Acidifier concepts in aquafeed – high quality feed additives

D
r Eckel has been selling feed additives since 1994. One
of our core competencies is the utilisation of organic
acids and their salts for animal nutrition – either as
silage enhancers, as preservatives or as acidifiers.
Acidifiers are well established in pig and poultry nutrition – espe-
cially of young animals (piglets and broiler chicks). The concept of
acidifiers has been successfully transferred from agriculture feed to
aquaculture feed during the last 10 years.
Here also, the technical qualities of a feed additive play a crucial role.
Technical features such as the fluidity, dust, corrosive, odor and hygro-
scopicity can be the cause of a whole range of problems and dangers
in the compound feed production. The quality of feed additives affects
both productivity as well as occupational safety.
In this article, we wish to share our experience regarding important
technical and functional aspects of this transfer.
What distinguishes acidifiers?
In general, acidifiers as functional feed additives are made from
organic acids and their salts. Typically organic acids and their salts are
included in the feed at a dosage between 1kg/t (0.1%) and 10 kg/t
(1%). Some publications report dosages of up to 20kg/t (2%) – but this
might have been just for research purposes. Which organic acids are
used as acidifiers? A number of different organic acids and salts can be
used as acidifiers. The most common acids and salts are:
formic acid or calcium formate and potassium formate as their most
important salts;
• acetic acid or its sodium salt sodium acetate
• propionic acid or calcium propionate
• butyric acid or sodium butyrate
• lactic acid or calcium lactate and – last but not least –
• citric acid with different salts.
Other organic acids and salts used are fumaric acid / fumarates,
malic acid / malates, sorbic acid / sorbates. All these organic acids can
be distinguished and classified by a number of properties. Very impor-
tant for the usage as feed acidifiers are differences regarding:
pka-value, because it determines the degree of dissociation in dif-
ferent pH-environments;
solubility, because it determines bioavailability.
Another important property is the molecular weight, because
it determines the number of acid molecules per gram. Finally the
nutritional value of organic acid can also be taken into consideration
because organic acid salts like propionates are good energy sources.
Acidifier concepts in aquafeed
– high quality feed additives
Figure 2 Mode of action of acidifiers in fish
Figure 1 Mode of action of acidifiers in shrimp
by Tilman Wilke, Product developer and Daniela Martin, Product management,
Dr Eckel GmbH, Germany
22 | INTERNATIONAL AQUAFEED | November-December 2015
FEATURE

What is the mode of
action of acidifiers?
Acidifiers have a several modes of action in the
feed and in the animal. The most important modes
of action are the antimicrobial effect and the stimu-
lation and activation of digestive enzymes. Other
relevant modes of action are an unspecific immune
stimulation (e.g. in Shrimp), the chelation of min-
erals (and enhancing absorption), its nutritional
value and its sensoric properties (taste, smell).
The antimicrobial action of organic acids is pillared
by the ability of organic acids to lower the pH of
the feed, to reduce the buffer capacity of feed,
to lower the pH-value of the stomach and finally
by the ability of organic acids to directly impair
pathogen cells. The direct effect on pathogen cells
is closely related to the pH-dependant behavior of
the acid molecule. Depending on its natural pKa
value an organic acid binds or releases H+ ions. If
the pH value of the environment is lower that the
acid’s pKa value (e.g. in the stomach), the acid will
bind the H+ ions and is said to be un-dissociated.
In the un-dissociated state the acid molecule are
unionized and can therefore easily penetrate the
cell walls of pathogen cells. Inside the pathogen
cell the pH environment is close to neutral and
therefore higher than the pKa value of the organic
acid. Under these circumstances, the acid releases
(dissociates) its H+ ion and the acid molecule
becomes ionized. Now the ionized acid molecules
are trapped in the pathogen cell and start to accu-
mulate. This accumulation will lead to a pH-drop
and intracellular damage in the pathogen cell. Or
the pathogen has to spend a lot of energy to pump
out the ionized acid molecules. As all this depends on a number of fac-
tors (pH environment, pKa value, pathogen cell membrane, and patho-
gen cell pH-sensitivity) it is easily understandable that the antimicrobial
effect of organic acids is not always easy to predict under all conditions.
