Separation and Characterization of A‐ and B‐Type Starch Granules in Wheat Endosperm

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Abstract
Mature wheat (Triticum aestivum L.) endosperm contains two types of starch granules: large A‐type and small B‐type. Two methods, microsieving or centrifugal sedimentation through aqueous solutions of sucrose, maltose, or Percoll were used to separate A‐ and B‐type starch granules. Microsieving could not completely separate the two types of starch granules, while centrifuging through maltose and sucrose solutions gave a homogenous population for B‐type starch granules only. Centrifuging through two Percoll solutions (70 and 100%, v/v) produced purified populations of both the A‐ and B‐type starch granules. Analysis of starch granule size distribution in the purified A‐ and B‐type granule populations and in the whole‐starch granule population obtained directly from wheat endosperm confirmed that the purified A‐ and B‐type starch granule populations represented their counterparts in mature wheat endosperm. Centrifugations through two Percoll solutions were used to purify A‐ and B‐type starch granule populations from six wheat cultivars. The amylose concentrations and gelatinization properties of these populations were analyzed. All of the A‐type starch granules contained higher amylose concentrations and had higher gelatinization enthalpies than did B‐type starch granules. Although A‐ and B‐type starch granules started to gelatinize at a similar temperature, B‐type starch granules had higher gelatinization peak and completion temperatures than did A‐type starch granules