味精:百年前, 池田夫人的秘方

Stephen Hiew  丘志祥

stephen thumbnailEarly chefs in Chinatown had given MSG the nickname of “shi fu”, the venerable title for a master or teacher.

早期在倫敦唐人街的大廚師,給味精起了「師傅」的稱號。

 

 

English

 

As a young student of medicine around 1980, I was bemused to learn of an illness known as Chinese Restaurant Syndrome. Apparently following Chinese food, some diners suffer from chest pain radiating to their arms, sweating, palpitations and general weakness. These are similar to symptoms of a heart attack and created panic, but are usually short lived and leave no lasting harm.

The syndrome was first described in 1968 by Dr Robert Ho Man Kwok in the respected New England Journal of Medicine. Similar reports soon followed suit and suspicions fell upon Monosodium Glutamate (MSG), a common ingredient of Chinese restaurant food. The reaction to MSG begins in 10 to 25 minutes and lasts from 45 minutes to 2 hours. Researchers noted that the amount of MSG that may be consumed before unpleasant effects set in varies widely from one individual to the next. The ballpark figure was estimated at five grams –ordinary dishes would contain sufficient quantities. The syndrome is diagnosed by enquiry about the symptoms. Most sufferers do not require treatment and do not have permanent effects.

Interestingly, Dr Kwok added that he had never experienced such a problem in his native China. Various surveys in North America have shown between 1 to 7 per cent of population are affected by this syndrome. However successive researchers have been unable to pinpoint MSG as the cause.

As the name implies, monosodium glutamate is formed from processed free glutamic acid (78%) and sodium salt (22%). The processed free glutamic acid is responsible for the unpleasant reaction. Glutamic acid is an amino acid – a building block for proteins – that occurs naturally in foodstuffs such as vine-ripened tomatoes, mushrooms and crab. Many proteins are inherently tasteless, but when fermented the amino acids produce various tastes, such as in soy sauce, cheese and anchovies.

The tastes of ordinary meat, poultry and fish come from various amino acids which include glutamic acid. In addition to the four basic tastes – sweet, sour, salty and bitter – a fifth taste has been recognised as “umami”, a broth-like or savoury taste. Umami has been revisited in the Sunday Times by the renowned chef Heston Blumenthal: “It’s a bit like introducing a new colour that we have been looking at all our lives but never recognised before.”

Most meats consist of 11 to 22 per cent by weight of glutamic acid. The butcher’s art of dry ageing steaks releases glutamic acid and another compound called inosine monophosphate (IMF). The particular flavours of different meats are accounted for by varying proportions of glutamic acid and IMF.

Condiments in Chinese cooking such as soya sauce and yellow bean sauce also owe their flavour to fermentation that produces glutamic acid. Besides Chinese food, MSG can be found in sauces, soups, gravy, pre-cooked meals and dried foods. According to an American physician George Schwartz, MSG is the third most popular spice – after salt and pepper – it is present in over two hundred and fifty ordinary items stocked by supermarkets.

MSG is said to make food flavours more intense, and enhance the taste of meat in particular. However, this effect reaches a ceiling at 60mg/kg. Concentration higher than this level makes food less palatable.

MSG was discovered just over a century ago. In 1908, Professor Kidunae Ikeda (池田菊苗), a biochemist at Tokyo Imperial University, was served a vegetable and tofu soup by his wife. Scientific curiosity prompted him to ask her about the secret behind such a delicious broth. His wife simply showed him dried seaweed, a heavy kelp called kombu. Ikeda eventually identified that the seaweed contains glutamate and that this produces the umami taste. The secret ingredient was born and quickly became popular.

Professor Ikeda found that meat, tomatoes as well as seaweed owe their flavours to one factor in common. In particular, Japanese seaweed or kombu has a high concentration of glutamate, about 1000mg per 100g.

At the time, a businessman named Saburo Suzuki (鈴木三朗助) was trying to extract iodine from kelp. On hearing about Professor Ikeda’s discovery, he was inspired to produce glutamate instead. Suzuki and Ikeda realised that the 0.1-0.2 grams they could extract from 10 kg of kelp was not commercially viable. They turned to the much cheaper soybean and wheat which also contained glutamate. Soon, the product Ajinomoto (meaning ‘element of taste’) was launched.

Glutamic acid dissolved in the form of glutamate gives rise to the umami taste. Salt forms such as monosodium glutamate dissolve more easily than glutamic acid crystals, which make them ideal flavour enhancers.

Interestingly, human breast milk also contains high levels of glutamate – ten times that of cow’s milk. Experts believe that the umami flavour, as well as the sweet taste of lactose, entices babies to feed.

Concerns were raised about the safety of MSG after scientists found that young animals that had MSG in their diets developed brain abnormalities, causing hormonal imbalance and obesity. This led to the exclusion of MSG from baby food in the 1970s.

Many rumours abound concerning effects of MSG – it stops children’s skeletons growing, causes hair to fall out, turns cola or beer into aphrodisiac, or predisposes men to produce male offspring.

