Equilibrium moisture content and heat of desorption of saffron

The equilibrium moisture contents of saffron (Crocus sativus L.) stigmas were determined experimentally using the standard gravimetric method at temperatures 30, 45 and 60 °C and water activity ranging from 11% to 83%. The sorption isotherm curves of saffron were sigmoidal in shape and decreased with increased temperature at constant relative humidity. Five selected isotherm models GAB, modified Henderson, modified Chung‐Pfost, modified Halsaey and modified Oswin were tested to fit the experimental isotherm data. Modified Oswin and modified Henderson models were found acceptable for predicting desorption moisture isotherms and fitting to the experimental data, respectively. The isosteric heats of desorption, determined from equilibrium data using the Clausius‐Clapeyron equation, were found to be a function of moisture content. The net isosteric heat of desorption of saffron varied between 1.38 and 5.38 kJ mol^?1 at moisture content varying between 2% and 20% (d.b).     

半干型荔枝干玻璃化转变研究

目的：确定冷冻干燥荔枝干的吸湿等温线,研究半干型荔枝干的玻璃化转变温度。方法：采用差示扫描量热法(DSC)。结果：半干型荔枝干的吸湿等温线与GAB 模型拟合程度好,呈现出“J”形。半干型荔枝干的玻璃化转变温度为－ 77.35℃,经过退火处理后,玻璃化转变温度提高约10℃,基本消除反玻璃化峰。经冷冻干燥处理后的半干型荔枝干的玻璃化转变温度比半干型荔枝干产品的高约7℃。     

Diffusivity,shrinkage and simulated drying of litchi fruit (Litchi Chinensis Sonn.)

Litchi (Litchi Chinensis Sonn.) is an important commercial fruit in Thailand and Vietnam. Litchi fruit is consumed both as fresh and dried products. Also most of the export of litchi is in the form of dried whole litchi fruit. Thermo-physical properties and drying model of litchi fruit is important for optimum design of litchi dryer. This paper presents moisture diffusivity, shrinkage and finite element simulated drying of litchi fruit. The moisture diffusivities of litchi were determined by minimizing the sum of square of deviations between the predicted and experimental values of moisture content of thin layer drying under controlled conditions of air temperature and relative humidity. The components in the form of cylinder for seed and seed stalk and slab for seed coat, shell and flesh were dried in thin layers at the air temperatures of 50, 60, 70 and 80 °C and relative humidity in the range of 10–25%. The mean diffusivity of flesh, seed and shell of litchi fruit increased with temperature and was expressed by the Arrhenius-type equation, but the diffusivities of seed coat and seed stalk were independent of temperature. The moisture diffusivities of seed coat and seed stalk were much lower than those of the other parts of the litchi. The shrinkage of litchi fruit has also been determined experimentally and it was expressed as a function of moisture reduction. A two-dimensional finite element model has been developed to simulate moisture diffusion in litchi fruit during drying. Shrinkage of the flesh and different component diffusivities of litchi during drying were also taken into account. The finite element model was programmed in Compaq Visual FORTRAN version 6.5. This finite element model satisfactorily predicts the moisture diffusion during drying. Moisture contents in the different components in the litchi fruit during drying were also simulated. This study provides an understanding of the transport processes in the different components of the litchi fruit.     

Water sorption isotherms of fresh and partially osmotic dehydrated pumpkin parenchyma and seeds at several temperatures

Experiments were conducted to determine the equilibrium moisture content of pumpkin (cv Cucurbita Pepo L.) at different temperatures (278.1 K, 298.1 K and 318.1 K) and relative humidities (8–91%). Fresh and partially osmotically dehydrated (using sucrose solutions) samples of pumpkin parenchyma were employed. The desorption isotherm of pumpkin seeds at 298.1 K was determined as well and was found to be similar to other sorption isotherms of other seeds with similar fat and protein compositions. No significant dependence of the equilibrium experimental data on the temperature or osmotic pre-treatment was found. Several common mathematical models were used to fit the experimental data. For the parenchyma tissue, statistical analysis proved that those of Halsey, Oswin, Chirife and GAB were the best, while for the seeds, the Henderson, GAB and Peleg models are preferable.     