The stimulation of digestive enzymes is the result of a stimulation of
physiological feedback mechanisms in the gut. The lowered pH-value
of the stomach increases the amount of pepsin in the stomach and the
amount of trypsin and lipase released by the pancreas.
From feed to feces acidifiers do their work at different stages of the
digestive tract. Starting in the feed, organic acids have a preservative
effect in the feed and after ingestion they reduce the buffer capacity of
the feed. Lowered buffer capacity is favorable, because a feed with a
high buffer capacity can raise pH value in the stomach, which, in turn
impairs the antimicrobial barrier function of the stomach. This barrier
function is supported by a pH-lowering effect of the acidifier. And
the pH lowering effects also leads to increased release of proteolytic
enzymes in the stomach and in the small intestine. In the small intestine
the acidifiers can modulate gut microflora, act as energy source and can
enhance absorption of nutrients (e.g. calcium and phosphor) through
formation of chelates.
If protected (encapsulated) acidifiers are used, acidifiers can do their
job even in more distal parts of the gut. The mode of action depends
on the morphological features of the gut. Some aquaculture species
might lack a stomach but that does not necessarily mean that they will
not benefit from acidic support. But the diversity in fish gut morphology
explains the difficulties to transfer acidifier formulas and dosages from
one aquaculture application to another. If one takes a look into the
large amount of scientific literature about acidifiers in aquafeed he will
rediscover a quite confusing pattern of what acidifiers works in which
species und what feeding and conditions.
What are the main effects of acidifiers in aqua feed?
As a result of the modes of actions described before, acidifiers in
aquafeed have the following effects at farm level:
• Higher growth rates (growth promoter)
• Increased protein digestibility
• Better feed conversion
• Improved immune response
• Reduced mortality
That means that acidifiers in aquafeed contribute to animal per-
formance, farm profit animal health, antibiotic reduction and resource
efficiency.
Processing considerations
If acidifiers shall be used in aquafeed, one has to take into consid-
eration some technical aspects. On the one hand the organic acids
need to reach the animal’s intestine. Therefore leaching from the feed
particle into the surrounding water must be avoided. The solubility
of the acidifier in the feed must not be too high. To achieve this, it
is recommended that acidifiers be mixed into the feed manufacturing
before the pelleting step.
On the other hand, the organic acids must be bioavailable to the
animal. Hence, particle size should fit to species requirements and
size. And although leaching must be avoided, the acidifier must be
soluble in the animals gut to be effective. Finally, the feed manufactur-
ing process has to guarantee a homogenous mixture of the acidifier
in the diet.
Causes of errors and failure costs
In the feed manufacturing process the choice of acidifier can
also make a difference. Acidic ingredients like free organic acids
November-December 2015 | INTERNATIONAL AQUAFEED | 23
FEATURE

can cause problems in the feed mill. Free organic acids can lead
to corrosive damage of machinery. They can cause chemical
burns to workers. And they can lead to unforeseeable chemi-
cal reactions with other feed ingredients. All this risks can be
avoided if one uses acidifiers that are made from natural salts
of organic acids (most common are calcium, potassium, sodium
salts).
Classic acidifiers consist of a single type of organic acid or a com-
bination of two. In order to further improve the concept of acidifiers
Dr Eckel has developed so-called next generation acidifiers. The most
important features are:
• A combination or at least three organic acids.
For example formic acid + citric acid + lactic acid
• Usage of calcium salts of the organic acids that are highly bioavail-
able and have high nutritional value
• Microencapsulation of a part of the organic acids
• Microencapsulation in combination with essential oils
• But also the technical qualities of a feed additive, which affect the
production, are crucial for the choice of acidifiers.