Actually, the human body normally contains an amount of glutamate, and in fact depends on glutamate for conducting commands in the nervous system and for memory. Some scientists worry about over-stimulating the brain by ingesting large quantities of MSG in a single meal.  However, scientific studies led by Dr Andrew Saxon of  the Allergy and Immunology Department at University of California found no connection between the Chinese restaurant syndrome and MSG.

The term ‘food additive’ often raises anxiety among consumers. The United States Food and Drug Administration has registered over three thousand additives. In fact, many of these are everyday ingredients such as spices, yeast and vanilla. Some items are regulated more tightly than others. MSG belongs to the category GRAS (generally recognized as safe), and its usage is exempt from control. 

A contrary view is that MSG may actually resolve a health problem. People are often advised to cut down on their salt intake. Experiments have found that a soup becomes tasty only when salt concentration reaches a certain level. With addition of MSG, salt usage can be reduced by two-fifths.

Glutamic acid was known during the Roman Empire, when salted fish was fermented into a sauce. This flavour enhancer helped Romans save consumption of precious salt. (Wikipedia)

Within the European Union, food labelling law requires ingredients to be listed, either by name (MSG or glutamic acid) or by their E numbers (E620 to E625). The EU also prohibits addition of MSG to certain products such as milk, fruit juice and chocolate.

Many consumers believe that MSG is a synthetic chemical and harmful, whereas chicken stock cubes are manufactured from chicken meat and nutritious. During the Beijing Olympics in 2008, the Brazilian team specified that their meals be free of MSG. In fact, chicken stock often contains up to 40% MSG as well as other flavourings.

Experienced chefs have revealed several taboos when using MSG:
• High temperature – temperatures above 90oC cause chemical change in MSG which may become toxic. Hence it is best to add MSG just before cooking is completed. For the same reason, it is not a good idea to add MSG to marinades.
• Low temperature – MSG does not dissolve well in cold water, to use on chilled dishes it should first be dissolved in warm water.
• Alkaline foods – MSG undergoes chemical change in alkaline solutions to produce an odorous substance, and thus is unsuitable for alkaline food such as preserved cuttlefish.
• Acidic foods – MSG cannot dissolve properly in acidic liquids.
• Sweet dishes – MSG will suppress the sweetness and result in an unpleasant taste.
• Overuse – Excessive amount of MSG results in a salty and bitter flavour.
• Eggs – Eggs themselves contain abundant glutamic acid, which combines with cooking salt to become MSG. Additional MSG is unnecessary and may worsen the taste.

The Chinese method of MSG manufacture was invented during the heady days of Shanghai in 1921. A chemicals entrepreneur Wen-Chu Wu (吳蘊初) discovered a process of producing glutamate from gluten, and called it wei-jing (味精), meaning essence of taste. His MSG factory in Hong Kong and its products have been well known for over 70 years.

MSG is such a major industry that recently the Hong Kong Customs and Excise exposed an illicit factory with 1,400 sacks of counterfeit  MSG.

Early chefs in Chinatown had given MSG the nickname of “shi fu”, the venerable title for a master or teacher. In their view, without the master’s presence not much could be achieved. A number of restaurants now declare that their menus are free of MSG. Experienced cooks are of the opinion that their clientele have been accustomed to a certain taste, and may find the dishes lacking in flavour if MSG were totally withdrawn. However, some chefs have replaced MSG with stock cubes or bouillon.

In 2007, the Michelin-starred chef Marco Pierre White caused a stir by admitting that he also used stock cubes in his recipes.

It seems therefore, while Chinese restaurant syndrome has gone, MSG or its derivatives are here to stay!

