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. Digital Re-print -
January | February 2013
Yeast in aquaculture
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2. FEATURE
Yeast in aquaculture
by Philippe Tacon PhD, Lesaffre Feed Additives, France
Y
east products are getting more tive price in regards to other protein sources percent dry matter and can contain from
and more popular in aquaculture. such as fish or soybean meal. Further appli- 40 to 60 percent crude protein nitrogen,
However many products (as a cations are being developed for yeast as 35-45 percent carbohydrates, and 5-9 per-
whole or as fractions) are on the aquacul- functional feed additives as probiotic live cent lipids. A quite important fraction of
ture market at the moment and differen- yeast, yeast fractions (yeast cell walls, yeast the nitrogen is under the form on nucleic
tiating between one from another can be extracts) or as a source for more purified acids (up to 12%) that can lead to produce
difficult. This small article aims at shading products such as beta-glucans and nucle- significant level of uric acid if consumed at
some lights on the subject and explains otides. The production process of yeast can high concentration, like meat. The amino
that all yeast products are not equal. allow the possibility to incorporate trace acid profile of yeast is close to soybean meal
minerals and then produce highly bioavail- and therefore well adapted to animal nutri-
Yeast is a unicellular organism belong- able organic trace minerals, also known as tion; it is rich in Glutamic acid and Lysine (up
ing to the kingdom of Fungi. More than a selenium and chromium yeast. to 8%). Yeast is naturally rich in B vitamins
thousand species have been found in two The pink yeast Phaffia rhodozyma, is such as biotin, thiamine and folic acid. It also
major phyla: Basidiomycota and Ascomycota naturally rich in astaxanthin and has been produces niacin but contrary to some belief
in which belong species able to duplicate used for some time as natural source of the does not produce B12 Vitamin. Ergosterol
by budding such as Saccharomyces cerevisiae. pigment in salmonids. Although now it tends which is a significant fraction of yeast cell
Due to their unique properties to grow to be replaced by bacterial products which wall, also is also a precursor of Vitamin D2
under aerobic conditions and produce gas have a higher concentration and whose cell by using UV treatments.
and ethanol under anaerobic conditions, some wall is more easily degraded. We will only
yeast (mostly S. cerevisiae) have been used for refer in the following article on products Baker’s yeast
the manufacture of fermented foods such as coming from S. cerevisiae origin. Even if their name remains Saccharomyces
bread , beer and wine for a long time. Yeasts cerevisiae (cerevisiae for beer), most of the
are also used as single sell protein source in Nutritional properties of yeast strains of Baker’s yeast have been selected
animal nutrition and in aquaculture under Typical dry yeast composition is 93-97 for their high fermentative power, particu-
various forms and larly useful for bakers. Strains
species (Torulaspora, are specific to the type of
Torulopsis, bread and the region where
Kluyveromyces, it is sold, in order to respond
Saccharomyces and to different bread making
caetera). They can conditions (French bread,
be found for example white bread, flat bread,
in shrimp and marine croissant, etc.) and resist to
fish larval feeds or different process conditions
included as a protein (osmotic pressure from high
source in aquafeeds. sugared bread, freezing, acid-
The reasons for ity of sour dough,…).
