Starch amylose content

Probably the most important carbohydrate polymer in food, certainly from a nutritional standpoint, is starch, and Chapter E2 presents three units that can be used for starch isolation and characterization. UNITE2.1 condenses many different starch isolation methods into one scheme for starch isolation from virtually any plant source. In this protocol, the author notes the care that must be taken to prevent starch degradation during isolation. unite2.2 presents a simple enzymatic analysis method that can be used for estimation of starch in food. Finally, unit E2.3 describes a colorimetric method to determine starch amylose content. Again, different combinations of the units in this chapter can be used to characterize starch from any source. 

Tukomane, T., and Varavinit, S. (2008). Classification of rice starch amylose content from rheological changes of starch paste after cold recrystallization. Starch/Stdrke, 60, 292-297. 

It is commonly believed that it is amylose that forms complexes with hpids, but complexation, which occurs concomitantly with the endothermic gelatinization, has been identified and provided evidence of the existence of amylopectin-lipid interactions (Ehasson, 1994). Apparent starch amylose content correlated well with enthalpies of amylose-lipid complexes (Villwock et al., 1999). Lipids are most likely to complex with amylopectin to the extent they do with amylose. The interaction depends on the amylose amylopectin ratio. If amylose is present, the first interaction is that between amylose and lipids, followed by a lipid-amylopectin interaction. This is a mixture of B- and V-pattem starches. The best complexes are formed by 100% amylopectin poorer complexes occur in a 50% solution due to the presence of amylose (Gudmudsson and Eliasson, 1990). 

Amylose Content, and Average Length of Unit Chain, of Starches... 

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. 

Cheetham, N. W.H. and Tao, L. (1998). Variation in crystalline type with amylose content in maize starch granules X-ray powder diffraction study. Carbohydrate Polymers. 36, 277-284. 

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. 

Gelatinization of sweet potato, tania, and yam tuber starches. Starch/Starke. 47, 298-306. Varavinit, S., Shobsngob, S., Varanyanond, W., Chinachoti, P., and Naivikul, O. (2003). Effect of amylose content on gelatinization, retrogradation and pasting properties of flours from different cultivars of Thai rice. Starch/Starke 55,410-415. 

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. 

Starch source Amylose content (%) Swelling power (g/g) (°C) Solubility (%) (°C) Organic ph osphorus contents (% dsb) Light transmittance (%, at 650 nm)... 

Collado, L. S., Corke, H. (1999). Heat-moisture treatment effects on sweetpotato starches differing in amylose content. Food Chem., 65, 339-346. 

Flipse, E., Keetels, C. J. A. M., Jacobson, E., Visser, R. G. F. (1996). The dosage effect of the wildtype GBSS allele is linear for GBSS activity, but not for amylose content absence of amylose has a distinct influence on thew physico-chemical properties of starch. Theor. Appl. Genetics, 92, 121-127. 

Table E2.3.I illustrates the total amylose content of field pea, oat, and potato starches. The values (which are means of triplicate measurements) are reproducible and the method can be used for all types of starches. Very high amylose containing starches (i.e., >50% amylose) may not yield consistent values if suitable precautions (see Critical Parameters and Troubleshooting) arc not taken during step 9. The method can easily accommodate small samples for microdeterminations, if necessary.

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