Wheat starch paste viscosity

Normal wheat starch has a higher pasting temperature (90.6°C) and produces a lower peak viscosity (96 RVU) than does normal maize starch (81.5°C and 159 RVU, respectively). In comparison, waxy wheat starch has a lower pasting temperature (62.5°C), but produces a higher peak viscosity (230 RVU) than does waxy maize starch (69.8°C and 200 RVU, respectively). The extraordinarily large differences between normal and waxy wheat starches (28.1°C and 134 RVU) are attributed to an amylose-phospholipid complex present in normal wheat starch.134... 

Almost all the starches investigated contain some phosphorus.124-126 In addition to phospholipids, phosphorus is also commonly found in starch as monostarch phosphate esters.6,7 Inorganic phosphate is present in some starches.124-126 Monostarch phosphate esters and phospholipids have different effects on starch paste properties.133,135 Monostarch phosphate esters, found in potato, shoti and other starches,6,7,136-140 increase paste clarity and paste viscosity.79 Little phosphate monoester is found in cereal starch.121,124,141,142 Phospholipids, found in normal cereal starches (e.g. wheat, rice and maize) decrease paste clarity and viscosity.133 31P-nmr spectroscopy has... 

Wheat starch possesses a unique combination of properties that is important to its utilization in various food and industrial products. Those properties are related to its color, purity, flavor, paste viscosity, paste clarity, paste texture and gel strength.27 28,311-315... 

Monosubstitution of wheat starch by acetyl or hydroxypropyl groups27 without crosslinking yields products with a reduced pasting temperature, and yields pastes with enhanced clarity and viscosity but with increased stringiness (Table 10.14). The usefulness of this product is somewhat limited and requires special applications. Amylose has been found to be hydroxypropylated —20% more than amylopectin in corn and potato starches at a molar substitution level of 0.1 (3.5% hydroxypropyl).425,426... 

Compared to native wheat starch, the sodium starch 1-octenylsuccinate derivative gives much higher peak and cold-paste viscosities, but with considerably reduced paste viscosity during the cooking cycle.27 This product also exhibits emulsifying properties. When the 1-octenylsuccinate derivative is complexed with aluminum ion, a modified wheat starch that flows freely when dry and resists wetting by water... 

Table 10.14 Comparison of amylograph viscosities and pasting temperatures of modified wheat starches (7.5% solids)a...

Monophosphorylation pastes made from starch monophosphates also have greater clarity, viscosity and stability than unmodified starches,64 but are sensitive to salts, especially polyvalent cations.65 Variability in residual ash can lead to variability in the viscosity of monophosphorylated starches. Monophosphate substitution also lowers the gelatinization temperature at 0.07 DS, a value much greater than is found in food starches, the gelatinization temperature is below room temperature. Native potato starch contains 0.07 to 0.09% bound phosphorus and wheat starch contains 0.055% phosphoms, primarily as phosphoglycerides in the latter case. The FDA allows up to 0.4% phosphate as phosphoms.58 Monophosphates were used commercially in the US until about 1970. 

Classification.—Commercial starches are classified, according to the viscosity of the paste produced, as thick- or thin-boiling. Wheat starch is a typical thin-boiling starch, as a 5% mixture of wheat starch in water yields a thin, translucent syrup, scarcely gelatinous at boiling temperature. Corn starch, on the other hand, is a characteristic thick-boiling starch. Its 5% mixture with boiling water is practically non-fluid. 

A higher amylopectin content of some starches leads to their higher gelatinisation temperatures, but the lowering which is observed in potato starch indicates the influence of phosphorylation in the latter. The relatively high pasting temperature and low peak viscosity of wheat starch has been attributed to its relatively high content of phospholipid impurities, which form helical complexes with the amylose chains as indicated above. 

The proportions and molecular weights of the amylose and amylopectin components determine the properties of the pastes and the final film (Table 11.2). A high proportion of amylose, e.g. in com and wheat starches, wiU cause the solution to gel on cooling. A high-molecular-weight amylopectin wiU take longer to disperse and will form a high-viscosity solution. 

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