440 
Journal of Agricultural Research 
Vol. XI, No. 9 
Table I. —Results with ninhydrin method of estimating the rate of hydrolysis of the pro¬ 
teins of milk 
% Sample. 
Total 
nitro¬ 
gen. 
Initial 
soluble 
nitro¬ 
gen. 
Initial 
ninhy- 
drin 
nitro¬ 
gen. 
48-hour 
soluble 
nitro¬ 
gen. 
48-hour 
ninhy¬ 
drin 
nitro¬ 
gen. 
Increase 
in 
soluble 
nitro¬ 
gen. 
Increase 
in nin¬ 
hydrin 
nitro¬ 
gen. 
Per cent. 
Per cent. 
Per cent. 
Per cent. 
1 Per cent. 
Per cent. 
Per cent. 
Boiled skim milk. 
O. 0586 
0. 0033 
0. 0029 
O. 0039 
O. 0032 
I. 02 
0. 51 
Skim milk + 3 per cent of 
sodium chlorid. 
.0586 
. 0108 
, 0029 
*0137 
.0031 
4 - 95 
•34 
Skim milk. 
.0586 
. 0108 
. 0029 
.0177 
.0032 
11. 77 
• 5 1 
The ninhydriu method indicated no increase in nitrogen when there 
was an actual increase of 11.5 per cent in the soluble nitrogen. This 
was further substantiated by work on a pure casein solution. This gave 
only a trace of nitrogen by the ninhydrin method, with no increase after 
evident proteolysis had taken place. This method of estimating the 
rate of hydrolysis of proteins was therefore abandoned as not being 
applicable to investigations with milk proteins. 
(< c) The influence op chloroform on proteolysis. —To prevent 
bacterial action in the samples, chloroform was added in amounts found 
ample by Harding and MacTean (rr) and Van Slyke (24). Skim milk 
to be analyzed at varying intervals extending over a long period of time 
was treated with 1 per cent chloroform, which, according to the above 
investigators and Babcock and Russell (5), should have only slightly 
inhibited proteolysis. As shown in Table II, the soluble nitrogen of 
this skim milk did not increase on standing. In verifying this result 
the soluble nitrogen was obtained by a Kjeldahl determination of the 
nitrogen in the total filtrate from the casein precipitation. Closer 
agreement in the duplicates could be obtained from the filtrates than 
from the casein itself. 
Table II. —Influence of chloroform on the proteolysis of milk as indicated by soluble 
nitrogen 
Sample. 
Chloro¬ 
form. 
Total 
nitrogen. 
Initial 
soluble 
nitrogen. 
Soluble 
nitrogen 
after 4 
days. 
Increase 
in soluble 
nitrogen as 
per cent 
of total. 
i. Skim milk. 
Per cent. 
I 5 
Per cent. 
O. 0583 
Per cent. 
O. 0129 
Per cent. 
O. 0183 
9. 26 
) 1.0 
•<> 5 8 3 
.0130 
. 0114 
-2. 74 
2. Skim milk_*.. 
/ -5 
•0531 
.0115 
. 0170 
10-35 
\ 1.0 
* 0531 
.0115 
, 0120 
.94 
3. Skim milk.. 
f 
. 0406 
. 0119 
.OI36 
4. l8 
\ 1.0 
. 0406 
. 0119 
. 0103 
“ 3*94 
4. Skim milk. 
1. 0 
•0547 
. 0106 
.OO79 
-4.93 
5. Buttermilk, neutral. 
( * S 
•0551 
.0125 
. 0201 
13. 60 
l i-o 
•0551 
.0125 
. OI74 
9. 80 
6. Buttermilk, neutral. 
1. 0 
.0463 
. 0064 
.OO59 
— 1. 08 