this extensive use is Baker’s yeast comes as
its excellent nutri- a pure and primary culture
tional contents, its grown on sugar substrate
easy supply in dried such as molasses. The pro-
form or under liq- duction is performed under
uid form when bak- very strict conditions in order
ery yeast plants or to maintain the genetic puri-
breweries are near ty, consistency, specificity and
aquafeed plants, and Figure 1: Yeast manufacturing process (primary grown culture) efficacy of the strains. (Figure
nowadays a competi- 1). It can be sold under differ-
26 | January - february 2013 Grain &feed millinG technoloGy

3. FEATURE
Table 1: Effect of live yeast Actisaf on growth and survival parameters in
tilapia under stress conditions. (n=3, P<0.05, measures with different letters
are significantly different)
Treatment Survival (%) SGR FCR PER summit is another and th
best-practice of semina
the value VIV eight v
CON 40% -10 fry 75.0ab 3.33a 3.11e 0.83ab adds to its events. by sup
Developed in oped
CON 40% -20 fry 64.8a 3.47a 3.26e 0.78ab close co-operation use d
with loyal advisors the fee
Act 40% - 10 fry 87.5bc 5.80d 1.43abc 1.89cd to VIV, this is a Yia
premium-quality Agent
Act 40% - 20 fry 92.6c 5.43c 1.01a 2.64d conference based speakin
on my personal explain
Act 27% - 10 fry 91.7bc 5.46cd 1.62bc 2.26c initiative,” he says. “the a
Figure 2: Schema of a process to produce yeast have
Act 27% - 20 fry 96.29c 5.24c 1.17ab 3.17e VIV Asia presents three special extracts and yeast cell walls
A very special seminar proces
features: CropTech-FeedTech Perendale Publishers will be tak- degree
Asia, focusing cost-effective feed ing part in one of the CropTech- contro
ent forms and packaging (instant dried yeast, Brewer’s yeast canproduction, MeatTech, highlighting concern is the sanitary safety March
be used to produce Another FeedTech Asia seminars on of tially u
active dry yeast, compressed, cream). yeast fractions, however due totechnologies tothese products. 2013. Called are sometimes
the latest the nature produce 13, Antibiotics ‘Digital engineering a mea
The primary grown culture controlled of brewer’s yeast and safe products that can be added to the process in order to this unique
the specificity of the used eas- in feed manufacturing’, prevent ductio
process makes also a very consistent base for production processes,ily the the consumers, and the VIV seminar with the yeast for nutri-the
by quality is less bacteria competing is for those working in Many
the production of yeast extracts, autolysed consistent than in baker’s yeast. Products Asia. and avoiding of milldecrease. It and aims at
Animal Health Summit ents area yield technology is there- the hu
yeast, yeast cell walls and their derivate: coming from brewery yeast tend to have a first confer- providing background information on
The summit is the fore possible that some antibiotic residues tic ap
nucleotides and beta-glucans. Yeast cell walls distinctive bitter smell and taste andto darker the rapidly intelligent solutions be left in the
ence in Asia a address and possibly other toxins might that have been include
produced from Baker’s yeast usually have a colour than the ones growing concerns about the use of product.
coming from baker’s final dried introduced to address processing order
high content of mannans. They are recognised yeast. antibiotics in animal protein produc- chain dilemmas. Fo
as good toxin binders. Fractions coming from tion, both at CEO and Autolysed yeast – Inactive Dried
technical “What’s unique for our industry ers wil
baker’s yeast have a light beige colour. Ethanol yeast Yeast
level. On a personal note, Berculo about this event is its format,” says develo
The most popular aquaculture application is particularly excited about the VIV and Autolysed publisher of Grain and
Ethanol yeasts are harvested after having Inactive Roger Gilbert, yeast come from will im
of Baker’s yeast is in hatcheries where it is performed alcoholic fermentation andSummit Asia. “The Feed Milling or Brewer’s magazine
Animal Health distil- primary grown cultures Technology yeast. benefit
a major feed source for artemia and rotifer lation for the
(see for example Couteau et al 1990). conventional
production
Brewer’s yeast of Bioethanol
Brewer’s yeast can be identified either from sugar-
as the ferment used in brewery industries cane, beet
(Yeast primary production) or the by-prod- sugar or grains
uct of these industries which is the form syrup. In the
mainly used in aquaculture. In the latter case, first case, the
yeast biomass is harvested from the fermen- yeast biomass
tation vats at the end of beer fermentation. is harvested
It can be sold under liquid form (18-20% and then dried
of dry matter) but preferentially as inactive with the recy-
yeast spray or drum dried. It can also been cled energy
grown as a more controlled product and used to heat
specific strains and find its way to human the vegetal
care as a food supplement and holistic thera- material. The
peutic, also known as natural brewer’s yeast. majority of
Brewer’s yeast for aquafeed applications ethanol yeast
is sold by trading companies as a commodity comes from
based on the protein content, or by local Brazil.
