Moisture sorption isotherms and thermodynamic properties of walnut kernels

The moisture sorption isotherm data of walnut kernels stored in a chamber, the relative humidity (r.h.) of which is regulated by atomizing humidifier, were determined at three different temperatures (25, 35 and 45 °C) and r.h. ranging from 10% to 90%. Eight models, namely the GAB, BET, Henderson, Iglesias and Chirife, Oswin, Peleg, Smith and Caurie equations, were fitted to the sorption data. Several statistical tests were adopted as the criteria to evaluate the fitting performance of the models. Of the models tested, the Peleg model gave the best fit to experimental data. The surface area of a monolayer was calculated. The BET equation was applied to the monolayer moisture content and the corresponding a_w values at which a monolayer forms are presented. The experimental data were also used to determine the thermodynamic functions such as isosteric heat of sorption, sorption entropy, spreading pressure, net integral enthalpy and entropy. The sorption isosteric heats for walnut kernels were determined by the application of the Clausius-Clapeyron equation to sorption isotherms obtained from the best-fitting equation. Isosteric heats decreased with increase in moisture content and approached the latent heat of pure water. Adsorption entropy increased with increasing moisture content, and then it decreased sharply with increase in moisture content. The spreading pressures (adsorption and desorption) increased with increasing water activity. Net integral enthalpy of adsorption increased slightly with moisture content to a maximum value. Thereafter, it remained constant. Net integral entropy of adsorption was negative in value and it decreased with increase in moisture content to a minimum value, and then increased slightly with increase in moisture content.     

Moisture sorption characteristics and glass transition temperature of apple puree powder

The aim of this study was to characterise the influence of different foam‐mat‐drying methods on the moisture sorption characteristics and glass transition temperatures of apple puree powder. Apple puree was foamed with the addition of 2.5% egg albumin and 0.5% methylcellulose. Convective air‐drying and microwave‐drying techniques were used. Also foamed puree with and without maltodextrin (6% or 15% w/w) was freeze‐dried. Moisture equilibrium data of powders were determined by using a static desiccator method in a water activity range of 0.0–0.903. Modulated differential scanning calorimetry (MDSC) was used to obtain the glass transition temperature. No effect of drying method on sorption properties and glass transition temperatures of apple puree powders was observed. The addition of maltodextrin to the apple puree caused an increase in T_g by 10–30 °C depending on the amount of incorporated additive. Addition of maltodextrin significantly reduced the hygroscopicity of apple puree powders.     

大蒜皮红色素理化性质研究

对大蒜皮红色素的理化性质进行了研究，结果表明，该色素在酸性溶液中稳定，对热稳定，但日光对色素有一定的降解作用。抗坏血酸、淀粉、柠檬酸、苯甲酸钠(＜l％)、蔗糖、几种金属离子对大蒜皮色素的色泽无不良影响，并且还有一定的增色作用。色素对H202、Fe3+离子较敏感。     

Moisture sorption isotherms and thermodynamic properties of safflower seed using empirical and neural network models

Experimental work was conducted to obtain the adsorption isotherms of safflower seed using a semi static gravimetric method at 25, 40, and 60 °C over a water activity range from 0.11 to 0.94. Fourteen isotherm equations and multilayer artificial neural network approach were employed to analyze the experimental data. In order to evaluate the goodness of fit of each model determination coefficient, Chi Square and root mean square error were used. The Peleg (at 25 and 40 °C) and Osvin (at 60 °C) models were selected to best describe the sorption isotherms of safflower seed. Accordingly, the results showed that the predicted values of ANN model were more accurate than those predicted by nonlinear regression method. The adsorption monolayer moisture content was also determined using Brunauer, Emmett and Teller equation. The monolayer moisture content values were 0.028, 0.024, and 0.022 gH₂O/g solid at 25, 40, and 60 °C, and the corresponding constant values of the Brunauer, Emmett and Teller equation were found to be ?13.029, ?10.873, and ?17.255, respectively. The safflower seeds heat of sorption values was also found. The heat of sorption values was large at low moisture content and decreased with an increase in the moisture content, whereas the magnitudes increase with increases in temperature and could be well adjusted by an exponential relationship. The experimental data revealed that enthalpy-entropy compensation theory was satisfactorily applicable to the moisture sorption behavior of the safflower seed.     

