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°C (up to 24 mon) and at −10°C (up to 120 d). The fluorescence ratio between two excitation/emission maxima (393/463 and 327/415 nm) was studied in the aqueous (δF _aq) and organic (δF _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)]. δF _aq showed good correlations with storage time (r=0.80 and r=0.72 at −18 and −10°C, respectively) and TBA-i (r=0.92 and r=0.81). Principal-component analysis grouped δF _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°C; BVT-N, TBA-i, and FFA at −10°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.