LACTIC ACID FORMATION IN ALCOHOLIC FERMENTATION BY YEAST

Abstract

mented media was always associated with the presence of contaminating organisms. Subsequently, its occurrence in alcoholic fermentations, free of bacteria, was established, and several theories were proposed in which lactic acid played the r?le of a three-carbon intermediate between sugar and the end products, carbon dioxide and alcohol. B?chner and Meisenheimer (3) on the basis of their work with yeast press juice, first reported lactic acid to be such an intermediate ; later, however, as a result of experiments made with pure yeast cultures, they concluded that live yeasts neither form nor ferment lactic acid. Slator (29) failed to agree with B?chner and Meisenheimer's early work, considering lactic acid as a by-product rather than intermediate in alcoholic fermentation. The proponents of the WohlSchade (6,18, 26) hypothesis held lactic acid to be an intermediate product in alcoholic fermentation. Neuberg and Tir (23), Fernbach and Schoen (9, 10), and Euler and Lindner (8), also presented evidence for the intermediate r?le of lactic acid in alcoholic fermentation. Among those who could not confirm this evidence were Kerb and Zeckendorf (16), and Kostychev and Frey (17). Oppenheimer (24) considered lactic acid to be a by-product of alcoholic fermentation. His work indicates that either dihydroxyacetone or glyceric aldehyde (probably the latter), may be regarded as precursors of lactic acid. Meanwhile Neuberg (20, 21, 22), presented evidence to show that methyl glyoxal was the precursor of lactic acid in both yeast fermentation and that brought about by animal tissues. He considered the formation of lactic acid from sugar quite probable. The foregoing as well as many other investigations (27, 28), of the r?le of lactic acid in alcoholic fermentation were conducted chiefly to determine the mechanism of its formation and cannot be cited as evidence of its occurrence as a by-product of normal alcoholic fermentation. The frequent occurrence of lactic acid bacteria in alcoholic fermentations makes many of the early investigations of doubtful value. Recent reports (1, 5, 7, 13) have postulated the formation of lactic acid as a by-product of alcoholic fermentation of sugar by pure yeasts. Durmishidze (5) concludes that lactic acid is a