8 
Journal of Agricultural Research 
Vol. II, No. i 
FORM IN WHICH VOEATlEE ACIDS OCCUR 
Another point concerning the relation of these acids to the flavor of 
cheese remains to be considered—that is, the form in which they are 
combined. It is not to be expected that the acids are all in the free state, 
for the proteolysis taking place during the ripening process gives rise to 
ammonia and possibly other basic substances. The exact course of this 
proteolysis has not been determined. In a ripe Roquefort cheese 
examined by Jensen 52.50 per cent of the total nitrogen was water- 
soluble, 23.64 per cent was precipitated by phosphotungstic acid, and 
4-99 P er cent was i n the form of ammonia. This is in accord with 
unpublished data of Dox, 1 who made a separation of the different classes 
of nitrogenous products by the method of Van Slyke and Hart (15, p. 
150). For a prime Roquefort he gives the distribution of nitrogen as 
follows: In caseoses, 10.7; in peptones, 8.6; in amino acids, 29.1; in 
ammonia, 6.1; insoluble, 45.5. Dox (6, p. 423) has, furthermore, iden¬ 
tified tyrosin among the amino acids. The work of these investigators 
indicates that probably all of the hydrolytic cleavage products of para¬ 
casein are to be expected in a ripe Roquefort cheese. 
Every Roquefort cheese examined in the laboratory of the Dairy 
Division has been decidedly acid to both litmus and phenolphthalein. 
The exact amount of acidity is difficult to measure, for such a complex 
mixture of weak acids and bases can not be accurately titrated. Ten 
grams of a well-ripened cheese having a distillation number of 43.9 were 
extracted three times with 50 c. c. of 95 per cent alcohol. This alcoholic 
extract required 57.0 c. c. of decinormal alkali for neutralization. Data 
given by Jensen show that the ammonia is not equivalent to the acidity 
calculated from the distillation number and the acid number of the fat. 
This does not take into account the acidity of the paracasein and amino 
acids. 
It is also to be remembered that the ammonium salts of the weak 
organic acids are so strongly hydrolyzed in an aqueous solution that they 
can not be crystallized from this solvent. However, they can be readily 
prepared by passing dry ammonia into a benzene solution of the acids. 
Ammonium caproate, caprylate, and caprate have been prepared in this 
manner. They are white needlelike crystals which readily give off the 
odor of the respective acids when exposed to the moisture of the air. The 
peppery effect of these salts when placed upon the tongue is quite similar 
to the effect of the free acids, but is less intense. 
From these considerations of the basic and acid substances of the 
cheese it is apparent that caproic, caprylic, and capric acids exist, both free 
and combined, and those combined are in such weak form of combination 
that their characteristic taste is not obscured. 
1 Dox, A. W. Records of the Storrs Agricultural Experiment Station. 
