“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 Bitter Sweet Umami Z X Y Salty Beef Chicken Yamaguchi, S. (1987)

Torii et al., In Umami: a basic taste, pp (1987) Umami preference is a marker of protein nutrition! Preference for umami is related to levels of dietary proteins Umami (MSG) NaCl 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 AspSerGluGlyAlaValMetIleLeuTyrPheLysHisArg Green Pink Red Full ripe (mg/100g)

Free glutamate in breast milk TauAspThrSerGlnGluGlyAlaValCysMetIleLeuTyrPheOrnLysHisArg (mg/100g) Total Glu intake = 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.”

Glutamic acid metabolized during digestive absorption Mouth Glutamic acid from Food Small intestines mucous membrane epithelial cell Glutamic acid 100% > 90% Blood Energy Protein biosyntheses Liver Glutamic acid Alanine, Glutamine Thermogenesis Hepatic portal vein

An liquid diet without Glu, does not elicit chemoreception

Sensors for Glutamate exist on Tongue & Alimentary tract Tongue (Taste buds) mGluR1 Small Intestine mGluR4 T1R1 Large Intestine mGluR4 & T1R1 mGluR4 mGluR4 & T1R1 mGluR4 mGluR4 & T1R1 Stomach mGluR1 & T1R1 T1R1 mGluR1 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 Saline Val Leu Ile Lys Trp Thr Phe Met Glu Gly Arg Ala Pro Cys Asp His Gln Asn Ser Tyr ( , 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.