Joint International Conference on Long-term Experiments ...

THE EFFECT OF LONG-TERM PHOSPHORUS FERTILIZATION ON THE
TRYPTOPHAN AND ZINC CONTENT OF FEED PEAS
Ágnes Elek- Zoltán Győri- Mária Borbély
University of Debrecen, Centre of Agricultural Sciences
Faculty of Agronomy Institute of Food Science, Quality Assurance and Microbiology
ABSTRACT
The quality of food is determined by the chemical composition. One of the most
important nutritional parameter is the protein, and also its amino-acid composition. Pea
samples from the control (0+0+0 kg/ha) and the 20 th treatment of the 1995 OTK research
were analysed from Putnok, Mosonmagyaróvár, Keszthely, Bicsérd, Hajdúböszörmény
and Iregszemcse research sites. We analysed the tryptophan content and its change as a
result of phosphorus and zinc fertilization of the pea samples. HPLC analysis was
performed at 110° C for 20 hours after alkaline hydrolysis. Our results show that high
rates of phosphorus fertilizers decreased the tryptophan content of peas.
Keywords: tryptophan, HPLC, zinc, amino acids, hydrolysis
INTRODUCTION
The quality of food is determined by the chemical composition. One of the most
important nutritional parameter is the protein, and also its amino-acid composition.
Amino-acid analysis is usually a good challenge for the analytical laboratories, even they
have the suitable instruments for the determination. Most of the amino-acids of proteins
in food and their raw materials can be analysed by acidic hydrolysis. Tryptophan has a
sensitive indult-group, therefore it degrades in acidic solution. For HPLC determination
we introduced a sample preparation with alkaline hydrolysis (Ba(OH)2). We analysed the
tryptophan content and change of samples from OTK long-term field trials as an effect of
phosphorus and zinc fertilization.
Correct determination of tryptophan in food and feed is very important, as this
amino acid is essential for monogastric animals. On the other hand, there are less data
about tryptophan content of feed, than for the other amino-acids. With full knowledge of
the recent research results, tryptohan seems to have even more important role in human
nutrition. Less tryptophan than it is necessary for human promotes the development of
nervous depression. Its role was proved also in migraine headache. It is well known that
consumption of feed with high protein content will decrease the tryptophan-level in the
brain, due to a competition among different amino acids, regarding their intake.
Triptrophan content determination requires special methods because of its sensitivity
in acidic conditions in the presence of oxygen. Measurement can be performed by ionexchange
chromatography (Moore and Stein, 1963; Dévényi 1971), photometry
(Matheson, 1974; Basha and Roberts, 1977; Votisky 1984).
The highest tryptophan yield was found in the case of short term hydrolysis (60 min),
performed with mercaptoethanesulfonicacid at high temperature. The most common
method is the HPLC determination following an alkaline hydrolysis of proteins with
Sodium- or Barium-hydroxide (Delhaye and Landry, 1992). This method was used in our
laboratory to measure the tryptophan content of some plant originated food raw materials.
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