Starch Granule Size Distribution in Storage Roots of Different Types of Sweetpotato Cultivars

【Objective】 An experiment was conducted to clarify the starch granule size distribution and the relationship between starch granule size and starch quality properties in storage roots of different types of sweetpotato cultivars.【Method】 Six starchy sweetpotato cultivars,five edible sweetpotato cultivars,and one dual-purpose sweetpotato cultivar were planted at Taian experimental site in Shandong Province,with randomized block design in 2009-2010 growing season.The volume distribution and number distribution of starch granule,and their relationship to the content of total starch and its components in storage root were determined.【Result】The starch granule in storage root was 0.39-55.14 μm in diameter,containing smaller type(diameter3.36 μm),mid-type(diameter 3.36-19.76 μm)and larger type(diameter19.76 μm)granules.The distribution frequency showed typical two-peak curve in starch granule volume and number,and the grain diameters were all equal to 3.36 μm.The volume of smaller type granule accounted for 9.8%-18.5% of the total starch granule,and the number of smaller type granule accounted for 97.7%-99.1% of the total starch granule.The volume percentage of 3.36 μm starch granule and the number percentage of 1.00μm starch granule were higher in edible sweetpotato than in starchy sweetpotato.The contents of total starch,amylose and amylopectin were negatively correlated with the volume percentage of smaller type(r=-0.772**,-0.730**,-0.774**)and middling type(r=-0.723**,-0.715**,-0.712**) starch granules,respectively,but positively correlated to larger type(r=0.746**,0.729**,0.738**) starch granule.The ratio of amylopectin to amylose was positively correlated with the volume percentage of smaller type(r=0.716**)and middling type(r=0.740**) starch granules,respectively,but negatively correlated to larger type(r=-0.745**) starch granule.【Conclusion】The rates of small starch grains in storage root of edible sweetpotato were higher,but the rates of big starch grains in storage root of starchy sweetpotato were higher.