still have flavor. “The absolute threshold for MSG was found to be 6.25 × 10-4 M” (Filer, 1997, p. 43). Therefore, the user does not need to put too much umami into food to make it taste good. According to experience that, to enhance the flavor of a meat dish, approximately half a tea spoon of MSG is enough; to enhance the flavor of a vegetable dish, around one or one and a half tea spoons of umami is adequate. There is something that is worth the consumer’s attention, which is using MSG in a non-consecutive method; the method means not adding umami intodishes in a periodical way. As for when the white crystals should be put in dishes, there is an possible explanation that umami should be involved in dishes when the food is well- done and removed from the heat supplier, which means it would not be decomposed and converted into pyroglutamates, which would do more than just ruin the flavor of foods.Besides the possible toxicity found from animal tests, there are also some possibilitiesthat the decomposed and reformed pyroglutamates from glutamates in a certain thermo-condition may have poisonous properties. “In the autoclaving processing, the solutions were heated to 135 ℃under 2.7 kg/cm2 pressure in screw-top glass bottles with bakelite caps and Teflon® seals (“SVL” ®, France). Conversion products were determined only after 30 min processing”(Sorbier, 1985, p. 350). It is showed that MSG under such temperature can be converted into pyroglutamates within half an hour. This issue indicates that use umami during cooking the thermal energy in pot may cause a breakdown of its bond, and it will probably reform to pyroglutamates. According to Soriber (1985), the speed of changing MSG into pyroglutamate was influenced by the pH values of the environment, where the extraordinary acidity condition accelerated the speed of the reaction; it showed that the fastest speed was found in the conditions of the pH values between2 and 3, despite other conditions such as temperature and oxygen. This result showed that the MSG user may find that the flavor of dish is changed when the vinegar is involved in cooking. Therefore it should be managed that either amount of umami could be raised or the amount of vinegars should be controlled, when cooking is involved, in order to maintain the good taste. Besides the influence on flavor of foods, pyroglutamate also has some toxic effects on the human body. In taking of too much pyroglutamates formed from decomposition of monosodium glutamate may induce denature of enzyme, which functioning asa catalytic bio-chemicals, also take part in metabolism in the body (Suzuki, 1999). This thing should attract users’ attention oncontrolling the amount of MSG used in dishes. According to Sorbier (1985), white crystals exposed in air for a longtime, will cause a slowly change toward to pyroglutamates; the salts will finally become a toxic contaminated additives, which would defiantly influence the health on the human body. Some people may suggest that it is good to seal the plastic bag, which has umami in it, would reduce the amount of contaminated crystals, which are formed by oxidation. Actually, the possibility of receiving damage from the mixture of monosodium glutamate and pyroglutamate is not high. However, the possibility of receiving damage from incurious cooking is higher compared with former.In conclusion, in this paper, the information about the background, the chemical property, the supply and demand of MSG is investigated. Also there is lots of potential toxicity of umami had been found though the studies of animal experiments and the research of converted product. Therefore, it can be concluded that the umami is not harmful to the priorities of conditions that using umami in a bearable range of humans, in a non-consecutive way, in a caution of avoid oxidation.ReferencesAiraudo, C. B., Sorbier, A. G. & Armand, P. (1987). A Research Note Stability of Glutamine and Pyroglutamic Acid under Model System Conditions: Influence of Physical andFood Science, v.52(n.6), p.p. 1750-1752.TechnologicalFactors.Chen, G. & Russell, J. B. (1989). Transport of Glutamine by Streptococcus bovis and Conversion of Glutamine to Pyroglutamic Acid and Ammonia. 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