Starches and gums are hydrocolloids frequently used in food systems to provide proper texture, moisture, and water mobility. Starch-gum interaction in food systems can change the starch granule swelling and its gelatinization and rheological properties. In this study, the effect of the addition of xanthan gum (XG), sodium carboxymethyl cellulose (SCMC), and carrageenan (CAR) at the concentrations of the 0.15, 0.25, 0.35 and 0.45% (w/v) on the pasting, thermal, and rheological properties of cassava starch was studied. The swelling power (SP) and the scanning electron microscopy (SEM) of the starch gels were also evaluated. The results obtained showed that xanthan gum (XG) had a strong interaction with the cassava starch penetrating between starch granules causing increase in pasting viscosities, SP, storage and loss (G', and G", respectively) modulus and reduction in the setback of the starch; sodium carboxymethyl cellulose (SCMC) greatly increased the pasting viscosities, the SP, and the storage and loss (G', and G", respectively) modulus of the starch-mixtures, mainly due to its greater capacity to hold water and not due to the interaction with cassava starch. Carrageenan (CAR) did not change any of the starch properties since there was no interaction between this gum and cassava starch at the concentrations used.
The purpose of this work was to investigate the viscoelastic properties of aqueous suspensions of crude collagen powder extracted from bovine hides and nonsubmitted to the hydrolysis reaction that leads to gelatin. The studied variables included the collagen concentration and the addition of xanthan gum or maltodextrin at varied concentrations during heating/cooling of the mixtures. Differential scanning calorimetry thermograms showed that the addition of polysaccharides decreased the endothermic peak areas observed at the denaturation temperature of collagen. The rheological properties of the pure collagen suspensions were highly dependent on concentration: 4% and 6% collagen suspensions presented a great increase in the storage modulus after heating/cooling, whereas for concentrations of 8% and 10% G′ decreased during heating and did not recover its original value after heating/cooling. The frequency sweeps showed that the thermal treatment was responsible by the strengthening of the interactions that formed the polymer network. Addition of 0.1% xanthan gum to collagen suspensions increased the gel strength, especially after heating/cooling of the system, whereas increasing gum concentration to 0.3% resulted in a weaker gel, which could indicate thermodynamic incompatibility between the biopolymers. Mixtures of collagen and maltodextrin resulted in more fluid structures than those obtained with pure collagen at the same collagen concentration and the range of temperatures in which these mixtures behaved as a gel decreased with increasing concentrations of both collagen and maltodextrin, suggesting incompatibilities between the biopolymers.
Isotermas de dessorção de pimentão verde e energia envolvida no processo Desorption isotherms of green bell peppers and the energy involved in the process*Autor Correspondente | Corresponding Author Recebido: Out. 01, 2014 Aprovado: Maio 18, 2015 ResumoEste trabalho teve como objetivos a obtenção das isotermas de dessorção do pimentão verde e a avaliação das propriedades termodinâmicas de sorção do fruto. As isotermas foram obtidas em função da temperatura (30°C, 40°C, 50°C e 60°C) em umidades relativas entre 4,0-90,0%. Os dados experimentais foram ajustados aos modelos matemáticos GAB, BET, Halsey, Henderson e Oswin para se descrever seu comportamento. Os resultados demonstram que o modelo de GAB descreveu com maior precisão as isotermas de dessorção do pimentão verde entre as faixas de atividade de água (a w ) selecionadas, em uma temperatura fixa. O calor isostérico de sorção (q st ) pôde ser determinado a partir de dados de sorção de umidade utilizando-se a derivada da equação de Clasius-Clapeyron, obtendo-se então o calor envolvido no processo de dessorção de umidade do pimentão verde fresco. A teoria da compensação entalpia-entropia ou isocinética foi aplicada aos dados experimentais, sugerindo que o processo de dessorção é conduzido pela entalpia. Palavras-chave: Calor isostérico; Secagem; Modelo de GAB; Compensação Entálpica-Entrópica. SummaryThis study aimed to obtain the desorption isotherms of green bell peppers and evaluate the thermodynamic properties of the moisture sorption of the fruit. The isotherms were obtained as a function of temperature (30°C, 40°C, 50°C and 60 °C) between 4.0 and 90.0% of relative humidity. The experimental data were fitted to the GAB, BET, Halsey, Henderson and Oswin mathematical models to describe their behaviour. The results showed that the GAB model described the sorption isotherms of green bell peppers with greater accuracy in the range of water activities (aw) selected, at a fixed temperature. The isosteric sorption heat (qst) could be determined from the moisture sorption data using the derivative of the Clasius-Clapeyron equation, to obtain the heat involved in the desorption process of the moisture of fresh green bell peppers. The enthalpy-entropy compensation or isokinetic theory was applied to the experimental data and suggested that the desorption process was driven by enthalpy.
