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Comparação dos metodos para determinação das bases nitrogenadas volateis (BNV) em pescado : parametros criticos e modificações
Arnaldo Yoshiteru Kuaye
DATA DE PUBLICAÇÃO
The objective of this work was to investigate and compare the methods of Lucke &Geidel, Instituto de Fomento Pesqueiro do Chile (IFOP) and IFOP modified in this study for determination of volatile nitrogen bases (VNB) in different species of fish. At the same time, it was studied the effect of hydrolysis of urea, caused by the distillation step, on the VNB value of dogfish flesh. It was shown that the VNB values were dependent on the methodology used for analysis, species of fish and storage time on ice. Comparison among the three methods reveled, regardless of the species, that the method of Lucke &Geidel gave higher VNB values than both the IFOP and the modified IFOP. Studies on the evolution of volati e nitrogen bases by the method of Lucke &Geide1 showed that these compounds continued to be distilled after 25 minutes of distillation. When the IFOP method was used, with previous protein precipitation, the VNB were completely distilled after 5 minutes. In the IFOP method, the substitution of trichloroacetic acid by sulfuric acid (2,5%) -sodium sulphate (7,5%) and magnesium oxide by a satured solution of Borax caused an increase of 10% in the VNB values. This increase was mainly due to TCA replacement. Model studies with pure urea solution and mixture of this solution with dogfish extracts revealed that the hydrolysis of urea during the procedure contributed up 49,70% of the total VNB of the extract. This hydrolysis was caused by distillation in alkaline medium. The initial values of VNB in sardine (Sardinella brasiliensis) fillets stored on ice, determined by the Lucke &Geidel, IFOP and modified IFOP methods, were 15,37, 8,46 mg and 9,98 mg, respectively. These differences creased with time and were not significant after 30 days storage. This behaviour was similar for whole sardines tilápia (Tilapia sp.). Regardless of the method, during the storage on ice the production VNB of dogfish slices increased in an exponentia1 manner. The Lucke &Geidel method gave values VNB of 54,14 mg and 361,42 in the 1st and 11th days of storage, respectively. In freshwater fish, tilapia and curimbatá (Prochilodus sp.) the production of VNB during the storage on ice increased slowly. The Lucke &Geidel method gave va1ues of VNB, for tilápia, of 21,32 mg and 32,56 mg in the 1st and 21st day of storage, respectively. The VNB values, for curimbatá, in the 1st and 11th day of storage were 18,52mg and 20,65 mg, respectively .