拓扑指数与荔枝挥发性成分保留指数的定量相关性研究

为探明挥发性成分对荔枝汁品质的影响,探讨荔枝的营养保健功能,以分子形状指数和电拓扑状态指数有效表征40 个妃子笑荔枝挥发性化合物的分子结构,建立能估算和预测荔枝挥发性成分保留指数的定量结构- 保留相关性模型,经多元线性回归分析筛选变量,建立的模型相关系数r 达到0.978,平均相对误差4.37%,估算值与实验值基本吻合。结果表明,分子形状指数和电性拓扑状态指数与保留指数之间有良好的线性关系。为检验模型的稳定性和预测能力,用Jackknifed 法检验的相关系数均在0.977 以上。     

Moisture adsorption isotherms of guar (Cyamposis tetragonoloba) grain and guar gum splits

Moisture adsorption isotherms of guar grain and guar gum splits were determined at 10, 20, 30 and 40 °C and 23-96% relative humidities using gravimetric method. The sorption data were fitted to six well-known sorption isotherm models (modified Chung-Pfost, modified Halsey, modified Henderson, modified Oswin, Chen-Clayton, and GAB models) using non-linear least square method. The GAB model was found the most satisfactory for representation of the equilibrium moisture content data for guar grain and guar gum splits. The equilibrium moisture content of guar gum splits was found to be significantly higher (p < 0.05) than that of guar grain. The isosteric heat of sorption was determined from the equilibrium moisture adsorption data using Clausius-Clapeyron type equation. Exponential relationship described well the dependence of isosteric heat of sorption on the equilibrium moisture content. The enthalpy-entropy compensation theory applied to sorption isotherms indicated enthalpy controlled sorption process.     

MOISTURE ADSORPTION ISOTHERMS AND ISOSTERIC ENERGY FOR ALMOND

The equilibrium moisture contents of almond were determined using the gravimetric‐static method at 15, 30, 55 and 75C for powder and 15, 55 and 75C for nut state of almond for water activity (a_w) ranging from 0.11 to 0.87. At a given a_w, 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 equations. The GAB model was found to be the most suitable for describing the sorption curves; the monolayer‐content values for the sorption at different temperatures are calculated. Also, the isosteric heats of adsorption of water were determined as a function of moisture content from the equilibrium data at different temperatures using the Clasius‐Clapeyron equation.     

Moisture sorption isotherms and thermodynamic properties of apple Fuji and garlic

The moisture equilibrium isotherms of garlic and apple were determined at 50, 60 and 70 °C using the gravimetric static method. The experimental data were analysed using GAB, BET, Henderson–Thompson and Oswin equations. The isosteric heat and the differential entropy of desorption were determined by applying Clausius–Clapeyron and Gibbs–Helmholtz equations, respectively. The GAB equation showed the best fitting to the experimental data (R² > 99% and E% < 10%). The monolayer moisture content values for apple were higher than those for garlic at the studied temperatures; the values varied from 0.050 to 0.056 and from 0.107 to 0.168 for garlic and apple, respectively. The isosteric heat and the differential entropy of desorption were estimated in function of the moisture content. The values of these thermodynamic properties were higher for apple (in range 48–100 kJ mol^?1 and 14–150 J mol^?1 K^?1) than for garlic (in range 43–68 kJ mol^?1 and 0–66 J mol^?1 K^?1). The water surface area values decreased with increasing temperature. The Kelvin and the Halsey equations were used to calculate the pore size distribution.     

