A STUDY OE SWEET POTATO VARIETIES. 15 
Numerous experiments were made to see whether the tendency to 
darken could be prevented by treatment of the potatoes with dif- 
ferent substances. Acetic, tartaric, and sulphurous acids were found 
to reduce the extent of the discoloration to a minimum, but they gave 
an undesirable flavor to the product. Sodium chlorid in various con- 
centrations was also tried. It was found that if whole sweet potatoes 
were placed in the can without packing closely and a 10 per cent 
salt solution was added to fill the air spaces, the discoloration was 
prevented. Water alone was just as effective in so far as it excluded 
the oxygen from the material. Some tests were made by dipping the 
potatoes in a 10 per cent salt solution and then filling into the can. 
It did not prevent discoloration in the presence of oxygen. Camp- 
bell (4) states that discoloration may be prevented by the use of 
sodium chlorid, but in these tests the salt was not effective if the ex- 
haust was insufficient, and when the exhaust was sufficient no salt was 
necessary. Proper exhausting is likewise essential to prevent the loss 
of the bright orange or yellow color which occurs when the caroti- 
noids that give this color are oxidized in the presence of air. 
The most effective way of preventing discoloration in the can and 
preserving the natural bright color is to handle the potatoes so that 
the material after cooking is exposed to the air for the shortest pos- 
sible time, filling the potatoes into the can at a temperature not below 
70° C, filling the can so that there is but a very small head space, and 
sealing at once. 
Sweet potatoes which have been properly handled during the can- 
ning operations will usually darken somewhat on exposure to the air, 
though ordinarily this is not sufficient to be objectionable. The amount 
of this discoloration depends largely upon the particular variety of 
potato used and especially upon the length of time the canned prod- 
uct has been held in storage. During these studies it was repeatedly 
demonstrated that whereas the canned potatoes opened and exposed 
to the air 10 days after packing showed discoloration on standing, the 
same varieties handled in the same way when opened one year after 
packing remained bright. This was found to hold true for all the 
varieties tested, but the explanation of the phenomenon can not yet be 
given. This fact may be of considerable practical significance. 
Of particular importance is the relation of sweet-potato diseases to 
discoloration. Even in potatoes which are only slightly affected by 
fungous disease the tendency to darken is very greatly increased, and 
discoloration can scarcely be prevented in such material. Moreover, 
the discoloration arising from this cause is more permanent and can 
not be destroyed by any simple means. In the canned product the af- 
fected portions become brown or black in color and give a very un- 
desirable appearance to the potatoes. In canning practice, therefore, 
all affected tissue must be carefully and completely removed. It has 
