Wheat amylose

Table 10.6 compares the average size (DPn) and size distributions of six laboratory-purified amyloses and one commercial sample of potato amylose, which were determined by classic colorimetric and fluorescent-labeling techniques using 2-ami-nopyridine. The data by the two techniques are consistent and show that wheat and other cereal amyloses are smaller in size than those from root and tuber starches. The molar distribution technique indicated that wheat amylose contained two molecular species, compared with one for rice and com amyloses.209,210 Moreover, the molar size distributions for the cereal amyloses are much narrower than those of the tuber amyloses, and the cereal amyloses contain a preponderance of molecules of DPn < 1000 whereas the tuber amyloses contain 78-95% of molecules with DPn > 1000, and even 3-5% above DPn 10000. None of the amylose samples in Table 10.6 showed molecules with less than DPn 200, possibly because they had been purified as alcohol-inclusion complexes.209... 

Table 10.9 Molecular properties of wheat amylose and its beta-limit dextrins as affected by starch source232...

Amylase occurs in many plants, such as barley, wheat, rye, soy beans, and potatoes, where it is generally accompanied by some a-amylase. [ -Amylase initiates hydrolysis at the nonreducing end of an amylose or amylopectin chain, and removes maltose units successively until the reducing end of the molecule is encountered in amylose or a branch is met in amylopectin. ( -Amylase is used commercially in the preparation of maltose symps. After P-amylase hydrolysis of amylopectin there remains a P-amylase limit dextrin. ( -Amylase has been used as a probe of the fine stmcture of amylopectin (43-46). 

Figure 4 [29] shows the (s) versus profiles for potato amylose and the amylose/amylopectin mixture from wheat starch corresponding to the concentration versus radial displacement data of Fig. 3. The s data used in the concentration dependence plot of Fig. 3 for wheat amylopectin comes from (s) vs. s analysis data of Fig. 2b and similar. The concentrations shown in the abscissa in Fig. 4 have been obtained from the total starch loading concentration normalised by the weight fraction of the amylopectin component estimated from the (s) vs. s profiles.

Fig. 4 Sedimentation velocity g (s) profiles for starch polysaccharides using DCDT+. The profiles correspond to the radial displacement plots of Fig. 2. a Potato amylose, sample concentration 8 mg/ml in 90% in dimethyl sulphoxide. Rotor speed was 50 000 rpm at a temperature of 20 °C. b Wheat starch (containing amylose, left peak and the faster moving amylopectin, right peak), (total) sample concentration 8 mg/ml in 90% dimethyl sulphoxide. Rotor speed was 35 000 rpm at a temperature of 20 °C. From [29]...

Fig. 16.—Mass, Q (mg/mL), of water-soluble products as a function of the content of amylose in starch. Variety of starch P, potato AM, amylomaize M, maize R, rice H, haricot bean MN, manioc WM, waxy maize B, bread wheat. Point P relates to potato starch after correction of the result attributable to high water content in that source (from Ref. 102).

Starch is the main energy reserve of superior vegetal plants. It is found in big quantities in wheat, potato, com and manioc. Starch is a homopolymer (99%) of D-anhydroglucopyranose units. Nevertheless, two different configurations exist amylose and amylopectin (Figure 5.18). The proportion of branched polymer is 70-80% (Park et al., 2007). Native starch is present in the form of partially crystalline (25-40% ) granules (up to 100 pm diameter), showing a complex structure, which has been the object of thousands of scientific papers. 

They concluded that these data supported Badenhuizen s17,18 suggestion that starch molecules are completely synthesized in the amyloplast stroma and are then deposited on the granule surface. Once the polysaccharides are part of the granule, there was no evidence of subsequent conversion of amylose to amylopectin.166 This is in contrast to conclusions drawn from long-term 14C-labeling studies of wheat starch.167,168 In results of these studies, amylose appeared to be synthesized first, and then transformed into amylopectin. These differences may be due to the different species used or to the widely different sampling times. 

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