Studies on the Physicochemical Properties of the Tubers of New Sweet Potato Lines

Abstract

This study was conducted with 17 new sweet potato lines and one commercial variety to investigate the physical and chemical properties of the tuber powder and to find out the relationship between tuber dry matter content, reducing sugar, starch content and enzyme activity of tuber amylase. The starch granular size of these sweet potatoes ranged from 8.05×7.25μ to 28.98×26.57μ. The viscosity of the tuber powder solution at 90℃ was about 20 times as large as that at room temperature. After cooling from 90℃ to room temperature the viscosity was much higher than that at 90℃. The average dry matter content of these new lines amounted to 36.6%, being much higher than that of Tainung 57(27.8%). Three new lines had a dry matter content more than 40%. The tuber moisture content ranged from 56.5 to 72.2%, Tainung 57 had the highest moisture content, being 8.3% higher than the average. The tuber starch content on dry basis ranged from 61.99 to 75.38%. More than half of the new lines had a higher tuber starch content than the average (67.93%). The tuber starch content on wet basis ranged from 18.42 to 30.68%. The commercial variety, Tainung 57, had the lowest tuber starch content on wet basis due to its low tuber dry matter content, while C 71-96 had the highest tuber starch content both on dry and wet basis. The average reducing sugar content was 3.71%. C71-196 had the highest value of 8.44%, while C66-33 had only 0.24%. The amount of the reducing sugar in tuber indicated that amylase more or less existed in the tuber. This enzyme can convert starch molecule into reducing sugar under normal pressure and temperature. High significant relationships were found between these physicochemical properties, namely, tuber dry matter content and tuber starch content on vet basis (r=0.97), tuber starch content on wet basis and tuber starch content on dry basis (r=0.77) and reducing suger content and amylase activity (r=0.98). Because of the close relationship between tuber dry matter and tuber starch content on wet basis, the tuber dry matter percentage could be used to evaluate the tuber starch content on wet basis. A regression equation Ŷ=0.82664 X-5.25795 was then derived, where Ŷ was the tuber starch content on wet basis and X was the tuber dry matter.