6 BULLETIlSr 1041, U. S. DEPAETMENT OF AGRICULTURE. 



dextrose and levulose and the nonreducing sugar of sucrose. The 

 presence of pentose, galactose, mannose, and maltose was excluded 

 by his tests. 



No reference has been found in the literature relative to the nature 

 of the coloring substances found in sweet potatoes. The possible 

 relation of some of these to the discoloration of the canned potato 

 makes it of interest to know something of their nature. Qualitative 

 tests made during the course of the present studies strongly indicated 

 that the chief coloring substances in the flesh of the deep-colored 

 varieties belong to the carotinoid group of chemical compounds. 

 F. M. Schertz, of the Office of Soil-Fertility Investigations, kindly 

 made for the writers analyses of material prepared from the Gold 

 Skin potato and reported a finding of about 0.0073 per cent of carotin 

 and a much smaller amount of xanthophyll. In several varieties a 

 deep-purple pigment is present in the skin and cortex. The solu- 

 bility of this pigment together with its chemical characteristics 

 strongly indicates that it is an anthocyan, but isolation of it in pure 

 form was not attempted. It has appeared to be associated to some 

 extent with the discoloration of the canned potato. 



The gummy latex present in the sweet potato is another substance 

 of considerable interest. There is no published work upon its chemi- 

 cal nature. Carver (5) reported the preparation of a rubber com- 

 pound which was probably made from some constituent of the latex. 

 Whether there is present a true rubber hydrocarbon is not known. 

 The latex is of interest here because in those varieties showing an 

 abundance of it the tendency of the canned product to discolor is 

 more pronounced. The various strains differ considerably in the 

 apparent quantity of latex which is present. 



The sweet potato as raw material for the manufacture of numerous 

 products has received considerable attention from several workers. 

 Carver (5) has reported, in addition to the rubber compound men- 

 tioned above, the preparation from it of starch, flour, ink, and adhe- 

 sive. 



Gore (6) has announced a method of preparing a palatable sirup 

 from the sweet potato. 



Mangels and Prescott {16) have reported the results of investiga- 

 tions upon the manufacture of sweet-potato flour by the " flake " 

 process. 



In books upon canning, the sweet potato is often spoken of and 

 directions given for handling the product, but no comprehensive 

 study of canning problems seems to have been made. 



EXPERIMENTAL CANNING TESTS. 



The experimental work upon the problem of canning sweet pota- 

 toes was begun in the fall of 1918. Surplus stocks from variety and 



