Zusammenfassung
Lysozym, Ribonuclease und Insulin wurden 1 bis 24 Std auf Temperaturen zwischen 80 und 180 °C trocken erhitzt. Die Aminosäureanalyse der erhitzten Proben ergab, daß die meisten Aminosäuren unterhalb 120 °C beständig sind. Darüber beginnt eine zunächst nahezu lineare Abnahme, die bei 160 °C einen kritischen Bereich erreicht. Apolar-aliphatische, saure und aromatische Aminosäuren sind insgesamt relativ beständig (Schädigungen im Mittel <20% nach 24 Std bei 180 °C). Bei den restlichen Aminosäuren steigt die Anfälligkeit in der Reihe Prolin, Arginin, Histidin, Cystein, Threonin, Lysin, Tryptophan, Serin und Methionin. Methionin wird bei maximaler Belastung zu 86% zerstört. Die Verluste an Trinitrobenzolsulfonsäure-reaktivem Lysin („verfügbarem Lysin”) betragen bei 100 °C 20%, während nach 24 Std bei 180 °C nahezu kein reaktives Lysin mehr vorhanden ist. Die Gewichtsverluste der erhitzten Proben betrugen maximal 11%, während die maximalen Proteinverluste zwischen 20 und 35% liegen. Für einige Aminosäureverluste wurden Reaktionsordnungen und Aktivierungsenergien bestimmt. Von den nachgewiesenen atypischen Aminosäuren („hot spots”) Lysinoalanin,allo-Isoleucin und Ornithin ist nur Lysinoalanin als Indikator für Aminosäureschädigungen nach trockener Erhitzung brauchbar.
Summary
Lysozyme, ribonuclease and insulin were exposed to dry heating for 1 to 24 h at temperatures between 80 and 180 °C. Amino acid analyses of the heated samples showed that most of the amino acids are stable up to 120 °C. Initially, at higher temperatures, an almost rectilinear decrease took place which reached a critical stage at 160 °C. Nonpolar aliphatic, acidic and aromatic amino acids were all relatively stable (maximum loss < 20% after 24 h at 180 °C). The lability of the other amino acids increased in the order proline, arginine, histidine, cysteine, threonine, lysine, tryptophan, serine, and methionine. Methionine was 86% decomposed after 24 h at 180 °C. Loss of trinitrobenzene sulfonic acid-reactive lysine (“available lysine”) reached 20% at 100 °C and essentially 100% after 24 h at 180 °C. Maximum loss in weight during heating was 11%, although maximum protein loss was between 20 and 35%. Reaction orders and activation energies were estimated for some of the amino acid losses. Of the atypical amino acids (“hot spots”) lysinoalanine,allo-isoleucine and ornithine that were detected, only lysinoalanine is useful as an indicator to detect amino acid damage after dry heating.
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We thank the Deutsche Forschungsgemeinschaft for supporting this work, Miss Marie-Luise Kern for her skillful technical assistance, and Mrs. Anneliese Mödl and Mrs. Angelika Langwieser for performing some of the amino acid analyses
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Weder, J.K.P., Sohns, S. Model studies on the heating of food proteins. Z Lebensm Unters Forch 176, 421–425 (1983). https://doi.org/10.1007/BF01042554
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DOI: https://doi.org/10.1007/BF01042554