茶多酚改性对聚乙烯醇膜吸湿特性及抗氧化活性的影响

研究含不同质量分数茶多酚的聚乙烯醇膜的吸湿特性和抗氧化活性。通过等温吸湿实验研究了含不同质量分数茶多酚（0%、0.5%、1%、1.5%、2%）的聚乙烯醇膜的吸湿特性,并基于常用的等温吸湿模型对实验数据进行拟合表征;通过1,1-二苯基-2-三硝基苯肼（1,1-diphenyl-2-picrylhydrazyl,DPPH）自由基清除实验分析了薄膜的抗氧化活性。结果表明：含不同质量分数茶多酚的聚乙烯醇膜均具有吸湿性,其等温吸湿曲线整体变化趋势相似,属于Ⅱ型等温吸湿曲线;薄膜的平衡含水率随水分活度的增加而显著增加（P＜0.01）,当水分活度大于0.6时,其平衡含水率增加幅度增大;茶多酚对聚乙烯醇膜的改性增加了其疏水性,在相同水分活度条件下,薄膜的吸湿性能随薄膜中茶多酚质量分数的增加而下降,但5 种聚乙烯醇膜之间差异不显著（P＞0.05）;GAB等温吸湿模型对薄膜吸湿性能的拟合效果最好,R2≥0.996;茶多酚对聚乙烯醇膜的改性使其具有抗氧化活性,DPPH自由基清除率随着薄膜中茶多酚质量分数的增加而显著提高（P＜0.01）,表明经茶多酚改性后的聚乙烯醇膜的抗氧化性能随薄膜中茶多酚质量分数的增加而增强。经茶多酚改性的聚乙烯醇膜具有吸湿和抗氧化功能,预示其作为塑料复合薄膜内层或中间层应用于湿度敏感型、含高脂肪等干燥易氧化食品包装具有较好的前景。     

SORPTION ISOTHERM BEHAVIOR OF OSMOCONVECTIVELY DEHYDRATED CARROT CUBES

Carrot cubes, osmotically pretreated with aqueous sodium chloride (10%, w/v), sucrose syrup (55°Brix), and mixture of sucrose and sodium chloride (50°Brix + 10%, w/v), were convectively dehydrated at 65C temperature up to final moisture content of 4–5% (wet basis). To study their equilibrium moisture content (EMC) behavior, the dehydrated carrot cubes were stored at temperature ranging from 10 to 50C and relative humidity ranging from 15–95% using static desiccator technique. Five isotherm equations, viz, Chung–Pfost, modified Henderson, modified Halsey, modified Oswin and modified exponential were applied to examine the data. Among the applied models, modified Oswin model was best fit for control (untreated) and salt‐treated samples, modified Hesley model for sucrose‐treated samples and two‐term exponential model for mixture of sucrose–salt treatment over the entire range of relative humidity and temperature. The EMC values of cubes osmotically pretreated with sodium chloride solution were highest among all pretreatments, and were lowest for control (unosmosed) samples.     

Water Adsorption and Glass Transition of Spray-Dried Soy Sauce Powders Using Maltodextrins as Carrier

Moisture adsorption isotherm and glass transition temperature of various spray-dried soy sauce powders containing different types and concentrations of maltodextrins were studied and compared. Maltodextrins of dextrose equivalent (DE)?=?5, DE?=?10 and DE?=?15, respectively, with concentrations of 20 or 40 % (w/v) were used as carrier agents. The equilibrium moisture content was reduced with increased maltodextrin concentration, whereas it was not apparently influenced by the value of maltodextrin DE. Both the Brunauer–Emmett–Teller (BET) and Guggenheim–Anderson–de Boer (GAB) models could be applied to simulate the moisture adsorption behaviour of the soy sauce powders. The monolayer moisture content of the powders was determined by fitting experimental data to the BET/GAB models with a _w up to 0.53, although both models could fit satisfactorily with the experimental data to a higher water activity level_. The glass transition temperatures (T _g) of the powders equilibrated under various water activities were determined using a differential scanning calorimeter. Increasing moisture adsorption of the soy sauce powders resulted in a T _g reduction, and the experimental T _g values fitted the Gordon–Taylor model well. The BET and Gordon–Taylor models were applied together to predict the critical moisture contents (i.e. 0.0464–0.0777 g water/g dry matter) and water activities (i.e. 0.032–0.241), above which the soy sauce powders become vulnerable to degradation and changes in their physicochemical properties.     

