KETO ACIDS IN BAKER'S YEAST AND IN FERMENTATION SOLUTION

Abstract

Keto acids In baker's yeast and in fermented glucose solutions were identified as 2,4-dinitrophenylhydrazones by thin-layer chromatography. Petroleum ether-ethyl formate-proplonic acid was used as solvent, and the chromatogram obtained was run once more in the same direction with petroleum ether-ethyl formate-formic acid. One spot of each keto acid component was obtained. The identification was confirmed by reduction of the keto acid hydrazones to amino acids, which were analysed by thin-layer chromatography. In yeast, as well as in fermentation solution, α-ketobutyric acid, α-ketoisovaleric acid and α-ketoisocaproic acid were found in addition to pyruvic acid and α-ketoglutaric acid. The yeast was found to contain about 2 mg. pyruvic acid, 1 mg. α-ketoglutaric acid and 10–70 μg. of the other keto acids per 100 g. fresh yeast. In the fermentation solution the amounts of keto acids per litre of solution were 10 and even 100 times as great. The fermentation solution of carboxylase-deficient A₅ stage of baker's yeast contained twice as much pyruvic acid, but only a fifth of the amount of α-ketoglutaric acid present in the fermentation solution of carboxylase-rich A₂ stage. The amounts of the other keto acids in the fermentation solution varied and were clearly lower.