London, October 2011

 
Bibliography

Ajinomoto_Co_Inc. (2003). Amino acids are what deliciousness is all about. Encyclopedia of amino acids.
Castleman, M. (1988). Beyong Chinese restaurant syndrome. Point Reyes: Los Angeles Times.
Daniels, D., Joe, F., & Diachenko, G. (1995). Determination of free glutamic acid in a variety of foods by high performance liquid chromatography. Food Additives and Contaminants, 21-29.
EUFIC. (n.d.). The facts on monosodium glutamate. Food Today.
Fahmy, A. (1997). Diet, Drink and Disease. London: Minerva Press.
Gore, M. E., & Salmon, P. (1980). Chinese restaurant syndrome: fact or fiction? The Lancet, 251-252.
International_Glutamate_Information_Service. (2011). Biography of Professor Ikeda.
Kenney, R. (1986). The Chinese restaurant syndrome: an anecdote revisited. Food and Chemical Toxicology, 351-354.
Lucas, D., & Newhouse, J. (1957). The toxic effect of sodium L-glutamate on the inner layers of the retina. AMA Arch Ophthal, 193-201.
McDermott, N. (2007). Chef Marco reveals his stock in trade -the Knorr chicken cube. Daily Mail.
Monti, P. (2007). Monosodium glutamate, the molecule that enhances taste in food. Molecule of the month.
Olney, J. (1969). Brain lesions, obesity and other disturbances in mice treated with monosodium glutamate. Science, 719-721.
Parkinson, R. (n.d.). Monosodium glutamate (MSG) -pros and cons. About.
Renton, A. (2005). If MSG is so bad for you, why doesn't everyone in Asia have a headache? The Observer.
Schaumburg, H., & Byck, R. (1968). Sin cib-syn: accent on glutamate. N Engl J Med, 105.
Smith, P. (2010, 3 19). Don't be scared of MSG. Food.
Taliaferro, P. J. (1995). Monosodium glutamate and the Chinese restaurant syndrome: a review of food additive safety. Journal of Environmental Health, vol 57.
US_Food_and_Drug_Administration. (2010). Food ingredients and colors. International Food Information Council (IFIC).
Vitrag. (2009). Chinese restaurant syndrome. MedicalGeek.
Warrell, D. A. (2010). Oxford Textbook of Medicine. Oxford: Oxford University Press.
Webster-Gandy, J., Madden, A., & Holdsworth, M. (2006). Oxford Handbook of Nutrition and Dietetics. Oxford: Oxford University Press.
Wikimedia_Foundation. (2010). Kikunae Ikeda. Wikipedia.
Wikipedia. (n.d.). Glutamic acid (flavor).
Wordwide_Health_Centre_Net. (2007). Monosodium glutamate: Poison the body to better the taste.
保山衛生. (2011). 雞精和味精的區別. bswsjd.gov.cn.
南京晨報. (2006). 兩男子自製催情藥. 南京晨報.
卡妙. (2010). 味精的七大禁忌. djjk.cn.
小倪. (2010). 發明味精的有趣故事. healthy.4738.com.
小天使. (2010). 可樂加味精 -配置春藥. LaluLalu.com.
康易網. (2007). 兒童食用味精過多難長高?. 39.net.
文匯報. (2008). 香港天廚上世紀30年代土瓜灣廠房. WenWeiPo.com.
曉娟. (2011). 探討味精吃多與掉髮之間的問題. jdzol.com.
清晨. (2000). 科學實驗證明吃味精和過敏沒有關係. sina.com.cn.
瀋陽晚報. (2008). 瀋陽奧運村趣聞. Xinhuanet.
王琛. (2010). 味精廠男員工都生兒子. blog.sina.com.cn.
生果日報. (2010). 製冒牌天廚味精 10人落網. news.hotpot.hk.
芝蘭健康網. (n.d.). 中國餐館症候群. Cheeryland International Inc.

 

繁體

 

1980 年代在大學醫學院,讀到一個名詞令我十分驚訝。所謂「中国餐館症候群」(Chinese Restaurant Syndrome),是形容某些食客在中餐廳用膳後,出現胸口疼痛並擴散至雙臂、流汗、心悸及全身無力的情況。由於症狀和心臟病發相似,以致引起恐慌,不過這種情形歷時短暫,而且未見有後患。

原來這個名堂是一位華裔醫生起的。1968 年,郭浩民(音譯,Dr Robert Ho Man Kwok)撰稿描述了他的經歷。文章在備受尊崇的《新英格蘭醫學雜誌》(New England Journal of Medicine)上發表,迅速引來類似的報告。目光很快地集注在中菜常用的一個原料,通稱「味精」的谷氨酸鈉(Monosodium Glutamate, MSG)。對味精的反應,在食用後 10—25 分鐘內出現,持續達 45 分鐘到 2 小時不等。至於進食多少味精才產生不良後果,研究所得是因人而異,平均數量在 5 克左右;一般菜式已含有足夠份量。這綜合徵全靠醫生詳細詢問有關症狀而作出診斷,沒有方法測試。 而大多數患者並不需要治療,也沒受永久的損傷。

奇怪的是,郭醫生在中國家鄉從來沒有遭遇過這樣的問題。在北美洲曾多次進行調查,顯示 1% 至 7% 的人口可能受到這種綜合徵的影響。但科研人員多年來卻無法證實味精為「元凶」。

天然食品如藤上熟的蕃茄、蘑菇、螃蟹,都含有谷氨酸。谷氨酸是氨基酸之一種,而所有蛋白質均由氨基酸構成。許多蛋白質本身是無味的,但經發酵後的氨基酸產生不同的口味,常見的醬油、乳酪和鳳尾魚就是如此。

一般的肉類、家禽和魚類特有的味道,來自各種氨基酸,其中也包括谷氨酸。而除了鹹、酸、苦、辣、甜之外,還辨認出一項「鮮味」,即是肉湯的味道。英國名廚師赫斯頓‧布盧門撒爾(Heston Blumenthal),曾在《星期日泰晤士報》(Sunday Times)作討論:“領悟出「鮮味」,猶如剛發現一個新的色彩,我們一生四處尋覓,但其實它一直近在眼前。”

大部份肉類含谷氨酸的比重是 11% 到 22%。肉店把牛排風乾(乾式熟化)的技術,會釋放谷氨酸和另外一種化合物肌苷酸(inosine monophosphate, IMF)。每種肉類裡,谷氨酸和肌苷酸佔不同比例,造成各自特有的味道。

