Six different variations of the extraction procedure applied to yeast cells of Saccharomyces cerevisiae and Candida utilis to optimize the production of yeast extract and isolation of nucleic acids were compared. The autolysis of C. utilis at 50 to 52°C without adding chemical agents was found to be the best for the production of yeast extract. The most suitable procedures used for the extraction of nucleic acids were those which were carried out from C. utilis at pH 7.5 (92°C) and the other with 0.4 M NH&H (40°C). Both these modifications yielded the highest amounts of polymer nucleic acids. Applying all procedures compared to S. cerevisiae an increased content of sterols (including d'~'-sterols, predominantly ergosterol) was detected.
Effect of composition of the medium used for the inoculum cultivation, of the age and amount of the inoculum was investigated using a 3-L glass fermentor with a working volume of 1 L. The highest productivity of the culture was obtained when using a 20% (V/V) 1-d inoculum grown in the MRS medium. Yields of lactic acid were 88-97%, while the L(+)-isomer represented about 80% of the total product.
By using an appropriate ratio of carbon source to mineral components, we obtained comparable citrate yields in media containing different concentrations of glucose. The enzyme system of inoculum passed on gradually from "growth" state to "production" state during the mould growth. In the starch medium, the critical factors of citric acid production are the aeration efficiency of the medium and the amylase formation of the strain. The air interruption exhibited a prolonged inhibition of the production rate but not of the citrate yield in glucose medium while those parameters in starch medium containing excessive urea were briefly but severely inhibited. After being affected by these unfavorable conditions, the production activity of Aspergillus niger could be restored by applying an appropriate fermentation process.
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