Yeast products are getting more and more popular in aquaculture. However many products (as a whole or as fractions) are on the aquaculture market at the moment and differentiating between one from another can be difficult. This small article aims at shading some lights on the subject and explains that all yeast products are not equal.

1. November | December 2012
Yeast in aquaculture
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The International magazine for the aquaculture feed industry

2. FEATURE
Yeast in aquaculture
by Philippe Tacon PhD, Lesaffre Feed Additives, France
Y
east products are getting more shrimp and marine fish larval feeds or included Nutritional properties of yeast:
and more popular in aquaculture. as a protein source in aquafeeds. Typical dry yeast composition is 93-97
However many products (as a The reasons for this extensive use is its percent dry matter and can contain from 40%
whole or as fractions) are on the excellent nutritional contents, its easy supply to 60 percent crude protein nitrogen, 35-45
aquaculture market at the moment and dif- in dried form or under liquid form when percent carbohydrates, and 5-9 percent lipids.
ferentiating between one from another can bakery yeast plants or breweries are near A quite important fraction of the nitrogen is
be difficult. This small article aims at shading aquafeed plants, and nowadays a competitive under the form on nucleic acids (up to 12%)
some lights on the subject and explains that price in regards to other protein sources such that can lead to produce significant level of
all yeast products are not equal. as fish or soybean meal. Further applications uric acid if consumed at high concentra-
are being developed for yeast as functional tion, like meat. The Amino acid profile of
Yeast is a unicellular organism belonging to feed additives as probiotic live yeast, yeast yeast is close to soybean meal and therefore
the kingdom of Fungi. More than a thousand fractions (yeast cell walls, yeast extracts) or as well adapted to animal nutrition; it is rich in
species have been found in two major phyla: a source for more purified products such as Glutamic acid and Lysine (up to 8%). Yeast
Basidiomycota and Ascomycota in which beta-glucans and nucleotides. The production is naturally rich in B vitamins such as biotin,
belong species able to duplicate by budding process of yeast can allow the possibility to thiamine and folic acid. It also produces niacin
such as Saccharomyces cerevisiae. incorporate trace minerals and then produce but contrary to some belief does not produce
Due to their unique properties to grow highly bioavailable organic trace minerals, also B12 Vitamin. Ergosterol which is a significant
under aerobic conditions and produce gas known as selenium and chromium yeast. fraction of yeast cell wall, also is also a precur-
and ethanol under anaerobic conditions, some The pink yeast Phaffia rhodozyma, is natu- sor of Vitamin D2 by using UV treatments.
yeast (mostly S. cerevisiae) have been used rally rich in astaxanthin and has been used for
for the manufacture of fermented foods such some time as natural source of the pigment Baker’s yeast
as bread , beer and wine for a long time. in salmonids. Although now it tends to be Even if their name remains Saccharomyces
Yeasts are also used as single sell protein replaced by bacterial products which have a cerevisiae (cerevisiae for beer), most of the
source in animal nutrition and in aquaculture higher concentration and whose cell wall is strains of Baker’s yeast have been selected
under various forms and species (Torulaspora, more easily degraded. We will only refer in for their high fermentative power, particularly
Torulopsis, Kluyveromyces, Saccharomyce et the following article on products coming from useful for bakers.Strains are specific to the
caetera). It can be found for example in S. cerevisiae origin. type of bread and the region where it is sold,
in order to respond to different bread making
conditions (French bread, white bread, flat
bread, croissant, etc.) and resist to different
process conditions (osmotic pressure from
high sugared bread, freezing, acidity of sour
dough,…).
Baker’s yeast comes as a pure and pri-
mary culture grown on sugar substrate such
as molasses. The production is performed
under very strict conditions in order to main-
tain the genetic purity, consistency, specificity
and efficacy of the strains. (Figure 1). It can
be sold under different forms and packaging
(instant dried yeast, active dry yeast, com-
pressed, cream).
The primary grown culture controlled
process makes also a very consistent base for
the production of yeast extracts, autolysed
yeast, yeast cell walls and their derivate:
nucleotides and beta-glucans. Yeast cell
walls produced from Baker’s yeast usually
Figure 1: Yeast manufacturing process (primary grown culture)
have a high content of mannans. They are
14 | InternatIonal AquAFeed | november-December 2012

3. FEATURE
FEATURE
important for vaccinator safety but on growth parameters in tilapia a
Table 1: Effect of live yeast Actisaf also the encounters as
under stress conditions. fish. contract vaccina-
safety and welfare of the(n=3, P<0.05, measures with different letters are
significantly different)
The fish are then delivered onto a stainless tion team, is poor
steel table where the fish then(%) vaccinated anaesthesia of PER
Treatment Survival are SGR FCR the
in a very specific area, with only a 3 mm toler- fish and also poor
ance. The team must achieve a 96 percent grading, prior to vac-
CON 40% -10 fry 75.0ab 3.33a 3.11e 0.83ab
accuracy target and considering most vaccina- cination of the fish.