中式烹飪調味品如醬油和黃豆醬的味道,亦經發酵生產谷氨酸而成。除了中菜,許多調味料、湯、肉汁、方便餐、乾糧中也可以找到谷氨酸鈉。一位美國醫生喬治‧施瓦茨(George Schwartz)指出,谷氨酸鈉是繼鹽和胡椒粉之後,第三普及的香料,在超市架上有超過二百五十種普通貨品含有這成份。

據了解,味精能夠增強口感,尤其是肉類的味道。然而,這個效果是有上限的。谷氨酸鈉濃度高於 60 毫克 / 公斤的水平,反而使食物難以入口。

味精的起源,大約一個世紀前在日本發現。時維 1908 年,東京帝國大學的生物化學家池田菊苗教授在家中用膳。科學家的好奇心促使他問妻子,她煮出美味蔬菜豆腐湯的秘方。池田夫人就拿乾海藻絲讓他看,那是一種稱為昆布的厚實海帶。池田最終確定了海藻中含有谷氨酸,才能產生鮮味。這樣秘密成份得以面世,並迅速走紅 。

池田教授發現,肉類、蕃茄及海藻有一個共通點:它們的鮮味都是基於同一因素。特別是日本的海藻或海帶,具有高濃度的谷氨酸,每 100 克含量大約 1000 毫克 。

當時,一位名叫鈴木三朗助的商人,正在試圖從海帶中提取碘。聽到池田教授的發現,他得到靈感,而轉向生產谷氨酸。鈴木和池田意識到,他們從 10 公斤的海帶中,才可以提取 0.1—0.2 克谷氨酸,是不可行的。他們改用較為便宜的大豆和小麥,其內也含豐富的谷氨酸。沒多久,他們推出稱為「味之素」的產品。

谷氨酸在溶解的形式才產生鮮味。鹽晶體形式的谷氨酸鈉(味精),更容易溶解,成為理想的增味劑。

有一點事實很有意思。人類母乳也含有谷氨酸,而且水平比牛奶的高 10 倍。專家認為,這般鮮味加上乳糖的甜味,能令嬰兒喜愛母乳。

科學家卻發現,給幼年的動物的飲食加入谷氨酸鈉,它們的大腦發育異常,並造成荷爾蒙不平衡和肥胖。這發現引起對味精安全問題的關切,並導致了在 1970 年代禁止嬰兒食品裡使用谷氨酸鈉。

關於味精對人體的影響,還有其他謠言四起:有說它令兒童骨骼停止成長,或導致頭髮掉光了,還有說混和可樂或啤酒會變成春藥,甚至有利丈夫一索得男。 

其實,正常人體含有相當數量的谷氨酸,基本上,神經系統傳遞命令和腦部記憶全靠谷氨酸。一些科學家擔心,在一餐中攝入大量的味精,會過度刺激大腦。

然而,在美國加州大學過敏及免疫學系(The Allergy and Immunology Department, University of California)的安德魯‧撒克遜(Andrew Saxon)博士領導下的科學研究,未有發現「中国餐館症候群」和味精之間有任何關係。

「食品添加劑」一詞,容或教消費者焦慮。事實上,美國食品和藥物管理局(The United States Food and Drug Administration)已登記的添加劑達三千多個,其中不乏日常使用的成分如香料、酵母和香草。其中某些添加劑比其他的監管來得緊密。味精屬於「一般認為安全」分類(generally recognized as safe, GRAS),如何使用是豁免受控制的。

從健康角度而言,有人持相反的觀點,以為味精可能解決一個問題。時下的人常被勸籲削減鹽的攝入量。實驗發現,令一個湯變得美味,鹽的濃度一定要達到一定水平。當加入味精後,需要使用鹽的份量可以減少五分之二 。

在羅馬帝國時期谷氨酸已為人所知。羅馬人把鹹魚發酵成味汁。當時鹽很寶貴,這味劑幫助羅馬人節省用鹽。

在歐洲聯盟內,食品標籤法律規定食品的成分,要依據名稱(味精或谷氨酸)或電子號碼(E620 到 E625)列明。歐盟也禁止了某些產品如牛奶、果汁和巧克力加入味精。

消費者常常以為,味精作為一種人工合成的化學品,是有害的,而雞精高湯粉湯塊,是雞肉製造的,較為有營養。2008 年北京奧運會期間,巴西隊指定要免味精的飯餸。但事實上,雞精中往往含有高達 40% 味精,以及其他調味料。

經驗豐富的廚師使用味精時,遵守幾個禁忌:

