The selective fermentation of glucose and fructose by brewer's yeast

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Abstract
Previous work has been mostly based on observations with the polarimeter. Here in addition was used the iodimetric method of measuring sugars, with control tests. The temp. coefficient of specific rotation was used to measure fructose. Brewers'' yeasts (top and bottom) ferment glucose faster than fructose in mixtures of the 2, both when the yeast is multiplying freely in the presence of various kinds of nutrients, and when nutrients are absent. The relative specific rates of fermentation of glucose and fructose in such cases are far more dependent upon the sp. of yeast and conditions of its nutrition than upon such factors as concentration of sugars in the medium, temp., and reaction. A yeast "trained" by continual subculturing in a medium of fructose and nutrients showed no change in its properties as regards selectivity. No fructose could be detected in a solution of glucose undergoing fermentation by living yeast. Zymin, prepared from brewers'' yeast, ferments glucose faster than fructose in a mixture of the 2. The temp. coefficients of esterification of glucose and fructose by zymin under conditions of phosphate concentration yielding the optimum esterification of glucose are approximately the same, viz., V25[degree]/V15[degree] = 2.q. Velocities of esterification of both sugars vary with reaction of medium, but ratio of velocities varies much less.

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