Equilibrium sorption isotherms and thermodynamic properties of starch and gluten

A modification of the GAB isotherm (Guggenheim–Anderson–De Boer) is proposed in order to correlate the sorption data for water activities higher than 0.9. The proposed isotherm retains the desirable properties of the GAB isotherm, i.e. good fitting in the range of a_w between 0.05 and 0.80, and also provides a noticeable improvement in the fitting quality for high values of a_w, by introducing a new term with an additional constant. Sorption data for native potato starch and gluten at different temperatures (2°C, 20°C, 40°C and 67°C) were well correlated for the whole a_w range. For starch at 67°C, the values of the constants of the proposed equation do not follow the same tendency obtained for lower temperatures, suggesting that the structure of the material could be changed due to the high temperature. The proposed isotherm can be of interest in the area of drying given that there are few isotherms that accurately represent sorption data at different temperatures in the zone of high a_w. Also, it can be useful to predict other thermodynamic functions. In addition, a new procedure is proposed to determine the isosteric heat by using a second order polynomial for representing the variation of moisture as a function of temperature at a fixed water activity.     

Water sorption isotherms and thermodynamic properties of pearl millet grain

The water sorption isotherms of pearl millet grain and the thermodynamic properties obtaining during the process of drying pearl millet were examined. Equilibrium moisture content (X_eq) was determined under several temperature (T) and relative humidity (RH) conditions. The X_eq data were correlated by six mathematical models. The modified Henderson was the model that best fitted the experimental data. The X_eq decreased with an increase in T at constant RH. Hysteresis was also studied; increasing T led to a decrease in this phenomenon. Integral isosteric heat of sorption (Q_st), differential entropy (ΔS) and the enthalpy–entropy compensation theory were studied. Q_st values decreased when X_eq increased because the Q_st values of adsorption were lower than Q_st desorption values. The values of ΔS decreased with increases in X_eq, because ΔS values were higher for desorption than for adsorption. The enthalpy–entropy compensation theory is valid for describing the water sorption processes of pearl millet grain.     

甘蓝型油菜籽水分解吸等温线及热力学性质

为了提高油菜籽储藏期间的稳定性,延长其保质期。采用静态称量法对油菜籽在20、30、40℃温度条件下的解吸特性进行研究,将实验数据用5种常见数学模型进行拟合并对最佳模型进行解析。采用净等量吸附热(q_(st))、扩张压力(Φ)、微分熵(ΔS)、净积分焓(q_(in))、净积分熵(ΔS_(in))以及焓熵互补等特征参数对其热力学性质进行描述。结果表明,油菜籽等温线属于Type Ⅱ类曲线,油菜籽的平衡含水率与水分活度呈正相关,一定水分活度下,平衡含水率与温度呈负相关;描述水分活度与平衡含水率关系最佳模型为GAB模型,不同温度条件下模型决定系数R~2的平均值为0.993 7,卡方x~2的范围为1.396 5×10~(-5)～0.778,残差平方和RSS最低值为4.189 6×10~(-6);较高Φ值能提高干燥速率,储藏过程中,较低Φ值能延长物料保质期;对ΔS_(in)与平衡含水率的关系分析得到最低ΔS_(in)值,在20、30、40℃条件下,籽粒内结合水和单分子层吸附水分子最稳定的平衡含水率分别为5.03%、4.92%以及4.88%。     

Moisture sorption isotherms of green chilli

The adsorption and desorption equilibrium moisture contents of green chilli were determined experimentally in relative humidity range of 11‐97% and at the temperatures of 20, 30, 40 and 50°C. The experimental procedure used was a dynamic method with periodically recording of sample mass. The effect of temperature on adsorption and desorption isotherms was found significant. Hystereses were observed for entire range of relative humidity and hysteresis loops decreased with the increase of temperature. Nine sorption isotherm models were fitted the experimental data at the temperatures of 20, 30, 40 and 50 °C. The modified Smith equation was the best fitted equation to the experimental data for relative humidity range of 11‐97% for the adsorption and desorption isotherms of green chilli.     

