Monosodium glutamate (MSG)

Monosodium glutamate (MSG, E621) is the sodium salt of glutamic acid, a non-essential amino acid that is the most abundant excitatory neurotransmitter in the mammalian central nervous system and one of the most prevalent amino acids in dietary protein. MSG was first isolated from seaweed (Saccharina japonica) by Japanese chemist Kikunae Ikeda in 1908, who identified it as the carrier of a distinct savoury taste he named "umami." Commercial production today uses bacterial fermentation of glucose by Corynebacterium glutamicum, yielding a pure, crystalline form. In food, MSG enhances and intensifies savoury, meaty, and broth-like flavour notes by stimulating umami taste receptors (primarily metabotropic glutamate receptor mGluR4) on the tongue, allowing reduction of salt and fat content while maintaining palatability.

JECFA has assigned MSG a not-specified ADI, on the basis that glutamate is a normal constituent of virtually all dietary proteins and is present as free glutamate in fermented foods including parmesan cheese (~1.2 g/100 g), soy sauce, tomatoes, and mushrooms — dietary sources that dwarf typical food additive contributions (evaluated 1987 and 2006). The absorbed glutamate undergoes rapid catabolism in enterocytes and is largely oxidised as an intestinal fuel before reaching systemic circulation; the blood-brain barrier is essentially impermeable to orally ingested glutamate at normal dietary concentrations, making neurotoxicity via the oral route physiologically implausible. "Chinese restaurant syndrome," the cluster of symptoms attributed to MSG in a 1968 letter by Dr Robert Ho Man Kwok in the New England Journal of Medicine, has been extensively studied in randomised, double-blind, placebo-controlled trials; no consistent causal relationship has been demonstrated at food use levels when subjects are blinded to MSG exposure.

MSG is authorised under EU Regulation (EC) No 1333/2008 with specific maximum levels (10 g/kg in most savoury applications) and is designated as GRAS in the United States by FDA (21 CFR §182.1). It is not permitted in foods for infants and young children in the EU. The persistent cultural stigma around MSG, particularly in Western markets, contrasts sharply with its scientific safety record and its universal acceptance in East and Southeast Asian cuisines for over a century. The ADI classification is not_specified, the same level assigned to ascorbic acid and lecithin.