Optimization of Yogurt Production Using Demineralized Whey

The effect of three independent fermentation variables: demineralized whey powder (0.0; 1.5 and 3.0%), lactic culture concentration (1.0; 2.0 and 3.0%) and mix treatment temperature (85; 90 and 95°C) was studied. Fermentation time to reach pH 4.3, instrumental consistency and appearance, visual consistency and taste of the product were evaluated. Product consistency increased as mix treatment temperature increased and demineralized whey powder decreased. The powder had a stronger influence on instrumental consistency than did temperature. Appearance was better when whey powder was used at 1.4 to 1.6%. Visual consistency decreased as whey powder increased but addition of demineralized whey powder did not negatively affect yogurt flavor.     

AMINO ACID COMPOSITION OF SOME BRAZILIAN SEAWEED SPECIES

Fourteen common seaweed species from northeastern Brazil were examined for protein content and amino acid composition. Protein content varied greatly among the species, ranging from 2.30% (dry weight basis) in Corallina offlcinalis to 25.60%, in Amansia multifida. The species Amansia multifida, Caulerpa sertularioides. Enantiocladia dupcrreyi, Solieria filiformis and Vidalia obtusiloba had protein levels comparable to those of many edible legume seeds, above 18%. They showed high levels of acidic amino acids and reasonable levels of essential amino acids, with methionine being the first limiting amino acid for most of the species. The exceptions were Sargassum vulgare that had a very high content of methionine and Caulerpa sertularioides in which lysine is the first limiting amino acid and methionine the second limiting one. All species are rich in phenylalanine/tyrosine and threonine, and six are very good sources of lysine. The potential use of these species as food and/or feed is discussed .     

RHEOLOGICAL PROPERTIES AND FLUID DYNAMICS OF COFFEE EXTRACT

The rheological behavior of coffee extract with different water contents (49 to 90%) was studied at a wide range of temperatures (274 to 365 K) using a concentric cylinder rheometer. The flow curves followed different models depending on the concentration and temperature level. Newtonian behavior was observed at high values of water content and temperature, changing to power law as these values were decreased. The Newtonian viscosity as well as the consistency and behavior index could be well correlated by functions simultaneously dependent on temperature and water content. The rheological parameters, together with experimental values of pressure loss in tube flow, were used to calculate friction factors. These showed to be in good agreement with those resulting from classical theoretical and empirical equations, thus confirming the reliability of the rheological measurements.     

Substituted Hydrated Calcium Silicates Obtained in Autoclave Hydration

Hydrated calcium silicates containing Al^3+] or Fe^3+] were prepared by autoclaving C₃S and β-C₂S in the presence of C₃A or C₂F at 190°C. Al^3+] and Fe^3+] diffuse into the crystal lattice of α-C₂SH and C₃SH_1.5. Solid solutions containing Al^3+] and Fe^3+] were placed in contact at 25°C with sources of sulfates, either in aqueous stirred suspensions or as pastes. Al^3+] and Fe^3+] remain stable in the solid solution, inhibiting the formation of ettringite. This absence of ettringite can explain the resistance of autoclaved cement pastes and concretes to sulfate attack.     

Kinetics of Dissolution and Equilibrium in Solution of Complex Ores

The development of the kinetic expression for the dissolution of a nickeliferous sulfide by ferric sulfate and of pyrite by oxygen and ferric sulfate on the basis of its oxidation mechanism is discussed. The rate of dissolution of complex ores is determined not only by the kinetics of the heterogenous reactions (solid-liquid reactions) but also by the homogenous reactions taking place simultaneously in the leach liquor. The liquid phase in a leaching system contains a large number of species which are simultaneously reacting with one another such as in acid-base and complexation reactions at near equilibrium or at equilibrium. The heterogenous mineral solid-leaching solution reactions are limited by the kinetics of dissolution and often do not reach equilibrium. During the leaching process, the concentrations of chemical species in the liquid phase adjust rapidly to the changes in the liquid phase analytical concentrations. Chemical equilibrium is maintained in the homogenous phase although the mineral-leach solution reactions are far from equilibrium. If the reactions of the solid with the leach solution is considered to take place in very small increments, the pertubations to the analytical concentrations within the liquid phase can adjust quickly and thus remain at equilibrium as the leaching reaction proceeds. Following the changes in the liquid phase concentrations during the leaching step can be useful in optimizing the dissolution process and specifying the influent conditions to achieve optimum conditions. It may also be possible to specify the conditions under which selective leaching can be attained. The partial equilibrium model is capable of characterizing the minerals dissolution reactions and the associated changes in solution species concentrations. The modeling of the dissolution of chalcopyrite by ferric sulfate, ilmenite by hydrochloric acid, uranium dioxide-pyrite by ferric sulfate-sulfuric acid, and uraninite by ammonmium carbonate-hydrogen peroxide systems are discussed.     

Engineering Analysis of Ablative Thermal Protection for Atmospheric Reentry: Improved Lumped Formulations and Symbolic – Numerical Computation

A computational approach for the engineering analysis of ablative-type thermal protection systems (TPS) in atmospheric reentry ballistic flights is communicated. We first propose an improved lumped differential approach for ablative thermal protection analysis, which involves the use of materials with low thermal diffusivity. The results obtained for a one-dimensional thermal ablation problem in a finite slab are compared against those obtained by previously reported lumped differential solutions. Benchmark results for the local nonlinear model, obtained through the generalized integral transform technique, are utilized to verify the proposed solution in a realistic ablation problem, consisting of a low thermal diffusivity material subjected to a prescribed net aerodynamic heating. In addition, an integrated symbolic–numerical system is constructed based on the Mathematica platform for the derivation and computation of all the related quantities along the flight, yielding the transient behavior of the TPS recession and thermal performance for both the constant and variable initial thickness along the vehicle nose region. An illustrative example of the computational tool and the typical results for an orbital platform in ballistic reentry flight are presented.     

PURIFICATION AND PARTIAL CHARACTERIZATION OF A LECTIN FROM THE SEEDS OF DIOCLEA GUIANENSIS1

A lectin was purified from seeds of Dioclea guianensis by Sephadex G-50 affinity chromatography. Apparent homogeneity of the lectin was demonstrated by native polyacrylamide gel electrophoresis, chromatography on DEAE- and CM-Sepharose, and immunochemistry. The lectin showed a carbohydrate specificity for D-mannose (D-glucose)-binding, had a requirement for Ca^?2 and Mn^?2, contained no covalently bound carbohydrate and had an amino acid composition characterized by high content of aspartic acid, serine and threonine, and low levels of sulfur-containing amino acids. At pH 7.5 it exists as two species of molecular weight about 100 and 47 kD and in dissociating solvents three subunits of approximate size of 30, 18 and 12 kD were obtained. The lectin agglutinated erythocytes from rabbit and chicken but not from human, cow, sheep, goat or pig and was toxic to brine shrimp (Artemia salina) larvae. It was relatively heat-stable, retaining half of its original activity even after 90 min at 70°C.