Sorption isotherms and thermodynamic properties of freeze‐dried colostral whey powders with different additives

Moisture adsorption isotherms of colostral whey (CW) powders with different additives (maltodextrin and sucrose) were determined using gravimetric static method at 15–35 °C in the water activity range of 0.067–0.76. The moisture adsorption isotherms obtained were typical sigmoid curves, and the modified‐Halsey and Guggenheim–Anderson–de Boer (GAB) equations gave the best fit to experimental data among five well‐known equations. Addition with maltodextrin into CW powders could effectively decrease equilibrium moisture content (EMC), whereas addition with sucrose increased EMC in the water activity of 0.43–0.76 at 15 and 25 °C and in the water activity of 0.21–0.76 at 35 °C, respectively. Thermodynamic properties including net isosteric heat of sorption and differential entropy were determined from adsorption data using Clausius–Clapeyron equation. The results showed that net isosteric heat of sorption of all the samples decreased exponentially with increasing EMC. Enthalpy–entropy compensation theory was applicable for adsorption process of all the samples, and the adsorption processes were enthalpy‐driven.     

Moisture sorption isotherms and isosteric heat for pistachio

The equilibrium moisture contents (EMC) of pistachio were determined using the standard static-gravimetric method at 15, 25, 35 and 40 °C for pistachio powder at 15, 35 °C for pistachio kernel and pistachio nut for water activity (a _w) ranging from 0.11 to 0.9. At a given water activity, the results show that the moisture content decreases with increasing temperature. The experimental sorption curves are then described by the BET, GAB, Henderson, Oswin, Smith and Halsey models. A nonlinear regression analysis method was used to evaluate the constants of the sorption equations. The Smith model was found to be suitable for describing the sorption curves. The isosteric heat of adsorption of water was determined as a function of moisture content from the equilibrium data at different temperatures using the Clasius–Clapeyron equation.     

大蒜精油的提取及微胶囊化的工艺研究

文章采用大蒜为原料，采用纤维素酶进行酶解，以95％的乙醇为溶剂，经浸渍和连续浸提所得的蒜素为心材，以食用胶为壁材，经均质、喷雾干燥而得大蒜油树脂微胶囊。通过正交试验获得微胶囊化的最佳工艺条件，最佳工艺条件为心材：壁材为1：3，进风温度150℃，进料速度为1．56L／h，进料浓度为35％。     

冻藏对小麦淀粉理化性质及热力学特性的影响

研究了冻藏对小麦淀粉颗粒表面形态、理化性质、热力学性质及凝沉特性的影响。通过扫描电镜(SEM)检测冻藏小麦淀粉颗粒,发现部分淀粉颗粒表面有破损;对冻藏后的小麦淀粉溶解度、粘度、膨润力、蓝值等进行测定,结果显示冻藏后淀粉溶解度和粘度分别增大了48.6%、43.2%;膨润力、蓝值分别降低8.41%、28.5%;采用示差量热扫描(DSC)测定冻藏小麦淀粉热力学性质变化,发现冻藏小麦淀粉糊化热焓降低了47.3%,糊化温度起止范围降低了10.60%;凝沉值降低了47.2%。研究表明冻藏后的小麦淀粉颗粒形态,理化性质、热力学性质均发生了明显改变。      

Sorption isotherms and thermodynamic properties of grated Parmesan cheese

This study focuses on isotherms, isosteric heat of sorption and enthalpy–entropy mechanism of water sorption of grated Parmesan cheese at simulating conditions of storage and drying processes. Isotherms were determined by gravimetric method using different saturated salt solutions. Samples were submitted to different temperatures, and several models were used to fit experimental data, GAB and modified GAB being those which best represented experimental data in all temperature ranges. The isosteric heat of sorption was calculated by Clausius–Clapeyron equation, and higher values of integral isosteric sorption heat were verified for storage temperatures. Besides it, both conditions showed higher values of sorption heat corresponding to low water content. This phenomenon was supported by the enthalpy–entropy compensation study, which demonstrated a higher spontaneity of water sorption for storage temperatures, confirming that the lower the water content of food products is, the stronger the intermolecular bonds of water are.     

