Selenium in Food:

Totals, Bioaccessibility

and Species.

Vicky Henderson

University of Plymouth

With Thanks to:

Dr. M. Foulkes

Dr. A. Fisher

Dr. R. Clough

Overview

Selenium: Importance

How much? (totals in foods)

How available? (measuring the bioaccessibility)

What form? (the selenium species in samples)

Selenium

Discovered in 1817

Originally regarded as

a toxic element.

More recently considered

an essential element.

Navarro-Alarcon et al 2008

appliedspeciation.com

Selenium in Food and the Human Body: A Review

Selenium

Deficient

<20 µg

Essential

60 µg – 70 µg

Toxic

>800 µg

Dumont et al Anal Bioanal Chem 2006

So, how much is in the food we consume?

Dietary Sources In This Study

Garlic

Mushrooms

Brazil Nuts

Sesame Seeds

Se Supplement Tablets

Brewer’s Yeast

Mussels

Rice

Corn Flour

Instrumentation

ICP-MS Thermo X Series 2

Element specific detection

Highly sensitive

Low detection limits – 10 ng / L

However selenium can prove problematic

Polyatomic interferences e.g. 40Ar36Ar+,40Ar37Cl+, and 40Ar38Ar+

Instrumentation

Problem Solving

Collision Reaction Cell Technology

(CRCT)

Sensitivity improvement – organic C

addition

Make-up gases

Larsen et al JAAS 1994

Result of Adding Organic Carbon

Standard

Analysed

LOD 76Se

µg/L

LOD 77Se

µg/L

LOD 78Se

µg/L

LOD 82Se

µg/L

10 g / L Se

no methanol

0.73 0.85 1.11 3.62

2 g / L Se

with 5%

methanol

0.77 0.67 0.27 1.01

All data acquired with XT cones in CRCT mode

Total Se Sample Preparation

Analysed ‘as eaten’ where possible

Mussels freeze dried

Sieved <500 µm

Hot block acid digestion

Triplicate samples

CRMs

Total Concentration Results.

Sample Mean Se Conc’ mg/kg and

SD

Garlic 0.031 0.02

Mushroom 0.063 0.02

Brazil Nut 0.637 0.12

Sesame Seeds 2.280 0.08

Brewer’s Yeast 0.114 0.01

Se Supplement Tablets 353 42.15

Mussels 3.204 0.67

Rice 0.214 0.03

Corn Flour Not Detected

CRM Wheat 1.55 0.03 (1.1 0.2)

CRM Dogfish 1.73 0.02 (1.4 0.09)

But.....

How important is the total

Se concentration?

Bioaccessibility Testing

Bioaccessibility: The fraction of a

substance that is available for absorption

through the GI tract into the bloodstream.

Ruby et al Env Sci Tech 1996

Used an in vitro model called Unified

Bioaccessibility Method (UBM) produced

by BARGE.

BARGE Method

%Bioaccessibility Mussels

% Bioaccessibility

Se Supplement Tablets

Speciation

Definition: The chemical

form in which an element

is found

Selenium Species

Organic selenium

Inorganic Selenium

Dumont et al Anal Bioanal Chem 2006

Instrumentation

http://www.speciation.net/Public/Document/2007/06/21/2914.html

Sample Preparation and

Separation

Trypsin enzymolysis, ~ 0.25g sample, at

pH 8, water bath for 4 hours at 37 C

followed by centrifugation.

HPLC Column :Hamilton PRP X-100 anion

exchange.

Mobile phase: NaH2PO4 (100mM), pH 6.8

at 1 ml / min. Gomez et al Anal Chim Acta 2008

Speciation Standards

Selenocysteine

SeleniteSelenomethionine Selenate

1 mg/L of each Se species

Selenium Species Present in Selenium Supplement Tablets

Selenite

Selenomethionine

0

5000

10000

15000

20000

25000

30000

35000

40000

0 100000 200000 300000 400000 500000 600000 700000

Co

un

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Time (ms)

Selenite?

Selenomethionine

Selenium Species Present in Selenium Supplement Tablets

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

0 100000 200000 300000 400000 500000 600000 700000

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Time (ms)

Selenite

Selenomethionine

Selenium Species Present in Selenium Supplement Tablets

0

100

200

300

400

500

600

0 100000 200000 300000 400000 500000 600000 700000

Co

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Time (ms)

Selenium Species Present in Mussels

% Bioaccessibility

Se Supplement Tablets

Main Conclusions

Selenium supplement tablets may

contain more than the nominal amount

stated on the packaging.

Approximately 10% of selenium in

these supplement tablets can be

deemed bioaccessible.

Selenium species present in the

supplement tablets studied were

selenomethionine and selenite.

Further work

To analyse selenium supplement tablets

from several companies.

To compare the selenium concentration of

a particular food grown in seleniferous and

non seleniferous countries.

To investigate the effect of cooking foods.

Optimise HPLC separation

Thank You.

Any Questions?