Note: Descriptions are shown in the official language in which they were submitted.
CA 02289090 1999-10-29
WO 98/49904 PCT/EP98/02503
METHOD FOR PREPARING HIGH OIL CONTENT FISH FEED PELLETS
The present invention. is directed to a method for
- preparing high oil content fish feed pellets, and in
particular such pellets which contain up to 50% by weight of
oil and from which only minor amounts of oil leak during
storage and use.
Fish fanning is an increasir_giy thriving industry in many
parts of the world. Fish feed for farmed fish is usually
produced in the form of pellets which contain a combination of
components which satisfy the nuts=tional rea_uirements of fish.
One of these recuirements is that the feed includes a source
of energy and this may be present in the feed as proteins,
carbohydrates, oils or any combination thereof. In general,
oils are included as at least one of the energy sources
because they are nutritionally excellent, are readily
available and are relatively inexpensive compared to the
alternative energy sources.
The oils presently used are liquid at ambient
temperature . If a significant quantity of oil is included in
the feed components prior to their extrusion into pellets,
then the oil interferes with the extrusion process and gives
pellets possessing relatively low strength. On the other
hand, if the oil is applied to pre-formed porous pellets of
the usual type, then it is found that the oil leaks out of the
pores both during storage and in use when the feed is immersed
in water. This is disadvantageous because both the energy
content of the feed diminishes and because the oil which leaks
out both pollutes and can cause feed-handling equipment to
malfunction.
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WO 98/49904 PCT/EP98/02503
2
At present, there is a demand from fish farmers for fish
feeds having an ever increasing energy content. Accordingly,
feed manufacturers are striving to prepare feeds having an oil
content of 30o by weight or more, but such high oil content
feeds suffer significantly from the problem or oil leakage.
Various solutions to the problem of oil leakage have been
proposed. Thus, JP-A-3-108 454 proposes to mix in an extruder
the conventional components for forming fish feed pellets in
combination with both a glycerol fatty acid ester and 10-50
wt.o of oil to produce feed pellets having a fat and oil
content of up to 50% by wt. However, it has since been found
that adding both the glycerol fatty acid ester and a
relatively high content of the oil to the feed formulation
prior to its extrusion can lead to difficulties in the
extrusion step, produces pellets of poor integrity and in any
event does not entirely solve the problem of oil leakage. In
a similar vein, it has been proposed in WO 95/07028 to treat
pre-extruded pellets with a heated mixture of a fish oil and a
lipid which is solid at ambient temperature. It is taught
that this mixture cools within the pores of the pellets to
form a crystalline structure in which the oil becomes trapped.
It has been found that the resulting pellets still suffer to
some extent from the problem of oil leakage.
It is an object of the present invention to provide a
method for preparing high oil content fish feed pellets which
have a reduced tendency to leak oil compared to pellets
presently available, and in particular those produced
according to the prior art acknowledged above.
CA 02289090 1999-10-29
PCT/EP 98/02503 3 73 -971 r2/su
Ewos Limited et al O~.C~~..1999
EP-A-0 688 025 discloses a fish feed composit~.on wi,ich comprises proteins,
:,
carbohydrates, fat, vitamins and trace elements. The feed is prepared by
extruding the
components for forming the matrix of fish feed including carbohydrates and
proteins into
pellets. The pellets are then coated with a mixture of edible oil which is
liquid at 40°C
and a saturated triglyceride and/or a saturated fatty acid thereof having a
melting point
above 40°C.
According to a first aspect, the present invention provides a method for
preparing fish
feed pellets comprising 10-50% by wt. of oil comprising the steps of:
(i) extruding a mixture comprising:
(a) components for forming the matrix of fish feed pellets including a source
of
carbohydrate and/or a source of protein, and
(b) an additive which is solid under ambient conditions selected from a lipid
and a
fatty acid;
to form porous pellets, and
(ii) absorbing oil into the porous pellets to prepare the fish feed pellets.
