Yeasts doubling times

Expression of eukaryotic genes in yeast has two main advantages (i) the yeast expression system contains many features of a eukaryotic expression system such as glycosylation or disulfide bond formation, and (ii) yeast is a very economical system. Yeasts are single cells, can be cultivated easily, feature fairly short doubling times, and require relatively inexpensive medium ingredients in many aspects they resemble bacteria. 

The yeast produced by continuous culture techniques is separated from the liquid medium and solvent washed by centrifugation or filtration techniques. After drying, a protein supplement is obtained, which contains 65-68% protein and is suitable for addition to animal feeds. This protein content compares very favorably with that of dry fish meal, which contains about 65%, and dry skim milk powder with about 32%. The SCP processes have operated on the thousands of tonne/year scale in the U.K., France, and Italy, but regulatory problems with facilities operating on unpurified gas oil feedstocks have caused some shutdowns [64]. Nevertheless, because of a cell mass doubling time of 2.5-3 hr and the efficient carbon conversion to protein of this technology, these developments deserve to be explored further. 

The working reactor volume is 20 ml Therefore, = 225/20,000 1.1 x 10" W/kg. This value is sufficiently low for use in animal cell bioreactors. The low power requirement can be attributed to the relatively very low wm used. The low vvm in turn is a result of the much lower oxygen utilization rate (lower peak OUR/higher doubling times as compared to bacteria/yeast in Table 7B.6 in such systems). 

Baker s yeast can also be used in the saturation of a,/i-unsaturated ketones. The reactions described share the following features (i) remote double bonds are not hydrogenated, (ii) the reaction rate is affected by substitution on or near the double bond and (iii) after a prolonged reaction time reduction of the oxo group can also take place (equations 39 and 40)109. 

Figure 2 shows that for corn stover at the highest tested severity parameter of 220°C for 32 min, inhibition of the yeast regarding to the control was as extreme as with the aspen wood samples shown in Fig. 1. It took more than double the amount of time for the higher-severity sample yeast to consume 50% of the glucose than in all the other samples, just as with the aspen wood sample at 220°C for 32 min.

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