Textural behavior of gels formed by rice starch and whey protein isolate: Concentration and crosshead velocities

ABSTRACT Fabricated food gels involving the use of hydrocolloids are gaining polpularity as confectionery/convenience foods. Starch is commonly combined with a hydrocolloid (protein our polyssacharides), particularly in the food industry, since native starches generally do not have ideal properties for the preparation of food products. Therefore the texture studies of starch-protein mixtures could provide a new approach in producing starch-based food products, being thus acritical attribute that needs to be carefully adjusted to the consumer liking. This work investigated the texture and rheological properties of mixed gels of different concentrations of rice starch (15%, 17.5%, and 20%) and whey protein isolate (0%, 3%, and 6%) with different crosshead velocities (0.05, 5.0, and 10.0 mm/s) using a Box-Behnken experimental design. The samples were submitted to uniaxial compression tests with 80% deformation in order to determinate the following rheological parameters: Young’s modulus, fracture stress, fracture deformation, recoverable energy, and apparent biaxial elongational viscosity. Gels with a higher rice starch concentration that were submitted to higher test velocities were more rigid and resistant, while the whey protein isolate concentration had little influence on these properties. The gels showed a higher recoverable energy when the crosshead velocity was higher, and the apparent biaxial elongational viscosity was also influenced by this factor. Therefore, mixed gels exhibit different properties depending on the rice starch concentration and crosshead velocity.

Ultrasonic Compression Tests on Aluminium

A study is presented into the effect of ultrasonic activation of the platen on the stressstrain relationship in compression tests on aluminium specimens. The aim is to gain some insights into the reported beneficial effects of ultrasonically excited tools in metal forming operations. The paper investigates the compression of aluminium specimens using a variety of different lubricants under conditions of constant crosshead velocity and superimposed longitudinal ultrasonic excitation of the platen. The study shows that the changes in the stress-strain relationship under ultrasonic excitation can be explained in terms of the superimposed oscillatory stress condition and that there is some evidence of small changes in the interfacial friction condition.

High-temperature creep of polycrystalline BaTiO3

Compressive creep of dense BaTiO3 having linear-intercept grain sizes of 19.3–52.4 μm was investigated at 1200–1300 °C by varying the oxygen partial pressure from 102 to 105 Pa in both constant-stress and constant-crosshead-velocity modes. Microstructures of the deformed materials were examined by scanning and transmission electron microscopy. The stress exponent was ≈1, the grain-size dependence was ≈1/d2, and the activation energy was ≈720 kJ/mole. These parameters, combined with the microstructural observations (particularly grain displacement and absence of deformation-induced dislocations), indicated that the dominant deformation mechanism was grain-boundary sliding accommodated by lattice cation diffusion. Because of the absence of an oxygen partial pressure dependence, diffusion was probably controlled extrinsically.

Flow Stress and Elongation of Superplastic Deformation in La55Al25Ni20 Metallic Glass

We have investigated the flow stress and elongation of superplastic deformation in a La55Al25Ni20 (at%) metallic glass that has a wide supercooled liquid region of 72 K before crystallization. The superplasticity that appeared in the supercooled liquid region was generated by the Newtonian viscous flow that exhibits the m value of unity. The elongation to failure was restricted by the transition of the Newtonian flow to non-Newtonian one and the crystallization during deformation. We succeeded in establishing the constitutive formulation of the flow stress in the supercooled liquid region. Its formulation was expressed very well by a stretched exponential function σflow=Dε exp(H*/RT) [1-exp(E/{ε exp(H**/RT)}0.82)]. Formulations describing the elongation to failure in constant-strain-rate and constant-crosshead velocity tests were, moreover, established. It was found from the simulation that the maximum elongation in the constant-strain-rate test reached more than 106% which was two orders of magnitude larger than that in the constant-crosshead-velocity test.