CON 40% -20 fry 64.8a 3.47a 3.26e
tors handle between 15-20,000 fish each this Poor anaesthesia of 0.78ab
is quite 40% - achievement!
Act some 10 fry 87.5bc 5.80d 1.43abc 1.89cd
the fish can lead to
The 40% are then returned to a recovery high mortalities. If
Act fish - 20 fry 92.6c 5.43c 1.01a 2.64d
tankAct 27% - 10come round from the anaes- fish are under anaes-
and should fry 91.7bc 5.46cd 1.62bc 2.26c
thetic within about two to three minutes. thetised, the whole
Act 27% - 20 fry 96.29c 5.24c 1.17ab 3.17e
There is always some level of mortality after process becomes
this high risk, stressful process but usually it is stressful and danger-
just a few fish, around toxin for every 100,000 ous for dried. It can also
recognised as good 100 binders. Fractions drum them (imag-
Figure 2: Schema of a process to produce yeast
fish vaccinated.baker’s mortalities immediately ine having a as a more
coming from High yeast have a light beige been grown major
extracts and yeast cell walls
colour. controlled product and
after vaccination are usually attributed to poor operation whilst
anaesthesia rather than aquaculture application only partly sedated!). find
The most popular the injection. specific strains and
of The consequenceshatcheries where it is a On way to human care as a food supplement tively high and and its amino acid content is
Baker’s yeast is in of poor vaccination its the other hand,
major feed source forapparent and rotifer (see ifand holistic therapeutic, also known as natural similar to baker’s yeast. Numerous works
usually only become artemia months after they are over
vaccination and can last et al 1990). brewer’s yeast.
for example Couteau up until harvest where anaesthetised, they have shown the efficacy of Brewer’s yeast to
Brewer’s yeast for aquafeed applications replace partially or totally the proteins found
the financially consequences become appar- risk not recover-
Brewer’s Yeast
ent. The main problems are: ing sold by trading companies as a commodity in fish and vegetable meal in fish and shrimp.
is quickly enough,
Incorrect needle depth resulting in either resultingon the protein content, or by local Shrimp feeds formulators typically incorporate
Brewer’s yeast can be identified either based in piles of
as the ferment used (needle too short) or fish in the in need to dispatch their slurry. The brewer’s yeast in their formula at the rate of
intra-muscular injection in brewery industries breweries recovery
internal primary damage, including granuloma tank causing the supply of these products can two to four percent.
(Yeast organ production) or the by-product quality and suffoca-
(needle too long) which results in the fish not tion inconsistent and depends greatly on the
of these industries which is the form mainly be or even worse, Brewer’s yeast can be used to produce
used in properly due to damage tocase, gut.
growing source of supply.
aquaculture. In the latter the yeast not recovering at all. yeast fractions, however due to the nature of
biomassnot harvested from the the disease
Fish is being immune to fermentation The nutritional content is similar as the brewer’s yeast and the specificity of the pro-
The other risk
because of incorrect dosage (or no It can be one here is to the
Innovative and proven
vats at the end of beer fermentation. vaccine) factorin baker’s yeast, but contains more trace duction processes, the quality is less consistent
being under liquid form (18-20% of dry matter) vaccinators. If as selenium and chromium. than in baker’s yeast. Products coming from
sold delivered. minerals such the
as problems spray or 29/10/2012 13:57
Two ridgewaybio_quarterpage_print.pdf
of the yeast products
but preferentiallymaininactive yeastSalmovac1 mineral oils used in of brewer yeast is rela- brewery yeast tend to have a distinctive bitter
The protein content
in aquaculture
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november-December 2012 | InternatIonal AquAFeed | 15
november-December 2012 | InternatIonal AquAFeed | 11

4. FEATURE
enzymes (notably pro- transfer from lab conditions to farm using
teolysis) or playing on commercial feeds.
the osmotic pressure All the work published so far was made
to rupture the cell wall with yeast either top dressed on feeds or
(plasmolysis). Different incorporated in pressed (uncooked) feeds.
