Action of dissolved substances upon the autofermentation of yeast

Abstract

During experiments upon the permeability of the yeast-cell it was found that, when yeast was immersed in a molar solution of sodium chloride, and allowed to stand at air temperature, the amount of gas produced by autofermentation was considerably greater than that given by a water control. The production of carbon dioxide by autofermentation of yeast is brought about by the action of at least two enzymes. The reserve material of the cell, for the most part glycogen, is first converted by a glycogenase into a sugar, which in turn is fermented by zymase with the production of alcohol and carbon dioxide. As the rate of autofermentation is considerably less than that produced by the same yeast in presence of excess of sugar, it follows that the rate of autofermentation is controlled by the rate of production of sugar within the cell, in other words, by the rate of action of the glycogenase. An increase in the rate of autofermentation, therefore, indicates greater activity of this enzyme within the cell. In order to investigate the action of solutions of various salts upon the rate of autofermentation of yeast, this was ascertained by measuring the volume of carbon dioxide evolved during successive intervals of time by means of the apparatus described by Harden, Thompson, and Young (1). The yeast employed was prepared from top-yeast as obtained from the brewery by pressing out the wort in a small hand press, it having been demonstrated (2) that practically the whole of the interstitial liquid can be removed in this way. A certain weight of such pressed yeast was carefully weighed into each of the fermentation flasks, and treated with a certain volume of the various liquids under experiment, controls being made with water. The liquids were saturated with carbon dioxide at 25°, the temperature of the water-bath.