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It is common to hybridize biopolymers for developing materials with combined properties or functionality. However, biopolymers are usually not fully compatible despite their chemical similarity, posing challenges to create mixed systems. Herein, we investigated how the gelation behavior and rheological properties of hydroxypropyl methylcellulose (HPMC), a thermal gel, and hydroxypropyl starch (HPS), a cooling gel, affect their miscibility and the phase structure of their mixed system. The dependence of the zero-shear viscosity for HPMC/HPS paste on biopolymer concentration in a double-logarithmic coordinate can be divided into two parts with the slopes being 11.9 and 2.8 respectively, indicating different degrees of intermolecular entanglement. A typical "sea-island" morphology was shown in the blends, and the phase structure (continuous or discrete) changed with varying HPMC/HPS blend ratio and temperature. This phase structure change can be well correlated to rheological parameters such as zero-shear viscosity, loss tangent, complex viscosity, and the Arrhenius equation correction coefficient (α). Biopolymer concentration, HPMC/HPS ratio, and temperature together controlled rheological properties and phase distribution for the mixed system. The relationship between rheological behavior and phase structure for HPMC/HPS understood from this work provides an insight into designing mixed biopolymer systems with desirable processability, structure, and properties. Image 1 • Hydroxypropyl methylcellulose (HPMC) and hydroxypropyl starch (HPS) mixture studied. • Strong rheological and gelation effects on the phase structure of HPMC/HPS shown. • HPMC/HPS blend ratio and temperature controls continuous/discrete phase change. • Phase structure correlated to zero-shear viscosity and Arrhenius coefficient α. • A schematic model to describe the temperature-induced conformational change. [ABSTRACT FROM AUTHOR]

Debranched starch (DBS) has attracted immense interest from the food, pharmaceutical, and cosmetic industries as a versatile ingredient. Herein, we firstly developed a simple fractionation method using an edible alcohol solution to separate DBS of different degrees of polymerization (DP). These DBSs were separated from debranched waxy corn starch on the basis of their differential solubility in aqueous/ethanol solutions of different volumetric ratios (1:1.5 and 1:3). Four DBS products were obtained with DP values of 23.53, 20.04, 9.14, and 6.75. The DBS (DP 23.53) exhibited higher iodine staining index values compared to DBSs of lower DPs. The thermograms of DBSs (DP 9.14 and DP 6.75) displayed no apparent peak, indicating their amorphous nature. Compared to freeze-drying, oven-dried DBS (DP 23.53) exhibited a higher relative crystallinity (72.0%). Therefore, the ethanol precipitation method developed here serves as a simple, scalable, and green approach for preparing DBS fractions of different molecular weights. [ABSTRACT FROM AUTHOR]

Effect of pressure with shear stress on the gelatinization of cornstarch with different amylose/amylopectin ratios (waxy 0/100; maze 23/77; G50 50/50; G80 80/20) was systematically investigated using a high-pressure rheometer. Onset and peak temperature of starch gelatinization as well as the peak viscosity were used to discuss the influence of pressure together with shear stress on the gelatinization of starch granules. The results showed that without shear stress, pressure could resist the gelatinization process due to weak swelling of starch granules and lower quantity of amylose released. However, the shear stress can simply counteract the influence of the pressure since its impact is much high on gelatinization. Under certain pressure and shear stress, both onset and peak temperatures of gelatinization were increased with increasing amylose content, which is in correspondence with the results from differential scanning calorimeter measurement, while the overall viscosity was lower when starches with a higher amylose content was used because part of its granular was not fully dissolved during the measurement. SAXS measurements were used to study the gel structure and stability of starch suspensions. It was found that the scattering intensity of starches in the measured range (0.1–1.0 nm −1 ) is G80 > waxy, indicating the amount of ordered semi-crystalline structures in amylose is higher. Peak values, q = 0.4 nm −1 and q = 0.2 nm −1 , detected for waxy starch under different shear rates, indicates that higher shear stress which plays a dominant role compared with pressure, resulted in more degradation in amylopectin, inhibiting the formation of aggregate structure. [ABSTRACT FROM AUTHOR]

This study aimed to develop a rapid ethanol annealing method by incubating pea starch and potato starch in 60% and 75% ethanol solutions at 95 °C for 0.5–3 h (to improve their heat, shear, and acid stability). The peak viscosities of the annealed starches decreased, the breakdown values declined to 0 cP, and the trough and final viscosities decreased remarkably. Furthermore, the pea starch transformed from a C-type to an A-type crystalline form, while the potato starch remained a B-type. Ethanol annealing also increased the pasting temperatures and decreased the enthalpy change values of the starches. When annealed in the 60% ethanol solution for 3 h, the pea starch showed the highest peak gelatinization temperature at 80.97 °C, which was 15.55 °C higher than the native starch. Moreover, the annealed starches showed remarkable decreases in swelling and solubility. Compared to traditional water annealing, this method could reduce the incubation period and lead to a higher gelatinization temperature of starch, which would have applications for thickening and stabilizing in the food system, for example, in the production of soups, puddings, and deep-fried foods. [Display omitted] • A new strategy for annealing starch in ethanol solution was studied. • The progress of ethanol annealing starch was shorter than that of water annealing. • Ethanol solution annealing treatment formed a complex between ethanol and amylose. • The thermal stability of starch was enhanced by ethanol annealing treatment. [ABSTRACT FROM AUTHOR]