Effect of nopal mucilage addition on physical, barrier and mechanical properties of citric pectin-based films.

This study considered the effect of the nopal mucilage (NM) fraction on the physical, barrier and mechanical properties of citric pectin-based (CP) films. Pectin aqueous dispersion 75 mL (2.0 g/100 g water) were mixed with 5 mL of glycerol and 20 mL of NM aqueous dispersions at different concentrations; namely, 5, 10, 12, 14 16, 18 and 20 g/100 g water. Films containing the highest NM content (20 g/100 g water) exhibited improved thermal stability. The addition of NM at relatively low concentration (0-10 g/100 g water) led to important modifications of mechanical properties, including elongation to break, tensile strength, and elasticity. Microstructural analysis showed that films containing between 14 and 20 g/100 g water of NM presented rough and fractured surfaces. As mucilage concentration in films was increased, the vapor water permeability decreased as result of better internal cohesiveness of components. The modification of the physical properties in CP films resulted from molecular and physical interaction of its components. In general, the combination of NM and CP for forming edible films led to enhanced thermal stability and higher water vapor permeability, which are prescribed properties for applications as food packaging.

Thermodynamic sorption analysis and glass transition temperature of faba bean (Vicia faba L.) protein.

Freeze-dried faba bean (Vicia faba L.) protein adsorption isotherms were determined at 25, 35 and 40 °C and fitted with the Guggenheim-Anderson-de Boer model. The pore radius of protein was in the range of 0.87-6.44 nm, so that they were considered as micropores and mesopores. The minimum integral entropy ranged between 4.33 and 4.44 kg H2O/100 kg d.s., was regarded as the point of maximum of stability. The glass transition temperature of the protein equilibrated at the different conditions of storage was determined, showing that the protein remained in glassy state for all cases. The protein showed compact and rigid structures, evidenced by microscopy analysis.

Effect of gelatinized flour fraction on thermal and rheological properties of wheat-based dough and bread.

This work considered gelatinized wheat flour fraction with properties similar to hydrocolloid to enhance the strength of dough network by improving water retention and rheological characteristics. The gelatinized (90 °C) fraction of the wheat flour was incorporated in the dough formulation at different levels (5, 10, and 20% w/w). The effects of the gelatinized flour (GF) fraction on the dough rheology and thermal properties were studied. The incorporation of GF induced a moderate increase of dough viscoelasticity and reduced the freezing and melting enthalpies. On the other hand, the changes in bread textural properties brought by incorporation of GF were insignificant, indicating that the gelatinized fraction acted as a binder that enhanced water trapping in the structure. SEM images showed a more heterogeneous crumb microstructure (e.g., gas cells, porous, etc.) bread prepared using GF. Drying kinetics obtained from TGA indicated that the water diffusivity decreased with the incorporation of GF, which suggested that the bread had a compact microstructure.

Impact of ghosts on the viscoelastic response of gelatinized corn starch dispersions subjected to small strain deformations.

Corn starch dispersions (5.0% w/w) were gelatinized by heating at 90°C for 20 min using gentle stirring. Under these conditions, ghosts, which are insoluble material with high amylopectin content, were detected by optical microscopy. Strain sweep tests showed that the gelatinized starch dispersions (GSD) exhibited a loss modulus (G″) overshoot at relatively low strains (∼1%). In order to achieve a greater understanding as to the mechanisms giving rise to this uncharacteristic nonlinear response at low strains, very small constant torques (from 0.05 to 0.5 µN m) were applied in the bulk of the GSD with a rotating biconical disc. This resulted in small deformations exhibiting torque-dependent inertio-elastic damped oscillations which were subjected to phenomenological modelling. Inertial effects played an important role in the starch mechanical response. The model parameters varied with the magnitude of constant small applied torque and could be related to microstructural changes of ghosts and to the viscoelastic response of GSD.

Acid hydrolysis of native corn starch: morphology, crystallinity, rheological and thermal properties.

The acid hydrolysis of native corn starch at 35 °C was monitored during 15 days. After this time, the residual solids were about 37.0 ± 3.0%. First-order kinetics described the hydrolysis data, giving a constant rate of kH = 0.18 ± 0.012 days(-1). Amylose content presented a sharp decrement of about 85% and X-ray diffraction results indicated a gradual increase in crystallinity during the first 3 days. SEM micrographs showed that hydrolysis disrupted granule morphology from an initial regular shape to increasingly irregular shapes. Fractal analysis of SEM images revealed an increase in surface roughness. Fast changes in the thermal effects were caused by molecular rearrangements after fast hydrolysis of amylose in the amorphous regions in the first day. Steady shear rate and oscillatory tests showed a sharp decrease of the apparent viscosity and an increase of the damping factor (tan(δ)) caused by amylose degradation.

In vitro digestibility, physicochemical, thermal and rheological properties of banana starches.

Banana starches (BS) were isolated from Enano, Morado, Valery and Macho cultivars. The BS possessed B-type crystallinity and an amylose content varying from 19.32 to 26.35%. Granules had an oval morphology with different major-to-minor axis ratios, exhibiting both mono- and bi-modal distributions and mean particle sizes varying from 32.5 to 45 µm. BS displayed zeta-potential values ranging between -32.25 and -17.32 mV, and formed gels of incipient to moderate stability. The enthalpy of gelatinization of BS affected the crystalline order stability within the granules. In-vitro digestibility tests showed fractions as high as 68% of resistant starch. Rheological oscillatory tests at 1 Hz showed that BS dispersions (7.0%, w/w) exhibited Type III behaviour, attributed to the formation of a continuous phase complex three-dimensional amylose gel reinforced by swollen starch granules acting as fillers. Amylose content and granules morphology were the main factors influencing the BS properties.