November | December 2012

Why check selenomethionine levels in selenium yeast?

The International magazine for the aquaculture feed industry

International Aquafeed is published five times a year by Perendale Publishers Ltd of the United Kingdom.All data is published in good faith, based on information received, and while every care is taken to prevent inaccuracies, the publishers accept no liability for any errors or omissions or for the consequences of action taken on the basis of information published. ©Copyright 2012 Perendale Publishers Ltd. All rights reserved. No part of this publication may be reproduced in any form or by any means without prior permission of the copyright owner. Printed by Perendale Publishers Ltd. ISSN: 1464-0058

Selenium yeast is commonly used in aquaculture to improve animal performance and meat quality. Samples of different selenised yeast

products were sourced in the EU and USA. QA departments of Trouw Nutrition International and Selko Feed Additives performed a laboratory analysis on these. Outcomes revealed remarkable differences between product samples on most effective and active compound, namely selenomethionine (SeMet).

Selenium is one of the essential trace elements in aquaculture. It can be added to aquafeed in two forms; as inorganic selenite or as organic selenium yeast. Each form has different metabolic routes and effects.

Organic selenium - selenised yeast - is regarded as a more effective way of supplementing selenium. With more frequent usage of selenised yeast and increasing amount of suppliers, benchmarking on quality becomes relevant. Selenised yeast mainly consists of selenomethionine (SeMet), which can be converted into selenocysteine (SeCys) by natural turnover from methionine into cysteine. SeMet is regarded by animals as normal methionine and absorbed and processed following the methionine pathway. The SeMet will be stored as methionine in

proteins and subsequently, tissues such as fillet or organs will be enriched with the selenium. This selenium is easily available when required for the synthesis of selenoproteins (Figure 1). This saves valuable time and ensures a fast and effective reaction in case of stress or a disease.

BenchmarkSeveral samples of selenised yeast were

sourced from the market and analysed for the most relevant selenium species at the University of Pau, CNRS, France. This research lab is known as professional and

repeatable for organic selenium species determination.

The value of selenised yeast was determined by the levels of total selenium, SeMet, SeCys and inorganic selenium. A total of 11 samples from different batches of a number of pro-ducers were examined. Samples were randomly numbered and sent to the lab for analyses by HPLC ICP-MS. Results are shown in Table 1. Most interest-ing is the variation in levels of SeMet. Some samples contained only half the level of SeMet compared to other samples (range from 24.8% to 69.7%). SeCys levels are, as expected, marginally present at all equal levels. Unexpectedly, Sample 6 contained a relative high level of inorganic selenium (13.3%).

Need of selenomethionine

Yeast is enriched with seleni-um through growing it in a medi-um with a controlled amount of selenium and a shortage of sulphur. If the yeast grows, it must synthesise methionine with selenium incorporated; SeMet. The higher the SeMet levels, the more beneficial the yeast will be as an organic selenium source for aqua species.

It is widely accepted in

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

Table 1:

Sam

ple Total

Selenium SeMet SeCys Inorganic Selenium

ppm ppm as Se

% of total Se

ppm as Se

% of total Se

% of total Se

1 3000 2090 69.7 140 4.6 < 2%

2 2260 1460 64.6 100 4.4 < 2%

3 2250 1110 49.1 70 3.3 < 2%

4 1910 920 48.3 190 9.7 < 2%

5 1890 1160 61.2 670 3.5 < 2%

6 1990 490 24.8 < 10 - 13.3%

7 2217 1069 48.2 51 2.3 < 2%

8 2377 1278 53.8 87 3.7 < 2%

9 2191 1092 49.8 59 2.7 < 2%

10 2027 854 42.1 49 2.4 < 2%

11 2239 1275 57.0 81 3.6 < 2%

26 | InternatIonal AquAFeed | november-December 2012

FEATURE

november-December 2012 | InternatIonal AquAFeed | 27

IAF12.06.indd 26 07/11/2012 17:41

52 | InternatIonal AquAFeed | november-December 2012

IAF12.06.indd 53 07/11/2012 17:43

scientific literature that SeMet is the most effective and active compound in selenised yeast bringing beneficial effects to organism. The percentage of SeMet of total Se is the best indicator for the value and bioavailability of the selenium out of the yeast.

