Selection and starch properties of sweetpotatoes with low and high amylose content

Sweetpotatoes with low or high amylose content were selected in order to develop new sweetpotato varieties for specific starch production, and the properties of their starches, including viscosity and retrogradation, were investigated. Near infrared analysis was adopted to measure amylose content because conventional methods like the blue value method using iodine need more time and labor. The correlation coefficient between the blue value method and near infrared analysis for amylose content was 0.861 (p < 0.01, n = 21) in 1998. The amylose content of 574 breeding lines or established cultivars was measured by near infrared analysis. Amylose content ranged from 12.1% to 21.3% , the mean value was 17.0% , and the standard deviation was 2.0 among 180 lines. The amylose content of lines with orange or yellow flesh was higher than that of lines with purple flesh. Lower and higher amylose lines were selected, and their amylose contents were measured the following year by the blue value method. In this case, amylose content ranged from 9.6% to 22.2%. Fourteen low amylose lines under 14% and 15 high amylose lines over 20% were selected. Some lines with low or high amylose had unique pasting and retrogradation properties. Furthermore, the correlation between amylose content and starch properties, like some pasting properties or retrogradation indexes, was significant. Starches of Kyukei 89376-12 and Tanegashimamurasaki with low amylose content exhibited higher peak viscosity and remarkable breakdown similar to the waxy corn. The starch of Kyukei 89376-12 with low amylose content retrograded slowly. That of Kyukei 93118-6 with high amylose content had the opposite properties. The amount and activity of GBSS, which is likely the key enzyme for amylose synthesis, were lower in Kyukei 89376-12 and higher in Shiroyutaka and Sunny-red with high amylose content. This result explained well the relationship between amylose content and GBSS activity.