Monday Article #23: MSG - Is it really beneficial or detrimental?

- A popular flavour enhancer that is striking controversial views worldwide! -


Glutamic acid, glutamate and MSG - Glu what?


Glutamic acid (Figure 1) is one of the non-essential amino acids found in the human body. Non-essential implies that this amino acid can be synthesised in the human body and does not need to be taken into the diet.


Glutamate (Glu) is the negatively charged salt form of glutamic acid and has a central role in the human body. Glu is the most abundant excitatory neurotransmitter in our nervous system and hence, Glu is required in much higher concentrations compared to other amino acids. Besides being involved with the nervous system, glutamate is also a key part of protein metabolism in the human body where it takes part in transamination reactions as part of the urea cycle which occurs in the mitochondria of hepatocytes. Glu is important in taste (umami), where it is used to produce monosodium glutamate, or better known as MSG (Figure 2).


MSG is a flavour enhancer used in Asian cuisines, particularly in Chinese and Japanese cuisines to bring about umami in their dishes. Umami is one of the five basic tastes, along with sweet, sour, salty and bitter. Scientists have discovered 2 glutamate-selective G protein-coupled receptors, mGluR4 and mGluR1, which are activated in the presence of Glu.



Discovery of MSG


MSG (Japanese = Ajinomoto) was first identified more than a hundred years ago (1909) by the Japanese chemist Dr. Kikunae Ikeda where he described umami as the fifth basic taste. MSG is found in food products ranging from fish to mushrooms! Not only that, society’s favourite Roquefort and Parmesan cheese also contain MSG!


Production of MSG


This flavour enhancer is actually widely produced using microbiological and biotechnological processes! The Gram positive anaerobic heterotroph Corynebacterium glutamicum is first cultured with ammonia and carbohydrates from sugar beets, sugar cane, tapioca or molasses. The bacterium will then excrete amino acids into a culture broth whereby L-glutamate is isolated. The biochemical process involved with MSG production is a well-known process - yes, the citric acid cycle (Figure 3)!


Wild-type strains of this bacterium produce about 10 g/L glutamic acid. However, recent genetically engineered yields are now upwards of 100 g/L!



The social impacts of MSG - the “Chinese Restaurant syndrome”


Although MSG is hailed as a success by the food industry, MSG does have a huge social impact on certain parties. In 1968 America, one such individual by the name of Dr. Robert Ho Man Kwok, wrote a correspondence letter to the New England Journal of Medicine, coining the term Chinese Restaurant syndrome (CRS) in which he suspected arose from MSG consumption from Chinese food. In his letter, Dr. Kwok mentioned he felt a plethora of symptoms, ranging from headaches to numbness of the neck and arms. This letter has caused a social uproar worldwide against the use of monosodium glutamate. However, the letter was soon uncovered as a hoax but there were many who believed the allegations made by Kwok.


There was also another major uproar in the US in January 2020 against the definition of CRS on the Merriam Webster dictionary website which was deemed inaccurate and racist by scientists and Asian-American celebrities respectively.


MSG and its impact on human health


There are actually many studies which have failed to show the chemical causes of the ‘alleged’ syndrome described by Dr. Kwok. There also has actually not been an approved mechanism linked to excessive MSG consumption. The US Food and Drug Administration has long approved MSG for consumption. Whilst there is still ongoing debate on this particular area of research, scientists agree that adding a moderate amount of monosodium glutamate should be a good and healthy practice. Only time will actually tell if we are able to have valid evidence demonstrating overconsumption of MSG.


Till then, the fable of MSG still remains: is MSG beneficial or detrimental?


 

REFERENCE(s):


Glutamate Introductory Content taken from : Professor John Barrow’s Protein Metabolism lectures for the BI25M7 Energy for Life Course,School of Medicine,Medical Sciences and Nutrition, University of Aberdeen.


Chaudhari, N., Pereira, E., & Roper, S. D. (2009). Taste receptors for umami: the case for multiple receptors. The American journal of clinical nutrition, 90(3), 738S-742S.


Zanfirescu, A., Ungurianu, A., Tsatsakis, A. M., Nițulescu, G. M., Kouretas, D., Veskoukis, A., ... & Margină, D. (2019). A review of the alleged health hazards of monosodium glutamate. Comprehensive reviews in food science and food safety, 18(4), 1111-1134.


MSG production Content taken from : Professor Ian Stansfield’s Industrial Microbiology lectures for the BI25M5 Microbes, Infection and Immunity Course,School of Medicine,Medical Sciences and Nutrition, University of Aberdeen.


What is MSG, and is it actually bad for you? TED-Ed YouTube (2021).

https://www.youtube.com/watch?v=EKgEj5asL3o


‘Chinese Restaurant Syndrome’ - what is it and is it racist? BBC News. (2020).

https://www.bbc.co.uk/news/world-us-canada-51139005


Figure 1 : Glutamic acid , amino Acid

Taken from: Wikipedia. Retrieved 7 April 2022,from https://en.wikipedia.org/wiki/Glutamic_acid


Figure 2 : Monosodium glutamate structure

Taken from: Wikipedia. Retrieved 7 April 2022, from

https://en.wikipedia.org/wiki/Monosodium_glutamate


Figure 3 : MSG production

Taken from: Prof Ian Stansfield’s Industrial Microbiology lectures. Retrieved 7 April 2022.


 

This article was prepared by Eldrian Tho Jiat Yang .

 

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