Potential of X-Ray Spectrometry and Chemometrics to Discriminate Organic from Conventional Grown Agricultural Products

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16
th

IFOAM Organic World Congress, Modena, Italy, June 16
-
20, 2008

Archived at http://orgprints.org/view/projects/conference.html



Potential of X
-
Ray Spectrometry and Chemometrics to
Discriminate Organic from Conventional

Grown Agricultural Products

Bortoleto, G. G.
1
, De Nadai Fernandes, E. A.
1
, Tagliaferro, F. S.
1
, Ferrari, A. A.
1

&
Bueno, M. I. M. S.
2

Key words: food authenticity, p
rincipal component analysis, X
-
ray spectrometry.

Abstract

This work describes an innovative analytical method based on X
-
ray spectrometry
combined with chemometrics which presents high potential to discriminate
conventional from organic grown tomatoes and
coffee beans. This novelty is based on
the irradiation of samples in a bench
-
top EDXRF equipment provided with a Rh tube
and further treatment of the spectral data using Principal Component Analysis (PCA).
Multivariate analysis results showed a tendency in

separating the samples according
to the production mode (organic or conventional). Regarding the spectra obtained, the
K
-
alpha peak of potassium showed to be the most responsible for discriminating
different categories of samples. The chlorine K
-
alpha pea
k presented high capability in
discriminating tomato and coffee samples from different origins. The method can be
useful for food quality control to rapidly classify samples since the measurements can
be done “in situ” with portable instruments. Neverthele
ss, it will be necessary to build
robust classification models with a larger number of samples.

Introduction

The market of organic products increases every year. In 2005 it achieved a value of
USD 37 billion, with most part of products consumed in North A
merica and Europe
(IFOAM, 2007). The consistent expansion of the organic agriculture results from the
increasing concern among consumers about food quality attributes associated with the
absence of chemical contaminants, negative environment impacts caused

by the
production system and use of bad labor practices (Fernandes et al., 2002;
Fernandes

et al., 2004). Considering that organic food reaches prices substantially
higher than conventional food, unscrupulous producers and traders would feel
encouraged to

offer fake products in the market. On the other hand i
mporters are
facing several difficulties for the discrimination of organic and conventional products,
mainly to detect and avoid frauds. Thus, i
t is clear the relevance of developing suitable
analytica
l methods to classify samples (Santos et al., 2006)
.

In this study, coffee and tomato, two agricultural products highly dependent on
synthetic fertilizers and pesticides when cultivated in the conventional system, were
analysed by energy dispersive X
-
ray f
luorescence (EDXRF) combined with
chemometrics. EDXRF is a technique based on the photoelectric phenomenon that
provides absorption/emission effects that generate energy spectra composed by
specific energies, corresponding to elements present in the sample
. The use of



1
Nuclear Energy Center for Agriculture (CENA), University of São Paulo (USP), PO Box 96, 13400

970
Piracicaba, São Paulo


Brazil,

E
-
mail lis@cena.usp.br

2

Institute of Chemistry, State University of Campinas (IQ
-
UNICAMP),
PO Box 6154, 13083

970
Campinas, São
Paulo


Brazil
,
E
-
mail

bell@iqm.unicamp
.br


16
th

IFOAM Organic World Congress, Modena, Italy, June 16
-
20, 2008

Archived at http://orgprints.org/view/projects/conference.html



chemometrics allows analysing simultaneously all the energies detected as a variable
of the model to be built.

The objective of this work was to evaluate the feasibility and potential of this analytical
method and use of chemometrics for the
discrimination of organic and conventional
grown agricultural products.


Materials and methods

Sampling and sample preparation

Test samples were obtained directly in the crop fields. Coffee beans were collected in
Santo Antonio do Amparo, Minas Gerais sta
te, a pioneer region in the production of
organic coffee in Brazil (Fernandes et al., 2002). Both conventional and organic
plantations of the same variety were cultivated in similar soil and climate. The cherries
were harvested and naturally dried in patio
s under sunlight and afterwards the outer
skin and pulp were removed in a hulling machine. The coffee beans were then
classified by size and sorted by density and color to remove defected ones. The
resulting bulk material consisted of 4 batches: one conven
tional, one in transition from
conventional to organic and two organics. For the tests, 5 samples of approximately
0.1

kg were taken from each batch and ground in a rotor mill reducing the particle
sizes to
<

0.5 mm
.

Tomato samples of the hybrid AP 533 wer
e collected in farms that adopt the organic
and conventional cultivation systems, respectively located in Borborema and Novo
Horizonte cities, São Paulo state, Brazil. The sampling was performed in areas of
2500 m
2

in both farms and twelve plants were rand
omly selected in each area. Four
ripe fruits with average weight of 100 g were taken from each plant. The samples were
transported to the Radioisotopes Laboratory (LRi/CENA/USP), Piracicaba, SP. The
fruits were thoroughly washed with tap water followed by
deionised water and cut in
halves for removing seeds. They were frozen at minus 18°C for 24

hours and freeze
-
dried at minus

52°C and 0.1 atm for 5 days. Particle size was also reduced (<

0.5 mm)
in a rotor mill.

