322 BIOLOGICAL ACTIVITIES OF YEASTS 



The Uses of Yeast. Because of its ergosterol (provitamin D) 

 content yeast -is a good source for the production of vitamin D by 

 irradiation. Yeast also contains thiamin, riboflavin, nicotinic acid, 

 pantothenic acid, pyridoxine, biotin, and p-aminobenzoic acid, all 

 considered vitamins of the B complex. It also contains large amounts 

 of protein, fat, and mineral salts. Hence it is not surprising that 

 there have been suggestions that yeast be used as a food supplement 

 for humans. Strains of "Torula utilis," yeasts belonging to the genus 

 Cryptococcus (see page 286), have been proposed as suitable for this 

 purpose. Irradiated yeast is used as a supplement in cattle feed. 



Yeast is also a good source of the enzyme invertase, which hydro- 

 lyzes sucrose to invert sugar, glucose and fructose. This enzyme is 

 used by the confectionery, baking, and syrup-manufacturing trades. 

 Yeast has also been said to yield beneficial results in some cases when 

 used therapeutically in the diet. Aside from the value derived from 

 its vitamin content, however, such medical benefits are questionable. 



It has been demonstrated that the yeasts, like some of the higher 

 biological forms, convert carbohydrates into lipoidal materials. 

 Yeasts normally produce lipids, but the rates of formation and the 

 amounts stored are not generally of enough consequence to warrant 

 industrial considerations. However, under national emergency con- 

 ditions, it has been proposed that waste carbohydrate materials be 

 used for the synthesis of lipids by yeasts. Lindner -^ carried on in- 

 vestigations in Germany during World War I in an attempt to pro- 

 duce, on an economically sound basis, fats from Endomycopsis 

 vernalis. Fink and his coworkers ^^ have also studied the produc- 

 tion of lipids from Geotrichum. For further discussion on this 

 subject, the reader is referred to Prescott and Dunn.^® 



More recently, yeast has been suggested for use in the micro- 

 biological assay of certain vitamins. AVilliams and his colleagues ^- 

 claim that in a medium deficient in thiamin but containing all the 

 other substances essential for the nutrition of yeast, the growth of 

 yeast is directly proportional to the amount of this vitamin added to 

 the medium. The development of yeast is measured turbidimetri- 

 cally. A weakness of this method is that yeast is stimulated by both 

 the pyrimidine and thiazole portions of the thiamin molecule as well 

 ^s by thiamin itself. Frey and his associates have also suggested 

 the use of yeast in ultramicrobiological ^ and microbiological *° fer- 

 mentation methods for the determination of thiamin. They have 

 utilized the fact that thiamin is a component of the coenzyme co- 

 carboxylase, for the enzyme carboxylase, which is essential for the 

 production of carbon dioxide from the anaerobic breakdown of sugar^ 