grades of autolysed Nevertheless some direct effects to the gut
yeast can be obtained maturation have been found in sea bass with a
depending on the level species extracted from the rainbow trout gut
of autolysis (from partial Debaryomyces hansenii (see the works from
to total). The final prod- Tovar-Ramirez and also the reviews by Chi et
uct is a mixture of cel- al 2006 and Gatesoupe 2007). Marine yeasts
lular content and yeast and yeasts isolated from fish seem a very
Figure 4: Cumulative mortality after immersion cell wall. Furthermore logical choice to use in species of aquaculture
with L. anguiilarum (blue line is control, orange line
is Pronady at 0.5g/kg. n=3, Pronady significantly
the autolysis process interest. However, such material is often dif-
decreases mortality at 120h. P<0.01) degrades protein and ficult to grow under industrial conditions and
forms peptides (dipep- did not lead to the development of an actual
tides to tetra peptides) product yet. The products on the market are
smell and taste and a darker colour than the and oligonucleic acids which are readily digest- therefore often from S. cerevisiae origin. It has
ones coming from baker’s yeast. ible by the animal. Again here depending on to be noted that up to now, no yeast prod-
the original yeast material used, autolysed and ucts have been registered in EU as a probiotic
Ethanol Yeast inactive yeast quality can be very different. in aquaculture.
Ethanol Yeast are harvested after hav- As an example of S. cerevisiae effects,
ing performed alcoholic fermentation and Live Yeast as probiotics (Lara Flores et al 2003, 2010) Table 2 shows
distillation for the conventional production Live yeast helps regulate the gut microbio- some works done in tilapia fry fed for 3 weeks
of Bioethanol from sugarcane, beet sugar ta. Its effects have been shown, first in human with feeds supplemented with Actisaf (also
or grains syrup. In the first case, the yeast where it can reduce diarrhoea, especially knwn as Biosaf) at 1 kg/T in two diets (40%
biomass is harvested and then dried with with children. Specific strains have then been and 27% proteins) and at 2 crowded condi-
the recycled energy used to heat the vegetal developed and produced industrially such as tions (1 fry per L or 1 fry per 2L).
material. The majority of ethanol yeast comes S. cerevisiae boulardii or S. cerevisiae Sc 47 All the yeast treatments also increased the
from Brazil. (Actisaf) for the animal nutrition market. It is alkaline Phosphatase activity, and we can see a
Production prices and selling prices are a common practice now to supplement feeds better improvement of feed conversion ratio
very low, however the quality, such as the to increase milk production in dairy cows (FCR) and survival under stressful conditions
protein content is very inconsistent. The sup- or help piglets
ply depends on the activity of the bioethanol survival.
plants and can also be inconsistent. Another Live yeast
concern is the sanitary safety of these prod- are charac-
ucts. Antibiotics are sometimes added to the terized by
process in order to prevent bacteria compet- their living
ing with the yeast for nutrients andavoiding cells count,
yield decrease. It is therefore possible that expressed by
some antibiotic residues and possibly other colony forming
toxins might be left in the final dried product. unit (cfu per
Autolysed yeast – Inactive Dried Yeast gram), typically
Inactive and Autolysed yeast come from ten billions
primary grown cultures or Brewer’s yeast. cfu/g. Dosages
They are major products within the food are made in
industry as flavour enhancers and in pet food the feeds as Figure 3: Number of pellets remaining in the feeding tray one
hour after feeding (n=4, YE are significantly different than
as feed attractants. They are used in aquacul- dilutions to get
control at P<0.05).
ture feeds as a source of protein and nitrogen. an efficient cfu
Brewer’s yeast, and its ethanol equivalent, is count per g of
mostly favoured as it is cheaper than baker’s feed, a 1000 fold dilution giving a 10e107 per (low protein percentage and crowded condi-
yeast. They are also easier supplied as yeast g of feed for example. Viability of the yeast is tions). There is also a better protein efficiency
suppliers prefer to sell the more controlled mandatory for its effect and cfus should be ratio (PER) and digestive enzyme activity
and tailored Baker’s yeast on food markets. checked before and after pelleting using plate when Actisaf is used.
