Page 72 - New additives and ingredients in the formulation of aquafeeds

preparation of feeds, as well as the effect of acid pH during passage through
stomach, before being active in the intestine of the targeted fish. For this
reason, incubation of PEE for several minutes at different temperatures
resembling those used during feed preparation (1-5 min at 130ºC or 30-120
min at 80ºC) was used as a preliminary evaluation of its stability. In addition,
PEE were incubated at pH 3 and pH 4 during different time periods. Finally, a
combination of thermal and pH treatments was also used to evaluate PEE,
as resumed in Figure 4.
The highest activity after such treatments was obtained from PPE prepared
with viscera of black scabbardfish, Baird’s slickhead, Argentine shortfin
squid and particularly of the redfish (Sebastes sp). Considering this result,
as well as the local availability of fresh material, this latter species was
selected to prepare the visceral PEE used to perform the first experiment
of nutritional evaluation. In a second experiment the assayed products were
obtained from black scabbardfish ( Aphanopus carbo) and the Argentine
shortfin squid (Illex argentinus).
Nutritional
evaluation of
feeds including
enzyme
extracts
obtained from
fish viscera
The nutritional evaluation was carried out in two different experiments. As
indicated previously, in the first one the assayed PEE was obtained from
the viscera of the redfish (Sebastes sp) and showed a total protease activity
of 3,400 U/g. Preliminary assays showed no reduction in the activity after
incubation at 80 ºC for 30 min at neutral or alkaline pH, although it was
affected to a great extent by acid environment; it showed a reduction by
more than 90% after incubation at pH 3.0. Nevertheless, due to the absence
of a completely functional stomach in the juvenile fish on which feeds should
be used, this was not considered a problem. The PEE was included at 10 g/
kg (34,000 U/kg feed) in a commercial feed for juvenile sea bream (Sparus
aurata) of 4 g initial weight. The feed was finely grounded and after addition
of the product, which was carefully mixed into the mass, it was re-pelletized
into the suitable size. The feed used as control was processed in the same
manner. The conditions of the biological test are detailed in Table 2.
Table 2. Conditions of the biological assay used to test the nutritional effects
of using PEE from viscera of redfish as nutritional additive in feeds for juvenile
seabream
Biological material Gilthead seabream juveniles 4 g initial weight
Aquaria 80 L tanks in open circulation of seawater
3 tanks/treatment and 25 fish/tank
Feeding protocol 3 moments food supply/day at 9:00, 12:00 and 15:00 PM.
Ration adjusted to fish weight
Controls Temperature and oxygen (daily)
Weight (each 7-10 days)
Feed consumption (daily)
Duration of the assay 50 days (including 10 days of acclimation)
70 Use of purified extracts from fish viscera as an enzyme additive in feeds for juvenile marine fish