698 



Journal of Agricultural Research 



Vol. XII. No. II 



is killed or disorganized and its synthetic activities reduced or destroyed, 

 certain hydrolytic enzyms are activated, and hydrolysis or splitting of 

 certain of the kernel constituents ensues. As a result, there is an accumu- 

 lation of the split products of starch and proteins, particularly dextrose 

 and amino acids. It is probable that the extent of starch hydrolysis 

 by amylases depends in large part upon the percentage of moisture in the 

 grain after it thaws out. If the kernels are nearly dry, less change \vill 

 occur than if the kernels contain considerable moisture. 



The dextrose which thus ac- 

 cumulates in the kernel is pre- 

 sumably available as substrate 

 for the respiratory enzyms. 

 In accordance with the law 

 of mass action, a greater con- 

 centration of substrate should 

 accelerate the rate of respira- 

 tion. There is an additional 

 factor in the case of frosted 

 wheat that would also tend to 

 result in an increased rate of 

 respiration at any particular 

 percentage of moisture. The 

 hydrolysis of the gluten sub- 

 sequent to thawing results in 

 products having a materially 

 lower water-imbibing capacity 

 than the normal gluten. In 

 fact, the amino acids formed 

 are not colloids, and form true 

 solutions. Consequently the 

 relative viscosity of frosted 

 grain at any moisture content 

 will be less than in normal 

 grain, the difiference depending 

 upon the extent of hydrolysis. 

 To ascertain the efifect of 

 frosting upon the rate of respiration, two samples of commercial 

 wheat containing frosted kernels were secured. These were marked 

 "moderately frosted" and "badly frosted," respectively. The 

 respiratory activity of these frosted samples was determined with 

 five different percentages of moisture present. Tables VIII and IX 

 show the respiration data of these two lots, while in Table X are 

 given the interpolated values at even percentages of moisture in com- 

 parison with sound spring wheat. The same data are shown graph- 

 ically in figure 4. There is a slight overlapping of the curves for the 



I 



I 



\ 





to 



Q /i? /S /^ /S /& /y' 



Fig. 3. — Graphs showing the rate of respiration of shriveled 

 ■wheat and of plump wheat of the same class. 



