HOW CHEMICAL ANALYSIS COMPLIES WITH THE
CONTEMPORARY REQUIREMENTS OF FOOD ASSESSMENT?
Jan F. Biernat
Department of Chemical Technology, Gdańsk University of Technology,
80-952 Gdańsk, Poland, E-mail: <biernat@chem.pg.gda.pl>
Consumption is not the aim of our life; the purpose of eating is to maintain life processes.
The same meaning was expressed the best by ancient Romans in the following aphorism:
Non vivimus ut edere, sed edimus ut vivere.
Food delivers ENERGY needed for life processes, it delivers components necessary for
reconstruction and restoration of body constituents. There is limitation concerning amount of
food we must consume and a minimum of its components. They allow chemical or biochemical
processes to occur in our bodies.
Food consists of minerals, proteins, carbohydrates, fats, vitamins, etc. The main question
whether the food composition correctly fulfills requirements of the organism or not could be
answered based on chemical analysis. Some food components, so called essential, are important
for its nutritive value. It concerns some minerals, essential and limiting amino acids, some fats,
etc. The amount of food we have to consume daily is determined by the abundance of the
essential and limiting components.
In addition, we expect the food to be not only of standard/high value but also to be
appetizing, it means tasty, with pleasant smell and suitable color.
Chemical analysis of food, due to its complex nature, is not simple. For example, in
drinking water up to one hundred components are to be determined routinuously! And more,
tasty water does not always mean healthy water!
Very important components of food are proteins. They are taste- and odorless. The
number of individual proteins (peptides, or amino acids) is enormously high. Therefore, food
analysis is usually limited to determination of total nitrogen content. Such determination gives
and indication of amino acids content, as the nitrogen content in proteins is almost constant.
Determination of different proteins during a short period of time is, at present, impossible. We
have to consider that some peptides or proteins are harmful. To this category belong for example
bacterial toxins, snake venoms and peptides/proteins of undesired amino acid sequence. In the
last case the proteins are toxic. Sequential analysis of proteins is very time-consuming. At
present, sequential analysis of a single protein requires few weeks. Determination of essential and
limiting amino acids that determine nutritive value of food is less time-consuming. Similar
problem exists with fats and abundance of unsaturated fatty acids that are required and that are
not synthesized inside our bodies. Related requirements are known for inorganic components.
Some plants selectively incorporate non-typical components from soil/water. So, tungsten
compounds are incorporated by carrot up to dangerous concentration level. Lettuce accumulates
an excess of nitrates and nitrites. This accumulation depends on composition of water used for
irrigation, on used fertilizers and components of a soil. Thus, analysis of some plants and flesh
should include specific determinations of non-typical components.
Unfortunately, food components of higher molecular weights as non-volatile, they are
also smell and taste deficient. Therefore, compounds of lower molecular weight that are naturally
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occurring or are artificially added to food create its acquisitiveness. It concerns for example
spices, pigments or dyeing materials. Frequently, they are of synthetic origin; usually the
additives contain some by-products of unknown biological properties. Determination of such byproducts is always difficult because of their very low concentration.
Food components are not infinitely stable. They undergo many processes caused by
microorganisms or by chemical reactions. The variability of food composition with time is an
additional problem in food assessment.
Thus, important question arises whether we the chemical analysis could be improved?
First, let think about the unprocessed source materials of plant or animal origin. In the
case of plants their composition generally could be treated as more unified, especially when they
are genetically identical and when they are grown under identical conditions (composition of soil,
water, used fertilizers, degree of illumination, microorganisms in soil, environment). Under such
conditions the composition of all specimens could be treated as (nearly) identical. It also concerns
tracer contaminations. If animal derived food is concerned, then even in the case of genetically
uniform samples their composition is not identical. It especially concerns proteins, among which
some are specific for each individual. Therefore assessment of such material is much more
difficult.
The monoclonal plants (or animals) should be rather uniform by respect of their
constituents. Looks like using food components from monoclonal organisms is the best solution
for chemical assessment. Its composition could be assumed as highly standardized. In this respect
food could be chemically assessed assuming composition of the used source materials. In this
case the food quality/composition is first of all determined by responsibility of their producers.
This way, if such materials will be processed under standard conditions, the components
of all dishes will be exactly uniform and nutritively well balanced.
Are we able to accept such foodstuff? Can we accept foodstuff of WORLD WIDE
identical composition and fitting well the requirements of our body, food with WORLD WIDE
identical taste, smell and appearance? In my opinion we cannot accept it.
As mentioned above, chemical analysis is very time-consuming. On the other hand, the
contemporary analytical procedures should be fast and economic and not involving very
sophisticated equipment. In this state of art, it is necessary to introduce new analytical tools.