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CA 02289090 1999-10-29
WO 98/49904 PCT/EP98/02503
4
a lipid-type emulsifier, such as a mono-, di- or tri-
glyceride. One such suitable lipid emulsifier is glycerol
monostearate. Suitable fatty acids include stearic or
palmitic acids.
The matrix components and the additive are mixed such
that the resulting mixture preferably includes 0.1-loo by wt.
of the additive, more preferably 1-6a by wt. and most
preferably 1.5-4o by wt.
Prior to extrusion, the mixture may be subjected to
conventional pre-conditioning. In pre-conditioning, the dry
components of the feed and the liquid components, either
heated or at ambient temperature, are separately introduced
into a pre-conditioning device where they are continuously
mixed, heated and moisturised by injection of hot water and/or
steam. The intense mixing of water and steam added to the dry
feed during pre-conditioning initiates cooking of the feed
components. Pre-conditioners have been utilised in the
production of fish feed pellets for many years. Most pre-
conditioners contain one or two mixing/conveying elements
which consist of rotating shafts with radially attached
pitched paddles. The apparatus used for pre-conditioning
includes atmospheric or pressurised chambers.
If pre-conditioning is used, then typical temperatures
adopted lie in the range 75-95°C. Moisture is added to the
components in an amount of 5-30o by wt. or the dry feed
components entering the pre-conditioner. It is also possible
to add a small content of oil, such as fish oil, into the
chamber of the pre-conditioner. In this case, the oil may
preferably be added in an amount of 0.5-20% by wt., more
CA 02289090 1999-10-29
WO 98/49904 PCT/EP98/02503
preferably 1-IO% by wt. and most preferably 2-5% by wt, based
upon the dry weight of the other feed components fed into the
pre-conditioner.
. The optionally pre-conditioned mixture is then extruded
to form porous pellets. The mixture is directed into an
extruder assembly which consists of a barrel segment and a
screw. It is here that the major transformation of the raw or
pre-conditioned formulations occurs which ultimately affects
final product characteristics. Extruders employed in fish
feed manufacture are generally classified as being of a single
or twin screw design. In both designs, the impact of final
product characteristics is affected by screw and barrel
profile, screw speed, processing conditions such as
temperature and moisture content, raw material characteristics
and die/knife selection. Appropriate selection of an extruder
and extruding conditions is well known to one skilled in this
technical art. If the mixture has not been pre-conditioned,
then liquids such as water, steam or oil are added directly
into the extruder barrel. If oil is added to the mixture at
this stage, then this is in the amounts as previously
mentioned in connection with pre-conditioning. It is also
possible to add a proportion of the oil into both the pre-
conditioner and the extruder such that the total added amount
lies in one or more of the ranges mentioned above.
In the resulting porous pellets, it is believed that the
lipid or fatty acid additive forms oil receptive lipophilic
structures with the carbohydrate and/or proteinaceous
components present in the basic dry feed mixture. It is these
structures which later attract and hold the oil absorbed into
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WO 98/49904 PCT/EP98/02503
6
the porous pellets in the subsequent step of oil absorption.
The extruded pellets have a density of about 200-800
g/cm', preferably about 500 g/cm3. Such pellets preferably
have an average pore size of 10-50 ~m and more preferably
about 20-40 Vim.
In a subsequent step, oil is absorbed into the porous
pellets to prepare the high oil content fish feed pellets of
the present invention. The oil may be a single compound or a
mixture of individual oil comt~ounds. In particular the oil
may be fish oil such as menhaden oil, herring oil or capelin
oil.
Ir. the step of absorbing oil into the porous pellets, 1
part by weight of the porous reed pellets are mixed with 0.05-
1.0 parts by weight of the oil, preferably 0.1-0.5 parts by
weight and most preferably 0.3-0.45 parts by weight. This
amount is suitably adjusted according to the desired oil
content of the resulting fish feed pellets.
The extruded feed pellets may be loaded with oil
immediately after extrusion, or may be stored for some time
prior to the oil loading step. The loading of the feed
pellets with the oil can be carried out by mixing, dipping,
spraying, coating or any other means. For example, loading
can be carried out by subj ecting the feed pellets and oil to
rotary mixing in a drum under normal pressure, but the
operation can also be carried out under elevated or reduced
pressure.
