[Factors Related to the Production of Histamine and Tyramine in Rice Bran Pickles].

Some rice bran pickles contain histamine (Him) and tyramine (Tym), which are nonvolatile amines, presumably produced by microorganisms during the fermentation process. When attempting to identify the histamine- and tyramine-producing bacteria from commercially available cucumber rice bran pickles containing Him and Tym, it was identified histamine-producing bacteria were found to be Raoultella ornithinolytica, and tyramine-producing bacteria were Lactobacillus curvatus. When those bacteria were cultured in media containing rice bran (the raw material for rice bran pickles), Him and Tym were produced. However, it was suggested that Him and Tym were not necessarily produced by the presence or absence of amine-producing bacteria, but rather, their production was affected by the amount of precursor amino acids and other bacteria that were present during rice bran pickles production.

[Content and Origin of Nonvolatile Amines in Various Commercial Pickles].

The content of nonvolatile amines (putrescine, cadaverine, histamine, tyramine, and spermidine) in commercial pickles and their raw materials was determined in order to investigate the origin of these amines and to evaluate possible health risks. The nonvolatile amine content varied depending on the type of pickle; histamine and tyramine contents were relatively high, namely, 6.0-264 and 2.0-369 µg/g, respectively, especially in soybean paste pickles and moromi pickles. Amines derived from raw materials were detected in soy sauce pickles, soybean paste pickles, and moromi pickles. However, the raw materials/vegetables of rice bran pickles, sake lees pickles, and malt pickles did not contain these amines, and so the amines in these pickles might have been produced by microorganisms during the fermentation process. Judging from the measured amine content of pickles, the potential health risk is estimated to be low.

Determination of Nonvolatile Amines in Foods by Improved Dansyl Derivatization Reaction.

An analytical method for the determination of nonvolatile amines (putrescine, cadaverine, histamine, tyramine, and spermidine) in foods was developed, using an improved dansyl derivatization technique. The five amines were extracted from food with 1% trichloroacetic acid. Three milliliter of extract was applied to a polymer-based strong cation exchange resin mini-column, which was washed with 5 mL of water, and eluted with 5 mL of 1 mol/L potassium carbonate solution. The eluate was dansylated, then 5 mL of toluene was added with shaking. The toluene layer was evaporated. The residue was taken up in 1 mL of acetonitrile and shaken with 1 mL of 5% proline in 1 mol/L potassium carbonate solution. The upper acetonitrile layer was collected, filtered, and subjected to HPLC. The limits of quantitation for putrescine and cadaverine in the samples were both 0.2 µg/g; those of spermidine, tyramine, and histamine were 0.8, 2.0, and 5.0 µg/g, respectively. The average recoveries of the five amines from nine foods exceeded 80%.