breweries in need to dispatch their slurry. Production
The quality and the supply of these products prices and
can be inconsistent and depends greatly on selling prices
the source of supply. are very low,
The nutritional content is similar as the however the
one in baker’s yeast, but contains more trace quality, such
minerals such as selenium and chromium. as the protein
The protein content of brewer yeast is content is very
relatively high and and its amino acid content inconsistent.
is similar to baker’s yeast. Numerous works The supply
have shown the efficacy of Brewer’s yeast depends on
to replace partially or totally the proteins the activity of
found in fish and vegetable meal in fish and the bioetha-
shrimp. Shrimp feeds formulators typically nol plants and
incorporate brewer’s yeast in their formula can also be
at the rate of two to four percent. inconsistent.
Grain &feed millinG technoloGy Grain &feed millinG technoloGy January - february 2013 | 27

4. FEATURE
They are major products within the food protein and forms peptides (dipeptides to the gut maturation have been found in sea
industry as flavour enhancers and in pet tetra peptides) and oligonucleic acids which bass with a species extracted from the rain-
food as feed attractants. They are used in are readily digestible by the animal. Again bow trout gut Debaryomyces hansenii (see
aquaculture feeds as a source of protein here depending on the original yeast material the works from Tovar-Ramirez and also the
and nitrogen. Brewer’s yeast, and its ethanol used, autolysed and inactive yeast quality can reviews by Chi et al 2006 and Gatesoupe
equivalent, is mostly favoured as it is cheaper be very different. 2007). Marine yeasts and yeasts isolated
than baker’s yeast. They are also easier from fish seem a very logical choice to use
supplied as yeast suppliers prefer to sell the Live yeast as probiotics in species of aquaculture interest. However,
more controlled and tailored Baker’s yeast Live yeast helps regulate the gut micro- such material is often difficult to grow under
on food markets. biota. Its effects have been shown, first in industrial conditions and did not lead to
Inactive yeast is a yeast that has been human where it can reduce diarrhoea, espe- the development of an actual product yet.
deactivated by high temperature drying cially with children. Specific strains have then The products on the market are therefore
(often spray drying). The cells come as a been developed and produced industrially often from S. cerevisiae origin. It has to be
whole and the cell wall is not ruptured mak- such as S. cerevisiae boulardii or S. cerevisiae noted that up to now, no yeast products
ing the access to intracellular material (amino Sc 47 (Actisaf) for the animal nutrition have been registered in EU as a probiotic in
acids, vitamins…) difficult. A way to access market. It is a common practice now to sup- aquaculture.
these materials is to partially hydrolyse the plement feeds to increase milk production in As an example of S. cerevisiae effects,
yeast cell wall to let the cellular content be dairy cows or help piglets survival. (Lara Flores et al 2003, 2010) Table 2 shows
partially released from the cell. This can be Live yeast are characterized by their living some works done in tilapia fry fed for 3
facilitated by activating the internal autolytic cells count, expressed by colony forming unit weeks with feeds supplemented with Actisaf
enzymes of the live yeast (autolysis), add- (cfu per gram), typically ten billions cfu/g. (also knwn as Biosaf) at 1 kg/T in two diets
ing external enzymes (notably proteolysis) Dosages are made in the feeds as dilutions (40% and 27% proteins) and at 2 crowded
or playing on the osmotic pressure to to get an efficient cfu count per g of feed, conditions (1 fry per L or 1 fry per 2L).
