Brewers' yeast and its derivatives have been used successfully in animal nutrition for decades. Leiber GmbH produces brewers' yeast products from their facilities in Germany, Poland, and Russia. Brewers' yeast is a high-quality byproduct of the beer brewing process, which is strictly regulated in Germany. Leiber produces various yeast derivatives for animal feed through processing, including inactivated yeast, autolyzed yeast with broken cell walls for improved nutrient availability, yeast cell walls containing beneficial glucans and mannans, and highly purified beta-glucans. These products provide nutrients, support immune function, and aid digestion when included in animal and aquaculture feeds.

1. BREWERS’ YEAST
PRODUCTS
B
rewers’ yeast and derived products
have been successfully used in animal
nutrition, including aquafeeds, for
several decades now. Leiber GmbH,
with two production sites in Germany
and further facilities in Poland and
Russia, have manufactured brewers’
yeast products for more than 60 years.
The following article will shed more
light on production background, well-known properties as well
as new insights into by-products of beer production and their
efficient use in aquaculture.
Reinheitsgebot: German Purity Laws
Beer brewing has a centuries-long tradition, and especially the
famous Reinheitsgebot, sometimes called the “German Purity
Law” of beer brewing. From the year 1516, this regulation has
enormously contributed to the great acceptance of beer as a high-
quality, food-grade product.
In fact, the Reinheitsgebot is a collective name for a series of
regulations limiting the ingredients for beer brewing to water,
barley (in specific cases wheat), hops and yeast.
Consequently, processing this yeast to a refined quality by
Leiber GmbH after the brewing process results in a premium,
standardised, quality consistent, guaranteed non-GMO raw
material free from other contaminants or additives (e.g. additional
flavor components, enzymes or even antibiotics and heavy
metals).
The yeast used during beer brewing is Saccharomyces
cerevisiae. The average cell size ranges between 5 – 13 µm with
the yeast cell wall being approximately 200 nm thick (which
constitutes 25 – 40 percent of the total dry mass of the cell).
For animal nutrition and dietetic purposes, brewers’ yeast can
be used as the whole, inactivated yeast cell (either drum-dried
or spray-dried). Furthermore, several products derived from the
yeast cell can be produced depending on the production process,
e.g. autolysed yeast, yeast cell walls, yeast extracts and highly
purified ß-glucans.
Inactivated, unextracted brewer’s yeast
Inactivated brewers’ yeast is characterised by a moderate to
high protein content of approximately 46 percent. Furthermore,
high levels of minerals and trace elements, amino acids, vitamins
and enzymes as well as many micro-nutrients are accumulated by
the fermentation process. All components are organically bound
and therefore highly bioavailable. Brewers’ yeast is especially
well-known for its high levels of B vitamins (with the exception
of vitamin B12), selenium and chromium.
Table 1 compares B vitamin contents and important trace
element levels of Leiber brewers’ yeast, soybean meal and fish
meal.
Autolyzed brewers’ yeast
Vertebrate as well as invertebrate organisms do not possess
the enzymes necessary for the breakdown of the yeast cell wall.
When the whole, inactivated yeast is administered through the
diet this can only be achieved through bacterial fermentation by
the gut microbiota.
Alternatively, the yeast collected from the breweries however
may be subjected to a gentle autolysis process, instead of direct
drying to produce inactivated, unextracted yeast.
This action is achieved by the yeast’s own enzymes, which
then leads to a break-up or perforation of the yeast cell wall. As
a result, the highly valuable cell contents including amino acids,
nucleotides and nucleosides, vitamins and trace elements, etc.
are released, and are therefore considerably easier and earlier
available to the organism during intestinal passage. This is
especially beneficial for organisms with a short digestive tract
like in shrimp.
Another characteristic of autolysed brewers’ yeasts are high
native levels of natural DNA and RNA components, named
nucleotides, nucleosides and pyrimidine and purine bases. They
are the building blocks for the synthesis of bases and nucleotides
for doubling of the DNA (cell division). During periods of
high requirements and physiological stress e.g. reproduction,
high growth and immunological stress; there is a clearly higher
demand for those components.
- excellent for use in aquafeeds
by Dr. Holger Kühlwein, Leiber GmbH, Germany
16 | March | April 2016 - International Aquafeed
FEATURE

