Free amino acids in dark- and white-muscle fish as determined by O-phthaldialdehyde precolumn derivatization

Free amino acids in fish reflect microbial spoilage, and are precursors of biogenic amines, factors of health concern and indicators of fish decomposi tion. The objective of this research was to quantify levels of free histidi ne, lysine, ornithine and glutamine, which may become originators of highly undesirable histamine, cadaverine and putrescine in fish tissue. Liquid ch romatography using o-phthaldialdehyde (OPA) pre-column derivatization, grad ient elution and a C18 column were used for separation. Histidine was highe r in white tissue of mahi-mahi and tuna than in red tissue. No significant difference in lysine levels was found between the two tissues of tuna. Glut amine and ornithine were higher in red tissue of mahi-mahi and tuna. Red sn apper had higher levels of lysine than histidine.