Food Chemical Studies on Starch Part 1. Effect of Urea on the Gelatinization of Potato Starch

Abstract

The swelling ratio and solubility of potato starch with urea were studied to elucidate the effect of urea on the gelatinization of starch. The swelling ratio and solubility were increased with the increasing of urea concentration and raising the temperature. The concentration of urea required for the initial gelatinization decreased on elavating the temperature as follows; 6 M/l at 20°C, 4.5 M/l at 30°C, 3.2 M/l at 40°C and 1 M/l at 50°C. The initial gelatinization temperature of potato starch at zero concentration of urea was estimated about 56°C, and this agreed with the result obtained by Kofler microscope methods. The swelling ratio above 3.5 M/l urea at 60°C was lower than those at other temperatures (2050°C). A lower swelling ratio is due to the decrease in the amount of precipitates because of a higher solubility at a higher temperature. There was not the increase of swelling ratio between 3.5?`5.5 M/l urea at 50°C and 6.58 M/l at 40°C. These results suggest that the swelling ratio is not primarily connected only to the degree of gelatinization. The urea inhibited the starch-iodine reaction, and inhibition of starch-iodine reaction by urea was remarkable at the low iodine concentration.