2. The organism can build up DNA and RNA by itself but only
with great energy expenditure and over a long period of time.
Thus, nucleotides are considered to be semi-essential; in order
to support and accelerate cell division, cell regeneration and cell
repair they need to be supplemented in sufficient amounts.
Brewers’ yeast cell walls
The production process may not stop after autolysis of
the yeast cells. High power centrifuges are used in order to
separate soluble and insoluble components; such as the yeast
cell walls. The soluble cell contents are then predominantly
processed into various products for the food industry. The
insoluble yeast cell walls are used for dietetic purposes and in
animal nutrition. Yeast cell walls are naturally rich in β-glucans
and mannanoligosaccharides (MOS), e. g. Leiber’s yeast cell
wall product Biolex®
MB40 contains approx. 25 – 30 percent
ß-glucans and 20 – 25 percent mannans.
Yeast cell wall supplementation leads to various effects in the
gastro-intestinal tract of the animal including a prebiotic effect
on beneficial gut microbiota, binding and deactivation of certain
mycotoxins and agglutination of a range of pathogens and
their toxins. Further direct and subsequent effects include the
formation of a biofilm on the gut mucosa (additional protective
layer against infections), the improvements in immunity as well
as increased growth performance and feed conversion.
The overall aim of using yeast cell wall products is the
improvement of gut health, which is considered highly important
in animal husbandry. The gut is in many cases the main port of
entry for pathogens; a breaking of these pathogens through the
intestinal barrier often leads to disease outbreaks.
Brewers’ yeast products however have an additional major
advantage over yeast products sourced from other industries
(e.g. yeasts from bioethanol production, baker’s yeast):
they contain bioactive hop substances which remain from
the beer brewing process. Hops have not only been used in
beer brewing for centuries to give the typical bitter taste, but
also to preserve the beer. Important hop constituents include
humolones (α acids) and lupulones (β acids) plus xanthohumol,
as well as significant amounts of polyphenols (> 10 percent).
While xanthohumol is attributed with having cancer-inhibiting
properties, alpha and beta acids help defend the hop plant
against predation and pathogens.
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Table 1: Vitamin and trace element levels (mg/kg dry matter; DM) of
various aquafeed ingredients.
Vitamins and trace
elements (mg/kg DM)
Leiber
Brewers’
yeast,
unextracted
Soybean meal
extracted
Fish meal
B1 133 5 2
B2 48 3 9
B6 48 6 6
Niacin 425 34 59
Biotin 0.9 0.3 0.1
Folic acid 19 1 0,4
Pantothenic acid 106 16 10
Copper 64 20 6
Selenium 1.1 0.3 1.6
Zinc 106 50 90
(Data for soybean meal and fish meal according to NRC, 1998)
International Aquafeed - March | April 2016 | 17
FEATURE

3. The bioactive hop components have calming, antioxidative, and
most importantly bacteriostatic effects. This bacteriostatic effect
has been proven in a range of inhibition tests against a pathogenic
Staphylococcus aureus strain with Leiber brewers’ yeast products,
and due to the high concentration of hop constituents on the yeast
cell wall, Biolex®
MB40 showed the strongest inhibiting effect on
Staphylococcus aureus and seems to be particularly effective in
this respect.
Highly purified ß-glucans
Saccharomyces cerevisiae ß-glucans are considered highly
effective immunomodulators. They are located in the middle of
the three layers of the yeast cell wall, and their actual function in
yeasts is to provide strength and rigidity against environmental
influences. By a particularly gentle process, developed by Leiber
GmbH, the (1,3)-(1,6)-ß-D-glucan molecules are isolated from
the brewers’ yeast cell wall. However, the original structure of
the glucan molecules is retained. As a result, their full biological
activity is guaranteed and Leiber®
Beta-S exerts an active
immune-modulating effect during intestinal passage. Due to
high levels (> 80 percent) of ß-glucans Leiber®
Beta-S is able to
effectively support the animals’ metabolism and immune system
in a long lasting manner.
ß-glucans are administered through feed to prophylactically
support and augment the competence of the immune systems
of aquatic species. The reason is that under today’s intensive
rearing conditions, a variety of stressors including pathogens,
high stocking densities, handling and transport and suboptimal/
poor water quality may occur and negatively affect the
animal’s immune status. These factors compromise the immune
competence of fish, subsequently promoting outbreaks of
infectious diseases. Immune modulators like ß-glucans which
activate the immune system can contribute to improve immune
status and animal performance.
Leiber®
Beta-S was shown to have a significant influence in
improving health and immunological status in fish when fed
to rainbow trout and carp in a dose-response trial for 4 weeks
supplemented to the feed at dosages of 0 g (control), 100 g, 200
g, 500 g and 1000 g per ton of feed. Analysis of various immune
parameters in blood serum after 4 weeks of feeding confirmed a
significant increase of the immune status.
Subsequently, trout were challenged with Aeromonas
salmonicida and carp with Aeromonas hydrophila to determine
if the increase in the immune status also translates into a higher
disease resistance. Indeed, compared to the control the survival
rates were significantly higher in both species with Leiber®
Beta-S supplementation after the challenges. It should also be
noted however that with the highest supplementation (1000 g/to)
the increase was less pronounced emphasising the importance of
meeting the optimal dosage.
In conclusion, an optimum dosage of 200 g Leiber®
Beta-S per
ton of feed is recommended for both species.
Conclusions
Brewers’ yeast is a high quality by-product of the beer brewing
industry and offers great opportunities to be refined into a whole
set of different products with specific properties in a sustainable
way. Depending on the aquaculture industry’s needs these
properties range from nutrient-rich and dietetic unextracted
brewers’ yeast to very sophisticated, highly purified ß-glucans
augmenting the immunocompetence of aquatic species in order to
aid in the reduction of disease outbreaks and mortalities.
Future investigations will further explore antimicrobial
properties of brewer’s yeast products which enable to formulate
feeds with functional benefits to face a new and sustainable future
in aquaculture.
18 | March | April 2016 - International Aquafeed
FEATURE