Mechanical properties and microstructure of apple peels during storage

The apple peel (i.e., outermost tissue) plays a crucial role in protecting and preserving apple life, as well as in reducing fruit injury. Apple peels of the Danxia and Starkrimson varieties were compared for their tensile properties, shear properties, and tensile-property variations after 0, 14, and 28 days of storage at room temperature. Apple peel microstructures were observed and imaged using scanning electron microscopy. Cubic polynomials proved superior for quantifying the stress–strain non-linear relationship of peels. With increased storage period, tensile strength and fracture strain gradually decreased but elastic modulus increased. The mechanical indices of Starkrimson peels were greater than those of Danxia peels after the same storage period. Significant differences between cultivars were observed in terms of tensile strength, elastic modulus, and shear strength; significant storage differences also existed for both cultivars. Mechanical properties were closely related to peel microstructures. Strengths and weaknesses mainly depended on the number and width of microcracks on the cuticle, cuticle form, cell aspect radio, and space between cells.     

澄清型黑蒜饮料的流变特性研究

本文通过采用DV-Ⅲ+型数字流变仪测定了不同温度条件下澄清型黑蒜饮料的流变特性。通过对拟合方程和所得参数的研究发现,在25、35、45℃的温度条件下,黑蒜饮料的流变曲线为一条过原点的直线,对曲线的拟合参数n值接近1,近似为牛顿流体类型;而在55℃和65℃的温度条件下,黑蒜饮料的流变曲线为一条过原点向下凹的曲线,对曲线的拟合参数n值大于1,符合胀塑性流体类型的特征。同时,在不同温度下测定了黑蒜饮料黏度的变化,通过Arrehenius方程η=K0exp（Ea/RT）相关变化进行拟合,可用来预测实际加工过程中澄清型黑蒜饮料温度对黏度的影响,为其加工生产提供理论指导。      

Dielectric Properties of Vegetables and Fruits as a Function of Temperature, Ash, and Moisture Content

ABSTRACT: The dielectric properties of 15 vegetables and fruits were measured at 2450MHz from 5 to 130 °C. Equations were developed as a function of temperature, ash, and either moisture content or water activity, and compared to literature equations. Dielectric constant of vegetables and fruits decreased with temperature and ash content. However, ash was not a factor in the equations produced separately for fruits. Dielectric loss factor changed quadrically with increasing temperature: first decreasing and then increasing. This transition temperature decreased with ash content. Ash increased the dielectric loss factor. Garlic and potato gave unusual results, which could be explained by the behavior of solutions of inulin and potato starch, respectively.     

Moisture sorption isotherms of grape pestil and foamed grape pestil

Moisture sorption isotherms of grape pestil and foamed grape pestil were determined using the static gravimetric method at 10, 20 and 30 degrees C. The overall shape of the curves was typical of sugar-rich materials. The effect of temperature on moisture content in the lower aw range was not significant (P > 0.05). Four models, namely the Brunauer, Emmet and Teller (BET), the Guggenheim, Anderson and DeBoer (GAB) the Halsey and the Oswin, were evaluated to determine the best fit for the experimental data. The BET and GAB models fitted well the data of the samples in the temperature and water activity range studied. The Clausius-Clapeyron equation was used to evaluate the isosteric heats of sorption.     

Effect of Surface Properties on Colloid Retention on Natural and Surrogate Produce Surfaces

Bacterial contamination of fresh produce is a growing concern in food industry. Pathogenic bacteria can attach to and colonize the surfaces of fresh produce and cause disease outbreaks among consumers. Surface properties of both bacteria and produce affect bacterial contamination; however, the effects of produce roughness, topography, and hydrophobicity on bacterial retention are still poorly understood. In this work, we used spherical polystyrene colloids as bacterial surrogates to investigate colloid retention on and removal (by rinsing) from fresh produce surfaces including tomato, orange, apple, lettuce, spinach, and cantaloupe, and from surrogate produce surface Sharklet (a micro‐patterned polymer). All investigated surfaces were characterized in terms of surface roughness and hydrophobicity (including contact angle and water retention area measurements). The results showed that there was no single parameter that dominated colloid retention on fresh produce, yet strong connection was found between colloid retention and water retention and distribution on all the surfaces investigated except apple. Rinsing was generally not efficient in removing colloids from produce surfaces, which suggests the need to modify current cleaning procedures and to develop novel contamination prevention strategies. This work offers a physicochemical approach to a food safety problem and improves understanding of mechanisms leading to produce contamination.