Zur Untersuchung der Lysinoalanin‐(LAL)‐Bildung in alkalischen Lösungen dienten als Modellproteine β‐Casein, das keine Disulfid‐ und Sulfhydrylgruppen enthält, und das schwefelhaltige β‐Lactoglobulin. In 5%igen Lösungen beider Proteine in 0,1 N NaOH wird LAL in Abhängigkeit von der Temperatur mit hohen Anfangsgeschwindigkeiten gebildet: bei 90 °C nach 15 min 0,020 mol LAL/mol β‐Casein‐min bzw. 0,019 mol LAL/mol β‐Lactoglobulin‐min.
Ein Unterschied im Verhalten beider Proteine ergibt sich nur aus der Zunahme des gebildeten LAL bei Temperaturerhöhung, sie ist im ß‐Casein größer als im β‐Lactoglobulin.
The sodium dodecylsulphate (SDS) binding capacities of secalin, gliadin and gluten in the presence of a very low SDS concentration were determined and compared to the SDS binding capacities of bovine serum albumin (BSA), beta-lactoglobulin, ovalbumin und beta-casein. The SDS binding capacities of endosperm proteins determined in phosphate buffer (pH 6.0) are very low. Only 0.6 microgram .. 0.8 microgram SDS were bound to 500 micrograms of the proteins. This low SDS binding capacities do not correlate with the expected hydrophobicity of these proteins. In comparison, 500 micrograms of ovalbumin, beta-lactoglobulin and BSA each bind 0.5, 5.9 and 13.5 micrograms SDS, respectively. According to literature the SDS binding capacities of these proteins are in correlation with the surface hydrophobicity determined with cis-parinaric acid using the fluorescence probe method. The SDS binding capacities of endosperm proteins increased in the presence of 0.1 N acetic acid and consequently 6.2 micrograms .. 6.9 micrograms SDS were bound to 500 micrograms of the corresponding proteins. beta-casein described as a highly hydrophobic protein binds only 0.9 micrograms SDS to 500 micrograms of it in phosphate puffer (pH 6.0) and 1.2 micrograms SDS in 0.1 N acetic acid, respectively.
Lysinoalanine (LAL) was determined in alkali-treated partial hydrolysates (PH) of casein, peptides isolated from these PH and in PH of field-bean protein to clarify whether intermolecular or intramolecular LAL bridges are preferentially formed. Furthermore, the formation of LAS in plasteins was studied as a contribution to plastein research. The formation of LAL in the peptide mixtures of beta-casein and the decrease of the LAL content in the PH (as compared to intact proteins) indicates that the formation of LAL favours the intramolecular cross-linking of polypeptide chains. The LAL content decreases as the degree of hydrolysis of the PH of the field-bean protein isolate increases, and depends upon the protease used in the production of the hydrolysates. The LAL contents of the alkali-treated plasteins are less than those of the initial hydrolysates. The decrease of the LAL content is directly proportional to the hydrolysis proceeding during the plastein reaction.
Der Einsatz unkonventioneller Proteine fUr ErnrUrungszwecke ist i. a. eingeschrW durch deren ungiinstige funktionelk Eigenschaften, ihre oft unausgewogene Aminoshezusammensetzung oder durch harWckig anhaftenden off-flavour. Eine Mtiglichkelt zur Veriinderung dieser Eigenschaften wird neuerdings in der enzymatischen Modi-
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