Ana Lúcia Gabas

Viscosity of Aqueous Carbohydrate Solutions at Different Temperatures and Concentrations

Experimental viscosity values of sucrose, glucose, and fructose aqueous solutions in a large range of temperatures (0 to 85°C) and concentrations (10 to 60% w/w) that might be encountered in food processes were obtained in order to contribute to extending the available database of food properties. The temperature dependence of viscosity could be adequately described by the Arrhenius model, and the activation energy was well represented by a unique function of the solute volume fraction, valid for sucrose, glucose, and fructose solutions.

Solids Rheology for Dehydrated Food and Biological Materials

Abstract Mechanical properties of food products and biological materials are greatly affected by the drying process and are considered one of the most important quality attributes of dehydrated products. The aim of this work was to review theoretical principles and mathematical modeling, analyzing the measurement techniques and major experimental results that exist in the literature about rheological properties of dehydrated foods and biological materials. Different methods of measuring rheological parameters (fundamental and empiric or imitative) are discussed and major experimental results, as well as the rheological models used in their analysis, published in recent years are presented.

Drying Kinetics of Tomato by Using Electric Resistance and Heat Pump Dryers

Abstract Drying kinetics of tomato was studied by using heat pump dryer (HPD) and electric resistance dryers with parallel and crossed airflow. The performance of both systems was evaluated and compared and the influence of temperature, air velocity, and tomato type on the drying kinetics was analyzed. The use of HPD showed to be adequate in the drying process of tomatoes, mainly in relation to the conversion rate of electric energy into thermal energy. The heat pump effective coefficient of performance (COPHT,EF) was between 2.56 and 2.68, with an energy economy of about 40% when compared to the drying system with electric resistance. The Page model could be used to predict drying time of tomato and statistical analysis showed that the model parameters were mainly affected by drying temperature.

Thermodynamic and Quality Properties of Lemon Juice Powder as Affected by Maltodextrin and Arabic Gum

Sorption isotherms of lemon juice (LE) powders with and without additives—18% maltodextrin (MA) or 18% gum Arabic (GA)—were determined at 20–50°C. Addition of additives was shown to affect the isotherms in such a way that, at the same water activity, samples LE + GA and LE + MA presented lower equilibrium moisture content and were not so affected by varying temperature. The net isosteric heats of sorption of juice powders with additives were higher (less negative) than those of lemon juice powders, suggesting that there are more active polar sites in the product without addition of GA or MA. In general, the quality properties decreased with the addition of maltodextrin and gum arabic and it was obtained similar values for LE + GA and LE + MA.

Enthalpy-entropy compensation based on isotherms of mango

SUMMARY ENTHALPY-ENTROPY COMPENSATION BASED ON ISOTHERMS OF MANGO. Moisture equilibrium data of mango pulp were determined using the static gravimetric method. Adsorption and desorption isotherms were obtained in the range of 30-70 C, to water activities (a ) from 0.02 to 0.97. The application of the GAB model to the experimental results, using direct nonlinear regression analysis, provided agreement between experimental and calculated values. The net isosteric heat of sorption was estimated from equilibrium sorption data, using the Clausius-Clapeyron equation. Isosteric heats of sorption were found to increase with increasing temperature and could be well adjusted by an exponential relationship. The enthalpy-entropy compensation theory was applied to sorption isotherms and plots of H versus S provided the isokinetic temperatures, indicating an enthalpy controlled sorption process. moisture content; thermodynamic properties; mango. o w ∆∆

