A STUDY OF 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 