The analysis of the main organic selenium metabolites (SeCys and SeMet) in relation to the total selenium level gives a strong evaluation on the success of the enrichment process during production. Most selenised yeast products contain 97-99 percent organic selenium of total selenium.

The dominant organic selenium form is SeMet, which can be accurately (< 5% variation) deter-mined. SeCys is present at fixed, low levels (2-5%)

and of minor importance. The remainders are SeMet precur-sors and SeCys/SeMet intermedi-ate amino acids. Most of these compounds are less or not valua-ble to the animal and are individu-ally present at very low levels in yeast.

Guaranteed high quality Selko Feed Additives markets its own

premium quality selenised yeast; Optimin SeY. On every batch, as well total selenium as selenomethionine content is checked. Minimal 63 percent selenium of total sele-nium must be in the form of SeMet for the batch to be released for customers. This defined quality guarantees that aqua species will get the most out of the selenium yeast (Figure 2).

A consistent and high level of SeMet offers numerous advantages. For example, when for-mulating feed a lower inclusion level is needed to meet requirements and saves costs without compromising animal performance. Besides,

when selenium enriched human foods such as fish fillets are marketed, consistent and high selenomethionine levels in the yeast feed is essential to make health claims on these foods.

A trial with rainbow trout evaluated differ-ent sources of selenium and their subsequent effect on selenium levels in the fillet. Results are presented in Figure 2 (feeding level in ppm), showing a significant enrichment with Optimin SeY over another selenised yeast and inorganic selenium.

ConclusionThe benchmark revealed large differences

in quality and consequently nutritional value of different products. It is beneficial for a fish feed company or fish producer to compare suppliers on SeMet levels and subsequent pricing. Choosing a product which guaran-tees selenomethionine is the best choice. It gives maximal benefits to animals, enriches animal products and lowers the cost of feed formula.

More InforMatIon:Email: wilbert.litjens@nutreco.comWebsite: www.selko.com

26 | InternatIonal AquAFeed | november-December 2012 november-December 2012 | InternatIonal AquAFeed | 27

FEATURE

!"#$%&'()*+,")*"-+-$&

!"#$%"&&'(")*"+

!""#$%&#'()&*#(+#,%-$(.&/012#$(#-(3*#"0&$4

!"##"$%&""'%"&&()("*)+

50.&2$6*(78 ,9:9,9#;<:

IAF12.06.indd 27 07/11/2012 17:41

www.aquafeed.co.uk

LINKS

• Seethefullissue• VisittheInternationalAquafeedwebsite

• ContacttheInternationalAquafeedTeam

• SubscribetoInternationalAquafeed

VOLUME 15 I S SUE 6 2 012

THE INTERNATIONAL MAGAZINE FOR THE AQUACULTURE FEED INDUSTRY

An overview of the UK fish vaccination industry

Why check selenomethionine levels in selenium yeast?

Extrusion technology for the production of micro-aquatic feeds

and shrimp feeds

EXPERT TOPIC– Salmon

IAF12.06.indd 1 07/11/2012 17:39

Thisdigitalre-printispartoftheNovember|December2012editionofInternationalAquafeedmagazine.Contentfromthemagazineisavailabletoviewfree-of-charge,bothasafullonlinemagazineonourwebsite,andasanarchiveofindividualfeaturesonthedocstocwebsite.Pleaseclickheretoviewourotherpublicationsonwww.docstoc.com.

Topurchaseapapercopyofthemagazine,ortosubscribetothepapereditionpleasecontactourCirculationandSubscriptionsManageronthelinkabove.

INFORMATIONFORADVERTISERS-CLICKHERE