Moisture sorption isotherms of sorghum malt at 40 and 50 °C

The desorption and adsorption equilibrium moisture isotherms of sorghum malt at the temperatures of 40 and 50 °C, over the water activity range of 0.1-0.9, were determined using the static gravimetric method. A non-linear regression programme was used to fit five moisture sorption isotherm models [Modified Henderson, Modified Chung-Pfost, Modified Guggenheim-Anderson-de Boer (GAB), Modified Halsey and Modified Oswin] to the experimental data. The models were compared using the standard error of estimate, mean relative percentage deviation, fraction explained variation and residual plots.The Modified Chung-Pfost model was found to be the best for predicting the desorption equilibrium moisture content, while the adsorption equilibrium moisture content was best predicted by the Modified Oswin model. The desorption and adsorption water activities were found to be best fitted by the Modified Oswin model.The moisture sorption isotherms were sigmoidal in shape and showed a marked effect of temperature. The span of the moisture sorption hysteresis loop formed, decreased with increase in temperature, while the size increased with increase in temperature.     

非渗透包装下双组分食品间水分扩散模型研究

采用Fick第二定律,结合食品等温吸湿模型和水分有效扩散理论,建立了非渗透包装下双组分食品间水分扩散模型;以饼干和琼脂凝胶包装为研究对象,基于实验表征等温吸湿模型和有效扩散系数,得到研究对象间水分扩散数值解并与实验结果进行对比分析。结果表明,理论模型与实验数据的吻合度高。     

包装对半干型荔枝干贮藏品质的影响

为了抑制半干型荔枝干在贮藏过程中果肉褐变、微生物生长,本试验研究了半干型荔枝干水分含量分布及其水分活度情况,探讨了不同包装技术,不同包装材料对半干型荔枝干贮藏效果的影响。结果表明:试验用荔枝干果肉平均含水量为36.51%,平均Aw>0.73。脱氧包装技术对延缓半干型荔枝干果肉褐变效果显著,并表现出良好的抑菌效果,保鲜剂与脱氧剂对荔枝干褐变的抑制具有协同作用,包装材料的遮光性对果肉褐变的影响不明显;普通包装方式下,荔枝干果肉褐变快,不同包装材料间荔枝干的贮藏效果相差不大,因此采用普通包装时,包装材料的选择以经济、美观为标准即可。     

固定床热风干燥模式对荔枝干制特性的影响

采用固定物料位置固定热端(模式I)、变换物料位置固定热端(模式II)和固定物料位置变换热端(模式III)三种模式对荔枝果实进行固定床热风多阶段干燥,分别测定了不同物料层(A、B和C三层)物料的热风风速、温度、水分含量、干燥速率、有效扩散系数(Deff)和体积收缩率。结果表明,不同的干燥层物料的热风和温度分布不均匀。经过四阶段共26 h干燥,模式I、II和III中整体样品的水分含量分别为45.70%、42.07%和41.18%。模式I中A层物料的终水分含量为28.44%,显著低于B层和C层样品(p<0.05),Deff为1.48×10-6m2/s,显著大于B层和C层物料(p<0.05)。模式II各层间物料终水分含量和Deff差异不显著(p>0.05),干燥较均匀。模式III中A层物料的终湿基含水量和Deff与B、C层的物料的相比差异不显著(p>0.05),干燥较均匀,可实现简约操作和规模加工。     

