L-histidine occurs in the bound form in proteins, but it is also present as the free amino acid in relatively high concentration in the tissues of certain fish e.g. tuna and mackerel.
Histidine decarboyxlase is found in some bacterial species. These include various species of Enterobacteriaceae, Clostridium, Vibrio, Photobacterium, and Lactobacillus.
The presence of most of the bacteria is often the result of unacceptable food-handling and hygienic practices.
Histamine, tyramine, and other amines such as putrescine, tryptamine, and cadaverine have been found in a variety of fermented foods including cheeses, meats, vegetables, fish products, and Oriental foods.
Histamine formed in food
