Amylopectin in starch

Review of the role of ADP-glucose pyrophosphorylase in the synthesis of amylose and amylopectin in starch granules. 

A further factor that causes the non-homogeneity of nitrostarch is the presence of the two components, amylose and amylopectin in starch. It has been demonstrated by nitrating each of these starch components separately that the nitration products differ from one another. Berl and Kunze [37] detected that amylopectin yields a product of a considerably higher viscosity than that resulting from the nitration of amylose. This effect may be attributable to the higher molecular weight of amylopectin. 

Sen, M., Thevanat, C., and Prioul, J.L. 1997. Simultaneous spectrophotometric determination of amylose and amylopectin in starch from maize kernel by multiwavelength analysis. J. Cereal Sci. 26 211-221. 

Svegmark, K., and Hermansson, A.-M. (1991). Distribution of amylose and amylopectin in starch pastes effects of heating and shearing. Food Structure, 10, 117-129. 

Amylose and amylopectin are the two main constituents of starch. Similarly to cellulose, starch is very common in plant cells. The proportion of amylose and amylopectin in starch varies, and cornstarch for example contains about 27% amylose and 73% amylopectin. 

Figure 11.2 Branched structure of amylopectin (in starch) and of glycogen. Reproduced from Tortora and Derrickson (2009) Principles of Anatomy and Physiology, 12th edn, Wiley International Student Version, New York. 2009 John Wiley Sons. Reprinted with permission of John Wiley Sons, Inc.

The major kinds of digestible carbohydrates in foods are the simple sugars (glucose and fructose), disaccharides (sucrose, maltose, and lactose), and polysaccharides (amylose and amylopectin in starch from plants, and glycogen from meat). The indigestible carbohydrates include cellulose and its derivatives, pectin (the substance that makes jam and jelly gel), and plant gums. 

Amylopectin (Section 25.15) A polysaccharide present in starch. Amylopectin is a polymer of a(l,4)-linked glucose units, as is amylose (see aniylose). Unlike amylose, amylopectin contains branches of 24-30 glucose units connected to the main chain by an a(l,6) linkage. 

In starch, glucose molecules are joined head-to-tail through oxygen atoms. A thousand or more glucose molecules may be linked in this way. either in long single chains (amylose) or branched chains (amylopectin). 

There are two types of glucose chains in starch. One is a simple chain called amylose, and the other is a complex branched form called amylopectin. In the starch grains in a plant, amylopectin makes up the bulk of the material, from 50 to 80 percent by weight, made up of several million amylopectin molecules per starch grain. The rest is a much larger number of the smaller amylose chains, made up of 500 to 20,000 glucose units in each chain. Amylopectin molecules are made of several million glucose units. 

Starch is the most important polysaccharide in the human diet. It consists of two t)q)es of molecules fhe linear and helical amylose and fhe branched amylopectin. Depending on fhe source, sfarch generally contains 20-25% amylose and 75-80% amylopectin. In contrast to the two polysaccharides mentioned in the Section III.C, it is a major energy... 

Cultures of B. subtilis were introduced into the stems of young potato plants by Suit and Hibbert104 in an attempt to bring about replacement of starch by another polysaccharide. Sections of some of the resulting potatoes gave little or no color with iodine, and were provisionally designated starchless potatoes. However, based on analogy with recent developments in starch chemistry, it seems probable that the starchless potato was free from amylose, and contained only amylopectin. 

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. 

A second reason for the turn-over in the osmotic modulus may arise from a decrease in A2 until it becomes zero or even negative. This would be the classical situation for a phase separation. The reason why in a good solvent such a phase separation should occur has not yet been elucidated and remains to be answered by a fundamental theory. In one case the reason seems to be clear. This is that of starches where the branched amylopectin coexists with a certain fraction of the linear amylose. Amylose is well known to form no stable solution in water. In its amorphous stage it can be brought into solution, but it then quickly undergoes a liquid-solid transition. Thus in starches the amylose content makes the amylopectin solution unstable and finally causes gelation that actually is a kinetically inhibited phase transition [166]. Because of the not yet fully clarified situation this turn-over will be not discussed any further. 

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