SIMULATION OF THE EVAPORATIVE COOLING PROCESS FOR TORTILLAS

A simulation model was developed to predict temperature, moisture content and water activity of evaporatively cooled tortillas. The overall model was based on three parts: (1) the predicted equilibrium moisture isotherm for the product, (2) a correlation model for predicting the saturated water vapor pressure for a given temperature, and (3) the energy and mass balances for simultaneous convective heat and moisture transfer between product and cooling air. The simulation model was verified with experimental data and was found to accurately describe the behavior of the tortilla cooling system. The model predicted the simultaneous decrease in temperature, moisture content, and water activity of the product exposed to varying simulated processing conditions. It was found that cooling air velocity and temperature had the primary effect on product cooling and moisture loss rates.     

Effect of osmotic pretreatment on equilibrium moisture content of dehydrated carrot cubes

The equilibrium moisture contents were determined for carrot cubes osmotically pretreated in salt, sucrose and salt plus sucrose combined solution using static method at 10, 25, 40 and 50 °C over a range of relative humidities from 14% to 95%. Six isotherm equations were applied for analysing the experimental data. Modified exponential equation, is the best equation for predicting the equilibrium moisture contents (EMC) of the dehydrated carrot cubes preosmosed in salt and sucrose plus salt solution, whereas modified Hasley equation is suitable for dehydrated carrot cubes preosmosed in sucrose solution over the relative humidity range of 14–95%. The EMC of carrot cubes osmotically pretreated with salt was highest among all pretreatments, and was lowest for un‐osmosed samples.     

不同品种荔枝果肉细胞抗氧化及抗增殖活性评价

为明确荔枝果肉的生物抗氧化和抗肿瘤保健功能,采用HepG2人肝癌细胞模型对我国南方地区主要种植的10种代表性荔枝品种果肉的细胞抗氧化活性(CAA值)和抗肿瘤细胞增殖活性进行了评价。结果表明,10种荔枝品种中,妃子笑荔枝果肉具有最大的CAA值,淮枝则最小;妃子笑抗HepG2肿瘤细胞增殖活性最强,糯米糍则最弱。荔枝果肉的CAA值与总多酚含量、总黄酮含量、多酚化学抗氧化能力指数(ORAC值)之间都有极显著的正相关性(p0.01),且与黄酮含量之间正相关性最大,说明荔枝果肉中起生物抗氧化作用的主要成分是黄酮类化合物;但荔枝果肉对HepG2肿瘤细胞的抗增殖活性与总多酚含量、总黄酮含量、ORAC和CAA值之间均呈现较弱的负相关性(p0.05),提示某些特殊酚类单体或其协同作用在抗肿瘤细胞增殖过程中发挥主要作用。     

Nano Zinc Oxide-Loaded Calcium Alginate Films with Potential Antibacterial Properties

In this work, zinc oxide nanoparticles-loaded calcium alginate films were investigated for their moisture uptake behavior at different temperatures. The equilibrium uptake data was interpreted quantitatively by GAB isotherm models. The monolayer moisture contents were 0.301 ± 0.003, 0.0214 ± 0.092, and 0.171 ± 0.102 at 20, 30, and 37°C, respectively. The water vapor transmission rate was found to be 0.816 ± 0.143, 1.42 ± 0.045, and 1.632 ± 0.064 g s⁻¹ m⁻² respectively. For the moisture content range of 0.2 to 0.6, the net ∆H and ∆S values were found to be 22.73 to 11.14 KJ/mol and 0.064 to 0.034 KJ/mol/K, respectively. The moisture uptake of films increased with water activity but showed negative temperature dependence. The enthalpy of sorption (∆H) and differential entropy (∆S) were determined at different moisture content values, ranging from 0.2 to 0.6 g/g db. The two parameters showed a higher degree of correlation. The equilibrium moisture content data was used to evaluate harmonic mean temperature T _hm. Finally, the biocidal action of films was tested against model bacteria Escherichia coli.