Data concerning the rheological behavior of high methoxyl pectin during gelation process

The present data concern the structuring kinetics of aqueous high methoxyl pectin (HMP) solutions at acid pH (3.1), constant pectin concentration (0.2% w/w) and sucrose concentrations ranging from 56 to 65% w/w. Consecutive frequency sweep was applied to samples immediately after their preparation. The generalized Maxwell (gM) model was used to describe the change of the mechanical spectra for each different sucrose concentration and to determine the viscoelastic parameters controlling the gelation of the HMP solutions. The viscosities in the sol region are explored in the range 0 to 55% 0 to 40% (w/w) sucrose concentration.


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The present data concern the structuring kinetics of aqueous high methoxyl pectin (HMP) solutions at acid pH (3.1), constant pectin concentration (0.2% w/w) and sucrose concentrations ranging from 56 to 65% w/w. Consecutive frequency sweep was applied to samples immediately after their preparation. The generalized Maxwell (gM) model was used to describe the change of the mechanical spectra for each different sucrose concentration and to determine the viscoelastic parameters controlling the gelation of the HMP solutions. The viscosities in the sol region are explored in the range 0 to 55% 0 to 40% (w/w) sucrose concentration.
& Data are provided in the present article.

Value of the data
Gelation mechanism of High Methoxyl Pectin solutions. Time evolution of the viscoelastic parameters. Role of sucrose in the 3D network of high methoxyl pectin.

Data
The present data concern rheological experiments and analysis performed on pectin aqueous solution (0.2% w/w) in presence of increasing sucrose concentrations (from 0% up to 65% w/w) in the sol (Fig. 1) and self-assembled regions.
In Fig. 2A the crossover times for the different sucrose concentrations are reported as a function of the frequency. In Fig. 2B, the behavior of the crossover times at different frequency values is shown as a function of the sucrose content of the samples. In both figures, t cr values lower than 10 min are obtained by extrapolation of the kinetic data with Eq. (1).
The generalized Maxwell (gM) model has been used to describe the change of the mechanical spectra for each different sucrose concentration and to determine the viscoelastic parameters controlling the gelation of the HMP (Fig. 3A and B; Fig. 4A and B). They are the equilibrium modulus, G e , representing the asymptotic value of the storage modulus for ω → 0, G i and λ i values corresponding to the relaxation modulus and the relaxation time of the i th Maxwell element, respectively. Data analysis is in perfect agreement with that performed with Friedrich-Braun model [1]. and highlights the role of sucrose in the structuring process of the High Methoxyl Pectin 3D network [2]..

Viscosity measurements
The viscosity measurements were performed at 20°C with a rotational controlled stress rheometer (AR-1000, TA Instruments, UK) by using a titanium cone-plate geometry (angle 0.0174 rad, radius 20 mm, truncation 26 μm). Shear rate ramps were performed in the sol region for samples prepared at the sucrose concentrations of 0, 20, 40, 50, and 55% w/w in the range 50-6500 s -1 .

Rheological measurements
Samples at different sugar concentrations (56, 57, 58, 59, 60, 62, and 65% w/w) were prepared by heating at 100°C for 10 min under stirring the potassium citrate buffer (12 mM, 22.5% w/w, pH 3.4) with sucrose and the right water quantity. A constant amount of the pectin stock solution was added to obtain a final concentration of 0.2 w/w and boiled for further 10 min. Finally, a few microliters of 50% citric acid solution was added to adjust the pH value to 3.1. The rheological monitoring of the gelation process was performed at 20°C with a rotational controlled stress rheometer (AR-1000, TA   Instruments, UK), equipped with a standard-size double concentric aluminum cylinder (rotor outer radius 21.96 mm, rotor inner radius 20.38 mm, stator outer radius 20.00 mm, cylinder immersed height 59.50 mm, gap 500 μm). A circulating bath thermostat was used for temperature control.
A series of consecutive frequency sweeps (logarithmic sequence of increasing values from 0.02 up to 30 Hz, time needed per sweep: 15 min) was carried out at constant strain amplitude (4 × 10 -3 ) for very prolonged times, ranging from 1400 (65% system) to 8500 min (56% system). The air/sample interface was coated with silicon oil to avoid sample evaporation.