The effect of using 2%and 10%sodium hydroxide solution as surface treatment of rape straw on its water vapor adsorption properties is analyzed in the relative humidity(RH)range of 0%to 98%.Scanning electron microscopy...The effect of using 2%and 10%sodium hydroxide solution as surface treatment of rape straw on its water vapor adsorption properties is analyzed in the relative humidity(RH)range of 0%to 98%.Scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),and Fourier-transform infrared spectroscopy(FTIR)are used to investigate the morphological,chemical and structural changes of the treated straw surface.The mineral particles formed on the surface after the treatment are analyzed using X-ray diffraction(XRD).The application of sodium hydroxide solution results in the disruption of the straw surface.As the concentration of sodium hydroxide increases,the disruption of the straw surface increases,and the ability of the straw to adsorb water vapor also increases over the entire RH range.In addition to the surface disruption and chemical changes caused by the alkaline treatment,the differences in the equilibrium moisture content of treated and untreated rape straw can also be attributed to the formation of minerals on the straw surface,namely calcite for the 2%sodium hydroxide solution,and gaylussite and thermonatrite for the 10%solution.展开更多
采用静态称量法测量30、40、50℃时豌豆种子的吸附等温线,对实验数据进行非线性拟合,并通过对净等量吸附热、微分熵、焓熵补偿、扩张压力、净积分焓和净积分熵等热力学性质参数的研究,分析种子吸附特性和进一步揭示吸附机理,为选择和优...采用静态称量法测量30、40、50℃时豌豆种子的吸附等温线,对实验数据进行非线性拟合,并通过对净等量吸附热、微分熵、焓熵补偿、扩张压力、净积分焓和净积分熵等热力学性质参数的研究,分析种子吸附特性和进一步揭示吸附机理,为选择和优化种子干燥和贮藏条件提供理论依据。实验结果表明,温度恒定时,平衡含水率随水分活度升高而升高,吸附等温线属于类型Ⅱ且GAB模型拟合效果最佳(R2=0.998 9,误差平方和为4.52×10-5);净等量吸附热和微分熵随着平衡含水率升高而降低的规律符合焓熵补偿理论,该理论反映出吸附过程是非自发反应,属于焓驱动,而当干基含水率达到25%时,净等量吸附热值接近纯水的汽化潜热(43.30 k J/mol);种子吸附过程的扩张压力随水分活度升高而升高,随温度升高而降低,当扩张压力一定时,净积分焓和净积分熵随着平衡含水率升高而降低,净积分熵达到最小值后逐渐升高,此最小值在30、40、50℃温度条件下分别为-137.79、-140.29、-137.74 J/(mol·K),对应的水分活度和平衡含水率分别为0.017、0.045、0.062和2.7%、2.5%、2.4%,这些条件可作为豌豆种子贮藏的最稳定条件。展开更多
Water sorption isotherms are unique for individual food materials and can be used directly to predict shelf life and determine proper storage conditions. In this context, the aim of this study was to determine the moi...Water sorption isotherms are unique for individual food materials and can be used directly to predict shelf life and determine proper storage conditions. In this context, the aim of this study was to determine the moisture adsorption isotherms of amaranth flour at 15℃, 25℃ and 35℃ in a range of water activity from 0.1 to 0.9. Experimental data were modeled using five equations commonly applied in the foods field. The goodness of the fit for each isotherm model was evaluated through the coefficient of determination, the variance due to error and the confidence interval of the estimated parameters. All models can predict the adsorption isotherms of amaranth flour, but the GAB equation gives a better understanding of the observed sorption behavior. Estimated adsorption monolayer water contents ranged from 6.4 g to 7.2 g of water per 100 g of dry material. It was observed by a weak dependence of water activity with temperature. For ensuring microbiological stability, water content in amaranth flour should not be higher than 13 g of water per 100 g of dry material.展开更多
This study aimed to determine the desorption isotherms and the thermodynamic properties of taioba leaves.For this,gravimetric-static method was used to determine the equilibrium moisture content(EMC)and water activity...This study aimed to determine the desorption isotherms and the thermodynamic properties of taioba leaves.For this,gravimetric-static method was used to determine the equilibrium moisture content(EMC)and water activity of taioba leaves at nine storage and drying temperatures(5-80℃).The proximate composition was also determined.The Clausius-Clapeyron and Gibb’s-Helmholtz equations were used to determine the net isosteric heat of desorption and differential entropy,respectively.The enthalpy-entropy compensation theory was also investigated.The relationship between water activity and equilibrium moisture content was best described by GAB model(R2adj≥0.987;χ^(2).10^(5)≤3.126;RMSE≤0.006)for the whole range of relative moistures and tempera-tures.The sigmoid-shaped type II was predominant at all temperatures.The net isosteric heat of desorption decreased from 8907.62 to 1120.15 J/mol as the moisture content increased.The linear relationship between enthalpy and entropy endorsed the enthalpy-entropy compensation mechanism in which TB>Thm,thus,an enthalpy-driven process.The free Gibbs energy was less than zero spontaneous(ΔGB_(storage)=-728.79 J/mol and ΔG_(Bdrying)=-1217.20 J/mol),indicating that water desorption is spontaneous.The spreading pressure varied from 0.001 to 0.05 J/m^(2) for all temperatures studied.The water surface area tended to decrease with increasing temperature,ranging from 185.71 to 251.97 m^(2)/g.Therefore,this study provided an understanding of the water desorption properties of taioba leaves,contributing to the development of storage and drying practices.展开更多
基金supported by the Czech Science Foundation,under project No.20-12166S.
