Chemical Methods for the Determination of the Freshness of Fish1 2

Abstract

Various objective methods to estimate the degree of freshness of fish and fishery products were compared. The total volatile nitrogen (TVN) and ammonia-nitrogen of carp flesh reached values of 30–33 mg% when carp stored at 0.4°C. and 25–27°C. began to have a bad odor. For catfish stored at 0–4°C. and 25–27°C. these values reached 20–30 mg%. Trimethylamine was not found in fresh and spoiled carp and catfish. The determination of trimethylamine as an index of spoilage cannot be used for these fresh-water fish. The determinations of tyrosine and volatile reducing substances (VRS) cannot be used to estimate the degree of freshness of fish if the temperature at which the fish had been stored is not known. If these two methods were combined with TVN and ammonia-nitrogen one could determine the degree of freshness of fish and the temperature at which the fish were stored. The determination of tyrosine combined with TVN and ammonia-nitrogen can give further support as to whether fish are absolutely fresh. If the temperature under which fish have been stored is known each of the tests used in this study can be applied individually to determine the degree of freshness of fish.

Sensory and Biochemical Quality Changes of Catla (Catla Catla) in Immediate and Delayed Icing and at Ambient Temperature

“…Results obtained in this experiment indicated statistically significant (p<0.05) differences between TMA-N content and storage time. Castell, (1949); Anderson and Fellers, (1952) and Somaatmadja et al, (1961) have confirmed the reduced amount of TMA-N in freshwater fish. Marrochi et al (1990) proposed TMA-N levels for first grade, second grade, and intermediate freshness as <1, 1-3, and 3-5 mg-N 100 g -1 .…”

Die Gehaltsänderungen der Stickstoffsubstanzen im Fleischgewebe der Brasse während der Eislagerung

“…J e 4 Filets wurden als Probe behandelt. Die Zeit der Probeentnahme wurde mit den einzelnen Yerderblichkeitsstadien in Einklang gebracht und auf 0, 2, 6, 10, I6 und 21 Tage festgelegt[I 11 Ein Wurfel Muskelfleisch von einer 8 x 4 cm groDen Flache wurde aus dem lateral-dorsalen Teil des Filets ausgeschnitten, in einer Fleischmaschine zerkleinert und30 Sek. lang bei 5000 U/Min.…”

“…3. Wassergehalt (durch Trocknung bei 105 "C).Fur weitere Bestimmungen wurde auf folgende Weise ein Extrakt erhalten: 10 g des homogenisierten Gewebes wurden mit30 ml eisgekuhlter, Ioyoiger Trichloressigsaure versetzt und in einem Porzellanmorser von 8 cm Durchmesser zerrieben. Nach 15 min.…”