Both organic coffee and tomato were produced

in accordance with the guidelines from
the Instituto Biodinâmico (IBD), an
International Federation of Organic Agriculture
Movements (
IFOAM)
accredited member, and the Associação de Agricultura Orgânica
(AAO), a Brazilian affiliated of IFOAM.


EDXRF analy
sis

For the trials, irradiation cells mounted with their bottoms having a 3 µm thick
polymeric film (Mylar
®
) were completely filled with the ground samples. Two replicates
for each sample were irradiated for 180 seconds under air atmosphere.

S
amples
irradi
ations were performed using an EDXRF equipment, model EDX 700, Shimadzu
(Kyoto, Japan), assembled with a rhodium X
-
ray tube and a Si(Li) detector, with
resolution of 180 eV. The voltage in the tube was 50

kV, with an applied current of
100 mA and beam col
limation of 10 mm.


Data Analysis

To proceed with the chemometric analysis, matrices of independent variables were
constructed in such a way that the columns refer to the spectrum energies with 2048
values (channels), whereas each line corresponds to one s
ample. The spectral data
16
th

IFOAM Organic World Congress, Modena, Italy, June 16
-
20, 2008

Archived at http://orgprints.org/view/projects/conference.html



were mean centred and submitted to a moving average smoothing with a segment
size equal 7. Afterwards the data were treated by Principal Component Analysis
(PCA), using The Unscrambler software, version 9.2, from Camo
®
. PCA results

were
validated by using the
leave
-
one
-
out

cross validation
method, also named Full Cross
validation method.

Results

Figures 1 and 2 show the results obtained by applying PCA to coffee and tomato
samples respectively. The score plots were constructed with
the first and second
principal components.


-0.10
-0.05
0.00
0.05
0.10
-0.02
-0.01
0.00
0.01
0.02
0.03
PC2 8%
PC1 73%
Transition
Conventional
Organic

Figure 1. Scores plot obtained by applying PCA for all coffee X
-
ray spectra



-0.08
-0.04
0.00
0.04
0.08
-0.04
0.00
0.04
0.08
PC2 25%
PC1 68%
Conventional
Organic

Figure 2. Scores plot obtained by applying PCA for organic and conventional
t
omato X
-
ray spectra

16
th

IFOAM Organic World Congress, Modena, Italy, June 16
-
20, 2008

Archived at http://orgprints.org/view/projects/conference.html



Discussion

The PCA results in Figure 1 present a clear separation between the organic,
conventional and in transition coffee samples. Regarding to PC1 axis it is possible to
observe the separation tendency between organic and convention
al coffee with 73%
of total explained variance. The PC2 axis shows that the in transition samples are
separated from the others with 8% of total explained variance. The results presented
in Figure 2 show a clear separation between organic and conventional
tomatoes. The
PC1xPC2 scores plot accounted for 93% of total explained variance. Even though the
tomatoes were produced in different farms and other factors may have contributed to
the discrimination process, the method showed to be sensible to the variati
ons
resulting from different management systems. In both cases, analysing the loading
results, it could be noted that the variables related to potassium K
-
peaks, element
present in high concentrations in coffee and tomato samples, influenced strongly on
sa
mple grouping. Considering the tomato samples, the loadings results also indicated
the strong influence of chlorine K
-
peaks on conventional and organic discrimination.
This finding may be related to the regular use of KCl in the conventional crops, which
a
dds substantial amounts of Cl in the system. For routine analyses, the proposed
method is very promising to distinguish organic from conventional grown food. It is
fast, non destructive and does not generate residues. As a further improvement, a
larger num
ber of samples must be analysed to provide a more robust classification
model to be applied in routine quality control of organic/conventional grown food.

Conclusions

EDXRF and multivariate statistical analysis indicated a good potential for the use of
th
e method in discriminating organic from conventional grown food. The technique
generates data in minutes, does not destroy the sample and can be carried out in
portable equipments avail
able on the market, allowing to
analyse samples
in situ.
These advanta
ges make it promising to be applied in routine quality control of organic
products for the determination of authenticity. However, more studies are required in
order to develop a robust model including a large number of samples from different
locations.

A
cknowledgments

FAPESP and CNPq for financial support.

References

Fernandes E. A. N., Tagliaferro F. S., Azevedo
-
Filho A., Bode P. (2002): Organic coffee
discrimination with INAA and data mining/KDD techniques: new perspectives for coffee
trade. Accred. Qu
al. Assur. 7: 378
-
387.

Fernandes E. A. N., Tagliaferro F. S., Bacchi M. A., Bode P., Santos L. G. C. (2004): INAA as a
tool to identify organically grown food. Trans. Am. Nucl. Soc. 91:847
-
848.

International Federation of Organic Agriculture Movements (2
007)
http://www.ifoam.org/press/press/pdfs/Statistics_2007_PR.pdf/
, (accessed 2007
-
10
-
30).

Santos L. G. C., Fernandes E. A. N.,
Bacchi M. A.,
Tagliaferro F. S., Tsai S. M. (2006
): Evaluation
of conventional and organic beans by instrumental activation analysis.
J. Radioanal. Nucl.
Chem. 270: 249

252.