Accordingly, some solutions may consist in application of very sensitive tests, using e.g.,
fluorescence of specific components caused by reaction with fluorescing reagents. Some other,
like electrochemical methods with the use of ion-selective or chemically modified electrodes
could be considered as a convenient analytical tool.
Such tests are always based on chemical reaction between receptor and substrate. In
accordance with the number of parameters determined, monitoring requires thousands of very
specific reactions. In this respect, application of sensors could be a good solution. However, also
in this case we have not sufficiently sensitive and selective receptors for all kind of food
components.
How to avoid problems with sensors requiring very specific receptors? At present, one of
the possible solutions is application of a set of sensors of low specificity. Some sets of this type
are well known as “artificial nose” or “artificial taste/tongue”. A set of such non-specific sensors
gives quite useful information on the quality of vapors, coffee, water, and other liquids. Their best
application is in comparing two or more samples and assessing their identity. Up to date, the
information obtained by this method has limited value. However, fast progress of this technique
is to be expected.
The number of useful receptors could be reduced if one receptor under different
conditions enables selective reaction with more than one substrate.
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In the case of compound 1 (Scheme) the small sized azocrown ethers (n = 1) in ionselective membrane electrodes creates high sodium over potassium selectivity. When n = 2, the
compounds create high potassium over sodium selectivity [1]. Spectroscopy is valuable method
enabling application of both these compounds for determination of lithium in non-aqueous
solution [2]. Similar properties possess electrodes covered with monolayers of highly lipophilic
derivatives of 1 [3].
n
O
O
O
N
R
N
R
1
n
n
O
O
N
H
O
N
R1
O
R1
N
N
N
N
H
O
3
2
O
R1
N
N
N
N
H
O
R1
N
N
OH
4
R
n
n
O
O
O
O
R1
R1
5
O
R1
OH
R
O
O
O
O
R1
n
O
O
O
O
O
R1
R1
N
H
N
N
H
N
N
N
N
N
N
N
6
N
N
N
OH
7
Compounds 2 – 4 in water-dioxane mixture recognize well lithium or sodium cations
by spectroscopic methods [4]. The selectivity depends on the size of macrocycle. The same
compounds show different selectivity when applied in ion-selective membrane electrodes.
Compounds 5 – 7 are cation-sensing materials in spectroscopic methods when acetonitrile
was applied as a solvent. Again, their application in membrane electrodes creates different
cation selectivity [5].
Compounds 2 were immobilized in an inorganic organic hybrid material. Such
material recognized well lithium cations present in aqueous solution [6].
References:
1. J.F. Biernat, E. Luboch, A. Cygan, BIOMEASUREMENTS: Electrical Measurements of Biochemical
Quantities, International Seminar, Jabłonna 1989, 1990, s. 359; J.F. Biernat, E. Luboch, A.
Skwierawska, R. Bilewicz, E. Muszalska, Biocybernetics and Biomedical Engineering 16, 125
(1996); D.G. Pijanowska, E. Luboch, J.F. Biernat, M. Dawgul, W. Torbicz, Sensors and Actuators,
B 58, 384 (1999).
2. M. Shiga, H. Nakamura, M. Takagi and K. Ueno: Bull. Chem. Soc. Jpn. 57, 412 (1984); L.M.
Goldenberg, N.N. Denisov, J.F. Biernat, J. Incl. Phenom., 38, 171 (2000).
3. J.F. Biernat, E. Luboch, A. Cygan, Yu.A. Simonov, A.A. Dvorkin, E. Muszalska, R. Bilewicz,
Tetrahedron, 48, 4399 (1992); E. Luboch, J.F. Biernat, E. Muszalska, R. Bilewicz, Supramolecular
Chemistry, 5, 201 (1995); I. Zawisza, R. Bilewicz, E. Luboch and J.F. Biernat, J. Electroanal. Chem.,
471, 156 (1999).
4. A. Skwierawska, H.D. Inerowicz and J.F. Biernat, Tetrahedron Lett., 39, 3057 (1998); Ewa WagnerWysiecka, Elżbieta Luboch, Barbara Marczak and Jan F. Biernat, Polish J. Chem., 75, 1457 (2001).
5. Ewa Wagner-Wysiecka, Elżbieta Luboch and Jan F. Biernat, J. Incl. Phenom., 41, 19 (2001).
6. Ewa Wagner-Wysiecka, Elżbieta Luboch, Andrzej Kłonkowski and Jan F. Biernat, Biocybernetics
and Biomedical Engineering 21(4), 67 (2001).
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