More and more people concern about supplementing dietary food with wheat bran to increase fibre content,but there has been little study of the sorption isotherms and isosteric heats of wheat bran fibre products,which ...More and more people concern about supplementing dietary food with wheat bran to increase fibre content,but there has been little study of the sorption isotherms and isosteric heats of wheat bran fibre products,which are important to the quality and storage durability of such commodities.This study collected equilibrium moisture content(EMC)and equilibrium relative humidity(ERH)data on six Chinese wheat bran products via the static gravimetric method and analysed their sorption isosteric heats.Results showed that all six wheat bran products had sigmoidal isotherms.The data were best fitted by polynomial,modified GAB,modified Oswin,and modified Halsey models.The relative safe moisture contents of the six wheat bran products were 12.20%–13.86%wet basis(w.b.).The heat of vaporization of wheat bran products approached the latent heat of pure water at around a moisture content(MC)of 22.5%and approximately 2450 kJ/kg.A process of extrusion and ultrafine grinding reduced the solid surface area and sorption isosteric heats of the monolayer,multilayer and condensed water regions in the wheat bran products.In the temperature range of 10–37℃,the EMC of sorption in monolayer,multilayer and condensed water regions decreased with increasing temperature.The milled rice to which 1%–3%200-mesh wheat bran product was added maintained its texture when made into cooked rice and its thermomechanical properties when made into rice dough.After processing by extrusion and ultrafine grinding,wheat bran products have a lower solid surface area and lower monolayer water content(Mm)and sorption isosteric heat values.Some 3%200-mesh wheat bran product can be added to cooked rice for increasing its fibre content and making it more nutritious.展开更多
Knowledge of the state of water balance of agro-food products is an essential step in drying or storage operations for preservation. Our study made it possible to determine the thermodynamic parameters which influence...Knowledge of the state of water balance of agro-food products is an essential step in drying or storage operations for preservation. Our study made it possible to determine the thermodynamic parameters which influence the storage conditions of fresh tomatoes grown in the south of Benin;and to predict its hygroscopic behavior during post-harvest storage. The desorption isotherms obtained at 40℃, 50℃ and 60℃, by the static gravimetric method using saturated saline solutions, are compared with those of the theoretical models of Brunauer, Emmet and Teller (BET), SMITH, PELEG and Guggenheim-Anderson-Boer (GAB). An adjustment of the experimental points, on the theoretical models, was made thanks to the numerical method which exploits the fminsearch algorithm under the MATLAB software, version R2018a. The GAB model at 50℃ faithfully reproduces the experimental desorption curves for water activities from 5.5% to 82.3%. The net isosteric heat of sorption was determined using the Clausius-Clapeyron equation, it increases when the degree of dehydration of the product increases. The applied isokinetic theory and enthalpy-entropy compensation are consistent.展开更多
基金the Operating Expenses of Basic Scientific Research Project of Central Public-interest Scientific Institution,China(JY2007)the Special Fund for Grain Scientific Research in the Public Interest of the State Administration of Grains,China(201313001-03-01)。
文摘More and more people concern about supplementing dietary food with wheat bran to increase fibre content,but there has been little study of the sorption isotherms and isosteric heats of wheat bran fibre products,which are important to the quality and storage durability of such commodities.This study collected equilibrium moisture content(EMC)and equilibrium relative humidity(ERH)data on six Chinese wheat bran products via the static gravimetric method and analysed their sorption isosteric heats.Results showed that all six wheat bran products had sigmoidal isotherms.The data were best fitted by polynomial,modified GAB,modified Oswin,and modified Halsey models.The relative safe moisture contents of the six wheat bran products were 12.20%–13.86%wet basis(w.b.).The heat of vaporization of wheat bran products approached the latent heat of pure water at around a moisture content(MC)of 22.5%and approximately 2450 kJ/kg.A process of extrusion and ultrafine grinding reduced the solid surface area and sorption isosteric heats of the monolayer,multilayer and condensed water regions in the wheat bran products.In the temperature range of 10–37℃,the EMC of sorption in monolayer,multilayer and condensed water regions decreased with increasing temperature.The milled rice to which 1%–3%200-mesh wheat bran product was added maintained its texture when made into cooked rice and its thermomechanical properties when made into rice dough.After processing by extrusion and ultrafine grinding,wheat bran products have a lower solid surface area and lower monolayer water content(Mm)and sorption isosteric heat values.Some 3%200-mesh wheat bran product can be added to cooked rice for increasing its fibre content and making it more nutritious.
文摘Knowledge of the state of water balance of agro-food products is an essential step in drying or storage operations for preservation. Our study made it possible to determine the thermodynamic parameters which influence the storage conditions of fresh tomatoes grown in the south of Benin;and to predict its hygroscopic behavior during post-harvest storage. The desorption isotherms obtained at 40℃, 50℃ and 60℃, by the static gravimetric method using saturated saline solutions, are compared with those of the theoretical models of Brunauer, Emmet and Teller (BET), SMITH, PELEG and Guggenheim-Anderson-Boer (GAB). An adjustment of the experimental points, on the theoretical models, was made thanks to the numerical method which exploits the fminsearch algorithm under the MATLAB software, version R2018a. The GAB model at 50℃ faithfully reproduces the experimental desorption curves for water activities from 5.5% to 82.3%. The net isosteric heat of sorption was determined using the Clausius-Clapeyron equation, it increases when the degree of dehydration of the product increases. The applied isokinetic theory and enthalpy-entropy compensation are consistent.
