Autolysis and Rancidity Development in Tropical Freshwater Fish Viscera during Fermentation

To develop an ensiling process to preserve the nutrients
in fish viscera, the offal was homogenised with 10%
(w/w) molasses. Propionic acid (0.5% v/w) was added
as an antimycotic agent. NaCI (2% w/w) and ethoxy-
quin (0.02% w/w) were added to see the effect on
autolytic changes and rancidity development, respec-
tively. Fermentation was carried out under
microaerophilic condition at 26+2°C. Total volatile
nitrogen, non-protein nitrogen, alpha-amino nitrogen
(autolytic changes) and free fatty-acid content
increased (P <O.O01) rapidly during the first 4 days
and then remained constant up to 8 days. Salt had no
influence on autolysis. Peroxide value (PV) increased
(P<O.O01) initially up to 3-4 days and then
decreased. A rapid increase (P <0.001) up to 2 days
and small (P>O.05) subsequent increase in iodine
value (IV) were observed. Thiobarbituric acid (TBA)
number increased linearly up to 8 days of fermentation
period. Ethoxyquin was effective in controlling oxida-
tive rancidity, as indicated by significantly (P <O.O01)
lower PVs and TBA numbers and higher IVs. Copy-
ated (Hassan & Heath, 1986). Fermentation ensiling
seems to be a more economical process compared to
acid ensiling, as the latter requires expensive acids.
Hence, in order to develop a fermentation ensiling
process for the preparation of silage from fish
viscera this work was undertaken. Our earlier
studies indicated that a minimum of 10% molasses is
required to effectively ferment fish viscera (Javeed
Ahmed & Mahendrakar, 1995) and a microbiolog-
ically stable silage product can be obtained by
further treating viscera with 0.5% propionic acid
(Javeed Ahmed et al., 1995). Chemical changes in
fermentation ensiling have not been studied as much
as in acid ensiling (Raa & Gildberg, 1982). Autolytic
changes and rancidity development which may affect
the nutritional quality of fish-viscera silage are
reported in the present paper.