In den in der vorliegenden Arbeit beschriebenen Versuchen wurde die selektive Acylierung der Hydroxy‐ und Aminogruppen von Casein vorgenommen und der Nährwert der Acylderivate mit Hilfe des Testorganismus Tetrahymena pyriformis abgeschätzt. Es wurde gezeigt, daß die Acylierung der Hydroxygruppen den Nährwert des Eiweißes nicht herabsetzt, während die Acylierung der Aminogruppen diese Kennziffer wesentlich verringert. Die Acylierung mit langkettigen Fettsäuren erhöht den Nährwert des Eiweißes unabhängig von der Acylierungsrichtung.

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The microbiological analysis with the test-organism Tetrahymena pyriformis W can be used successfully to measure the relative nutritive value of the biomass and protein isolates from different yeasts for screening the groups of micro-organisms to choose those of the desired quality. In general, this method is rapid, comparatively cheap and gives the possibility to test large numbers of samples simultaneously. According to the literature and our own results, the relative nutritive value, the percentage of absorbed "N", retained by test-organism and used for its growth and multiplication expressed as cell count and given in relation to a standard protein (casein) is generally in a good agreement with results obtained with animals. This microbiological method is promising for investigating the influence of certain technological operations on the quality of protein. The investigation has been performed by the use of Baker's yeast Saccharomyces cerevisiae, of fodder yeast Candida, grown on oil hydrocarbons and on wood hydrolysates, yeasts Hansenula and Mycoderma, grown on a medium containing ethanol as the sole carbon source. The best results were obtained with the yeast grown on the ethanol-containing medium. The biological value of the biomass of yeast Hansenula is 91% and of protein isolate 96% as related to casein as the standard protein.