In the chapter 3 Auguste Escoffier, The Essence of Taste from the novel Proust was a neuroscientist by Jonah Lehrer, the famous discovery of a fifth taste is explained. Kikunae Ikeda discovered that the tongue is not only able to taste food that is sour, bitter, sweet, and salty but as well umami, which means delicious in Japanese. Ikeda was looking for the essence of this unknown taste, the secret ingredient that dashi (a classic Japanese broth made from Kombu) and veal stock had in common. He finally found his secret molecule and it was glutamic acid which is the precursor of L-glutamate. Glutamic acid is tasteless, it is only when the protein is ionized that it degenerates into L-glutamate which is an amino-acid that the tongue can taste. Glutamic acid can be ionized by cooking, fermentation, or by ripening in the sun. However, glutamate is an unstable molecule that can meld itself into different chemicals who are not delicious. Ikeda found that glutamate had to be bound to a stable molecule that the tong does enjoy. This molecule is salt, Ikeda was able to distill a metallic salt from brown kelp: MSG, monosodium glutamate.

I found this chapter from Proust was a neuroscientist very interesting, one of the main focuses of the chapter is how Escoffier used broth to enhance his meals. I have always loved food and especially French food; I believe this is why knowing how we appreciate it captivated me so much. The aim of my blog post is to see more in detail how our tongue perceives all these tastes.

Humans have different numbers of taste buds which creates variations in taste sensitivity among human beings. On average, the human tongue has between 2000 and 4000 taste buds. Inglis J. Miller and Frank E. Reedy Jr. present in their article Variations in human taste bud density and taste intensity perception, an experiment made with sixteen subjects. They were divided into two groups by the rank order of their taste bud densities. The results show that the group with a higher density had on average 374 (±134) taste pores per square centimeter while the group with a lower density had on average 135 (±43) taste pores per square centimeter.  The higher density group had an average fungiform papilla density 1.8 times greater, and 1.5 times more taste pores than the lower density group. The subjects also had to rate the intensity for four suprathreshold concentrations of five taste stimuli placed on the same region of the tongue where the pores were counted. The subjects who reported some tastes as more intense were the ones with higher fungiform taste bud densities. We have always thought that we sense the five different tastes in different areas of the tongue, but this was proved wrong. All the tastes can be sensed on all parts of the tongue. However, the sides of the tongue are more sensitive overall, and the back of our tongue is more sensitive to bitter tastes. In addition, we do not only have taste cells on the tongue but in the back of our throat, on our epiglottis, in our nose and sinuses, and from the throat to the upper part of the esophagus. Every week, the sensory cells responsible for how we perceive taste in the taste buds renew themselves.

In the Journal of Ultrastructure Research, Raymond G. Murray and Assia Murray present the Fine structure of taste buds of rabbit foliate papillae. An electron microscopy of over 200 taste buds from foliate papillae of rabbits has shown that two distinct cell types exist. The slender “dark cells” possess centrioles with crossbanded rootlets and are intimately related to nerves. As well, they contain granules which are apparently precursor to the dense substance of the taste pit. The broader “light cells” are virtually enclosed by the “dark cells” and are extensively in contact with nerves in a manner suggestive of synapses but without typical specialization. Raymond G. Murray and Assia Murray believe that “light cells” are gustatory elements, while “dark cells” are supporting elements with possibly a gustatory function as well.

Bibliography

10 Fun Facts About Your Tongue and Taste Buds. OnHealth. 2016 Jun 21 [accessed 2020 May 6]. https://www.onhealth.com/content/1/tongue_facts

Lehrer J. Proust was a neuroscientist. Edinburgh: Canongate; 2012.

Miller IJ, Reedy FE. Variations in human taste bud density and taste intensity perception. Physiology & Behavior. 2003 Feb 14 [accessed 2020 May 6]. https://www.sciencedirect.com/science/article/abs/pii/003193849090374D

Murray RG, Murray A. Fine structure of taste buds of rabbit foliate papillae. Journal of Ultrastructure Research. 2004 Nov 8 [accessed 2020 May 6]. https://www.sciencedirect.com/science/article/abs/pii/S0022532067802247