Starch structure in developing kiwifruit

Starch is the major component of kiwifruit at the time of commercial harvesting. The structural changes of starches from 2 kiwifruit varieties (Hayward and Gold3) at different growing stages up to commercial harvesting time were studied. During the fruit growth, the starch content (dry weight basis) increased from ~2% to 46% (Hayward) and 58% (Gold3) and the starch granules enlarged from 4 to 10 μm. The polymorph type of the starches remained as B-type and the amylose contents (AC) levelled off (~10–12%, Hayward) or increased (~15 to 19%, Gold3) throughout the fruit developing. The external and internal structures of amylopectins remained similar as the starch granules enlarged in expanding kiwifruit, suggesting a homogeneous molecular structure from the centre towards the periphery of a kiwifruit starch granule. This is the first report to provide the structural information on B-type starch granules in developing fruit. The results of the structural changes shared similarity as well as differences with other types of the starches in developing crops including kidney bean and various cereals. The comparative analysis suggests that the evolution of amylopectin structure in developing crops largely depends on the botanical source, and the dynamics of AC appeared to be independent of that of amylopectin structure.