Abstract
The fact that yeast in high concentration ferments glucose very rapidly has been put to considerable use in the analysis of blood and other biochemical material. The fermentation can be so regulated that small quantities of glucose are completely broken down in a few minutes at room temperatures. The evolution of CO2 takes place so rapidly that the red color of phenol red (indicator) in a weakly alkaline glucose-yeast mixture turns to yellow in a few seconds.
In an attempt to apply this phenomenon as a means of quantitative observations in the study of fermentation processes, several serviceable procedures were tried out. The one to be described promises usefulness as the basis of a rather simple analytical technique.
The reagents employed are: (a) 0.01 molecular sodium carbonate solution, (b) 0.06% aqueous solution of phenol red, and (c) a 20% yeast suspension prepared by rubbing up 20 g. of commercial baker's yeast in water and making up the volume to 100 cc.
The procedure is as follows: Measure into a test tube 5 cc. of the sugar solution to be studied. Add one drop of phenol red and adjust the reaction to slight alkalinity (pink color, pH 7.2 to 7.4). Introduce into each of 2 other test tubes 5 cc. of the yeast suspension and 2 drops of phenol red, and add dropwise of the standard sodium carbonate solution until a distinct pink color persists for at least 30 seconds. To one of the yeast tubes 5 cc. of neutral (or neutralized) water are added; this serves as blank. The content of the other yeast tube is transferred into the tube containing the sugar, and the 2 fluids are immediately mixed by inversion of the stoppered tube.
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