基于非渗透包装的米威化饼干二组分食品间水分扩散特性研究

以二组分食品—米威化饼干为试验对象,在23℃条件下通过水分吸附动力学试验及水分扩散系数理论表征非渗透包装条件下米威化饼干二组分间水分有效扩散系数模型;通过Fick第二定律结合各组分初始条件、边界条件及各组分等温吸湿模型求得各组分间水分扩散的含水率与时间变化的关系,并在含水率介于0.02～0.12时对理论模型进行试验验证分析。结果表明,理论模型与试验数据吻合度高。     

孔隙结构和脂肪含量对饼干水分吸附特性的影响

采用动态水分吸附法研究不同孔隙率和脂肪含量的发酵饼干在25℃下的水分吸附动力学特性,基于GAB模型和无限大平板模型确定其等温吸湿曲线和有效水分扩散系数。结果表明:孔隙率对饼干平衡水分含量几乎没有影响,而随着脂肪含量的增加,饼干的平衡水分含量逐渐下降。GAB模型能成功拟合饼干的等温吸湿数据。饼干的有效水分扩散系数随含水量变化先增大而后逐渐减小,有效水分扩散系数在水分含量为10 g/100 g(干基)左右时达到最大值。初始孔隙率87%、76%和68%的最大有效水分扩散系数分别为7.8×10-10m2/s、5.6×10-10和3.4×10-10m2/s,这与水分扩散机理从以气态传输为主向以液态传输为主的转变有关。增加脂肪含量会显著降低水分扩散系数,有效水分扩散系数从最大值5.6×10-10m2/s下降到2.3×10-10m2/s。     

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。     

冻干海参的吸附等温特性研究

冻干海参由于具有多孔性的特质,在贮藏过程中容易吸湿,从而使自身水分活度升高,引起微生物的生长而变质.对冻干海参的吸附等温特性进行研究,从而为冻干海参的贮藏提供理论和试验依据.通过模拟不同相对湿度的贮藏环境下冻干海参吸湿等温曲线的测定,结合农产品吸附理论的常用模型进行吸附等温曲线的拟合,得出冻干海参的吸湿特性,并找到较为准确的预测模型.     

米威化饼干二组分食品的等温吸湿特性及模型表征

在23,30,45℃条件下对饼皮、馅料的等温吸湿规律进行静态称重法研究,同时对试验数据进行常用等温吸湿模型的Matlab软件拟合,得到3个温度下的等温吸湿曲线。结果表明:饼皮、馅料的等温吸湿曲线均为反S型,在一定的水分活度条件下,随着温度的升高平衡含水率先增加后减少。当水分活度介于0.35～0.90时饼皮和馅料最合适的模型分别是Lewicki模型和Peleg模型,根据多组分食品等温吸湿特性模型理论获得了表征米威化饼干等温吸湿特性的组合模型。     

储藏条件下糙米水分扩散规律研究

为探讨储藏条件下糙米籽粒的水分扩散规律,以环境温度和相对湿度为影响因素,采用全因素组合试验方法设计试验,应用静态称重法对糙米籽粒进行了不同温度和相对湿度条件下的吸附与解吸试验,推导出储藏条件下糙米籽粒的水分扩散系数求解方程,求出不同储藏温湿度以及不同原始含水率条件下糙米籽粒的水分扩散系数,应用SAS软件拟合出关于储藏条件下糙米水分扩散系数的二次回归方程。结果表明:储藏环境温湿度及含水率显著地影响糙米水分扩散规律,研究结果可以为探讨糙米水分分布及传递机理提供理论参考。     

根据Vrentas-Vrentas理论模拟小麦粉的水分吸附滞后：模型参数χ及k表示为Fermi函数的形式

水分吸附及其滞后现象广泛存在并对食品加工及食品品质具有重要影响。采用动态水蒸气吸附分析仪测定了小麦粉在3个温度条件下的吸湿、解吸平衡水分,然后基于Vrentas-Vrentas(VV)理论进行模拟分析。结果显示,小麦粉的水分吸附滞后程度随温度升高而减小,吸湿与解吸曲线在高水分区域重合,据此提出一个确定玻璃化转变水分的方法。不论吸湿还是解吸,其Flory-Huggins相互作用系数χ皆随水分体积分数而变化,本实验提出采用Peleg改进的Fermi函数表示这种关系。在根据吸湿的χ参数模拟解吸时,VV模型中的参数k随体积分数变化可以表示为Fermi函数的形式。     

魔芋葡甘聚糖及其衍生物保湿性能研究

考察魔芋葡甘聚糖(KGM)及其衍生物魔芋超强吸水剂(KSAP)的吸湿、保湿性能,并与甘油、丙二醇进行对比。测定KGM 和KSAP 的水分吸附等温线,采用回归分析建立数学模型。结果表明：KSAP 的吸湿、保湿性能优于甘油和丙二醇。水分吸附等温线属于第Ⅲ型,在给定的水分含量下,KSAP 的水分活度最低,保湿性能最好。Peleg 模型拟合效果最好,BET 模型和GAB 模型拟合显示KSAP 的单分子层水分含量最高,分别为14.59%和15.42%。     

