Jan. IS. 1915 Changes in Sweet Potatoes During Storage 341 



and 0.77 per cent, the invert sugar content of the Southern Queen 

 having shown no increase in cold storage. In all cases the proportion 

 was approximately 4 to 5 parts of cane sugar to i of reducing sugar. 



SUMMARY 



During its growth the sweet-potato root is characterized by a very low 

 sugar content. The reserve materials from the vines are almost wholly 

 deposited as starch. 



Immediately after the roots are harvested there occurs a rapid trans- 

 formation of starch into cane sugar and reducing sugars. This initial 

 transformation seems to be due to internal causes and is largely inde- 

 pendent of external conditions. Even at a temperature of 30° C. both 

 cane sugar and reducing sugars accumulate during this initial period 

 in excess of the quantity used in respiration, while during subsequent 

 periods the quantity of reducing sugar diminishes at that temperature 

 as a result of respiration. These initial changes seem to be associated 

 with the cessation of the flow of materials from the vines. 



In sweet potatoes stored at a temperature of 11.7° to 16.7° C, the 

 moisture content remains fairly constant. There is a gradual disappear- 

 ance of starch during the first of the season (October to March) and 

 probably a re-fomiation of starch accompanied by a disappearance of 

 cane sugar during the latter part of the season (March to June). The 

 changes in reducing sugar are less marked than those in cane sugar. 

 The changes in starch and cane sugar appear in a general way to be 

 correlated with the seasonal changes in the temperature. 



In sweet potatoes kept in cold storage (4° C.) there is a rapid dis- 

 appearance of the starch and an accompanying increase in cane sugar. 

 These changes do not attain a state of equilibrium at that temperature, 

 as the sweet potatoes invariably rot by the action of fungi before the 

 changes have reached their maximum. At both high and low tem- 

 peratures cane sugar is the chief product formed by the conversion of 

 starch in the sweet potato. The quantity of invert sugar in the root at 

 any time is comparatively small. 



LITERATURE CITED 

 Appleman, C. O. 



1914. Biochemical and physiological study of the rest period iji tlie tubers of 

 Solanuni tuberosum. Md. Agr. Exp. Sta. Bui. 183, 226 p., 17 fig. 

 Baranetzky, J. 



1884. [Ueber die jahrlichc Periodc der Starkespeicherung in den Zweigen unscrer 

 Baume.] In Bot. Centbl., Bd. 18, No. 18, p. 157. 

 Bryan, H. A., Given, A., and Straughn, M. N. 



191 1. Extraction of grains and cattle foods for the determination of sugars: A 

 comparison of the alcohol and the sodium carbonate digestions. U. S. 

 Dept. of Agr., Bur. Chcm. Circ. 71, 14 p. 

 69733°— 15 5 



