Extraction of chromium from yeast biomass | Ekstrakcija kroma iz kvasne biomase

English. 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 C in chemically defined medium containing 1mM CrCl3 or Na2Cr2O7 (20 ?M 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 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.

Slovenian. Celokupni krom v kvasni biomasi ni dober pokazatelj količine organsko vezanega oz. biološko aktivnega kroma. Namen študije je bil preizkusiti različne reagente za ekstrakcijo organsko vezanega kroma iz kvasnih celic in protoplastov ter optimizirati parametre ekstrakcije. Kvasovke Candida intermedia ZIM 156 smo namnoževali 12 oz. 22 ur pri 28 C v kemijsko definiranem gojišču z dodanim 1 mM CrCl3 oz. Na2Cr2O7 (20 ?M Cr6+). Izprane kvasne celice smo suspendirali v reagentih za ekstrakcijo (0,05 M EDTA, 0,7 M CH3COONa, 0,1 M NH3, 0,1 M Na4P2O7.10H2O) ter suspenzije inkubirali pri 28 C. Optimizirali smo čas ekstrakcije, mešanje med ekstrakcijo in koncentracijo suspenzije kvasovk v EDTA. Iz dela kvasnih celic smo pripravili protoplaste in iz njih ekstrahirali krom. Vsebnosti kroma v ekstraktih, celokupnega kroma v kvasni biomasi in kroma v protoplastih smo določili z atomsko absorpcijsko spektroskopijo. Na podlagi dobljenih rezultatov smo kot najprimernejši reagent za ekstrakcijo izbrali EDTA, najugodnejši čas ekstrakcije 21 ur, pri čemer stresanje ni potrebno. Iz rezultatov je tudi razvidno, da se z EDTA iz kvasnih celic ekstrahira približno enak delež kroma kot iz protoplastov, kar velja za obe uporabljeni kromovi spojini v gojišču. Ne moremo pa zaključiti, ali je bil krom, ekstrahiran iz protoplastov, intracelularnega izvora ali je bil vezan v celičnih membranah. Zato bi bilo potrebno v nadaljnjih raziskavah natančneje določiti lastnosti ekstraktov z EDTA, predvsem identificirati spojine, na katere je vezan krom.