Modification of a colorimetric method for histamine analysis in fish meal

This study describes the modifications necessary to apply the colorimetric method for histamine detection in fish meal. Although the original colorime tric method works well with fish flesh, difficulties were observed during f iltration of the homogenised sample and column separation when it was appli ed to fish meal. In this study, the reason for the problems encountered was studied by processing fish meal using different parts of fish. It was foun d that the problem was caused by the presence of bone in the sample, which suggested that calcium in bone reacted with potassium hydroxide (KOH) used to adjust pH during the experiment. This was confirmed by a chemical test r eacting calcium carbonate with KOH solutions at different concentrations. T he reaction was reversible in acidic conditions with trichloracetic acid (T CA) or hydrochloric acid (HCl). Several tests were applied before the filtr ation and neutralization stage of the method to solve the problems occurred . Centrifugation of the homogenised sample similar to 20 min at 23 000 g an d filtration of the aliquot after neutralisation gave the best result among the tests applied. The method was further modified by evaluating the suita ble sample size, TCA volume and TCA concentration used as well as simplifyi ng the moisture content application for fish meal. Other minor alterations were also suggested for both original and modified method at the preparatio n stage of diazotizing solution and absorption measurement. (C) 2000 Elsevi er Science Ltd. All rights reserved.