4 BULLETI^r 1041, U. S. DEPARTMENT OF AGEIGULTURE. 



It will be seen from Table 1 that the sweet potato has a low mois- 

 ture content ; it is high in total carbohydrates and low in fat, fiber, 

 and protein. The protein content is slightly lower than that of the 

 Irish potato; but about half of the total nitrogen calculated as pro- 

 tein in the Irish potato is really in the form of amids, whereas in 

 the sweet potato, as shown by Keitt {11), no amids are present. 

 The low crude-fiber content indicates high digestibility, and the 

 fuel value is also seen to be high. 



From the standpoint of the canner the acidity of the sweet potato 

 is of considerable importance, since it affects the transformations 

 which take place within the can both during and after processing 

 and likewise has an important bearing upon sterilization. Published 

 data upon this subject, however, are meager. BigeloAv and Cath- 

 cart {2) approached the subject from the standpoint of the hydrogen- 

 ion concentration and give the results of six determinations upon 

 canned sweet potatoes from different sources packed in Xo. 2^ and 

 No. 3 cans and processed at different temperatures for variable lengths 

 of time. Their determinations place the Ph value for sweet potatoes 

 at between 5.27 and 5.56, with an average of 5.39. According to 

 the findings of these authors the hydrogen-ion concentration of the 

 canned sweet potatoes is a little lower than string beans and green 

 peppers and slightly higher than spinach. Lima beans, peas, and 

 corn show a considerably less hydrogen-ion concentration, and pump- 

 kins and carrots somewhat more. 



In the present investigations the titratable acidity was determined 

 upon the canned material of each of the varieties and strains under 

 study. The material examined was in the form of pie stock, which 

 was packed dry into No. 2 tin cans and processed for 45 minutes at 116° 

 C. Samples of 10 grams each were shaken up in 100 c. c. of distilled 

 water, boiled one minute to expel carbon dioxid, and titrated with 

 N/10 NaOH, using phenolphthalein as an indicator. From 3.2 to 

 7.3 c. c. of the standard alkali were required to neutralize the acidity 

 of these 10-gram samples. These figures represent the extremes, the 

 average of the 43 varieties and strains being 4.5 c. c. which shows 

 that the sweet potato is quite low in acidity. The average titratable 

 acidity was slightly higher in samples packed in 1920 than those 

 packed in 1919, but this fact is not considered significant, as in some 

 varieties the acidity was higher in 1919 than in 1920. The differences 

 in acidity among the varieties were small, and in these tests they 

 could not be correlated with keeping qualities, discoloration, or any 

 other significant quality. They therefore seem to be too small to be 

 of importance. 



The most important constituents of sweet potatoes are the carbo- 

 hydrates, and since the nature and relative proportions of these 

 fundamentally affect the physical character and quality of the 



