DETECTION OF YEAST EXTRACTS. 21 



Methods of Detection. 



Searl a suggests as a method for detecting yeast products added to 

 meat preparations, that a solution of the extract be boiled one or two 

 minutes with a modified Fehling's solution. In the presence of yeast 

 extract a bluish-white precipitate is obtained. Arnold and Mentzel b 

 claim that a slight bluish-white precipitate is given even with pure 

 meat extracts, but by experience an analyst learns to detect by this 

 method the presence of about 20 per cent of yeast extract in meat prep- 

 arations. Micko c suggests the determination of kreatin and xanthin 

 bodies as a means of determining the nature of the extract. Wintgen d 

 states that the filtrate from the zinc sulphate precipitate obtained 

 in the determination of albumoses is entirely clear in the case of meat 

 extracts, but somewhat turbid with yeast extracts. This he finds to 

 be true even when the best S. & S. filter paper is employed. By this 

 method the authors could detect from 20 to 30 per cent of added yeast 

 extract. 



E. Baur and H. Barschall'' have applied the colorimetric test, as out- 

 lined by Folin, for kreatinin to meat and yeast extracts. They find 

 no kreatin or kreatinin in yeast extracts and base a distinction 

 between the two on this test. Salkowski-^ has studied the various 

 carbohydrates of yeast and gives several tests for yeast gum. 



The most reliable test is unquestionably the determination of 

 kreatin. A yeast extract -contains no kreatin and in a typical meat 

 extract there is found from 10 to 20 per cent of the total nitrogen in 

 the form of kreatin and kreatinin. The distribution of the various 

 xanthin bases also is different in the two kinds of extracts; in meat 

 extracts, according to Micko/ xanthin and hypoxanthin predominate, 

 while in yeast extracts adenin and guanin predominate. 



Result of Tests. 



A test for yeast extracts consisting in boiling the samples for one or 

 two minutes with an unmodified Fehling's solution was tried. Four 

 samples were tested with the following results: 



Color of precipitate. 



A. Meat extract Very deep violet color. 



B. Yeast extr?ct Very deep green color. 



C. 50 per cent yeast and 50 per cent meat extract Intermediate color. 



D. 25 per cent yeast and 75 per cent meat extract Violet color, not as 



strong as A. 



This test is of value as a qualitative and a confirmatory -test for 

 yeast extracts in the presence of meat extracts. 



aPharm. J., 1903, 7.7:516 and 704; 1904, 72:86. 



&Pharm. Ztg., 1904, 49:176. 



cZts. Nahr. Genussm., 1902, 5:193; 1903, 6:781. 



dArch. Pharm., 1904, 242:537. 



«Arb. kaisert. Gesundheitsamte, 1906, 24:562. 



/Ber. d. chem. Ges., 1894, 27:499. 



S'Loc. cit. 