用Weibull函数分析单粒莲子热风干燥的水分扩散系数和活化能

为了研究单粒莲子在不同温度(50、60、70、80、90℃)条件下热风干燥的干燥特性、水分扩散系数及活化能,利用Weibull函数及经验模型对单粒莲子干燥过程进行模拟分析。结果表明:Weibull函数和Midilli模型可以很好地拟合单粒莲子的热风干燥过程;尺度参数α随干燥温度的升高而减小(p0.05);干燥温度对形状参数β的影响较大(p0.05);计算得到干燥过程中估算的水分扩散系数为(8.79×10~(-9)~2.45×10~(-8))m~2/s,水分有效扩散系数为(4.73×10~(-10)~1.31×10~(-9))m~2/s,活化能为22.61 kJ/mol,水分扩散系数随温度的升高而增大。该研究为Weibull分布函数应用于莲子干燥提供参考。     

中短波红外线对冬枣粉杀菌效果及品质的影响

研究了不同条件中短波红外线处理对冬枣粉菌落总数、霉菌酵母的杀菌效果,对水分、色泽的影响,并应用Weibull模型对不同处理条件下冬枣粉的杀菌效果进行拟合。结果表明:随着温度的升高和时间的延长,杀菌效果增强,水分含量降低,色差值变大;110℃处理5 min和120℃处理1 min时可全部杀死霉菌和酵母。Weibull模型动力学曲线的决定系数R~2均大于0.98,χ~2、RMSE的值分别小于0.020 0和0.070 0,拟合效果较好。中短波红外线对冬枣粉杀菌处理的最佳工艺条件为120℃、1 min。     

MOISTURE DIFFUSIVITY DATA COMPILATION FOR FOODSTUFFS: EFFECT OF MATERIAL MOISTURE CONTENT AND TEMPERATURE

There is a wide variation of the reported experimental data of moisture diffusivity of solid food materials, making difficult their utilization in drying and other applications. Published values of moisture diffusivity in various foods were retrieved from the literature, and these were classified and analyzed statistically to reveal the influence of material moisture content and temperature. Empirical models, relating moisture diffusivity to material moisture content and temperature, were fitted to all examined data for each material. The data were screened carefully using residual analysis techniques. The most promising model was proposed, which is based on an Arrhenius-type effect of temperature and it uses a parallel structural model to take into account the effect of material moisture content.     

Moisture Migration in Solid Food Matrices

ABSTRACT: The goals of this study were to measure moisture migration in a porous solid matrix simulating a real food (flour dough) and to accomplish heating of the solid matrix. An off-line technique and a microwave temperature controller system were developed for measuring moisture concentration under isothermal heating condition. A temperature profile of a cylindrical dough sample was achieved by accurate control of microwave energy input and preheated carrier gas temperature. Results showed a simplified 1st order kinetic model adequately predicted moisture loss in dough samples. Effect of temperature on the rate constant was adequately modeled by the Arrhenius relationship. The rate constant was found to be affected by porosity of the dough sample.     

THERMAL DIFFUSIVITY MEASUREMENTS of WHEAT FLOUR and WHEAT FLOUR DOUGH

A simple technique was used to measure thermal diffusivity of whole wheat flour and whole wheat flour dough at various levels of moisture and temperatures. the experimental values showed good agreement with the calculated values. It was found that thermal diffusivity of dough increases with moisture and temperature below 60C, but above 60C its value decreases. This is attributed to physico-chemical changes, e.g., starch gelerinization and protein coagulation. Due to these changes swelling and softening of dough occur, which reduce the ability of dough to diffuse thermal energy, thus lowering the value of the thermal diffusivity. Based on the experimental value of wheat dough at various moisture levels and temperatures, the following equation is proposed: α= (7.957 − 0.6346 M + 0.217 T + 0.008 M²− 0.00176 T²− 0.00051 M × T) × 10-7     

Modeling rehydration of porous food materials: II. The dual porosity approach

Following the foundation for physical modeling of rehydration (Troygot et al., 2011), the Richards equation together with the independently evaluated characteristic curve yielded a close approximation for the early stage (1000 s) of rehydration data. It was revealed that the porosity of wheat groats (WG) and freeze-dried carrots consists of inter- and intra-particles porosities playing a distinct role on the rehydration kinetics. A dual porosity mobile-immobile model was suggested for modeling water flow by capillarity in the inter porosity and by water-content difference (diffusion-type) in the intra porosity. The model fits the overall rehydration process well. A double Weibull distribution model predicted also well the experimental rehydration data for freeze-dried carrots verified the above, demonstrating the roles for both diffusion and relaxation in a dual-porosity structure. The physically-based model combined with the characteristic curve, hydraulic conductivity function, and a transfer coefficient for rate-limited exchange between inter- and intra-particles porosities was adequate for modeling the rehydration process of porous food.     

