Calculation of fermentation parameters from the results of a batch test taking account of the volume of biomass in the fermenting medium
The values of fermentation parameters calculated from the measured concentrations of substrates and/or products may be significantly affected by the volume of biomass in the fermenting medium. Corrections proposed in this paper should be evaluated and, depending on their magnitude, considered in order to obtain more representative results.
Preparation of Organic Selenium Yeast by Fed-Batch Fermentation
Selenium is highly proper prepare essential element for the development of mammals and its incorporation in yeast could serve to Selenium enriched yeast. Production of Selenium (Se) enriched yeast was studied by fed-batch fermentation technology using synthetic nutrients to minimize the influence of sulfur and glucose used as the carbon sources. The effect of Selenium (Se) on yeast growth was also evaluated by employing. Se-adapted yeast cultures in continuous fermentation. Fedbatch fermentation with a total of 100 ppm of Sodium selenite in the medium (Na 2 SeO 3 ), yielded 32.09 g L -1 of dry yeast cell biomass containing 3758 ± 6.5 ppm of organic Se. The resultant product had the Methylene Blue Reduction Test (MBRT) timing of > 25 min, indicating the highest accumulation of organic Se. The elemental analysis showed the sulfur content was reduced by 37% in selenium yeast (Se-yeast) than the normal yeast produced without Se supplementation. There was a reduction in the experimental biomass yield of Se-yeast by 18 g L -1 than the theoretical biomass yield in response to the Se addition. A morphological analysis of the normal and Se enriched yeast cells using scanning electron microscopy indicated a reduction in cell size by 0.88 Pm in response to Se supplementation.
Some observations on oscillatory changes in the growth rate of Saccharomyces cerevisiae in aerobic continuous undisturbed culture
Oscillatory changes in the growth rate were observed in undisturbed continuous culture of Saccharomyces cerevisiae on sugar‐cane molasses media when nitrogen sources (2.56 to 6.17 g/liter of ammonium sulfate or 1.22 g/liter of urea) were added to the feeding mash and when the air rate was 1.3 to 1.6 v/v/m. The oscillations were not affected by the addition of yeast extract. The suppression of the nitrogen source during the continuous test leads to a nonoscillatory transient state. No oscillations occurred at all when no nitrogen source was added to the medium and/or the air rate was equal to zero or equal to about 3.3 v/v/m. The oscillatory responses of the system were affected by a previous anaerobic continuous cultivation of the yeast.