Novel histamine measurement by HPLC analysis used to assay histidine decarboxylase inhibitory activity of shoyuflavones from soy sauce.

An easy and highly sensitive method for measuring histamine by HPLC analysis coupled with precolumn derivatization was established. The amino group of histamine was completely colorimetrically labelled with 4-N,N-dimethylamino-azobenzene-4'-isothiocyanate (DABITC) in the presence of sodium bicarbonate at 90 degrees C for 5 min. The derivative was sensitively and easily analyzed by HPLC on a Cosmosil 5SL column using CHCl3/N,N-dimethylformamide/H2O (210:90:4) containing 0.4% acetic acid. Using the established method, histidine decarboxylase (HDC) inhibitory activities of three tartaric acid isoflavone derivatives, named shoyuflavones, isolated from soy sauce were examined in vitro by measuring the histamine produced by HDC. They showed intense inhibition of the activities of HDC from both mouse mastocytoma P-815 cells and Clostridium perfringens.