rupture the cell wall (plasmolysis). Different a 1000 fold dilution giving a 10.107 per g All the yeast treatments also increased
grades of autolysed yeast can be obtained of feed for example. Viability of the yeast the Alkaline Phosphatase activity, and we can
depending on the level of autolysis (from is mandatory for its effect and cfus should see a better improvement of feed conver-
partial to total). The final product is a mix- be checked before and after pelleting using sion ratio (FCR) and survival under stressful
ture of cellular content and yeast cell wall. plate counts. conditions (low protein percentage and
Furthermore the autolysis process degrades Despite the increasing use of yeast as crowded conditions). There is also a better
Figure 4: Cumulative mortality after immersion with
L. Anguiilarum (blue line is control, orange line is Figure 3: Number of pellets remaining in the feeding tray one
Pronady at 0.5g/kg. n=3, Pronady significantly decreases hour after feeding (n=4, YE are significantly different than
mortality at 120h. P<0.01) control at P<0.05).
a probiotic in terrestrial animals, there are protein efficiency ratio (PER) and digestive
only a few numbers of works studying its enzyme activity when Actisaf is used.
effect in fish as a gut functions stabiliser. Live yeast can be used directly on farm,
The major reason is that live yeast where it has been showed (empirically) to
does not resist the severe condi- improve water quality in shrimp and fish
tions of the manufacturing processes ponds. It is either used alone or mixed with
of aquafeeds (high temperatures, bacteria. Farms producing mash feed onsite
steam, long condi- also add yeast in order to degrade cellulolytic
tioning times, see material to ensure a better digestion.
Aguirre-Guzzman
et al 2002). The Yeast culture or fermented yeast
studies are then dif- Yeast culture is a particular product in
ficult to transfer from which yeast is allowed to ferment. Yeast
lab conditions to farm using biomass, substrate and fermented extracel-
commercial feeds. lular metabolites are then dried.
All the work published
so far was made with yeast Yeast extracts
either top dressed on Yeast extracts (YE) come from the fur-
feeds or incorporated ther hydrolysis and purification of autolysed
in pressed (uncooked) yeast. Insoluble yeast cell walls are separated
feeds. Nevertheless from the cellular content by centrifugation.
some direct effects to YE are very soluble, rich in peptides (up to
28 | January - february 2013 Grain &feed millinG technoloGy

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6. FEATURE
Figure 5: Yeast rich in organic selenium manufacturing process
65%-70% of the product), free amino-acids feeding when YE are included. (Tacon and and eliminate them from the intestine. It
like glutamic acid and vitamins. They also Suyawanish 2011). is also suspected that the mannanes act as
contain a high level of nucleic acid which can prebiotics promoting the growth of benefi-
be further purified to increase the level of Yeast cell walls cial bacteria.
tasty 5’ nucleotides. They are used in aquac- Yeast Cell Walls (YCW) represent the YCW have been shown to be effective
ulture in functional feeds, and hatcheries, as shell of the yeast cell and are roughly 40-50 to improve the resistance to bacterial chal-
a source of nucleotides complementing the percent of the mass of the cell. YCW are lenges in numerous aquaculture species.
de novo synthesis of cells in multiplication composed mainly of fibrous polysaccharides Beta glucans have to be use carefully in
and helping boost immunity and anti-stress glucans with beta 1,3 and beta 1,6 links, (50% aquaculture as some experiments report/
mechanisms. and 8% respectively ), mannans under the negative effects in fish when used for
Autolysed yeast and inactive yeast are form of Mannoproteins (40%) and chitin prolonged periods at high concentrations.
commonly mistakenly sold under the label (2%) (see Lippke and Ovalle 1998). Further This can be avoided by careful choosing the
yeast extract in aquaculture. A good way to purification can lead to the production of source of YCW and using them either at
differentiate them is to look at the carbo- either purified beta-glucans (50% and up) high concentration (2 kg/T) only for a short
hydrate levels. Autolysed yeast has a level and mannoprotein (often used in wine mak- period, or a low concentration continuously
around 20-22% (mostly from the remaining ing for clarification). The presence of these (0.5 g/Kg).