Technical characteristics of feed additives (such as flowability, dust,
corrosive, odor, Hygroscopy) can be the cause of a number of errors
and risks in the compound feed production. Some of these errors are
very common, for example, Blockages. From a business perspective,
any error is associated with failure costs. The failure cost of increased
cleaning effort, increased system wear and reduced belt speed can be
summarised under the heading of productivity. A second group of fail-
ure cost includes costs resulting from accidents at work, the work and
organisational effort for the handling of hazardous substances and the
cost of labour protective equipment. This failure costs can be avoided
if care is taken when selecting a feed additive by their technical quality
characteristics.
It is worth paying attention to
flowability and dust formation
The use of raw materials with good flow properties and little dust
formation directly affects the operating speed in the compound feed
production and thus has a direct impact on the profitability of the com-
pany. In addition, the dust fraction has an effect on the work-security
at the production plant.
The formation of large dust clouds during production means higher
product losses, risk of segregation or bonding of silos and augers.
The tendency to form scale is closely related to the flowability.
The particle size distribution has - together with the particle shape
and the moisture content of a commodity - influence on its flowability
(Schüttgutrheologie). This applies to the fluidity of the following rule
of thumb: the smaller the particles, the flatter the particles are formed,
and the more residual moisture contained in the product, the worse
the flowability of a feed additive.
Buffered acids protect man and machine
Organic acids are widespread feed additives and have been tried
themselves in practice conditions as preservatives and as feed acids. In
its liquid form, these acids have the disadvantage to be irritating and
corrosive (figure 3). They degrade biological tissue such as skin and
mucous membranes, as well as materials made of metal, concrete and
stone.
Dealing with diluted formic acid is dangerous for the employees,
and it can cause considerable damages such as corrosion to storage
areas and machines.
With respect to storage areas and equipment companies are
faced with the choice between investing in corrosion-resistant facilities
and the regular replacement of corroded parts. A solution to these
problems are buffered acids. Formic acid buffered with ammonia,
FEATURE
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yields a blend of formic acid and ammonium formate,
which has only a corrosion rate of 40 mpy (mm / year)
- in contrast to the corrosion rate of 180 mpy in pure
formic acid.
In addition to the corrosive action of some acid
products also have a very strong odor. Using the salts
of the organic acids is very beneficial. They have the
same good antimicrobial effects and are contrary to the
acids odorless.
When mixing feed additives, it can also lead to
undesirable chemical reactions. Reactions in which
much heat is generated are particular critical. Because
the temperatures may damage the machine and change
the ingredients of the feed. Due to the variety of raw
materials and additives, chemical reactions can hardly be
predicted with the use of reactive additives in produc-
tion plants. Figure 4 shows that a highly exothermic
reaction leads to a sudden heating of the mixture when
using normal formic acid (left picture). When using a
specially formulated, reacted acid mixture, however, there is no heating
in the mixer observed (right picture).
Microencapsulation of organic acids
The encapsulation leads to a slow release of the encapsulated ingre-
dients (organic acids and essential oils) alongside the gastro-intestinal
tract. Endogenous lipase enzymes digest the fat capsule material. The
spectrum of particle sizes ensures that the release happens at all differ-
ent parts of the gut. The encapsulation of a part of the organic acid is
beneficial because it is a method to prevent leaching. This is especially
important in animals that do not swallow whole feed particles but
masticate their feed (like Shrimp). Furthermore, the encapsulation leads
to a slow release effect of free organic acids throughout the gut. Finally,
when organic acids are released in the most distal part of the gut they
can build an antimicrobial barrier against ascending infections. The
essential oils are protected by microencapsulation in order to transport
them to the target site (small and large intestine). Here, they can unfold
their antimicrobial potential.