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WO 98/49904 PCT/EP98/02503
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In a preferred aspect of the present invention, the
loading is carried out at below ambient pressure and in
particular by vacuum coating as described in any of DE-A-2 933
261, EP-A-0 556 883 or GB-A-2 232 573. The loading methods
described in these publications are incorporated herein by
reference. Such methods are preferred as they enable
relatively high amounts of the oil to be loaded and absorbed
by the feed pellets. Thus it is preferred that the extruded
pellets are first subjected to reduced pressure and then
simultaneously or subsequently the pellets are contacted with
the oil. The pressure applied during this step is around 1-
50kPa, preferably 10-30kPa. The loading step of absorbing oil
in the pellets is carried out for 30 seconds-30 minutes, more
preferably 1-5 minutes. Commercial apparatus is readily
available which is suitable for this step, and a specific
example is the apparatus sold under the Trade Mark "Vario Vac"
manufactured Dorit Maschinen Handels AG. After carrying out
the absorption of the oil into the porous pellets under
reduced pressure, the pressure is returned to ambient
pressure. This increase in pressure forces the oil into the
interior of the porous feed pellets.
In one particularly preferred aspect of the present
invention, the step of vacuum coating the porous pellets with
oil is repeated one or more further times in order to adsorb
further oil into the pellets. In this case, the individual
vacuum coating steps may be carried out in the same way.
Between the vacuum coating steps, the atmosphere may be
returned to atmospheric pressure although it is also possible
to increase it to less than atmospheric pressure before
applying the second or even a subsequent vacuum coating step.
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WO 98/49904 PCT/EP98/02503
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Coating of oil is carried out such that the resulting
fish feed pellets contain a total of 10-50 % by wt. of oil,
more preferably 20-50 o by wt. of oil and most preferably 30-
40 o by wt of oil.
Detailed crystallographic analysis of the resulting
pellets has revealed that there are no crystal structures
formed between the additive and the oil. Accordingly, the
mechanism of the trapping of the liquid oil in the pellets
provided by the present invention is clearly fundamentally
different from that relied upon in the pellets produced in
accordance with WO 95/07028.
According to a further aspect, the present invention
provides high oil content fish feed pellets obtainable by the
method previously described. Further, a method is also
provided for farming fish comprising preparing high oil
content fish feed pellets as described above and then feeding
such pellets to fish. The fish feed pellets provided by the
present invention can be fed to any type of farmed fish
including yellowtail, sea bream, halibut, yellow jack, carp,
trout, eel, cat fish, or most preferably salmon.
The high oil content fish feed pellets provided by the
present invention have lower levels of oil leakage than
previously available fish feeds, and in particular lower
levels than fish feed pellets produced according to the
methods of JP-A-3-108 454 and WO 95/07028. Accordingly, the
pellets provided by the present invention are advantageous in
that they suffer very little oil loss during storage and in
use which means that they are both economically and
environmentally advantageous.
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WO 98/49904 PCT/EP98/02503
9
The invention will now be described in more detail
according to the following Examples and Comparative Examples
which should not be considered to limit the scope of the
appended Claims.
Examples
Fish feed pellets A-E were prepared having the following
formulations
FEED A (Comparison)
Ingredient F'
Fishmeal 47.5
Soya Meal
Cereals (wheat/suprex corn) 10
Binder (Modified Starch)
Vitamins 0.5
Minerals 2
Fish oil 30
FEED B (Comparison)
Ingredient Feed
Fishmeal 47
Soya Meal g
Cereals (wheat/suprex corn) lp
Binder (Modified Starch) 2
Vitamins 0.5
Minerals 2
Hydrogenated Rapeseed Oil p.g
Fish oil 29.7
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WO 98/49904 PCT/EP98/02503
FEEDS C-E (Invention)
Ingredient Feed o
Fishmeal 47.5
Soya Meal g
Cereals (wheat/suprex corn) 7
Binder (Modified Starch? 2
Vitamins 0.5
Minerals 2
Glycerol Monostearate 3
Fish oil ~ 30
Each of the feeds A-E was prepared by mixing the basic
components including meal, cereals, binder, vitamins and
minerals together with 3°s by wt. of fish oil based upon the
total weight of the mixture. Further, in the case of Feeds C-
E, 3% by wt. of glycerol monostearate was added together
respectively with 3, 5 or 8o by wt. of fish oil into the pre-
conditioning unit. The feeds were then pre-conditioned at a
temperature of about 85°C together with 18% by wt. water based
upon the weight of dry feed mix entering the pre-conditioner.
