Dynamic rheological properties of wheat starch gels as affected by chemical modification and concentration

Abstract

In this study, dynamic rheological properties of wheat starch gels in the linear viscoelastic region (LVE), as a function of starch concentration (8 and 12% w/w) and chemical modification (cross‐linking and hydroxypropylation) were studied. The hydroxypropylated wheat starch (HPWS) gels in both concentrations had greater yield stress values at flow point (τf = 48.3–166.4 Pa) compared to the native (NWS) and cross‐linked (CLWS) wheat starches. In addition, all the loss‐tangent values (tan δLVE) were obtained in the range of 0.08–0.17, indicated predominantly elastic behavior of the starch gels. Unlike the NWS and CLWS samples which exhibited an intermediate behavior between a weak and an elastic gel (tan δ = 0.14–0.64), the HPWS samples relatively showed an elastic gel behavior (tan δ = 0.10–0.11), which was not influenced by the concentration. CLWS had higher pasting temperature (Ts = 61.8 °C), final viscosity (η*f= 739.0 Pa.s), setback viscosity (SB = 646.8 Pa.s) and lower maximum viscosity (η*max = 519.0 Pa.s) and breakdown viscosity (B = 426.8 Pa.s) than the others. The results suggest that the HPWS (in terms of viscoelastic properties) and CLWS (in terms of paste properties) have specific dynamic rheological properties which can be applied in different gel‐like foods.

Viscoelastic Properties of Gelatinized Dispersions of Maize Starch Modified by Solid‐State Milling

“…According to the rule stated by Cox and Merz (1958), the complex viscosity h* is equal to steady-shear viscosity h at equal values of angular frequency v and shear rate g. This rule has been found to hold for a number of polymer melts and homogeneous solutions, whereas it is not valid for gels with high-density entanglements or aggregates (Gunasekaran and Mehmet Ak 2000). The gels formed on the base of native maize starch and maize milled starch in the time range of 0.5-10 h did not follow the Cox-Merz rule, with h* > h, similar to the results obtained for native wheat (Yousefi and Razavi 2015) and potato (Yoneya et al 2003) starches. The gels formed on the base of native maize starch and maize milled starch in the time range of 0.5-10 h did not follow the Cox-Merz rule, with h* > h, similar to the results obtained for native wheat (Yousefi and Razavi 2015) and potato (Yoneya et al 2003) starches.…”

Starch-Galactomannans Mixtures: Rheological and Viscosity Behavior in Aqueous Systems for Food Modeling

“…At the end of the temperature sweep G' was higher than the G", representing the gel-like behavior that a frequency sweep can support, expressing the formation of a three-dimensional gel network by the intergranular contact of swollen granules [19]. A further increase in temperature led to a G' decrement, indicating that the gel structure was destroyed during prolonged heating as presented in a temperature sweep performed to rice starch [20].…”

“…Weak gels have intermediate rheological properties between solutions and real gels, under small deformation; weak gels mechanically behave like real gels, but with increasing deformation, the three-dimensional network undergoes a progressive failure into smaller clusters [20], while the tan δ values directly state the G'/G" ratio.…”

“…At the end of the temperature sweep G' was higher than the G", representing the gel-like behavior that a frequency sweep can support, expressing the formation of a three-dimensional gel network by the intergranular contact of swollen granules [19]. A further increase in temperature led to a G' decrement, indicating that the gel structure was destroyed during prolonged heating as presented in a temperature sweep performed to rice starch [20].Many factors affect the gelatinization of starch. A positive correlation between the gelatinization temperature of starch and the branch-chain length of amylopectin is that long branchchains of amylopectin form thermally stable crystallites [21]; therefore, granule botanical source can be important for the development of rheological properties.…”

“…The hot pastes begin to cool, after becoming more elastic and start to develop solid properties. Transitions from viscous paste to an elastic gel can be evaluated by storage modulus (G'), and loss modulus (G"), the loss tangent being (tan δ =G"/G') [20]. The starch gel can behave more like a solid (a small tan δ, G' is much larger than G"); this reflects a recoverable deformation or more like a liquid (a large tan δ, G' is smaller than G"); it means that the energy employed to deform the gel is dissipated.…”