Silage from tropical fish 1. Proteolysis

Summary Acid silages were prepared from silverbelly (Leiognathus sp.) at 30°C with 3% (w/w) of 98% formic acid. After 14 days, total protein solubilization was 45-50%, of which 80% was TCA soluble and collagen solubilization was 42%. Centrifugation of 14 day old silage gave a cystine-rich undigested sediment and a liquor with a low tryptophan content. Gel chromatography of the liquor of a 14 day old silage showed it to be composed of at least two fractions: one consisting of protein fragments of molecular weight greater than 5000 daltons and the other of free amino acids and small peptides. Soluble collagen breakdown products were found predominantly (75%) in the high molecular weight fraction. A mechanism for the solubilization of collagen by the action of acid pH, elevated temperature and non-specific proteases is proposed. The limited autolysis in silverbelly silage is compared with that found in cold water fish silages and attributed principally to the resistance of warm water fish collagen to the effects of acid pH and temperature during ensilation.