Assessment of quality changes in frozen sardine (Sardina pilchardus) by fluorescence detection

The formation of fluorescent compounds was tested as a quality assessment during the frozen storage of sardine at -18 degrees C (up to 24 mon) and at -10 degrees C (up to 120 d). The fluorescence ratio between two excitation/emission maxima (393/463 and 327/415 nm) was studied in the aqueous (delta F-aq) and organic (delta F-or) extracts after Bligh and Dyer extraction of the white muscle. Fluorescence results were compared to common quality indices [total volatile base-nitrogen (TVB-N); conjugated dienes; thiobarbituric acid index (TBA-i); and free fatty acids (FFA)]. delta F-aq showed good correlations with storage time (r = 0.80 and r = 0.72 at -18 and -10 degrees C, respectively) and TBA-i (r = 0.92 and r = 0.81). Principal-component analysis grouped delta F-aq with quality indices that are sensitive for the assessment of fish damage during frozen storage at both temperatures (TBA-I and FFA at -18 degrees C; TVB-N, TBA-i, and FFA at -10 degrees C). According to these results, fluorescence detection of interaction compounds in the aqueous phase can provide an accurate method to assess quality differences during frozen storage of fish.