Inactive yeast is a yeast that has been counts. Live yeast can be used directly on farm,
deactivated by high temperature drying (often Despite the increasing use of yeast as where it has been showed (empirically) to
spray drying). The cells come as a whole a probiotic in terrestrial animals, there improve water quality in shrimp and fish
and the cell wall is not ruptured making the are only a few numbers of works studying ponds. It is either used alone or mixed with
access to intracellular material (amino acids, its effect in fish as a gut functions stabi- bacteria. Farms producing mash feed onsite
vitamins…) difficult. A way to access these liser. The major reason is that live yeast also add yeast in order to degrade cellulolytic
materials is to partially hydrolyse the yeast does not resist the severe conditions of material to ensure a better digestion.
cell wall to let the cellular content be partially the manufacturing processes of aquafeeds
released from the cell. This can be facilitated (high temperatures, steam, long condi- Yeast Culture or fermented yeast.
by activating the internal autolytic enzymes tioning times, see Aguirre-Guzzman et al Yeast culture is a particular product in
of the live yeast (autolysis), adding external 2002). The studies are then difficult to which yeast is allowed to ferment. Yeast bio-
16 | InternatIonal AquAFeed | november-December 2012

5. FEATURE
Figure 5: Yeast rich in organic selenium manufacturing process
mass, substrate and fermented extracellular in functional feeds, and hatcheries, as a aquafeed in shrimp. In a trial performed in
metabolites are then dried. source of nucleotides complementing the Thailand with white shrimp L. vannamei.
de novo synthesis of cells in multiplication Feed containing YE at 2 kg/T of feed was
Yeast Extracts. and helping boost immunity and anti-stress presented in feeding trays at the corner of
Yeast extracts (YE) come from the mechanisms. hapas and the remaining feed was counted
further hydrolysis and purification of Autolysed yeast and inactive yeast are after one hour. We can see a faster feed-
autolysed yeast. Insoluble yeast cell walls commonly mistakenly sold on the label ing when YE are included. (Tacon and
are separated from the cellular content yeast extract in aquaculture. A good way Suyawanish 2011).
by centrifugation. YE are very soluble, to differentiate them is to look at the
rich in peptides (up to 65%-70% of the carbohydrate levels. Autolysed yeast has Yeast Cell walls
product), free amino-acids like glutamic around 20-22% (mostly from the remaining Yeast Cell Walls (YCW) represent
acid and vitamins. They also contain a high YCW) whereas YE contain only three to the shell of the yeast cell and are roughly
level of nucleic acid which can be further six percent of carbohydrates. 40-50 percent of the mass of the cell.
purified to increase the level of tasty 5’ The small peptides and free amino acids YCW are composed mainly of fibrous
nucleotides. They are used in aquaculture in YE can also prove a potent attractant for polysaccharides glucans with beta 1,3 and
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november-December 2012 | InternatIonal AquAFeed | 17

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7. FEATURE
FEATURE
a beta 1,6 links, (50% and 8% respectively ), tration (2 kg/T) only for a short period, or as both alpha and beta forms)or mannans.
s are mannans under the form of Mannoproteins a low concentration continuously (0.5 g/Kg). Not all the YCW are equal. Efficiency should
(40%) and chitin (2%) (see Lippke and An example of sea-bass juveniles fed with be checked as a prerequisite to use, or
PER Ovalle 1998). Further purification can lead Pronady (a YCW of the Lesaffre group) at change, YCW.
to the production of either purified beta- 0.5 g/kg of feed for 8 weeks can be seen At LFA we have conducted a survey
.83ab glucans (50% and up) and mannoprotein in Figure 4, showing a significant protection of four YCW (2 bakery and 2 brewery
(often used in wine making for clarifica- against L. Anguillarum without any growth yeasts) produced in 4 of our own factories
.78ab
tion). The presence of these compounds difference with the control. However a mini- in the same L. Anguillarum challenge in sea
.89cd often leads to the mislabelling of YCW as mal amount of YCW seems needed to be bass supplemented at 0.5 g/kg of feed for
2.64d MOS or Beta-glucans. ingested before challenge in order to provide 8 weeks. Only 2 responded significantly (1
2.26c These two carbohydrate types are very an efficient immunostimulation and so there bakery, 1 brewery), the remaining 2 had even
3.17e interesting for the aquaculture market, beta- might be a gap period when the product is negative results at 4 weeks (lower survival
glucans are direct stimulators of the immune not efficient. (data from Dr. Morgane Henry, than control). This result shows first that not
systems in shrimp and fish, upon the stimula- Hellenic Center for marine Research , 2011) all is understood in the way these products
can also
tion of specific Schemacellsa(granulocytes or
Figure 2: blood of process to produce yeast YCW products, depending on the quality work and that one particular YCW cannot
s a more
Mannans are involved in the of the autolysed yeast separation, contain
macrophages). and yeast cell walls
extracts be replaced by another.