MATHEMATICAL MODELING OF HEAT AND MOISTURE TRANSFER-RELATED PROPERTIES OF INTERMEDIATE MOISTURE APPLIES

Mathematical models for heat and moisture transfer-related properties of intermediate moisture apples were developed. The models of thermal properties were based on a linear dependence of thermal conductivity on temperature and moisture content, a logarithmic dependence of bulk density on moisture content, and a linear dependence of specific heat on moisture content. The effect of moisture content and temperature on moisture diffusivity was modeled by an exponential relationship. The sorption data were adequately fitted by the Modified Henderson's equation.     

Specific Heat, Thermal Conductivity, Density, and Thermal Diffusivity of Mexican Tortillas Dough

A split-split unit experiment was conducted and analyzed to determine the specific heat, thermal conductivity, density, and thermal diffusivity of Mexican corn-based tortillas dough (MCTD) as a function of processing time, temperature, and moisture content (wb). The data indicated that thermal conductivity and thermal diffusivity were significantly influenced by processing time, and respective components of temperature and moisture content. Specific heat and density varied with levels of moisture content and temperature. Thermal conductivity, specific heat, density, and thermal diffusivity could each be predicted separately by a polynomial equation.     

Glass transition and state diagram for freeze-dried Agaricus bisporus

Sorption isotherms and state diagram of freeze-dried Agaricus bisporus were developed to further investigate the connection between the two distinct criteria of food stability. Sorption isotherms of freeze-dried A. bisporus were determined by the gravimetric method and the data were modeled by GAB model. The GAB monolayer moisture content was calculated to be 6.2 g/100 g (d.b.). The glass transition temperature of freeze-dried A. bisporus was determined by differential scanning calorimetry. The state diagram was composed of the freezing curve and glass transition line, which were fitted according to Clausius–Clapeyron model and Gordon–Taylor model, respectively. The state diagram yielded maximally-freeze-concentrated solutes at 0.704 solids with the characteristic temperature of glass formation being −77.9 °C. The state diagram and sorption isotherms of freeze-dried A. bisporus are useful in evaluating the storage stability as a function of temperature and moisture content as well as optimizing drying and freezing conditions.     

Moisture Diffusivity Coefficient and Convective Drying Modelling of Murta (Ugni molinae Turcz): Influence of Temperature and Vacuum on Drying Kinetics

In this study, murta (Ugni molinae Turcz) or murtilla berries were dried in single layer at air temperatures of 50, 60 and 70 °C under vacuum and atmospheric pressure conditions. The effect of drying air temperature and vacuum on the basic dehydration characteristics of murta was determined. For the kinetic modelling, ten mathematical expressions were fitted to the experimental data. Kinetic parameters and diffusion coefficients as evaluated by an Arrhenius-type equation, showed temperature dependency. Fick’s second law was used to calculate the effective moisture diffusivity that varied from 3.10 to 11.27?×?10^?10 m²/s and from 5.50 to 11.30?×?10^?10 m²/s with activation energy values of 59.27 and 34.30 kJ/mol for atmospheric pressure and vacuum drying, respectively. According to the statistical tests applied, the Midilli–Ku?uk model obtained the best-fit quality on experimental data, followed closely by the Weibull distribution model, the Page and the modified Page models.     

低温低湿条件下海鳗冷风干燥动力学特性

利用两级除湿热泵干燥装置模拟低温、低湿环境,研究海鳗干燥动力学特性。研究结果表明,海鳗低温、低湿冷风干燥时无恒速干燥阶段,而是一开始就进入降速干燥。在整个降速干燥过程中存在2个阶段,即第一降速干燥阶段和第二降速干燥阶段。分析了两阶段中水分扩散特性。采用非线性回归分析比较不同的干燥模型,在试验条件下Page模型拟合较优,并求得模型表达式。通过菲克第二扩散定律和Arrhenius方程求得实验条件下的有效水分扩散系数及扩散活化能分别为(2.6197～4.0224)×10-10m2/和15.23kJ/mol。     

Application of effective diffusivity approach for the moisture content prediction of tortilla chips during baking

Fick's law of diffusion and an empirical model were used to describe moisture transport in tortilla chips during baking. An empirical model based on regression of moisture content in terms of baking time and temperature slightly over predicted the moisture content of samples. There was a good agreement (R²=0.93) between experimental results and predicted values with the empirical model. The model based on effective diffusivity approach also predicted the moisture content fairly good. Both liquid and vapor diffusion was effective in the transport of vapor. Liquid diffusion and vapor diffusion were dominant in the beginning and toward to end of baking, respectively. The average moisture diffusivity of samples was calculated using a nonlinear regression of moisture content data during baking. The range for the average effective diffusivity was 6.25×10⁻¹⁰-10.98×10⁻¹⁰ m²/s and the diffusivity coefficient increased with increasing temperature. There was an Arrhenius type relationship between effective diffusivity coefficient and baking temperature.