Food hyGiENE & saFEty 21
Nitrogen/protein determination
validated by combustion method
ereals and seeds are significant toxic waste since they involve the use of mercury
Liliana Krotz, Elena Ciceri
and Guido Giazzi outline
how recent advances in
C
components of the human diet and or selenium catalysts during the digestion step.
the principal part of feeding stock All these disadvantages have ended the
for domestic animals. One of the dominance of the Kjedahl method as the
the combustion method
most important nutrients of cereals and seeds is preferred technique for nitrogen/protein
have made it perfectly
protein. The monitoring of protein amount, determination in food. On the contrary, the
suitable to cope
effortlessly with the wide
through the estimation of nitrogen, must be capabilities of the combustion method have
array of food safety
accurate in order to determine the nutritional been improved to make it faster, safer and more
laboratory requirements
quality of cereals and seeds. If the amount of reliable than the traditional Kjeldahl method.
such as accuracy,
nitrogen is multiplied by a factor depending on Designed to offer an alternative to the
day-to-day reproducibility the kinds of protein expected to be present in Kjeldahl methodology for dedicated nitrogen
and high sample
the food, then the total protein content can be and nitrogen/protein analysis in food, the
throughput.
determined. In addition to its dietary upgraded combustion method features a large
importance, the protein content has also sample load of 2g, ensuring maximum accuracy
become a guideline for some cereal trade and reliability of results as well as improved
Liliana Krotz, Elena Ciceri
et Guido Giazzi soulignent
transactions. productivity capabilities, reducing sample
comment les récents
handling time and minimising matrix effects.
The Kjeldahl method
progrès de la méthode
The technique reduces the need for sample
de combustion ont rendu The Kjeldahl method is the method for the preparation and is capable of processing more
tout à fait possible de quantitative determination of nitrogen in samples than the Kjeldahl method in only a few
s’adapter sans effort à la
chemical substances. For many years, the minutes. Consumable costs associated with
grande variété d’exigences
Kjeldahl method has been the internationally- sample preparation are also minimised and
en matière de sécurité
recognised method for estimating protein safety in the laboratory is increased.
alimentaire au laboratoire,
à savoir : précision,
concentration in food, due to its universality, The advanced combustion method features
reproductibilité d’un jour
precision and reproducibility. an automatic carbon dioxide (CO
2
) adsorber
à l’autre, et traitement
Currently, it is the standard method against regenerating technology, which is automatically
d’un grand nombre
which all other methods are judged. activated to adsorb the CO
2
generated during
d’échantillons. Nevertheless, the Kjeldahl method is associated the combustion.
with many major downfalls. It is not capable of The combustion method has been approved
providing measurements of true protein content and adopted by the Association of Official
Liliana Krotz, Elena Ciceri
and different correction factors are required for Analytical Chemists (AOAC) and the American
und Guido Giazzi stellen
different proteins to account for different amino Association of Cereal Chemists (AACC).
dar, wie die vielfältigen
Laboranforderungen
acid sequences. The official methodology requirements for
☞
für die
The Kjeldahl method is a multi-
Nahrungsmittelsicherheit,
stepped process, including sample
wie Genauigkeit, tägliche digestion in boiling sulphuric acid,
Reproduzierbarkeit und neutralisation with sodium hydroxide
hoher Probendurchsatz,
solution, distillation of the resulting
durch die jüngsten
ammonia gas into a trapping solution,
Fortschritte im Bereich
titration with an acid solution and
Verbrennungsverfahren
ideal unterstützt werden..
determination of the amount of
nitrogen and protein by calculation.
The entire process may require over
four hours to be completed while all
steps, excluding digestion, require
continuous technician contribution.
In addition, handling boiling
sulphuric acid, especially with the
addition of concentrated caustic
solution, is a particularly hazardous Fig. 1. A Thermo Scientific FLASH 4000 nitrogen/protein
task. Kjeldahl analyses also generate analyser was used to validate the combustion method.
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