duct and
binding to pathogenic bacteria (especially also significant percentages of proteins and
and find
those with pili having mannose receptors) lipids. It should be noted that the lower the Selenium Yeast
man care as a food supplement tively high intestine. its amino acid contentthe higher of level of carbo-
and eliminate them from the
and and
It level of proteins,
is
Yeast can be induced to be a source of
rapeutic, also known as naturalthatsimilar to baker’s yeast. hydrates, and worksthe better immunostimu-
is also suspected the mannanes act as Numerous then organic selenium, mainly under the form of
prebiotics promoting the growth of the efficacy of Brewer’s yeast YCW is. Various quality of
have shown beneficial lation from the to seleniomethionine, which is then stored in
east for aquafeed applications replace partially or totally YCW are on found
bacteria. the proteins the animal production market proteins. During the growth of baker’s yeast,
ng companies as a commodity shown and be effective and fish and shrimp. can be found between
YCW have been in fish to vegetable meal in major differences selenium is added to the medium and is
protein content, or bythe resistance to feeds formulators typically incorporate on the strain, the sub-
to improve local Shrimp bacterial chal- products depending replacing sulphur in methionine. The excess
eed to dispatch their slurry. The aquaculture yeast in their formula at theto produce the yeast, and event
lenges in numerous brewer’s species. Beta strate used rate of of selenium is then eliminated by careful
glucans have to be two to four percent.
supply of these products can use carefully in aquacul- the drying process. washing steps (see Figure 5) to ensure that
t and depends greatly on experiments report yeast can be used to produce
ture as some the Brewer’s negative Mannans represent as most 25-27 per- the selenium left is 97-99 percent organic.
ly. effects in fish when yeast fractions, however due to the naturegood quality YCW from pri-
used for prolonged cent of YCW in of Selenium yeast should be then checked for
onal content is similar high the brewer’s yeast and the specificity of the pro- but can be found as low
periods at as concentrations.. This can be mary grown yeasts the highest percentage of selenomethio-
yeast, but contains morecareful choosing processes, the quality 9 less consistent
avoided by trace duction the source of as is percent in crude preparation coming nine and the consistency between batches.
as selenium andand using them than in at high concen- Productsindustry by-products. Glucans or poly-
YCW chromium. either baker’s yeast. from coming from Seleniomethionine is the main carbon-asso-
ontent of brewer yeast is rela- brewery yeast tend to have a distinctive bitterfrom 18 To 40 percent.
glucose can range ciated form of selenium in the animal’s body
YCW Protein and then allow making organic selenium
level remains which are readily available when oxidative
ming
the most con- stress reactions occur.
Upco r 2013
venient indica- The main application would be in aquacul-
fo tor of quality, ture as fish meal is a main supply of selenium
E vents World Aquaculture the best prod- and the development of diets with less fish
ucts being those meal will require compensation of selenium
The international triennial
conference & exposition of having lower in aquafeed formulae. Such an application
World Aquaculture Society nitrogen con- could be useful in preventing the oxidation
3
tent. The vari- of poly unsaturated fatty acids (PUFA) in
ability between fish flesh. Chromium yeast is seldom used in
February 21 - 25, 2013
batches can also aquaculture diets.
Nashville, Tennessee For all info contact us on
sia be very high.
USA www.was.com
worldaqua@aol.com Texture should Conclusion
be checked first. Yeast products are getting more fre-
Aquaculture Europe
Good YCW quently used in aquaculture. Some appli-
often have a cations are promising as the use as an
August 9 - 12, 2013
smooth, fine alternative source of proteins or as a sanitary
Trondheim, Norway
texture, low and welfare enhancer. However many prod-
Organised by European Aquaculture
Society granulometry ucts ranging from crude ethanol yeast by-
For all info contact us on and a light beige products to more purified beta-glucans are
www.easonline.org colour. There is available on the market. Therefore potential
W Making Sense of Science also the tenden- users must accurately select them in func-
at cy to believe tion of their targeted application. It is also
Asia Pacific Aquaculture that all YCW as important to select a reliable source of
December 10-13th, are the same the products to ensure a consistency of the
and that dif- supply.
2013
ferentiation of
Ho Chi Minh City, Vietnam
products must
For all info contact us on be done to the More InforMatIon:
www.was.com
worldaqua@aol.com
highest level of Website: www.lesaffre.com
glucans (some-
times measured
18 | InternatIonal AquAFeed | november-December 2012
012 | InternatIonal AquAFeed | 15

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