Extraction of chromium from yeast biomass | Ekstrakcija kroma iz kvasne biomase
2008
Pas, M., Ljubljana Univ. (Slovenia). Biotechnical Fac., Food science and Techology Dept. | Milacic, R., Institut Jozef Stefan, Ljubljana (Slovenia) | Raspor, R.
Total chromium in yeast biomass does not indicate well the amount of organically bound or biologically active chromium. The study presented in this paper investigated different reagents for extraction of organically bound chromium from yeast cells and yeast protoplasts and different parameters of extraction procedure. Yeasts Candida intermedia ZIM 156 were cultivated for 12 or 22 hours at 28 deg C in chemically defined medium containing 1mM CrCl3 or Na2Cr2O7 (20 microM Cr6+). Washed yeast cells were resuspended in appropriate reagents for extraction (0.05 M EDTA, 0.7 M CH3COONa, 0.1 M NH3, 0.1 M Na4P2O7 10H2O) and suspensions were incubated at 28 deg C. Extraction time, mixing conditions and concentration of yeast suspension in EDTA were optimized. An aliquot of yeast cells was used to prepare protoplasts from which chromium was extracted. Chromium content in extracts, in yeast biomass and in protoplasts was analysed by atomic absorption spectrometry. On the basis of our results EDTA was chosen as the most appropriate reagent for extraction, optimal extraction time was 21 hours without shaking. Furthermore, the results obtained for both chromium compounds showed, that the amounts of extracted chromium from yeast cells and from protoplasts were approximately the same. Nevertheless, we can not conclude, whether chromium, which was extracted from yeast protoplasts originated from cell interior or from yeast cell membranes. In further research exact properties of EDTA extracts should be determined and chromium compounds in the extracts should be identified.
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