Fractionation of Starch

To analyze the structure of starch, it’s necessary to separate its components amylose, amylopectin, and sometimes intermediate material (IM). To do this, the fatty material is removed by Soxhlet extraction in 85% methanol. The starch granules are then dissolved using 90% DMSO, 6-10 M urea solution, or 0.5 M KOH/NaOH. High pH and heat should be avoided to prevent degradation. Amylopectin aggregates may remain in the solution, but to get a more complete sample, the dissolved starch is precipitated in ethanol and redissolved.

Starch is composed of different components such as amylose, amylopectin, and sometimes IM, which need to be separated before performing a structural analysis. Soxhlet extraction with methanol is used to remove fatty material from starch granules. The granules are then dissolved using DMSO, urea, or KOH/NaOH solutions. Starch fractionation can be achieved using methods such as Schoch’s or Lansky’s method, where amylopectin is obtained in the supernatant while amylose is precipitated using a butanol or thymol complex.

There’s another way to separate starch called the Matheson and Welsh method. Instead of separating amylose, this method separates amylopectin by using a protein called lectin concanavalin A. After the amylopectin is separated, the lectin is broken down with a protease. This method is expensive and can only be used on a small scale, and the resulting amylopectin may still contain branched IM.

GPC has been used for small-scale fractionation of starch, where amylopectin is easily collected as it is eluted at the void volume of the column. However, amylose is partly included in the gel particles. In some cases, IMs have been reported to elute with volumes intermediate to that of amylopectin and amylose. Sepharose CL 2B is a common media used for this method, and it is eluted with an alkaline solution.

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