The document discusses analyzing samples of selenium yeast products to determine their selenomethionine (SeMet) levels. An analysis of 11 samples from different producers found their SeMet content varied widely, from 24.8% to 69.7% of total selenium. SeMet is regarded as the most effective organic selenium form. Choosing yeast with high and consistent SeMet guarantees more benefits to farmed animals and enrichment of their products.

1. November | December 2012
Why check selenomethionine levels in
selenium yeast?
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2. FEATURE
Why check selenomethionine
levels in selenium yeast?
by Wilbert Litjens, Technical manager Optimin & Betaine and Paul Perucchietti, Product manager Optimin, Selko Feed Additives,
The Netherlands
S
elenium yeast is commonly used proteins and subsequently, tissues such as fillet Benchmark
in aquaculture to improve animal or organs will be enriched with the selenium. Several samples of selenised yeast were
performance and meat quality. This selenium is easily available when required sourced from the market and analysed
Samples of different selenised yeast for the synthesis of selenoproteins (Figure 1). for the most relevant selenium species at
products were sourced in the EU and This saves valuable time and ensures a fast and the University of Pau, CNRS, France. This
USA. QA departments of Trouw Nutrition effective reaction in case of stress or a disease. research lab is known as professional and
International and Selko repeatable for organic selenium
Feed Additives performed species determination.
a laboratory analysis on The value of selenised yeast
these. Outcomes revealed was determined by the levels
remarkable differences of total selenium, SeMet, SeCys
between product samples and inorganic selenium. A total
on most effective and of 11 samples from different
active compound, namely batches of a number of pro-
selenomethionine (SeMet). ducers were examined. Samples
were randomly numbered and
Selenium is one of the sent to the lab for analyses
essential trace elements in by HPLC ICP-MS. Results are
aquaculture. It can be added shown in Table 1. Most interest-
to aquafeed in two forms; ing is the variation in levels of
as inorganic selenite or as SeMet. Some samples contained
organic selenium yeast. Each only half the level of SeMet
form has different metabolic compared to other samples
routes and effects. (range from 24.8% to 69.7%).
Organic selenium - selenised SeCys levels are, as expected,
Table 1:
yeast - is regarded as a more marginally present at all equal
effective way of supplementing Total Inorganic levels. Unexpectedly, Sample 6
SeMet SeCys
Sample
Selenium Selenium
selenium. With more frequent contained a relative high level of
usage of selenised yeast and ppm as % of ppm as % of % of total inorganic selenium (13.3%).
ppm
Se total Se Se total Se Se
increasing amount of suppliers,
benchmarking on quality Need of
becomes relevant. Selenised 1 3000 2090 69.7 140 4.6 < 2% selenomethionine
yeast mainly consists of 2 2260 1460 64.6 100 4.4 < 2% Yeast is enriched with seleni-
selenomethionine (SeMet), um through growing it in a medi-
3 2250 1110 49.1 70 3.3 < 2%
which can be converted um with a controlled amount
into selenocysteine (SeCys) 4 1910 920 48.3 190 9.7 < 2% of selenium and a shortage of
by natural turnover from 5 1890 1160 61.2 670 3.5 < 2% sulphur. If the yeast grows, it
methionine into cysteine. 6 1990 490 24.8 < 10 - 13.3% must synthesise methionine with
SeMet is regarded by animals 7 2217 1069 48.2 51 2.3 < 2% selenium incorporated; SeMet.
as normal methionine and The higher the SeMet levels, the
8 2377 1278 53.8 87 3.7 < 2%
absorbed and processed more beneficial the yeast will be
following the methionine 9 2191 1092 49.8 59 2.7 < 2%
as an organic selenium source
pathway. The SeMet will 10 2027 854 42.1 49 2.4 < 2% for aqua species.
be stored as methionine in 11 2239 1275 57.0 81 3.6 < 2% It is widely accepted in
26 | InternatIonal AquAFeed | november-December 2012

4. FEATURE
and of minor when selenium enriched human foods such
importance. The as fish fillets are marketed, consistent and
remainders are high selenomethionine levels in the yeast feed
SeMet precur- is essential to make health claims on these
sors and SeCys/ foods.
SeMet intermedi- A trial with rainbow trout evaluated differ-
ate amino acids. ent sources of selenium and their subsequent
Most of these effect on selenium levels in the fillet. Results
compounds are are presented in Figure 2 (feeding level in
less or not valua- ppm), showing a significant enrichment with
ble to the animal Optimin SeY over another selenised yeast and
and are individu- inorganic selenium.
ally present at
very low levels in Conclusion
yeast. The benchmark revealed large differences
in quality and consequently nutritional value
scientific literature that SeMet is the most Guaranteed high quality of different products. It is beneficial for a fish
effective and active compound in selenised Selko Feed Additives markets its own feed company or fish producer to compare
yeast bringing beneficial effects to organism. premium quality selenised yeast; Optimin suppliers on SeMet levels and subsequent
The percentage of SeMet of total Se is the SeY. On every batch, as well total selenium pricing. Choosing a product which guaran-
best indicator for the value and bioavailability as selenomethionine content is checked. tees selenomethionine is the best choice. It
of the selenium out of the yeast. Minimal 63 percent selenium of total sele- gives maximal benefits to animals, enriches
The analysis of the main organic selenium nium must be in the form of SeMet for the animal products and lowers the cost of feed
metabolites (SeCys and SeMet) in relation batch to be released for customers. This formula.
to the total selenium level gives a strong defined quality guarantees that aqua species
evaluation on the success of the enrichment will get the most out of the selenium yeast
process during production. Most selenised (Figure 2).
yeast products contain 97-99 percent organic A consistent and high level of SeMet offers More InforMatIon:
selenium of total selenium. numerous advantages. For example, when for-
Email: wilbert.litjens@nutreco.com
The dominant organic selenium form is SeMet, mulating feed a lower inclusion level is needed Website: www.selko.com
which can be accurately (< 5% variation) deter- to meet requirements and saves costs without
mined. SeCys is present at fixed, low levels (2-5%) compromising animal performance. Besides,
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november-December 2012 | InternatIonal AquAFeed | 27

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