ResumoO objetivo deste trabalho foi avaliar a cinética de secagem e os parâmetros de qualidade -conteúdo de vitamina C, reidratação e textura -de fatias de abacaxi liofilizadas em função da espessura e da temperatura de congelamento. Abacaxis do tipo Havaí, variedade Smooth Cayenne, foram fatiados transversalmente em espessuras de 0,5, 1,0 e 1,5 cm. As fatias foram congeladas nas temperaturas de -14, -24 e -34 °C, sendo, em seguida, conduzidas ao liofilizador. Uma parcela das amostras era destinada ao estudo da cinética de secagem pela pesagem periódica das mesmas, enquanto outra foi reservada para os testes de qualidade. O teor de vitamina C foi quantificado por adição de ácido oxálico na amostra e titulado com 2,6-diclorofenolindofenol. O parâmetro de textura avaliado foi a dureza, por testes de compressão em texturômetro, enquanto a reidratação foi obtida pela pesagem das amostras antes e após a imersão em água destilada por 5 min. Os resultados do presente trabalho mostraram que existe uma forte dependência da cinética de secagem e dos atributos de qualidade de fatias de abacaxi liofilizadas em função das condições utilizadas durante a etapa de congelamento, mesmo sendo este classificado como congelamento lento. Por outro lado, a taxa de congelamento não é a única variável que tem influência sobre a cinética de secagem e os atributos de qualidade. A combinação de temperatura e umidade, tanto durante a liofilização propriamente dita, quanto durante a etapa de reidratação, tem influência sobre a transição vítrea do material que, por sua vez, afeta a extensão do colapso estrutural sofrido pelo produto. Palavras-chave:Abacaxi; Liofilização; Cinética; Qualidade. SummaryThe aim of this study was to evaluate the drying kinetics and quality parameters -vitamin C content, rehydration and texture -of freeze dried pineapple slices, according to the thickness and temperature of freezing. Pineapples of the Hawaii type, Smooth Cayenne variety, were sliced transversely with thicknesses of 0.5, 1.0 and 1.5 cm. The slices were frozen at temperatures of -14, -24 and -34 °C, and then freeze dried. One part of the samples was used to study the drying kinetics by periodic weighing, while the other was reserved for the quality tests. The vitamin C content was quantified by adding oxalic acid to the sample and titrating with 2,6-dichlorophenolindophenol. The texture parameter evaluated was that of hardness, evaluated by compression tests in a texturometer, while rehydration was determined by weighing the samples before and after immersion in water for 5 min. The results of this study showed there was a strong dependence of the drying kinetics and quality attributes of the dried pineapple slices on the conditions used during the freezing step, even though this was classified as slow freezing. Nevertheless the freezing rate was not the only variable that influenced the drying kinetics and quality attributes. The combination of temperature and humidity, both during the freeze drying process itself, and also during the rehydration ste...
ResumoO Estado do Paraná vem consolidando-se como o maior produtor e exportador da carne de frango no Brasil. As propriedades termofísicas, entre as quais a condutividade térmica, a difusividade térmica e a massa específica, são parâmetros importantes a ser considerados em projetos e operações que envolvam processamento térmico, como pasteurização, esterilização e cocção, e sistemas de refrigeração e congelamento. Neste contexto, o objetivo deste trabalho foi investigar estas propriedades termofísicas -condutividade térmica, difusividade térmica e massa específica -da carne do peito de frango, em função da umidade e da temperatura. A condutividade térmica foi avaliada pelo método da sonda linear com geração interna de calor; a difusividade térmica baseou-se no método de Dickerson, e a massa específica foi quantificada por picnometria. As três propriedades foram bastante afetadas pelo conteúdo de umidade, com um aumento nos valores da condutividade e difusividade térmica em teores de umidade mais altos, enquanto a massa específica teve um resultado inverso, com amostras mais densas à medida que o teor de umidade era reduzido. O efeito da temperatura conduziu a um aumento nos valores da difusividade e da condutividade térmica; porém, para a massa específica, de um modo geral, promoveu seu abaixamento. Palavras-chave: Condutividade térmica; Difusividade térmica; Massa específica; Transferência de calor. SummaryThe state of Paraná has consolidated itself as the largest producer and exporter of poultry meat in Brazil. The thermophysical properties, including thermal conductivity, thermal diffusivity and specific mass are important parameters to be considered in projects and operations involving thermal processing such as pasteurization, sterilization, cooking, refrigeration and freezing. Thus the aim of this study was to investigate the thermophysical properties -thermal conductivity, thermal diffusivity and specific mass -of chicken breast meat as a function of moisture content and temperature. The thermal conductivity was measured by the linear probe method with internal generation of heat, thermal diffusivity was determined based on the method of Dickerson, while the density was measured by pycnometry. The three properties were strongly affected by moisture content, with an increase in the values of conductivity and thermal diffusivity at higher moisture contents, while the specific mass, or density, showed the opposite result, with denser samples at lower moisture contents. The effect of temperature led to an increase in the values for thermal diffusivity and thermal conductivity, but in general led to a lowering of the specific mass. Campinas, v. 16, n. 4, p. 278-284, out./dez. 2013
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