3. FOOD ChEMISTRy & bIOTEChNOLOGy 3.1. Lectures

Chem. Listy, 102, s265–s1311 (2008) Food Chemistry & Biotechnology
P84 ChEESE SPECIES IDENTIFICATION by
MuLTIVARIATE ANALySIS OF ELEMENTAL
DATA
MARTIn POLOVKA, MILAn SUHAJ AnD MáRIA
KOREňOVSKá
Department of Chemistry and Food Analysis, VÚP Food
Research Institute, Priemyselná 4, P. O. Box 25, 824 75 Bratislava,
Slovak Republic,
polovka@vup.sk
Introduction
To guarantee cheeses’ authenticity, responsible food control
authorities need to dispose of reliable analytical traceability
techniques that enable to check whether the products are
correctly described and labelled, or not.
In the recent years, extensive literature data on the
methods of analysis applicable to the detection of mixtures of
milk from different species either in raw or even in processed
milk products are available. A large number of methods are
applicable to detect the presence of different milk species in
cheeses, as well. 1–4
Multivariate analysis represents valuable tool, making
possible the categorization of different food samples via the
consideration of many variables that can be measured, often
in a single analytical level. In addition, multivariate analysis
of chromatographic, electrophoretic or elemental data is considered
to be the powerful method for the discrimination of
cheeses based on the different geographical origin, varieties
and quality or for the consideration and monitoring of cheese
maturation.
As follows from previously published data, the concentration
ranges of some elements in milk and cheese are
strongly dependent on animal species and feeding, season of
sample collection, environmental conditions and manufacturing
processes, as well. 5–11 Coni et al. revealed, that the concentration
of selected trace elements (e. g., of Al, Ba, Cd, Co,
Cr, Cu, Fe, Mg, Mn, ni, Pb, Pt, Sr and Zn) differ significantly
for sheep and goat milks and for their related products 5 . The
mineral composition of ewes’, cows’, and goats’ milk and
of samples of different pure-milk cheeses made from them
was analysed by Martin-Hernandéz using the stepwise discriminant
analysis, reaching the 76 % correct classification of
cheeses according to milk species 6 . Another statistical study
dealt with the comparison of metal composition of different
types of milks based on the presence of Se, Fe, Cu, Zn, na,
K, Ca, Mg, brought 98% correct classification of the samples
for each type of milk 7 . Discriminant analyses of some
elemental data were successfully used by Koreňovská et al.
for the identification of cheeses’ region of origin. 8–10 Using
the same approach, 94.1 % of Mahon cheese samples were
correctly classified into traditional and industrial groups, and
89.7 % of samples into fresh, half-ripened, ripened and oldripened
groups. 11
As follows from the above-presented data, the authentification
of cheeses using the elemental markers requires
s765
reliable data, obtained by analytical methods of high specificity
and sensitivity, e. g. by atomic absorption spectrometry
(AAS).
In this paper, the identification and discrimination of
cows’, sheeps’ and goats’ cheeses from different Slovak regions
using the selective elemental data and pattern recognition
analysis is presented.
Experimental
S a m p l e s C h a r a c t e r i s a t i o n
Commercially available samples of 54 cow hard cheeses
of Emmental and Edam type, 116 sheep (40 hard and
76 bryndza type) and 20 goat cheeses, all of the Slovak origin
were analyzed to the content of selected elemental markers
(Ba, Cr, Cu, Hg, Mg, Mn, ni and V) by AAS. These markers
were chosen on the base of geochemical characterization of
Slovak regions 12 .
R e a g e n t s
All chemicals were of analytical grade. nitric acid of
suprapure quality and stock solutions of respective metal
(Ba, Cr, Cu, Hg, Mg, Mn, ni, and V at the concentration of
1.00 g dm –3 , each) were purchased from Merck (Darmstadt,
Germany). Lanthanum chloride (5%) used as ionic suppressor
was delivered from SMÚ (Bratislava, Slovakia).
A A S C o n d i t i o n s
Respective cheese sample (0.5 g) was digested in a mixture
of 4 ml of 65 % HnO 3 and 0.5 ml H 2 O 2 , using the Milestone
MLS 1200 MEGA (Sorisole, Italy) microwave digestion
system.
Perkin Elmer 4100 atomic absorption spectrometer
(norwalk, CT, USA) equipped with a deuterium lamp background-correction
system and HGA 700 graphite tube atomizer
with pyrolytically coated graphite tubes and flame was
used. The presence and concentration of Mg and Mn metals
were determined from atomic spectrometry measurements,
using an air/acetylene flame. Metal elements of Ba, Cr, Cu,
ni, and V were detected on graphite tube atomizer, as previously
described by Koreňovská and Suhaj. 8–10
The accuracy of results was verified by standard addition
method. The accuracy of method used for metal elements
determination was estimated by means of two reference
materials (nCS ZC 73008, rice and nCS ZC 73013, spinage)
to be 98–125 %. Recovery of the method was assessed by
the analysis of fortified cheese samples; mean recoveries of
elements reached 96–109 %. Finally, the combined standard
uncertainty was 5.3–14 %.
D e t e r m i n a t i o n o f H g
For the determination of mercury in cheeses, single –
purpose mercury analyser AMA 254 (Altech, Prague, Czech
Republic) was used. The BCR-150 skim milk powder (Brussels,
Belgium) served as reference material. 8–10