Salting kinetics and salt diffusivities in farmed Pantanal caiman muscle

A criacao de jacare do Pantanal (Caiman crocodilus yacare) em cativeiro tem sido estimulada, e entre as tecnicas de processamento de sua carne, a salga e um processo de conservacao relativamente simples e de baixo custo. O objetivo deste trabalho foi estudar a cinetica de difusao de cloreto de sodio em carne de jacare do Pantanal criado em cativeiro, durante a salga umida. Foram utilizados volumes limitados de salmoura e os experimentos foram realizados com relacoes salmoura/musculo de 3, 4 e 5, com concentracoes de salmoura de 15%, 20% e 25% em peso e temperaturas de 10, 15 e 20oC. A solucao analitica da segunda lei de Fick, considerando difusao unidimensional em uma placa infinita em contato com uma solucao bem agitada de volume limitado, foi utilizada para calcular os coeficientes de difusao efetivos de sal e estimar o conteudo de cloreto de sodio nos files. Obteve-se boa concordância entre o modelo analitico considerado e os dados experimentais. As difusividades do sal nos files ocorreram na faixa de 0,47x10-10 a 9,62x10-10 m2/s.

Rheological and thermophysical properties of blackberry juice

Rheological and thermophysical properties were determined for blackberry juice, which was produced from blackberry fruit at 9.1 ± 0.5 °Brix and density of 1.0334 ± 0.0043 g cm-3. The concentration process was performed using a roto evaporator, under vacuum, to obtain concentrated juice at about 60 °Brix. In order to obtain different concentrations, concentrated juice was diluted with distilled water. Rheological measurements were carried out using a Rheotest 2.1 Searle type rheometer. In the tested ranges, the samples behaved as pseudoplastic fluids, and the Power-Law model was satisfactorily fitted to the experimental data. The friction factor was measured for blackberry juice in laminar flow conditions of pseudoplastic behavior. Thermal conductivity, thermal diffusivity and density of blackberry juice at 9.4 to 58.4 °Brix were determined, in triplicate, at 0.5 to 80.8 °C. Polynomial regression was performed to fit experimental data obtaining a good fit. Both temperature and concentration showed a strong influence on thermophysical properties of blackberry juice. Calculated apparent specific heat values varied from 2.416 to 4.300 kJ.kg -1 °C in the studied interval.

Freezing point and thermal conductivity of tropical fruit pulps: Mango and papaya

The freezing point depression of mango and papaya pulps was measured by using a simple apparatus, consisting of two major sections: a freezing vessel and a data acquisition system. The thermal conductivity of both pulps as a function of frozen water fraction and temperature was also investigated by using a coaxial dual-cylinder apparatus. Thermal conductivity above the initial freezing point was well fitted by polynomial equations. Below the freezing point, the thermal conductivity was strongly affected by both the frozen water fraction and temperature. Simple equations in terms of frozen water fraction and temperature could be fitted to the experimental data of freezing point depression and thermal conductivity.

Influence of Fluid Concentration on Freezing Point Depression and Thermal Conductivity of Frozen Orange Juice

Abstract The freezing point depression (FPD) of orange juice at different concentrations was measured by using a simple apparatus. Results showed that the initial freezing point decreased approximately 90% with the increase of juice concentration between 46° and 66°Brix (water content respectively between 52.8 and 32.8% w/w). The thermal conductivity of orange juice as a function of fluid concentration was also investigated by using a coaxial dual‐cylinder apparatus. Below the freezing point, the thermal conductivity was strongly affected by both the orange juice concentration and temperature. Simple equations in terms of water content and temperature could be adjusted to experimental data of FPD and thermal conductivity.

Changes of Density, Thermal Conductivity, Thermal Diffusivity, and Specific Heat of Plums During Drying

The thermal properties of plums (Prunus domestica) and prunes were investigated in the moisture content of 14.2-80.4% (wet basis) near room temperature (approximately 28°C). The apparent density of the fruits increased from 1042.9 to 1460.0 kg/m3, and the bulk density increased from 706.6 to 897.5 kg/m3 as the plums were dried, following classical empirical models as a function of moisture content. It was found that specific heat, effective thermal diffusivity, and effective thermal conductivity of the prunes increased with the moisture content of the samples, which can be represented by using different empirical models.