Susceptibility of yeasts isolated from dairy products to cystatin
Chrzanowska, J.E-mail:[email protected] | Krajewska, E. | Saleh, J. | Szoltysik, M. | Trziszka, T.(Wroclaw Agricultural University (Poland). Dept. of Animal Products Technology)
The study aimed at analysing the possibility of applying cystatin isolated from hen eggs, as a natural inhibitor of sulfhydryl proteinases, for growth inhibition of some yeast cultures isolated from dairy products. The selected strains: Candidaa famata AII4b, Yarowia lipolytica JII1a, Rhodotorula rubra and Geotrichum candidum MII3b were incubated for 9 days in milk supplemented with cystatin at the concentration of 100 mcg/ml. Milk samples were collected in specified time intervals and determined for: yeast growth, pH and the degree of protein degradation by measuring the increase in free amine group content both in the fraction soluble at pH 4.6 and in phosphotungstic acid, and by means of the electrophoretic separation in polyacrylamide gel. In milk containing cystatin, the smallest growth was observed for Rhodotorula rubra yeasts. During incubation of that strain, the lowest degree of milk protein degradation was also reported, irrespective of the presence or a lack of cystatin. The Geotrichum candidum MII3b strain appeared to be the least susceptible to the inhibitor's presence, however, during its growth in cystatin-containing milk, negligibly slower degradation of proteins was observed
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