1. 高溫
溫度高於攝氏 90 度導致的化學變化,味精可能成為有毒的。因此,最好是在煮食差不多完成前才放味精。同樣原因,醃肉時及早加味精,也應該避免。

2. 低溫
味精不易溶於冷水,若涼盤要使用味精,應先在溫水中溶解。

3. 鹼性食物
鹼性溶液令味精進行化學變化,產生有異味的物質,味精從而不適合魷魚乾之類的鹼性食品。

4. 酸性食物
味精不可以充分溶於酸性液體。

5. 甜味菜式
味精會抑制甜頭,變為不倫不類的味道。

6. 過度使用
過量味精會造成既咸又苦的味道 。

7. 雞蛋
雞蛋本身含有豐富的谷氨酸,與食鹽結合已成為味精。再加入味精是多餘的,弄巧反拙。

中國的味精,是於 1921 年在動盪的上海發明的。從事化工的企業家吳蘊初,發現從麵筋生產谷氨酸的過程,並把製成品稱為味精。他在香港的天廚味精廠,成立迄今已超過七十年,眾所周知。

最近香港海關揭發了非法工廠,尋獲 1400 袋假冒的味精。味精工業規模龐大,於此可見一斑。

早期在倫敦唐人街的大廚師,給味精起了「師傅」的稱號。他們解釋,假如沒有師傅在場,能做成甚麼樣子呢!時下愈來愈多食肆聲明,他們的菜式不含味精。然而,有經驗豐富的廚師認為,客戶或已習慣了一定的味道,如果全面停止使用味精,他們可能會覺得菜餚缺乏風味。不過,也有一些廚師以雞精代替味精。

2007 年,米芝蓮(Michelin)星級廚師馬可‧皮埃爾‧懷特(Marco Pierre White)披露,他的食譜也用雞精高湯塊,引起不小的轟動。

看來,這「中国餐館症候群」似乎已成醫學史上一段逸事,但味精和類似的調味品,來日方長呢!

 

參考書目:

Ajinomoto_Co_Inc. (2003). Amino acids are what deliciousness is all about. Encyclopedia of amino acids.
Castleman, M. (1988). Beyong Chinese restaurant syndrome. Point Reyes: Los Angeles Times.
Daniels, D., Joe, F., & Diachenko, G. (1995). Determination of free glutamic acid in a variety of foods by high performance liquid chromatography. Food Additives and Contaminants, 21-29.
EUFIC. (n.d.). The facts on monosodium glutamate. Food Today.
Fahmy, A. (1997). Diet, Drink and Disease. London: Minerva Press.
Gore, M. E., & Salmon, P. (1980). Chinese restaurant syndrome: fact or fiction? The Lancet, 251-252.
International_Glutamate_Information_Service. (2011). Biography of Professor Ikeda.
Kenney, R. (1986). The Chinese restaurant syndrome: an anecdote revisited. Food and Chemical Toxicology, 351-354.
Lucas, D., & Newhouse, J. (1957). The toxic effect of sodium L-glutamate on the inner layers of the retina. AMA Arch Ophthal, 193-201.
McDermott, N. (2007). Chef Marco reveals his stock in trade -the Knorr chicken cube. Daily Mail.
Monti, P. (2007). Monosodium glutamate, the molecule that enhances taste in food. Molecule of the month.
Olney, J. (1969). Brain lesions, obesity and other disturbances in mice treated with monosodium glutamate. Science, 719-721.
Parkinson, R. (n.d.). Monosodium glutamate (MSG) -pros and cons. About.
Renton, A. (2005). If MSG is so bad for you, why doesn't everyone in Asia have a headache? The Observer.
Schaumburg, H., & Byck, R. (1968). Sin cib-syn: accent on glutamate. N Engl J Med, 105.
Smith, P. (2010, 3 19). Don't be scared of MSG. Food.
Taliaferro, P. J. (1995). Monosodium glutamate and the Chinese restaurant syndrome: a review of food additive safety. Journal of Environmental Health, vol 57.
US_Food_and_Drug_Administration. (2010). Food ingredients and colors. International Food Information Council (IFIC).
Vitrag. (2009). Chinese restaurant syndrome. MedicalGeek.
Warrell, D. A. (2010). Oxford Textbook of Medicine. Oxford: Oxford University Press.
Webster-Gandy, J., Madden, A., & Holdsworth, M. (2006). Oxford Handbook of Nutrition and Dietetics. Oxford: Oxford University Press.
Wikimedia_Foundation. (2010). Kikunae Ikeda. Wikipedia.
Wikipedia. (n.d.). Glutamic acid (flavor).
Wordwide_Health_Centre_Net. (2007). Monosodium glutamate: Poison the body to better the taste.
保山衛生. (2011). 雞精和味精的區別. bswsjd.gov.cn.
南京晨報. (2006). 兩男子自製催情藥. 南京晨報.
卡妙. (2010). 味精的七大禁忌. djjk.cn.
小倪. (2010). 發明味精的有趣故事. healthy.4738.com.
小天使. (2010). 可樂加味精 -配置春藥. LaluLalu.com.
康易網. (2007). 兒童食用味精過多難長高?. 39.net.
文匯報. (2008). 香港天廚上世紀30年代土瓜灣廠房. WenWeiPo.com.
曉娟. (2011). 探討味精吃多與掉髮之間的問題. jdzol.com.
清晨. (2000). 科學實驗證明吃味精和過敏沒有關係. sina.com.cn.
瀋陽晚報. (2008). 瀋陽奧運村趣聞. Xinhuanet.
王琛. (2010). 味精廠男員工都生兒子. blog.sina.com.cn.
生果日報. (2010). 製冒牌天廚味精 10人落網. news.hotpot.hk.
芝蘭健康網. (n.d.). 中國餐館症候群. Cheeryland International Inc.

