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
ts
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
Co
un
ts
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
un
ts
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?