Thermophysical properties of mango pulp (Mangifera indica L. cv. Tommy Atkins)

The density, heat capacity and thermal conductivity of mango pulp (Mangifera indica L. cv. Tommy Atkins) were determined at moisture contents of between 0.9 and 0.52 kg kg(-1) (w.b.) and temperatures of between 20 and 80 degrees C. The experimental data were satisfactorily fitted (explained variation values >99.1%) as functions of the moisture content and temperature by using multivariate linear models. In the range of conditions considered, the moisture content exhibits a greater influence on the studied properties than temperature. (C) 2009 Elsevier Ltd. All rights reserved.

Kinetics of osmotic dehydration and air-drying of pumpkins (Cucurbita moschata)

Kinetics of osmotic dehydration (OD) and effects of sucrose impregnation on thermal air-drying of pumpkin slices were investigated. A simplified model based on the solution of Fick's Law was used to estimate effective diffusion coefficients during OD and air-drying. In order to take into account shrinkage, average and variable thicknesses were considered. Pumpkin slices were dehydrated in sucrose solutions (40%, 50% and 60%, w/w, 27 degrees C. The effective water diffusion coefficients were higher than the sucrose, and low diffusivity dependence with solution concentration was observed. Samples non-treated and pre-treated in 60% osmotic solutions during one hour were dried in a hot-air-dryer at 50 and 70 degrees C (2 m/s) until equilibrium was achieved. Pre-treatment enhanced mass transfer during air-drying. Great volume reduction was observed in pre and non-treated dried samples. Using variable thickness in the model diminished the relative deviations between predicted and experimental OD and drying data. (C) 2007 Elsevier Ltd. All rights reserved.

Time-dependent effects of lead on rat reproductive functions

The effects of exposure to lead on endocrine function and the reproductive parameters were studied in pubertal rats treated with 1.0 g l(-1) lead acetate in drinking water for 20 days (subacute group) or 9 months (chronic group) in addition to i.v. injections of lead acetate (0.1 mg 100 g(-1) body wt.) every 10 (subacute group) or 15 days (chronic group). Although basal levels of testosterone were higher both in plasma and in testes of acutely intoxicated animals, the circulating levels of luteinizing hormone (LH) were not affected in either group, nor was the LH-releasing hormone content of the median eminence. The density of [I-125]LH/human chorionic gonadotrophin (hCG) binding sites in testicular homogenates was reduced by saturnism in both groups, concomitant with a significantly increased apparent affinity constant of the hormone-receptor complex. These data can be viewed as the result of a mixture of specific lead toxicity (e.g. at the enzyme level) with other more general actions (e.g. at the level of the hypothalamus-pituitary-testicular axis).

Relation between quality and rheological properties of lactic beverages

The physicochemical (pH, fat and total solids content), sensory (appearance, consistency and taste), and rheological characteristics of five different commercial brands of lactic beverages were determined. Rheological measurements were obtained at 5 degreesC and 25 degreesC using a Brookfield rheometer. The experimental data were described by the power law and Herschel-Bulkley models. The ANOVA of the results were conducted using an incomplete block design, and using Tukey test. Samples showed a significant difference (P less than or equal to 0.05%) for fat content and pH. There was a significant difference in total solids content only among Nestle (A), Batavo (C), and Parmalat (D) samples. Sensory evaluation showed more global acceptability for Nestle; however, Nestle and Vigor (E) lactic beverages obtained better results for appearance than for consistency and taste. Batavo obtained the best score for taste. All test samples exhibited non-Newtonian behavior, with thixotropy. Upward curves showed pseudoplastic behavior, while downward curves showed dilatant behavior with the exception of the Nestle sample, at 25 degreesC. Lactic beverages from all brands analyzed showed similar rheological behavior. (C) 2001 Elsevier B.V. Ltd. All rights reserved.

Diffusion coefficients during osmotic dehydration of tomatoes in ternary solutions

The apparent diffusion coefficients for sucrose, NaCl and water during osmotic dehydration of tomatoes in ternary solutions were determined. Long time experiments (up to 60 h) were carried out in order to determine equilibrium concentrations inside tomatoes, whereas short time experiments (up to 4 h) were performed to provide detailed information on kinetics of water loss and solids gain at the beginning of osmotic treatment. The mass transfer rates for water and solutes showed to be dependent of NaCl and sucrose concentrations in osmotic solution and simple regression models as functions of solutes concentration were determined for diffusion coefficients. Salt and sucrose diffusivities showed to be interdependent, with increasing NaCl concentration causing the enhancement of water loss, at the same time that higher sucrose contents hindered the excessive salt penetration. (C) 2003 Elsevier Ltd. All rights reserved.