简体

 

1980 年代在大学医学院,读到一个名词令我十分惊讶。所谓「中国餐馆症候群」(Chinese Restaurant Syndrome),是形容某些食客在中餐厅用膳后,出现胸口疼痛并扩散至双臂、流汗、心悸及全身无力的情况。由于症状和心脏病发相似,以致引起恐慌,不过这种情形历时短暂,而且未见有后患。

原来这个名堂是一位华裔医生起的。1968 年,郭浩民(音译,Dr Robert Ho Man Kwok)撰稿描述了他的经历。文章在备受尊崇的《新英格兰医学杂志》(New England Journal of Medicine)上发表,迅速引来类似的报告。目光很快地集注在中菜常用的一个原料,通称「味精」的谷氨酸钠(Monosodium Glutamate, MSG)。对味精的反应,在食用后 10—25 分钟内出现,持续达 45 分钟到 2 小时不等。至于进食多少味精才产生不良后果,研究所得是因人而异,平均数量在 5 克左右;一般菜式已含有足够份量。这综合征状全靠医生详细询问有关症状而作出诊断,没有方法测试。而大多数患者并不需要治疗,也没受永久的损伤。

奇怪的是,郭医生在中国家乡从来没有遭遇过这样的问题。在北美洲曾多次进行调查,显示 1% 至 7% 的人口可能受到这种综合征状的影响。但科研人员多年来却无法证实味精为「元凶」。

天然食品如藤上熟的蕃茄、蘑菇、螃蟹,都含有谷氨酸。谷氨酸是氨基酸之一种,而所有蛋白质均由氨基酸构成。许多蛋白质本身是无味的,但经发酵后的氨基酸产生不同的口味,常见的酱油、乳酪和凤尾鱼就是如此。

一般的肉类、家禽和鱼类特有的味道,来自各种氨基酸,其中也包括谷氨酸。而除了咸、酸、苦、辣、甜之外,还辨认出一项「鲜味」,即是肉汤的味道。英国名厨师赫斯顿‧布卢门撒尔(Heston Blumenthal),曾在《星期日泰晤士报》(Sunday Times)作讨论:“领悟出「鲜味」,犹如刚发现一个新的色彩,我们一生四处寻觅,但其实它一直近在眼前。”

大部份肉类含谷氨酸的比重是 11% 到 22%。肉店把牛排风干(干式熟化)的技术,会释放谷氨酸和另外一种化合物肌苷酸(inosine monophosphate, IMF)。每种肉类里,谷氨酸和肌苷酸占不同比例,造成各自特有的味道。

中式烹饪调味品如酱油和黄豆酱的味道,亦经发酵生产谷氨酸而成。除了中菜,许多调味料、汤、肉汁、方便餐、干粮中也可以找到谷氨酸钠。一位美国医生乔治‧施瓦茨(George Schwartz)指出,谷氨酸钠是继盐和胡椒粉之後,第三普及的香料,在超市架上有超过二百五十种普通货品含有这成份。

据了解,味精能够增强口感,尤其是肉类的味道。然而,这个效果是有上限的。谷氨酸钠浓度高於 60 毫克 / 公斤的水平,反而使食物难以入口。

味精的起源,大约一个世纪前在日本发现。时维 1908 年,东京帝国大学的生物化学家池田菊苗教授在家中用膳。科学家的好奇心促使他问妻子,她煮出美味蔬菜豆腐汤的秘方。池田夫人就拿干海藻丝让他看,那是一种称为昆布的厚实海带。池田最终确定了海藻中含有谷氨酸,才能产生鲜味。这样秘密成份得以面世,并迅速走红。

池田教授发现,肉类、蕃茄及海藻有一个共通点:它们的鲜味都是基于同一因素。特别是日本的海藻或海带,具有高浓度的谷氨酸,每 100 克含量大约 1000 毫克 。

当时,一位名叫铃木三朗助的商人,正在试图从海带中提取碘。听到池田教授的发现,他得到灵感,而转向生产谷氨酸。铃木和池田意识到,他们从 10 公斤的海带中,才可以提取 0.1—0.2 克谷氨酸,是不可行的。他们改用较为便宜的大豆和小麦,其内也含丰富的谷氨酸。没多久,他们推出称为「味之素」的产品。

谷氨酸在溶解的形式才产生鲜味。盐晶体形式的谷氨酸钠(味精),更容易溶解,成为理想的增味剂。

有一点事实很有意思。人类母乳也含有谷氨酸,而且水平比牛奶的高 10 倍。专家认为,这般鲜味加上乳糖的甜味,能令婴儿喜爱母乳。

科学家却发现,给幼年的动物的饮食加入谷氨酸钠,它们的大脑发育异常,并造成荷尔蒙不平衡和肥胖。这发现引起对味精安全问题的关切,并导致了在 1970 年代禁止婴儿食品里使用谷氨酸钠。