The pressure applied during pre-conditioning was about 0.25
MPa.
The pre-conditioned mixture was then extruded using a
Wenger TX-57 twin screw extruder operating at 325 kg/hr with
the addition of further steam and water. The resulting
pellets had a diameter of 9 mm, a length of 11 mm and were
roughly cylindrical in shape. The resulting extruded pellets,
containing approximately 22o by wt. of moisture, were then
passed through a dryer where the moisture content was reduced
to approximately 7% by wt.
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The extruded pellets were then vacuum coated with oil by
firstly applying a vacuum of around 20 kPa to the pellets,
spraying fish oil on the pellets, releasing the vacuum to
atmospheric pressure then repeating these steps in a second
vacuum coating step. After the second vacuum coating step,
the pellets are ready for use. In the case of Feed B, the oil
was applied as a heated mixture in combination with 3% by wt.
of the mixture of hydrogenated rapeseed oil in accordance with
the teaching of WO 95/07028. It has been found that inclusion
of greater amounts of hydrogenated rapeseed oil in the oil
mixture does not lead to any greater anti-leakage effect in
the final pellets. Thus addition of 3o by wt. of the
hydrogenated rapeseed oil (equivalent to 0.8% by wt. in the
final pellets) has been found to provide optimum results
within the teaching of WO 95/07028.
The extent of oil leakage from each of the Feeds A-E was
then measured by the following method. Firstly, about 5 g of
the Feed being tested were placed on a filter paper in a Petri
dish. In order to simulate the effect of bag storage, 150 g
weight was then placed on an upturned Petri dish lid resting
on the pellets. The dishes were then placed overnight in a
heat cabin at 40°C. Simultaneously, a control dish with
filter paper only was prepared in order to measure and
compensate in the leakage calculations for the weight loss
from the filter paper due to moisture evaporation. Leakage
was then calculated based upon the increase in weight of the
filter paper as a percentage of the initial weight of the feed
pellets taken.
The following Table sets out the results of the oil
leakage tests applied to Feeds A-E
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WO 98/49904 PCT/EP98/02503
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Table
Sample AnalysisLeakage
Description
F % by s s by o by % by Fat % by Rela-
by wt wt of
a wt wt fish wt wt content oil whichfive
oil ~~z
GMS1 fish added fish inclu-of finalleaked
in from
d added oil the oil ded pellets pellets
pre- in
during
added the test
oil
to con- added in %
the b
y
dry to ditionerby coatingwt
the
d~ mixture
mix vacuum
mix
coating
A 0 3 0 27 0 34.3 39.5 100
B 0 3 0 27 3 35.1 25.5 65
C 4 3 3 24 0 36.1 15.4 39
D 4 3 5 22 0 35.7 4.1 10
E 4 3 8 I 19 0 35.9 5.4 ~ 131
GMS1 is Glycerol Monostearate
HROZ is Hydrogenated Rapeseed oil
It will be seen from the results above that Feed A which
includes no additive looses over 39o by wt. of the absorbed
oil. In comparison, the Feed B formulated generally in
accordance with WO 95/07028 looses only around 25o by weight
of its oil. On the other hand, the Feeds C-E formulated in
accordance with the present invention leak significantly less
oil, and in particular feeds in which oil is added to the pre-
conditioner have extremely low levels of oil leakage compared
to the Comparative Feeds A and B . Such relatively low levels
of oil leakage could not have been predicted on the basis of
the prior art.
SUBSTITUTE SHEET (RULE 26)
