Glutamic acid is a natural constituent of many fermented or aged foods, including soy sauce, fermented bean paste, and cheese, and is also a component of hydrolyzed protein such as yeast extract.The sodium salt of glutamic acid, monosodium glutamate (MSG), is a widely used additive in the food industry.lutamic acid is a natural constituent of many fermented or aged foods, including soy sauce, fermented bean paste, and cheese, and is also a component of hydrolyzed protein such as yeast extract.