Amylose, starch source

Starch source Amylose, % Average (a) by metky-lation length of t b) by Periodate oxidation tnit chain (c) calc, for amylopectin from (6) References... 

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

Shibanuma et al.232 examined the molecular structures of starch isolated from three Japanese wheat varieties, one Australian standard white wheat and one US western white wheat. The data presented in Tables 10.9 and 10.10 again indicate that the properties and structural features of amylose and amylopectin are dependent on the starch source. The molecular sizes of amylose and amylopectin were larger in the US wheat compared to the corresponding starch fractions from the Australian and Japanese wheat starches. Among the five wheats, the two preferred for salt noodles in Japan, the Japanese variety Chihoku and the Australian standard white, contained a higher proportion of branched amylose and a lower number of chains per amylose... 

Mayer, J. M. (1993). Processability and characterization of starch-blend films produced using different starch sources and amylose amylopectin ratios. 206th National Meeting, Am. Chem. Soc., Div. Food Agric. Sci., Chicago, IL, Abstract 129. 

The ratio of amylose to amylopectin also varies, depending on the source of the starch it ranges from 17 to 70% amylose and a corresponding 83 to 30% amylopectin. SeeO Table 2 for a list of different starches and their composition of amylose and amylopectin. Usually amylopectin is present as the major component, with a common ratio of 1 3 or 25% amylose and 75% amylopectin. There are mutants, however, such as, waxy barley, waxy maize, waxy rice, waxy potato, and waxy sorghum that are 100% amylopectin and there are the high-amylose starches. 

Figure 6 X-ray microcomputed tomography. An axial cross-section through a freeze-dried 15-minute swollen high-amylose starch pellet, in which variations in X-ray attenuation provide evidence of an outer surface membrane. The pellet size is 3.0 (height) x 3.3 (width). The membrane thickness is 300 pm on the right and left edges (at mid height) and 450 pm at the top and bottom sides of the pellet. The smooth layer ranges from 130 pm on the right and left edges to 200 pm on the top and bottom sides. Source From Ref. 159.

Starch is a natural polymer available in large quantities from various sources. It can be obtained from different plants for which it is the most common source of polysaccharides of energetic reserve. In its native state, starch consists of semicrystalline granules insoluble in water. It is composed of two polysaccharides, branched amylopectin and essentially linear amylose. Starch is cheap, environmentally friendly and a completely biodegradable biopolymer, which has been also used to reinforce NR composites as filler. 

Techniques for the separation of amylose and amylopectin have not been developed to commercial feasibility. Instead, selections and improvements of the starch source are made. Waxy corn has been developed especially to provide a starch free of the difficulties, particularly retrogradation, caused by amylose. 

The ratio of amylose and amylopectin varies according to starch source. Chemical structures of starch, such as molecular sizes of amylose, branch-chain lengths... 

The relative amounts and molar masses of amylose and amylopectin vary with the starch source, yielding to materials of... 

There are some starch sources with high amylose content and others with a high percentage of amylo-pectin. Again, plant breeding can help to modify the contents of both components or to adjust a certain ratio for a specific use. 

Starch can also be directly used to form edible or biodegradable films. Different sources of starch, high amylose starch, and modified starch (Wolff et al, 1951 Roth and Mehltretter, 1967 Mali and Grossmann, 2003 Mali et al 2006) have been used to form self-supporting films by casting from aqueous solution. These films appear to have moderate oxygen barrier properties but poor moisture barrier and mechanical properties, which limit their commercial applications. 

A second type of recrystaUization has been reported if the starch is plasticized with glycerol. Ehiring storage the amylose and amylopectin can recrystaUize into stractures of type A or B. The recrystaUization rate depends on the starch source, amylose content, and storage conditions. When the ambient moisture content increases, the amount of crystalline structures rises. Similarly, with an increase in storage time (particularly at ambient moisture levels over 60%) the number of B-type crystallites increase [20, 28]. 

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