YCW) whereas YE contain only three to six compounds often leads to the mislabelling of An example of sea-bass juveniles fed with
percent of carbohydrates. YCW as MOS or Beta-glucans. Pronady (a YCW of the Lesaffre group) at
The small peptides and free amino acids These two carbohydrate types are very 0.5 g/kg of feed for 8 weeks can be seen
in YE can also prove to be a potent interesting for the aquaculture market, beta- in Figure 4, showing a significant protection
attractant for aquafeed in shrimp. In a trial glucans are direct stimulators of the immune against L. Anguillarum without any growth
performed in Thailand with white shrimp L. systems in shrimp and fish, upon the stimula- difference with the control. However a
vannamei. Feed containing YE at 2 kg/T of tion of specific blood cells (granulocytes or minimal amount of YCW seems needed
feed was presented in feeding trays at the macrophages). Mannans are involved in the to be ingested before challenge in order
corner of hapas and the remaining feed was binding to pathogenic bacteria (especially to provide an efficient immunostimulation
counted after one hour. We can see a faster those with pili having mannose receptors) and so there might be a gap period when
30 | January - february 2013 Grain &feed millinG technoloGy

7. FEATURE
the product is not efficient. (data from Dr. alpha and beta forms)or mannans. Not associated form of selenium in the ani-
Morgane Henry, Hellenic Center for marine all the YCW are equal. Efficiency should mal’s body and then allow making organic
Research , 2011) be checked as a prerequisite to use, or selenium which are readily available when
YCW products, depending on the quality change, YCW. oxidative stress reactions occur.
of the autolysed yeast separation, contain At LFA we have conducted a survey The main application would be in aqua-
also significant percentages of proteins and of four YCW (2 bakery and 2 brewery culture as fish meal is a main supply of
lipids. It should be noted that the lower the yeasts) produced in 4 of our own facto- selenium and the development of diets with
level of proteins, the higher of level of carbo- ries in the same L. Anguillarum challenge less fish meal will require compensation of
hydrates, and then the better immunostimu- in sea bass supplemented at 0.5 g/kg selenium in aquafeed formulae. Such an
lation from the YCW is. Various quality of of feed for 8 weeks. Only 2 responded application could be useful in preventing
YCW are on the animal production market significantly (1 bakery, 1 brewery), the the oxidation of poly unsaturated fatty acids
and major differences can be found between remaining 2 had even negative results at 4 (PUFA) in fish flesh. Chromium yeast is
products depending on the strain, the sub- weeks (lower survival than control). This seldom used in aquaculture diets.
strate used to produce the yeast, and event result shows first that not all is under-
the drying process. stood in the way these products work Conclusion
Mannans represent as most 25-27 per- and that one particular YCW cannot be Yeast products are getting more fre-
cent of YCW in good quality YCW from replaced by another. quently used in aquaculture. Some appli-
primary grown yeasts, but can be found cations are promising as the use as an
as low as 9 percent in crude preparation Selenium yeast alternative source of proteins or as a sanitary
coming from industry by-products. Glucans Yeast can be induced to be a source and welfare enhancer. However many
or poly-glucose can range from 18 To 40 of organic selenium, mainly under the products ranging from crude ethanol yeast
percent. YCW Protein level remains the form of seleniomethionine, which is then by-products to more purified beta-glucans
most convenient indicator of quality, the stored in proteins. During the growth are available on the market. Therefore
best products being those having lower of baker’s yeast, selenium is added to potential users must accurately select them
nitrogen content. The variability between the medium and is replacing sulphur in in function of their targeted application. It is
batches can also be very high. Texture methionine. The excess of selenium is also as important to select a reliable source
should be checked first. Good YCW often then eliminated by careful washing steps of the products to ensure a consistency of
have a smooth, fine texture, low granu- (see Figure 5) to ensure that the selenium the supply and the quality.
lometry and a light beige colour. There is left is 97-99 percent organic. Selenium
also the tendency to believe that all YCW yeast should be then checked for the
More InforMatIon:
are the same and that differentiation of highest percentage of selenomethionine
products must be done to the highest level and the consistency between batches. Website: www.yeast-science.com
of glucans (sometimes measured as both Seleniomethionine is the main carbon-
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