关于味精对人体的影响,还有其他谣言四起:有说它令儿童骨骼停止成长,或导致头发掉光了,还有说混和可乐或啤酒会变成春药,甚至有利丈夫一索得男。

其实,正常人体含有相当数量的谷氨酸,基本上,神经系统传递命令和脑部记忆全靠谷氨酸。一些科学家担心,在一餐中摄入大量的味精,会过度刺激大脑。

然而,在美国加州大学过敏及免疫学系(The Allergy and Immunology Department, University of California)的安德鲁‧撒克逊(Andrew Saxon)博士领导下的科学研究,未有发现「中国餐馆症候群」和味精之间有任何关系。

「食品添加剂」一词,容或教消费者焦虑。事实上,美国食品和药物管理局(The United States Food and Drug Administration)已登记的添加剂达三千多个,其中不乏日常使用的成分如香料、酵母和香草。其中某些添加剂比其他的监管来得紧密。味精属于「一般认为安全」分类(generally recognized as safe, GRAS),如何使用是豁免受控制的。

从健康角度而言,有人持相反的观点,以为味精可能解决一个问题。时下的人常被劝谕削减盐的摄入量。实验发现,令一个汤变得美味,盐的浓度一定要达到一定水平。当加入味精后,需要使用盐的份量可以减少五分之二 。

在罗马帝国时期谷氨酸已为人所知。罗马人把咸鱼发酵成味汁。当时盐很宝贵,这味剂帮助罗马人节省用盐。

在欧洲联盟内,食品标签法律规定食品的成分,要依据名称(味精或谷氨酸)或电子号码(E620 到 E625)列明。欧盟也禁止了某些产品如牛奶、果汁和巧克力加入味精。

消费者常常以为,味精作为一种人工合成的化学品,是有害的,而鸡精高汤粉汤块,是鸡肉制造的,较为有营养。2008 年北京奥运会期间,巴西队指定要免味精的饭菜。但事实上,鸡精中往往含有高达 40% 味精,以及其他调味料。

经验丰富的厨师使用味精时,遵守几个禁忌:

1. 高温
温度高于摄氏 90 度导致的化学变化,味精可能成为有毒的。因此,最好是在煮食差不多完成前才放味精。同样原因,腌肉时及早加味精,也应该避免。

2. 低温
味精不易溶于冷水,若凉盘要使用味精,应先在温水中溶解。

3. 碱性食物
碱性溶液令味精进行化学变化,产生有异味的物质,味精从而不适合鱿鱼干之类的碱性食品。

4. 酸性食物
味精不可以充分溶于酸性液体。

5. 甜味菜式
味精会抑制甜头,变为不伦不类的味道。

6. 过度使用
过量味精会造成既咸又苦的味道 。

7. 鸡蛋
鸡蛋本身含有丰富的谷氨酸,与食盐结合已成为味精。再加入味精是多余的,弄巧反拙。

中国的味精,是于 1921 年在动荡的上海发明的。从事化工的企业家吴蕴初,发现从面筋生产谷氨酸的过程,并把制成品称为味精。他在香港的天厨味精厂,成立迄今已超过七十年,众所周知。

最近香港海关揭发了非法工厂,寻获 1400 袋假冒的味精。味精工业规模庞大,于此可见一斑。

早期在伦敦唐人街的大厨师,给味精起了「师傅」的称号。他们解释,假如没有师傅在场,能做成什么样子呢!时下愈来愈多食肆声明,他们的菜式不含味精。然而,有经验丰富的厨师认为,客户或已习惯了一定的味道,如果全面停止使用味精,他们可能会觉得菜肴缺乏风味。不过,也有一些厨师以鸡精代替味精。

2007 年,米芝莲(Michelin)星级厨师马可‧皮埃尔‧怀特(Marco Pierre White)披露,他的食谱也用鸡精高汤块,引起不小的轰动。

看来,这「中国餐馆症候群」似乎已成医学史上一段逸事,但味精和类似的调味品,来日方长呢!


2011 年 10 月 草于伦敦

- - -

参考书目:

Ajinomoto_Co_Inc. (2003). Amino acids are what deliciousness is all about. Encyclopedia of amino acids.
Castleman, M. (1988). Beyong Chinese restaurant syndrome. Point Reyes: Los Angeles Times.
Daniels, D., Joe, F., & Diachenko, G. (1995). Determination of free glutamic acid in a variety of foods by high performance liquid chromatography. Food Additives and Contaminants, 21-29.
EUFIC. (n.d.). The facts on monosodium glutamate. Food Today.
Fahmy, A. (1997). Diet, Drink and Disease. London: Minerva Press.
Gore, M. E., & Salmon, P. (1980). Chinese restaurant syndrome: fact or fiction? The Lancet, 251-252.
International_Glutamate_Information_Service. (2011). Biography of Professor Ikeda.
Kenney, R. (1986). The Chinese restaurant syndrome: an anecdote revisited. Food and Chemical Toxicology, 351-354.
Lucas, D., & Newhouse, J. (1957). The toxic effect of sodium L-glutamate on the inner layers of the retina. AMA Arch Ophthal, 193-201.
McDermott, N. (2007). Chef Marco reveals his stock in trade -the Knorr chicken cube. Daily Mail.
Monti, P. (2007). Monosodium glutamate, the molecule that enhances taste in food. Molecule of the month.
Olney, J. (1969). Brain lesions, obesity and other disturbances in mice treated with monosodium glutamate. Science, 719-721.
Parkinson, R. (n.d.). Monosodium glutamate (MSG) -pros and cons. About.
Renton, A. (2005). If MSG is so bad for you, why doesn't everyone in Asia have a headache? The Observer.
Schaumburg, H., & Byck, R. (1968). Sin cib-syn: accent on glutamate. N Engl J Med, 105.
Smith, P. (2010, 3 19). Don't be scared of MSG. Food.
Taliaferro, P. J. (1995). Monosodium glutamate and the Chinese restaurant syndrome: a review of food additive safety. Journal of Environmental Health, vol 57.
US_Food_and_Drug_Administration. (2010). Food ingredients and colors. International Food Information Council (IFIC).
Vitrag. (2009). Chinese restaurant syndrome. MedicalGeek.
Warrell, D. A. (2010). Oxford Textbook of Medicine. Oxford: Oxford University Press.
Webster-Gandy, J., Madden, A., & Holdsworth, M. (2006). Oxford Handbook of Nutrition and Dietetics. Oxford: Oxford University Press.
Wikimedia_Foundation. (2010). Kikunae Ikeda. Wikipedia.
Wikipedia. (n.d.). Glutamic acid (flavor).
Wordwide_Health_Centre_Net. (2007). Monosodium glutamate: Poison the body to better the taste.
保山卫生. (2011). 鸡精和味精的区别. bswsjd.gov.cn.
南京晨报. (2006). 两男子自制催情药. 南京晨报.
卡妙. (2010). 味精的七大禁忌. djjk.cn.
小倪. (2010). 发明味精的有趣故事. healthy.4738.com.
小天使. (2010). 可乐加味精 -配置春药. LaluLalu.com.
康易网. (2007). 儿童食用味精过多难长高?. 39.net.
文汇报. (2008). 香港天厨上世纪30年代土瓜湾厂房. WenWeiPo.com.
晓娟. (2011). 探讨味精吃多与掉发之间的问题. jdzol.com.
清晨. (2000). 科学实验证明吃味精和过敏没有关系. sina.com.cn.
沈阳晚报. (2008). 沈阳奥运村趣闻. Xinhuanet.
王琛. (2010). 味精厂男员工都生儿子. blog.sina.com.cn.
生果日报. (2010). 制冒牌天厨味精 10人落网. news.hotpot.hk.
芝兰健康网. (n.d.). 中国餐馆症候群. Cheeryland International Inc.

 

Author 作者

 

Dr Stephen Hiew has been Cantonese teacher at Ming-Ai Institite since 2010. He is bilingual, and also knows Mandarin and Russian. During 20 years as a doctor, inter-cultural health issues like healthy ethnic foods fascinated him. He is passionate about communication skills, and had taught university students and overseas doctors. His educational work was presented in over ten countries and described in a book. Stephen maintains interests in people and society, and has gained a law degree. In his spare time he serves in a Chinese healthcare charity in London. He is looking forward to a new life soon.

 

 

丘志祥醫生為明愛學院導師,自 2010 年起擔負廣東話教育工作,一絲不苟的治學態度,嚴謹又不乏幽默的教學風度,深受學生的好評。他自幼深諳中英文,中外古今、文史哲醫,無不涉獵,尤其對俄國文化研究有較深的造詣。行醫二十餘年,致力於研究行為醫學和文化背景(飲食習慣等)對健康的影響。丘醫生擅長於醫患溝通,曾教導大學生和海外醫師十多年,其教育工作成果在十余國家刊物發表,並收錄於專業書籍中。對社會懷有強烈責任感的他,持之以恆地為慈善事業貢獻自己的力量,其中倫敦華人健康志願機構是他慈善工作的核心。近年修獲法律文憑。目前,他正期待新的機遇新的挑戰的來臨。

 

 

丘志祥医生为明爱学院导师,自 2010 年起担负广东话教育工作,一丝不苟的治学态度,严谨又不乏幽默的教学风度,深受学生的好评。他自幼深谙中英文,中外古今、文史哲医,无不涉猎,尤其对俄国文化研究有较深的造诣。行医二十余年,致力于研究行为医学和文化背景(饮食习惯等)对健康的影响。丘医生擅长于医患沟通,曾教导大学生和海外医师十多年,其教育工作成果在十余国家刊物发表,并收录于专业书籍中。对社会怀有强烈责任感的他,持之以恒地为慈善事业贡献自己的力量,其中伦敦华人健康志愿机构是他慈善工作的核心。近年修获法律文凭。目前,他正期待新的机遇新的挑战的来临。