Size distribution of waxy corn endosperm starch granules

Seven waxy corn varieties were used as test materials and their endosperm starch granules' diameters,volumes,surface areas and quantity distributions were measured by a laser diffraction particle size analyzer so as to clarify the size distribution of waxy corn endosperm starch granules.The results showed that the starch granule sizes were 0.375—30.07 μm,the upper limit was 22.73—30.07 μm,and the mean was 12.33—14.60 μm.Both starch granule volume and surface area distributions presented a triple humped curve,and the quantity distribution a unimodal curve.According to the concave point of volume distribution curve,the starch granules could be divided into small size( 3.519 μm),medium size(3.519—7.422 μm) and large size(7.422 μm).Among the 7 varieties the ratios of small-,medium- and large-sized granules' volumes to the total volume were respectively 11.25% —12.46% ,1.79% —6.98% and 80.77% —86.96% ,the ratios of small-,medium- and large-sized granules' surface areas to the total surface area were respectively 54.28% —57.13% ,2.50% —8.26% and 35.97% —40.38% ,and the ratios of small-,medium- and large-sized granules' quantities to the total quantity were respectively 98.71% —99.39% ,0.20% —0.76% and 0.39% —0.53% .It was clear that the waxy corn endosperm starch was mainly composed of small starch granules which had the largest contribution to surface area,and the large starch granules had the largest contribution to volume.The intervarietal comparison indicated that among the 7 varieties the size distributions of small starch granules were not significantly different but those of medium and large starch granules were significantly different.