2.4.1. Determination of total volatile basic nitrogen (TVB-N)
Total volatile basic nitrogen (TVB-N) was determined through
direct distillation of the fish homogenates after the addition of
MgO. The distillate was collected in a flask containing a 2% aqueous
solution of boric acid and a mixed indicator consisted of 0.1%
methyl red and 0.1% bromocresol green in ethanol. Afterward, the
boric acid solutionwas titrated with 0.1 N H2SO4 solution (Goulas &
Kontominas, 2005). The TVB-N value (mg N/100 g of fish) was
determined according to the consumption of sulfuric acid.