Utilization of Aspartic Acid and Asparagine by Yeast

Abstract

MUCH work has been carried out upon the mechanisms whereby yeast is able to utilize nitrogen from amino-acids for its nutrition, and the mechanisms worked out by Ehrlich and Stickland illustrating nitrogen uptake are well known^1,2. These and other authors (for example, Thorne³) have been concerned with the value of amino-acids to yeasts simply as sources of nitrogen. Working with aspartic acid and asparagine, however, we have for some time observed that yeast growth has been stimulated under some conditions to a remarkable extent if either aspartic acid or asparagine has been present in nutrient solutions containing sugars and inorganic salts and nutrilites under various conditions of wort aeration. Under several conditions of experimental procedure, always with good aeration, it has been found that aspartic acid and asparagine added in relatively large amounts have always had the effect of increasing the yield of yeast obtained from a standard amount of fermentable sugar. Thus, under one set of conditions, it has been found that the addition of 1 gm. of asparagine would yield an additional 2.7 gm. of yeast (at 27 per cent dry matter) or 0.729 gm. of yeast dry matter. Also, while we have never been able to obtain yields of yeast (at 27 per cent dry matter) greater than 210 per cent of the hexose sugar supplied, this figure has, under some conditions, been greatly exceeded when either aspartic acid or asparagine has been present in the wort in sufficient amount.