FERMENTATION OF AMINO ACIDS 329 



to the quantities of leucine or isoleucine added and rise, under 

 favourable conditions, to as much as 7 per cent ; furthermore, 

 it was found that although the leucine parted with its 

 nitrogen in the form of ammonia, the latter substance was not 

 lost, but appeared to be taken up by the yeast in the produc- 

 tion of new protein material ; this observation led to trying 

 the effect of adding ammonium salts, when it was found that 

 the yeast, finding these latter to be an easier source of 

 nitrogenous food, gave up attacking the leucine, and conse- 

 quently less amyl alcohol was produced. 



These experiments therefore prove that amino acids can 

 be fermented by yeast with the production of alcohols in 

 much the same way as sugars can be fermented. The practi- 

 cal importance of these discoveries can be gauged from the 

 fact that the production of amyl alcohol * or fusel oil by the 

 yeast fermentation of sugar has always been a source of 

 trouble to spirit distillers, and necessitated elaborate processes 

 for refining ; these researches have provided both an explana- 

 tion of the cause and a remedy for the evil.f 



Since, moreover, other amino acids besides the leucines are 

 also found to be attacked in a similar way with the production 

 of a number of widely different products, some of which are 

 aromatic, it is easy to account for the different flavours which 

 are peculiar to the various alcoholic beverages, all of which 

 are ultimately produced by alcoholic fermentation of sugars in 

 presence of different proteins. 



The destruction of amino acids by enzymes derived from 

 yeasts, fungi or bacteria with the formation of different bye- 

 products, may also account for the flavours of different 

 cheeses, as well as the odour of flowers ; the substance phenyl 

 ethyl alcohol, for example, which was produced by the fer- 

 mentation of phenyl alanine, 



CgHgCHaCHNH.jCOOH + H.O = CbH^CHoCH.OH + CO., + NH;, 

 Phenyl alanine Phenyl ethyl alcohol 



being the chief odoriferous constituent of rose oil. 



* Besides these alcohols, other substances, such as succinic acid, glycerin, etc., 

 are produced, but they also probably owe their origin to amino acids. 



t A knowledge of the cause of the amyl alcohol production is also import- 

 ant from the point of view of increasing the yield of this substance, since large 

 quantities of amyl alcohol are required for the preparation of amyl acetate, used 

 as a flavouring material for confectionery, and as a solvent in the manufacture 

 of varnish, smokeless powder, etc. 



