Manufactured feeds are an essential part of modern commercial aquaculture, providing the balanced nutrition needed by farmed species. Much of aquaculture’s recent growth can be attributed to improved formulations, resulting in superior physical and nutritional feed properties. As more intensified culture systems are developed, greater emphasis has been placed on critical optimisation of the properties of aquaculture feeds, all of which contribute to a more economically sound feed conversion ratio.

1. M
anufactured feeds are an essential part of modern
commercial aquaculture, providing the balanced
nutrition needed by farmed species. Much of aquacul-
ture’s recent growth can be attributed to improved
formulations, resulting in superior physical and nutritional feed
properties. As more intensified culture systems are developed,
greater emphasis has been placed on critical optimisation of the
properties of aquaculture feeds, all of which contribute to a more
economically sound feed conversion ratio.
Phytogenic feed additives
In farmed aquatic species, the benefits of phytogenic feed addi-
tives, or botanicals, have been reported in several scientific studies.
Their plant-derived active ingredients (e.g. phenols and flavonoids)
can exert multiple effects in animals, including improvement of feeding
conversion ratio (FCR), digestibility, growth rate, reduction of nitrogen
and phosphorous excretion, improvement of the gut microbiota and
health status.
The extrusion process
During extrusion, ground, blended ingredients are processed at
high temperatures, moisture and pressure levels compared to conven-
tional steam pelleting. Normally, the process begins by steam treating
ingredients, raising the moisture by 20 percent to 30 percent and
reaching temperatures of 65˚ to 95˚C. The mixture is then conveyed
into a pressurised extrusion barrel (extruder) where it is cooked to
a temperature of 130˚ to 180˚C for anywhere from 10 seconds to
one minute. In these conditions, starch present in the mixture readily
gelatinizes. The cooked mixture is then extruded through a die plate.
When the mixture emerges from the pressurised chamber, some of
the superheated water mixture vaporises, causing a rapid expansion in
the volume of the pellets, which are then cooled and dried.
Extrusion has proven key to producing fish feeds with desired char-
acteristics in terms of floatability, durability, and water stability. While
most fish feeds rely on extrusion, the heat, moisture and pressure that
this introduces can render essential oils, which are volatile substances
contained in phytogenic feed additives, less effective.
Encapsulation of phytogenics
One of the most frequent conventional encapsulation techniques
is microencapsulation. Microencapsulation is a technology that coats
tiny particles of various substances in a sealed capsule. A benefit of
microencapsulation of essential oils is that can considerably limit any
strong odors or flavors, therefore avoiding potential palatability issues
for some sensitive species such as shrimp. Traditional microencapsula-
tion consists of a filled core surrounded by a wax or fat shell that, once
it bursts, discharges its contents.
In contrast to mononuclear, or single core, capsules, matrix encap-
Extrusion, essential oils and
fish feed optimisation
Advanced microencapsulation improves
delivery of phytogenic feed additives
Figure 1: Conventional coating (Micro-encapsulation) vs. matrix-
encapsulation (Digestarom® P.E.P. MGE) of essential oils
Figure 2: Improved recovery rates for of Digestarom® P.E.P. MGE
compared to non-encapsulated essential oils
by Rui Gonçalves and Gonçalo A. Santos, Biomin Holding GmbH, Austria
16 | INTERNATIONAL AQUAFEED | November-December 2015
FEATURE

2. sulation homogeneously distributes active compounds into a carrier
(Figure 1). As a vehicle for delivering phytogenic compounds, matrix
capsules offer a number of advantages over conventional single core
capsules. First, they are more robust and therefore better able to
protect phytogenic ingredients during feed processing (pelletization or
extrusion) and storage, avoiding ingredient losses. Second, botanical
substances are evenly distributed throughout the matrix, allowing for
continuous release in animals’ digestive tracts. Third, matrix capsules
provide better technological properties: they are dust-free, have excel-
lent flow ability and are easy to dose.
Proven results
In one trial the thermal stability of Digestarom® P.E.P. MGE a
matrix-encapsulated phytogenic feed additive was tested in controlled
extrusion conditions for a commercial sea bream diet. A batch of
30kg of the diet was then extruded reaching temperatures of 110 ˚C.
A non-encapsulated phytogenic, containing exactly the same essential
oils (EO), was used as a control.
Samples were taken after mixing and extrusion process for both
treatments. Results showed Digestarom® P.E.P. MGE had a superior
thermal stability (+14.6%), when compared with the non-encapsulated
phytogenic (Figure 2).
The second trial evaluated the efficacy of the matrix-encapsulated
phytogenic (Digestarom® P.E.P. MGE) supplemented feed, comparing
control (non-supplemented) feed and feed supplemented with non-
encapsulated essential oils. In the 12-week trial with gilthead sea bream
(Sparus aurata) at the University of Algarve in Portugal, fish were fed
a low fishmeal diet (14%), supplemented with a Digestarom® P.E.P.
MGE or the non-encapsulated essential oils, or without supplementa-
tion (negative control). Dietary supplementation with Digestarom®
P.E.P. MGE showed an FCR improvement of 12.5% when compared
with negative control, while non-encapsulated essential oils showed
an improvement of only 8.5% (Figure 3). Specific growth rates (SGR)
and weight gain (WG) were also improved by Digestarom® P.E.P.
MGE when compared to control or to non-encapsulated phytogenic
(Table 1).
The aquaculture industry’s continued pursuit of more efficient and
sustainable production means that phytogenic feed additives will have
a more prominent role in fish diets in the coming years. In light of the
widespread use of extrusion to produce fish feed, matrix encapsula-
tion offers a way to effectively deliver phytogenic compounds and
improve animal performance, as demonstrated by trial results.
Table 1. Growth performance parameters
Treatment SGR
(%/day)
WG (%bw/day)
Control 1.76 3.17
Digestarom® P.E.P. MGE 1.82 3.40
Non-encapsulated
phytogenic
1.80 3.25
Figure 3: Feed conversion ratio during experiment, for different
treatments
November-December 2015 | INTERNATIONAL AQUAFEED | 17
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