Amylopectin in potatoes

Figure 5.16 Schematic model for the arrangement of amylopectin in potato starch. Crystalline layers containing double helical linear segments in amylopectin molecules form a continuous network consisting of left-handed helices packed in tetragonal arrays. Neighboring molecules are shifted relative to each other by half the helical pitch. (Adapted with permission from reference 3)...

P. A. M. Steeneken, Reactivity of amylose and amylopectin in potato starch, Stdrke/Starch, 36 (1984) 13-18. 

Svegmark, K., Hermansson, A.M., 1991. Distribution of amylose and amylopectin in potato starch paste — effects of heating and shearing. Food Strucmre 10, 117—129. 

Number average molecular weight, dalton, g/ mol, amu 1,800,000 (amylopectin in potato) Bertoft, E Blennow, A,Adv. Potato Chem. Technol., 83-98,2009. 

Starches can be separated into two major components, amylose and amylopectin, which exist in different proportions in various plants. Amylose, which is a straight-chain compound and is abundant in potato starch, gives a blue colour with iodine and the chain assumes a spiral form. Amylopectin, which has a branched-chain structure, forms a red-purple product, probably by adsorption. 

The variation between the starch from different plants is considerable. The percentage of amylose varies from 27% in maize starch through 22% in potato starch to 17% in tapioca starch. The waxy maizes are unusual in that they are almost pure amylopectin. This is extremely convenient because it avoids the need to separate amylopectin from amylose chemically. 

The data19 summarized in Figure 1 show that the extent of the hydrolysis of soluble potato starch by barley beta amylase reaches a limit which is independent of the concentration of the amylase. The data are typical of the action of beta amylases on unfractionated starches, when the hydrolyses are carried out at or near pH 4.5.1 3 6 19 20 Under these conditions, the hydrolysis of unfractionated starches usually ceases when 60 to 64% of the maltose theoretically obtainable from the substrate has been formed. The exact value of the limit obviously will depend upon the concentration of amylopectin in the starch and upon its structure. 

Fig. 7. 134C-N.m.r. Spectrum ofDiphenylborinate Complex of Potato Amylopectin in...

This ehapter eonsiders the reeent view on moleeular structures of the amylose and amylopectin components in potato and how they are organized to form characteristie structures inside the stareh granules. The phosphorylation of starch, and the synthesis of its eomponents in normal and genetieally modified potatoes, is also discussed. 

Bertoft, E. (2007a). Composition of clusters and their arrangement in potato amylopectin. Carbohydr. Polym., 68, 433 46. 

Takeda, Y, Hizukuri, S. (1982). Location of phosphate groups in potato amylopectin. Carbohydr. Res., 102, 321-327. 

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