文摘The effect of using 2%and 10%sodium hydroxide solution as surface treatment of rape straw on its water vapor adsorption properties is analyzed in the relative humidity(RH)range of 0%to 98%.Scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),and Fourier-transform infrared spectroscopy(FTIR)are used to investigate the morphological,chemical and structural changes of the treated straw surface.The mineral particles formed on the surface after the treatment are analyzed using X-ray diffraction(XRD).The application of sodium hydroxide solution results in the disruption of the straw surface.As the concentration of sodium hydroxide increases,the disruption of the straw surface increases,and the ability of the straw to adsorb water vapor also increases over the entire RH range.In addition to the surface disruption and chemical changes caused by the alkaline treatment,the differences in the equilibrium moisture content of treated and untreated rape straw can also be attributed to the formation of minerals on the straw surface,namely calcite for the 2%sodium hydroxide solution,and gaylussite and thermonatrite for the 10%solution.
文摘采用静态称量法测量30、40、50℃时豌豆种子的吸附等温线,对实验数据进行非线性拟合,并通过对净等量吸附热、微分熵、焓熵补偿、扩张压力、净积分焓和净积分熵等热力学性质参数的研究,分析种子吸附特性和进一步揭示吸附机理,为选择和优化种子干燥和贮藏条件提供理论依据。实验结果表明,温度恒定时,平衡含水率随水分活度升高而升高,吸附等温线属于类型Ⅱ且GAB模型拟合效果最佳(R2=0.998 9,误差平方和为4.52×10-5);净等量吸附热和微分熵随着平衡含水率升高而降低的规律符合焓熵补偿理论,该理论反映出吸附过程是非自发反应,属于焓驱动,而当干基含水率达到25%时,净等量吸附热值接近纯水的汽化潜热(43.30 k J/mol);种子吸附过程的扩张压力随水分活度升高而升高,随温度升高而降低,当扩张压力一定时,净积分焓和净积分熵随着平衡含水率升高而降低,净积分熵达到最小值后逐渐升高,此最小值在30、40、50℃温度条件下分别为-137.79、-140.29、-137.74 J/(mol·K),对应的水分活度和平衡含水率分别为0.017、0.045、0.062和2.7%、2.5%、2.4%,这些条件可作为豌豆种子贮藏的最稳定条件。
基金support of the Swedish International Development Agency(Sida).
文摘Water sorption isotherms are unique for individual food materials and can be used directly to predict shelf life and determine proper storage conditions. In this context, the aim of this study was to determine the moisture adsorption isotherms of amaranth flour at 15℃, 25℃ and 35℃ in a range of water activity from 0.1 to 0.9. Experimental data were modeled using five equations commonly applied in the foods field. The goodness of the fit for each isotherm model was evaluated through the coefficient of determination, the variance due to error and the confidence interval of the estimated parameters. All models can predict the adsorption isotherms of amaranth flour, but the GAB equation gives a better understanding of the observed sorption behavior. Estimated adsorption monolayer water contents ranged from 6.4 g to 7.2 g of water per 100 g of dry material. It was observed by a weak dependence of water activity with temperature. For ensuring microbiological stability, water content in amaranth flour should not be higher than 13 g of water per 100 g of dry material.
基金the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior-Brasil(CAPES)-Finance Code 001the Conselho Nacional de Desenvolvimento Científico e Tecnológico(CNPq)-Award Number:314459/2021-9.
文摘This study aimed to determine the desorption isotherms and the thermodynamic properties of taioba leaves.For this,gravimetric-static method was used to determine the equilibrium moisture content(EMC)and water activity of taioba leaves at nine storage and drying temperatures(5-80℃).The proximate composition was also determined.The Clausius-Clapeyron and Gibb’s-Helmholtz equations were used to determine the net isosteric heat of desorption and differential entropy,respectively.The enthalpy-entropy compensation theory was also investigated.The relationship between water activity and equilibrium moisture content was best described by GAB model(R2adj≥0.987;χ^(2).10^(5)≤3.126;RMSE≤0.006)for the whole range of relative moistures and tempera-tures.The sigmoid-shaped type II was predominant at all temperatures.The net isosteric heat of desorption decreased from 8907.62 to 1120.15 J/mol as the moisture content increased.The linear relationship between enthalpy and entropy endorsed the enthalpy-entropy compensation mechanism in which TB>Thm,thus,an enthalpy-driven process.The free Gibbs energy was less than zero spontaneous(ΔGB_(storage)=-728.79 J/mol and ΔG_(Bdrying)=-1217.20 J/mol),indicating that water desorption is spontaneous.The spreading pressure varied from 0.001 to 0.05 J/m^(2) for all temperatures studied.The water surface area tended to decrease with increasing temperature,ranging from 185.71 to 251.97 m^(2)/g.Therefore,this study provided an understanding of the water desorption properties of taioba leaves,contributing to the development of storage and drying practices.
