An international team of authors has reviewed the issue and published new data on glutamate intakes in Europe, its role in biochemical and metabolic processes and any differences between glutamate added as a food additive and that derived naturally from protein.
Questions of whether glutamate can cross the placental barrier and if the umami taste receptor is specific for glutamate have also been addressed, as has the role of MSG in improving the palatability of food for elderly populations whose appetite is waning.
MSG intensifies and enhances flavour without having a taste of its own, and also has the properties to act as a nutrient, as well as a dietary and salt substitute.
The use of the ingredient, popular in many Asian cuisines, looks set to increase its presence in the west.
Indeed, the global market for fermentation products is expected to rise by 4.8 per cent per year, to reach €13.6 billion in 2009.
Lysine and monosodium glutamate (MSG) are the largest products in this category.
Japanese firm Ajinomoto dominates the amino acid market, with more than 25 per cent of the market for lysine alone and 30 per cent of the MSG.
ADM and BASF also figure in the handful of players that dominate the landscape.
The authors noted that since 1997, two new studies have investigated the effect of glutamate on the lungs and found no adverse effects.
Some people have reported asthma attacks after the consumption of oriental meals, but when 109 asthmatics were tested none showed reactions to oriental food and none reacted to oral glutamate.
A rat study showed that high dose glutamate supplementation improved the immune status of rats recovering from chemotherapy.
Otherwise, information on the effects of high glutamate concentrations on immunological parameters was scarce.
A clear description of a phenotype which conferred sensitivity to glutamate has not been identified.
The authors also noted that dietary glutamate enhanced glucose-induced insulin secretion, consistent with the observation that there are stimulatory glutamate receptors on pancreatic beta cells.
In terms of fetal development, animal studies suggested that even doses well above normal physiological levels would not trespass into the fetal circulation.
Breast milk contains measurable amounts of free glutamate, so it is pointed out that infants consequently consume higher amounts of free glutamate/kg bodyweight than they are likely to do in later life.
Source: European Journal of Clinical Nutrition 2007, 61: 304-313.