“Discovery” of MSG …

Dr. Kikunae Ikeda(1908)

An attentive taster will find out something common in the complicated taste of asparagus, tomatoes, cheese and meat, which is quite peculiar and cannot be classed under any of the well defined four taste qualities, sweet, sour, salty and bitter.

(Prof. K. Ikeda’s presentation at the 8th Int’l Congress Appl. Chem., Chicago, 1912)

Basic taste categories

Sour

BitterSweet

Umami

Z

X

Y

Salty

Beef

Chicken

Yamaguchi, S. (1987)

Torii et al., In Umami: a basic taste, pp513-563 (1987)

Umami preferenceis a marker of

protein nutrition!

Preference for umami is related tolevels of dietary proteins

Umami (MSG)

Umami (MSG)

NaCl NaCl

NaClNaCl

Umami (MSG)

Umami (MSG)

Tomato’s full, rounded 'meaty' flavor comes from its heavy load of glutamates, and this flavor is reinforced by its unique crimson color.

0

20

40

60

80

100

120

140

160

180

Asp Ser Glu Gly Ala Val Met Ile Leu Tyr Phe Lys His Arg

Green

Pink

Red

Full ripe

(mg/1

00g)

Free glutamate in breast milk

0

2

4

6

8

10

12

14

16

18

20

TauAsp Thr Ser Gln Glu Gly Ala Val Cys Met Ile Leu Tyr Phe Orn Lys His Arg

(mg/100g) Total Glu intake = 0.393 g/kg/day!

“No MSG” labels …

• “While technically MSG is only one of several forms of free glutamate used in foods, consumers frequently perceive the term MSG to mean all free glutamate.

• For this reason, FDA considers foods whose labels say "No MSG" or "No Added MSG" to be misleading if the food contains ingredients that are sources of free glutamates, such as hydrolyzed protein.”

http://vm.cfsan.fda.gov/~lrd/msg.html

Glutamic acid metabolized during digestive absorption

Mouth

Glutamic acid from Food

Small intestines mucous membrane epithelial cell

Glutamic acid100% > 90%

Blood

Energy

Protein biosyntheses

Liver

Glutamic acid

Alanine,

Glutamine

Thermogenesis

Hepatic

portal vein

Liquid diet

171005

15

25

35

45

5

15

25

35

45

MSG (+)

Aff

eren

t N

erve

Res

pon

se

(sp

ikes

/sec

)

MSG (-)

Gastric Afferents of Vagus

5

Time (min)

An liquid diet without Glu, does not elicit chemoreception

Sensors for Glutamate exist on Tongue & Alimentary tract

Tongue (Taste buds) mGluR1

Small IntestinemGluR4 T1R1

Large Intestine mGluR4 &

T1R1

mGluR4

mGluR4 & T1R1

mGluR4

mGluR4 & T1R1

Stomach

mGluR1 & T1R1

T1R1mGluR1mGluR1

Intake of protein is recognized by umami receptors in the tongue and visceral receptors in the GI tract.

Increase of Gastric Afferent Activity

Amino Acid solution (150mmol/L, 2mL)

Glutamate-Sensing by the Gastric Vagus

SalineValLeu

IleLysTrpThrPheMet

GluGlyArgAlaProCysAspHisGlnAsnSerTyr

0 10 20 30 (, Spikes/sec)

AAs

Glutamate facilitated the gastric emptying of a protein-rich meal without influence on that of water or carbohydrate meal.

Free glutamate is an important substance for efficient protein digestion and absorption.

Gastroenterology (2006) 130(4), S2, A246,

Clinical Trial: Implications

Summary

The results clearly provide direct evidences of brain activation by post-oral stimuli with taste substances via either neural (vagal) or humoral signaling pathway.

Activated forebrain regions and signaling pathways

After infusion of taste substances in the stomach, several forebrain regions (cortex, basal ganglia, limbic system, and hypothalamus) were activated.

MSG-induced brain activation, but not glucose-induced one, was substantially reduced after vagotomy.