Comparison of the official EC method for the determination of total volatile bases in fish with routine methods

The determination of total volatile bases (TVB) is probably the oldest objective chemical method for assessing the spoilage of fishery pro­ ducts. It was proposed about a century ago and was already published as standard method for the inspection of fish in Germany in the first years of this century (KÖNIG, 1910). This simple method is still widely used. A European Union directive on fish hygiene specifies that if the organ­ oleptic examination reveals any doubt as to the freshness of the fish, inspectors may use TVB as chemical check (EU, 1991). The European Commission Decision of 8 March 1995 fixes the TVB limit values for three categories of fishery products and specifies the analysis methods to be used. The reference method involves steam distillation of an extract deproteinised by perchloric acid (PCA). For routine work, three other techniques are also allowed i. e. microdiffusion according to CONWAY (1947), direct distillation with magnesium oxide (ANTONACOPOULOS, 1968) and distillation of an extract deproteinised by trichlor­ acetic acid (TCA) (Codex Alimentarius, 1968). The aim of the present work was to compare the EC-reference method (PCA method) with the direct method (MgO method) and the TCA extraction method, using two types of apparatus: the compact Antona still and a semi-automatic Kjeldahl distilling unit (Kjeltec).