Starch pasting temperature

Hydroxyethyl group introduction at low DS results in distinct modification of physical properties. Among these are decreased gelatinization temperature range (126), increased granule swelling rate (127), and decreased abiUty of starch pastes to gel and retrograde. 

DSC revealed that the XG and starch did not interact synergistically and hence did not promote the formation of three-dimensional network structures. However, the hydrocolloid significantly decreased the retrogradation and syneresis of the starch paste, particularly in blends with a starch/XG ratio of 8.5/1.5. Mixing 1% or 2% tamarind XG with 9% cornstarch resulted in an increase in the paste viscosity from 385 to 460 and 560 BU (Brabender units), respectively [298]. The XG is associated with starch, as was evident from the lowering of the pasting temperature and the synergistic increase in pseudoplasticity and yield value of the blend pastes. However, carboxymethylated and hydroxypropylated XGs showed a diminished interaction. 

Potato starch shows the highest peak viscosity and the lowest pasting temperature with moderate final viscosity and lower setback (Liu et al., 2003), compared to other commercial starches. This indicates that potato starch gelatinizes rather easily compared to other starches, producing more viscous pastes that easily break. 

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... 

Figure 8.14 Changes in the complex modulus (G ) (solid lines) of low shear (LS) and high shear (HS) starch pastes as a function of time during heating and cooling (dotted lines indicate the temperature profiles).151...

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... 

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

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