Rheological properties and fluid dynamics of egg yolk

The rheological behavior of egg yolk was studied at a range of temperatures (277-333 K) using a concentric cylinder viscometer. Rheological behavior was pseudoplastic and flow curves fitted by the power law model. The consistency and behavior indexes, dependent on temperature, were expressed by an Arrhenius-type equation. The rheological parameters, together with experimental values of pressure loss in tube flow were used to calculate friction factors. The good agreement between predicted and observed values confirmed the reliability of the equations proposed for describing the flow behavior of the egg yolk. (c) 2005 Published by Elsevier Ltd.

Laminar flow of soursop juice through concentric annuli: Friction factors and rheology

Laminar axial flow of a pseudoplastic fluid food (soursop, juice) in annular ducts has been experimentally investigated. In the first part of the manuscript, the rheological behavior of soursop juice, being essential for the annular flow analysis, was completely determined from 9.3 to 49.4 degrees Brix and temperatures from 0.4 degrees C to 68.8 degrees C, using a rotational rheometer equipped with coaxial cylinders. In order to test the adequacy of the rheology results, pressure loss data in the laminar pipe flow were collected and then experimental and theoretical friction factors were compared, showing excellent agreement, which indicated the reliability of the Power-Law model for describing the soursop juices. In the second part, pressure loss in annular regions was measured and used to estimate friction factors, which were then compared to those resulted from analytical and semi-analytical equations. The principal contributions of this article are to provide a review on the determination of friction factors-Reynolds number of pseudoplastic fluids in annuli, and also supply extensive new experimental data on the rheological properties and pressure loss of an important shear-thinning fluid food, which is of particular interest for the food engineering process design. (c) 2006 Elsevier Ltd. All rights reserved.

Huge values of room-temperature dielectric constants in pellets of poly(3-methylthiophene)

Room temperature data of impedance and phase angle in pellets of electrochemically synthesized ClO4- doped poly(3-methylthiophene) (P3MT) were analyzed assuming the sample being represented by a parallel resistor-capacitor (RC) circuit or by a series RC circuit. The last assumption proved to be the correct one, and to confirm it we use the sample as the RC component of a resistor-capacitor-inductor series resonator. We discuss the possibility of this RC series behavior to be due to a charge-density wave characteristic also evidenced from the huge values of the low-frequency dielectric constant of the system.

Density, heat capacity and thermal conductivity of liquid egg products

Density, heat capacity and thermal conductivity of liquid egg products, such as egg white, egg yolk, whole egg and various white and yolk blends, were determined as affected by temperature and water content ranging from 273 to 311 K and 51.8 to 88.2% (mass), respectively. Polynomial models fitted the experimental data very well, showing a linear relationship both for temperature and water content. (c) 2005 Published by Elsevier Ltd.

Effect of apparent viscosity on fluidized bed drying process parameters of guava pulp

Pressure drop and minimum fluidization velocity were experimentally studied in a vibro-fluidized bed of inert particles subjected to different vibration intensities during drying of guava pulp. Maltodextrin was added to the pulp in order to prevent stickiness between particles and the consequent bed collapse. Pulps were initially concentrated, resulting in pastes with different soluble solids content, and a constant fraction of maltodextrin was guaranteed in the final pulp samples. The pulp rheological behavior as affected by temperature and total soluble solids content, including maltodextrin, was evaluated and the effect of pulp apparent viscosity on pressure drop and minimum vibro-fluidization velocity were investigated. Two types of inert particles -3.6 mm glass beads and 3 mm Teflon cylinders were tested and, due to lower pressure drop presented by Teflon cylinders during operation of the dry vibro-fluidized bed, these particles were adopted for pulp drying process. Increasing pulp apparent viscosity caused a considerable increase in the vibro-fluidized bed pressure drop during pulp drying and, as a consequence resulted in a larger value of minimum vibro-fluidization velocity. on the other hand, the negative effect of increasing apparent viscosity could be attenuated by increasing the fluidized bed vibration intensity, which could prevent stickiness between particles. (c) 2006 Elsevier Ltd. All rights reserved.