Some essential oils have the ability to increase the permeability of
the cell wall of pathogenic bacteria. Hence, they have an own antimi-
crobial effect and they make organic acids more effective. In laboratory
tests we compared the antibiotic effect of an essential oil, an organic
acid and a combination of both against common food-borne patho-
gens. It came out, that the combination was way more effective than
Figure 3:
Aqueous
solutions of
formic acid form
highly corrosive
solutions. The
figure shows
an incipient
corrosion
damage
to an acid
collecting basin.
The storage
unbuffered
solutions requires
acid-resistant
containers and
pipes.
November-December 2015 | INTERNATIONAL AQUAFEED | 25
FEATURE
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the single substances. From a technical point of view the encapsulation
has some pitfalls. One has to ensure that the encapsulation material is
degradable by the target species. Further the particle size of the cap-
sules has to be adapted to the size of the animals. When encapsulated
acidifiers are to be added to the pelleting process one has to ensure
that the capsules survive the pelleting process.
Feeding trials
Although there is a large body of evidence about the effectiveness of
acidifiers in aquafeed, Dr Eckel conducted studies and trials to develop
and advance our acidifier products. A few of them shall be described here.
In a laboratory study at Kasetsart University (Bangkok, Thailand)
we investigated the immunological effects of our next generation
acidifier on antimicrobial genes (AMPs: C-type lectin and penaeidin)
of Pacific White Shrimp in different culture periods. It came out
that during harvest perdiod, C-type lectin and penaeidin and pro-
phenoloxidase gene expression of treated shrimp were significantly
increased. The researchers concluded that the acidifier up-regulated
the expression of AMP genes, which is seen as extremely positive to
cultured shrimp especially when there are challenges from pathogens,
bacterial or viral (e.g. Vibrio spp, White spot virus, IMNV, EMS, etc.).
This implies a strong health promoting effect from our next genera-
tion acidifier. Indeed, in another feeding trial this health promoting
effect could be verified. In this trial – also conducted at Kasetsart
University – different dosages of the acidifier (0% control, 0.3%,
0.6%, 0.9%, 1,2%) had been compared in a 60 days trial. The health
related measurement variables (survival rate, total bacteria count in
hemolymph at day 60, Vibrio count in hemolymph at day 60) were
significantly improved in the 0.3% group compared to the control
group. In addition, the results indicate a dose-effect relationship from
0.3% to 1.2%. Although there was a trend so increased body weight
gain with higher inclusion rates, this was not statistically significant. But
protein digestibility was measured as well and significantly improved
from 75% up to 84%. In another tank trial study with Pacific White
Shrimp at nursery stage the growth promoting effect was prominent.
After 21 days of feeding with a next generation acidifier at 0.3%
weight gain was significantly improved from about 0.2g to 0.5g in all
three replicates.
In a commercial scale trial with Tilapia (178 tons of fish biomass)
the growth promoting effect and the health promoting of next gen-
eration acidifiers were observed again: Survival rate in the treatment
group was 20% higher than in the control group without acidifier.
At the same time feed conversion was improved from 1.17 to 1.08.
Similar results were reported to us from a Tilapia nursery farm where
the ponds with acidifier in the feed produced bigger fingerlings (size
22) than the control group without acidifier (size 24) in the same
amount of time.
Obviously, the concept of acidifiers had been successfully
transferred from agriculture to aquaculture. Acidifiers have a strong
antimicrobial effect, they can enhance protein digestion and they
are able stimulate the immune system of Shrimp. The numerous
combinations of species, feeding practices and husbandry systems
make it difficult to compare the success or failure of different acidi-
fiers under different settings. From our research and development
efforts and the feedback from our customers we conclude, that
next generation acidifiers with microencapsulated organic acids
and essential oils are advantageous compared to classic acidifiers
because of their stronger antimicrobial power. At farm level, next
generation acidifiers as additives for aquafeed lead to increased
growth performance, better feed conversion and reduced mortality
and less need for antibiotics. This contributes to the farms profit
and to sustainability of the production.
FEATURE

Acidifier concepts in aquafeed – high quality feed additives

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