Amylopectin amylose content

Amylum Mixed amylose and amylopectin Amylose content 15-25 % Amylopectin content 75-80 % n = 100-2000 Prepared from potato and com 0.5-3 % water solution boiled, NaOH, soda... 

Pea starch granules are oval, sometimes fissured, with a diameter of 20-40 ym (13). Molecular and structural characteristics of the two main components of field pea starch—amylose and amylopectin—are important in determining functional properties (25,26). Smooth field pea starch concentrate contains 97.2% starch of which 30.3-37.8% is amylose (9,23,25-27), and wrinkled pea starch concentrate contains 94.8% starch, which is 64% amylose (26). The gelatinization temperature of smooth pea starch is between 64 to 69 C, and that of wrinkled pea starch is greater than 99 C to 115 C. Gelatinization temperature depends on maturity of field pea seed and amylose content (26,27). 

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. 

Jane, J., Chen, Y. Y., Lee, L. F., McPherson, A. E., Wong, K. S., Radosavljevic, M., and Kasemsuwan, T. (1999). Effects of amylopectin branch chain length and amylose content on gelatinization and pasting properties of starch. Cereal Chem. 76, 629-637. 

Most potato starches are composed of a mixture of two polysaccharides, a linear fraction, amylose, and a highly branched fraction, amylopectin. The content of amylose is between 15 and 25% for most starches. The ratio of amylose to amylopectin varies from one starch to another. The two polysaccharides are homoglucans with only two types of chain linkage, a-(l 4) in the main chain and a-(l 6)-linked branch chains. Physicochemical properties of potato and its starch are believed to be influenced by amylose and amylopectin content, molecular weight, and molecular weight distribution, chain length and its distribution, and phosphorus content (Jane and Chen, 1992). 

To determine the amylose content of starch, the iodine reaction has been most commonly used because amylose and amylopectin have different abilities to bind iodine. The methods such as blue value (absorbance at 680 nm for starch-iodine complex using amylose and amylopectin standards), and potentiometric and amperometric titration have been used for more than 50 years. These procedures are based on the capacity of amylose to form helical inclusion complexes with iodine, which display a blue color characterized by a maximum absorption wavelength (kmax) above 620 nm. During the titration of starch with iodine solution, the amount (mg) of iodine bound to 100 mg of starch is determined. The value is defined as iodine-binding capacity or iodine affinity (lA). The amylose content is based on the iodine affinity of starch vs. purified linear fraction from the standard 100 mg pure linear amylose fraction has an iodine affinity of 19.5-21.0mg depending on amylose source. Amylopectin binds 0-1.2mg iodine per 100mg (Banks and Greenwood, 1975). The amylose content determined by potentiometric titration is considered an absolute amylose content if the sample is defatted before analysis. 

Starch (20 mg, dry basis) in water (10 mL) is heated at certain temperatures in sealed tubes for 30 minutes. The tubes are then cooled to room temperature and centrifuged. Supernatant is withdrawn and its amylose content is determined according to the method of Williams et al. (1970). The value of amylose leaching reflects the association of amylose, and interactions between amylose and amylopectin in the starch. 

Species and/or cultivar differences are also observed in other starch properties and in the properties of isolated amylose and amylopectin. To illustrate, purified amylose samples have been shown to differ in (3-amylolysis limit and average DP.64,67,124 Purified amylopectin samples have also been shown to differ in (3-amylolysis limit, average length of unit chains and viscosity.64,66 67 124,125 Campbell et al.121 observed a range of amylose content from 22.5% to 28.1% in 26 maize inbreds selected for maturity, kernel characteristics and pedigree. Starches from these non-mutant genotypes also differed in thermal properties (DSC), paste viscosities and gel strengths. 

A mutant of starch synthase II has also been isolated in Chlamydomonas rein-hardtii 193 this mutant, st-3, accumulated only 20-40% of the amount of starch present in the wild type. The enzyme lacking in the mutant was starch synthase II, one of the two starch synthase isoforms present in C. reinhardlii.m There was an apparent increase in the amylose content, and in a modified form of amylopectin. The changes noted in the mutant amylopectin were a decrease in the number of intermediate-size chains (DP 8-50) and an increase in short chains (DP 2-7). The conclusion made was that this starch synthase II was responsible for synthesis of intermediate-size... 

Substances commonly found in starch granules are amylopectin, amylose, molecules intermediate between amylose and amylopectin, lipid (including phospholipids and free fatty acids), phosphate monoester and proteins/enzymes. The contents and the structures of amylopectin and amylose play major roles in the functional properties of starch. However, lipids, phospholipids and phosphate monoester groups have significant effects on starch functional properties, even though they are minor constituents. 

Iodometric assay of amylose on cereal starches is most often done on lipid-extracted starch, and the amylose content from that assay is termed apparent amylose 145 or total amylose. 123 When the iodometric assay is performed on a lipid-extracted starch and the amylose content is corrected for interference from extra-long chains on amylopectin, the assay gives absolute amylose or real amylose. 145 Iodometric assay of starch that has not been lipid-extracted gives lipid-free (uncomplexed) amylose. Subtraction of total amylose from lipid-free amylose gives lipid-complexed amylose.123 The use of the term apparent amylose to designate lipid-free amylose is avoided in this chapter. All amylose percentages are calculated based on starch. 

The viscosity of a starch paste is mainly a function of the size of swollen granules. Waxy maize starch has smaller granules, so its swelling power is less than that of amylopectin potato starch. The peak viscosity of amylopectin potato starch, in comparison to potato starch and waxy maize starch, is shown in Figure 11.7. The gelatinization properties of amylopectin starch resemble those of potato starch. With reduced amylose content, the peak viscosity occurs as a lower temperature as swollen granules are weak and can be ruptured more easily with shear. 

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