Selective fermentation

Abstract

Pentoses, particularly xylose, retard the fermentation of hexoses by brewer''s yeast. Expts. with the Kluyver and the Barcroft-Warburg apparatus show decrease in rate of CO2 development by about I for glucose-xylose mixtures 1:1. However, the total amount of CO2 evolved is sometimes increased. This "pentose-effect" is caused, at least in part, by competitive diffusion. The rate of diffusion of numerous carbohydrates was compared, suppressing fermentation by iodoacetic acid for the tests on fermentable sugars. Speed of diffusion decreases in the order xylose-glucose-galactose - d -arabinose - l. -arabinose - mannitol -rhamnose -lactose, for brewer''s and baker''s yeast. Diffusion studies permit the differentiation of extracellular, intracellular and chemically bound water in pressed yeast. The inability of Saccharomyces marxianus to ferment maltose is not due to lack of diffusion.