Friction factors and rheological properties of orange juice

The rheological behavior of Brazilian orange juice with different water content (0.34-0.73 w/w) was studied at a wide range of temperatures (0.5-62 degrees C) using a concentric cylinder viscometer. The results indicated that the juices behave as pseudoplastic fluids with yield stress, being represented by the Herschel-Bulkley model. The rheological parameters were fitted as functions of both temperature and water content in the tested range. Based on dimensional analysis it was proposed a modified Reynolds number (Re-M), which includes the Herschel-Bulkley parameters. Experimental data of friction factors during heating and cooling processes of orange juice in laminar flow through circular tubes could be well correlated as a function of Re-M. (C) 1999 Elsevier B.V. Ltd. All rights reserved.

Effect of maltodextrin and arabic gum in water vapor sorption thermodynamic properties of vacuum dried pineapple pulp powder

Moisture equilibrium data of pineapple pulp (PP) powders with and without additives - 18% maltodextrin (MD) or 18% gum Arabic (GA) - were determined at 20, 30, 40 and 50 degrees C by using the static gravimetric method in a water activity range of 0.06-0.90. The obtained isotherms were sigmoid, typical type 111, and the Guggenhein-Anderson-de Boer (GAB) model was fitted to the experimental data of equilibrium moisture content versus water activity. Addition of additives was shown to affect the isotherms in such a way that, at the same water activity, samples PP + GA and PP + MD presented lower equilibrium moisture content and were not so affected by varying temperature. The net isosteric heats of sorption of pulp powders with additives were higher (less negative) than those of pineapple pulp powders, suggesting that there are more active polar sites in the product without addition of GA or MD. An empirical exponential relationship could describe the heat of sorption dependence on the material moisture content. (C) 2007 Elsevier Ltd. All rights reserved.

Evaluation of water and sucrose diffusion coefficients in potato tissue during osmotic concentration

The water and sucrose effective diffusion coefficients behavior were studied in potato tubers immersed in aqueous sucrose solution, 50% (w/,A), at 27 degreesC. Water and sucrose concentration profiles were measured as function of the position for 3, 6 and 12 h of immersion. These were adjusted to a mathematical model for three components that take into account the bulk flow in a shrinking tissue and the concentration dependence of the diffusion coefficients.The binary effective coefficients were an order of magnitude lower than those for pure solutions of sucrose. These coefficients show an unusual concentration dependence. Analysis of these coefficients as functions of the concentration and position demonstrates that, cellular tissue promotes high resistance to diffusion in the tuber and also the elastic contraction of material influences the species diffusion. (C) 2003 Elsevier B.V. Ltd. All rights reserved.

Influence of low and high levels of grain defects on maize wet milling

Yields and starch pasting characteristics obtained from wet milling of maize samples with low and high levels of defect grains were compared to those from sound samples. Defect grain groups ere established taking into account the defect degree. Thus the first group consisted of fermented, molded, heated and sprouted grains and the second of insect damaged. hollow, fermented (up to 1/4) grains and those injured by other causes. The grain groups, if present at low levels in the samples, 10% for first group and 17% for second group did not affect the chemical composition of starch and its pasting properties. obtained by the rapid visco analyser. Samples with high levels of grain groups (up to 100%). affected wet milling yields and starch viscosity. Samples with 100% of grains in the first group decreased starch, germ yield and peak viscosity and increased gluten yield. Samples with 100% of grains in the second group decreased germ and fiber yield but increased starch yield. (C) 2002 Elsevier B.V. Ltd. All rights reserved.

Behavior of plant tissue in osmotic solutions

The effect of the concentration of sucrose solutions on the cellular structure of potato tissue in equilibrium at 27 degreesC was Studied. Two different methods of investigation were used to determine the volume of the different phases composing the cellular tissue of the potato when in equilibrium with the solutions. one based on data of the concentration itself and the overall volume of 2 mm slices after 48 h at equilibrium, and the other on microscopic images of cells in thin slices of fresh tissue stained with neutral red after an hour in equilibrium to show protoplasts, vacuoles and plasmolysis spaces. The results of these methods were compared with those obtained by a predictive thermodynamic approach considering the semipermeability of cell membranes. Phase volume data obtained from microscopic analysis were more similar to what was predicted by the theoretical model than those obtained by means of composition measurement. where the long equilibrium time apparently led to the loss of semi permeability of the cell membranes, since total volumes calculated without consideration of the cell membranes were similar to those measured. This suggests that the length of time of osmotic dehydration brings about a change in cell structure and the consequent involvement of a different mechanism in mass transfer. (C) 2002 Elsevier B.V. Ltd. All rights reserved.