Fresh fish waste was manufactured into fish silage using formic acid to reduce pH to 3.5. The pH remained below 4.0 for up to 30 days. The chemical composition (g/kg) of silage varied with the type of raw material; moisture 726 to 803 (mean 764); oil 3 to 71 (mean 38); ash 35 to 72 (mean 51); protein 144 to 161 (mean 147). During the first 8 days after silage manufacture, concentrations of the low-salt-soluble and insoluble protein fractions decreased while the non-protein nitrogen content increased. Silage viscosity continued to decrease with time up to day 15. The ensiling process caused a sharp initial decrease in the total number of bacteria, in lactic acid bacteria and in coliform species followed by a more gradual decrease up to 48 h. A comparative study of silage manufactured from flat-fish frames (A) and round-fish heads (B) at pH 3.5 or 4.5, showed chemical composition (g/kg) of 726 and 777 moisture; 70 and 3 oil; 55 and 70 ash; 149 and 150 protein for A and B, respectively. Silage viscosity showed greater decreases at pH 3.5 than at pH 4.5. Silage manufactured from round-fish heads showed greater viscosity decreases at both pH levels.
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Irish Journal of Agricultural and Food Research © 1993 TEAGASC-Agriculture and Food Development Authority