Effect of Tomato Paste on Rheological Properties and Particle Size Distribution of Model Oil-in-Water Emulsions

The role of tomato paste in stabilizing model o/w salad dressing formulations pre-stabilized with xanthan and propylene glycol alginate was studied at levels of tomato paste ranging from 3 to 12% using creep measurements, steady shear measurements and particle size measurements. The addition of tomato paste shifted the particle size distribution to lower values; this distribution was a function of aging time. Creep and steady shear measurements showed an increase in rheological parameters and an increase in viscosity, respectively, suggesting that at higher or equal levels of 6% tomato paste the stability of the o/w emulsion was enhanced significantly.     

USE OF THE BIRD-LEIDER EQUATION IN FOOD RHEOLOGY

Shear stress development at inception of a constant shear rate was studied for marshmallow cream, peanut butter, squeeze margarine, tub margarine, whipped butter, whipped cream cheese and whipped dessert topping using the cone and plate geometry of the Rheometrics Mechanical Spectrometer. For most foods studied transient shear stresses showed increasing shear stress oversoots with increasing shear rate. At the highest shear rate of 100 s^?1, transient stresses were as large as 425% of the steady state shear stresses, with the actual magnitude of overshoot depending on the particular food investigated. The Bird-Leider equation was chosen to model this time dependent flow behavior by incorporating both steady viscous and elastic properties of the foods. By assuming that the viscosity function and primary normal stress coefficient followed power-law behavior, and constructing a time constant from the calculated parameters, the Bird-Leider model provided a good prediction of maximum and steady state stresses as well as the time at which they occur, but only a crude prediction of shear stress decay. The model supplied two more empirical constants “a” and “b” where “a” can be regarded as a pseudo-elastic modulus. Variation in “a” with shear rate shows that all materials studied are nonlinear viscoelastic.     

EFFECT OF SALT ON THE STABILITY OF PROPYLENE GLYCOL ALGINATE/XANTHAN GUM/POLYSORBATE-60 STABILIZED OIL-IN-WATER EMULSIONS

Stabilization mechanism of salt, as a dissolved electrolyte, in oil-in-water emulsions in the presence of stabilizers and/or emulsifiers, propylene glycol alginate, xanthan gum and/or polysorbate-60 has been studied using rheological techniques, particle size analysis and surface tension measurements. Salt affected the stability of the ternary system, propylene glycol alginate/xanthan gum/polysorbate-60, depending on the emulsifier/stabilizer ratio. Creep measurements indicated that low salt concentrations were particularly effective when PGA:X ratios were used in the presence of PS-60. In both PGA:X and PGA:X/PS-60 systems salt did not affect the particle size distribution during aging. Surface tension measurements were in agreement both with particle size distribution and high shear rate experiments.     

Comparison of Steady Shear and Dynamic Viscoelastic Properties of Guar and Karaya Gums

Steady shear and small amplitude dynamic viscoelastic properties of suspensions of guar gum and gum karaya in the range of shear rates/frequencies between 0.1 and 100 set⁻¹ were compared. For all concentrations of guar at small shear rates/frequencies steady viscosity (η) is equal to dynamic viscosity (η^′) when corresponding shear rates and frequencies are equal. At large shear rates, steady viscosity (η) is equal to complex viscosity (η*); primary normal stress coefficient (ψ₁) is approximately equal to (2η″/ω). For gum karaya, it was shown that (η″/ω) is nonlinearly related to primary normal stress coefficient (ψ₁) and dynamic viscosity (η′) is nonlinearly related to steady viscosity (η).     

ISOLATION AND SOME PROPERTIES OF THE THERMOSTABLE β-GALACTOSIDASE OF PYROCOCCUS WOESEI EXPRESSED IN ESCHERICHIA COLI

The enzyme with β-galactosidase activity from E. coli BL21(DE3) transformant containing the gene encoding enzyme from Pyrococcus woesei (DSM 3773) was isolated using cell extraction in 0.01 M phosphate buffer (pH 7.2), protein thermopredpitation at 85C, precipitation at acetone/extract ratio of 1:1 (v/v) and gel filtration on Sephadex G-200. The increase in the enzyme specific activity was determined using ONPG as substrate. The activity increased from 2.9 × 10³ U/mg protein to 37 × 10³ U/mg. Thermoprecipitation removed 78% of E. coli protein and retained 92% of the cell extract activity. The acetone precipitation and gel filtration applied in the next purification steps led to homogeneous enzyme with specific activity of 37,700 U/mg protein. The isolated enzyme had a half-life of 23 h and 9 h during incubation at 85C and 100C, respectively, in 0.1 M citrate-phosphate buffer (pH 5.4).     

A GRAMMAR-THEORETIC TREATMENT OF MULTIAGENT SYSTEMS

A variant of cooperating and distributed grammar systems—the so-called colony—is studied to capture some aspects of multiagent systems consisting of a finite number of very simple autonomous agents. A colony is considered as a set up from a finite number of regular grammars generating finite languages that cooperate without any explicit predefined strategy. Generative power and hierarchical properties of colonies are investigated. The behavioral (generative) stability of colonies as well as a modified model augmenting agents by ‘clocks’ is studied. It is proved that the generative power of colonies with augmented components overcomes the generative power of colonies without clocks.     

Suboptimal state estimation algorithm for non-linear discrete-time distributed-parameter systems

A non-linear discrete-time distributed-parameter system may be described by stochastic partial differential equations. Some state variables are measured at selected points of the system space. For this system a suboptimal state estimation algorithm is proposed. The error covariance matrix is calculated by an approximate approach. This simplification considerably reduces computer calculations in comparison with an optimal algorithm. Finally, the digital simulation of a non-linear DPS demonstrates the effectiveness of the suboptimal estimator.     

A note on achieving low-level rationality from pure reactivity

The paper connects a decision-theoretic model of rationality and a generative (grammar-theoretic) model of multiagent systems called colonies. The decision-theoretic notion of the low-level rationality of agents is introduced. Then, a characterization of a subclass of low-level rational agents is given in the formal framework of colonies. In other words, it is proved that at least the low-level rationality of some agents can emerge from activities of their autonomous purely reactive and individually non-rational components.