荔枝肉干燥过程平衡含水率模型研究

采用静态法分别测定了荔枝肉在25、40、55℃和10%～85%相对湿度范围内的吸湿和解吸平衡含水率,分析温度和相对湿度对荔枝肉平衡含水率的影响。以相关系数和标准误差作为评价指标,对Chang-Pfost、Halsey和Oswin3个数学模型和平衡含水率曲线进行了拟合研究,比较了不同的平衡含水率模型对实验数据的拟合精度,发现Oswin修正模型较适合于描述荔枝肉的平衡含水率曲线,分别给出了荔枝肉解吸和吸湿平衡含水率的Oswin方程式。     

芹菜平衡含水率的实验研究

在芹菜的加工和贮藏过程中,等温线是其重要性质之一。取相对湿度10%～90%范围,测定20℃、30℃和40℃条件下芹菜的等温解吸和吸湿平衡含水率,绘出等温平衡曲线,对4个模型和平衡含水率曲线进行拟合研究,结果表明,Modified-Hendenson模型对芹菜平衡含水率的拟合效果最好。     

烟叶在高温湿度环境中平衡含水率的数学模型

为研究加工过程烟叶的吸湿过程,采用动态法测定了在60,70和80℃3个温度点下,30%～90%范围内7个相对湿度点的烟叶增湿特性曲线,再根据增湿特性曲线得到烟叶的平衡含水率,并用GAB模型对平衡含水率曲线进行拟合。结果表明:GAB模型可以较好描述烟叶在高温湿度环境中的平衡含水率并确定了模型参数,预测值与实验值比较吻合,相关系数r2=0.980。     

湖南黑毛茶等温吸湿模型建立及霉变安全性研究

为了探讨黑毛茶的陈化及成品茶的安全贮存特性,本研究通过静态称质量法测定了湖南黑毛茶在20、30、 40 ℃,水分活度为0.010 3～0.981 8条件下的吸湿特性,建立不同温度下黑毛茶的吸湿曲面响应模型及等温吸湿曲 线;对等温吸湿曲线进行了非线性回归拟合,并在温度25 ℃和相对湿度85%、87%、90%的条件下进行模拟仓储。 结果显示：湖南黑毛茶等温吸湿曲线为Ⅱ类曲线,不同温度（20、30、40 ℃）条件下,黑毛茶吸湿平衡时间随着 温度的升高而缩短,分别为14、10、6 d,并随着温度的升高而呈现平衡含水率降低的规律;3 个温度条件下黑毛茶 的曲面响应模型呈现一定的规律特性,GAB及Osiwin模型较优地拟合了黑毛茶的等温吸湿曲线,特定条件下模拟仓 储10 d,相对湿度85%的条件下未见生霉现象,相对湿度87%的条件下出现局部霉变,相对湿度90%的条件下霉变 严重。     

DDGS中水溶性成分比例与吸湿平衡的关系及其模型拟合

可再生的燃料酒精产量剧增导致其主要副产品(干酒糟/DDG和含可溶物的干酒糟/DDGS)产量迅速增加。但对其吸湿解吸平衡的研究报道非常少。吸湿解吸平衡与其持水力和加工与贮存性能密切相关。采用静态平衡重量法,利用饱和盐溶液制备了11个相对湿度环境(11.3%~97.3%,对应的水活度(wateractivity,Aw)为0.113~0.973),研究比较了市场上4种不同DDGS在常压下25℃时的吸湿平衡,比较了9个模型的拟合效果,并将水溶性成份比例(water soluble part,WSP)作为变量纳入模型。平衡含水率随WSP含量的增加而上升,随湿度的增加其平衡含水率的差异迅速扩大。BY、GDW、GAB、Oswin和Lewicki模型较好地模拟了单一DDGS的吸湿平衡结果,而引入WSP变量后改进BY模型(mBY)具有最好的拟合精度(R2=0.9983,平均相对偏差P=4.29%)。其次为改进的Peleg、GDW、GAB、Oswin和Lewicki。Henderson、Halsey和Chung-Pfost模型及其改进型拟合程度不佳。WSP含量与中性洗涤纤维含量线性负相关。由GAB估计的单层水随WSP线性增加。     

贮藏温湿度对糙米平衡含水率的影响

为解决糙米贮藏过程中含水率随贮藏温湿度变化的问题,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平衡含水率试验,分析了温度、相对湿度对糙米平衡含水率的影响规律.利用SAS软件处理试验结果,拟合了Henderson等5种经典模型的参数并评价了拟合效果,确定了最佳拟合模型及其优化参数.结果表明,修正GAB模型及其优化参数组合最适合描述糙米籽粒的吸附和解吸平衡含水率,其相关系数分别为0.998 3和0.9977.     

马铃薯全粉平衡水分吸附等温线与吸附等热研究

采用静态称重法在温度10～35℃、相对湿度11%～96%范围内测定了五种马铃薯全粉的平衡水分/平衡相对湿度(EMC/ERH)数据,确定了多项式方程、修正3参数Guggenheim-Anderson-de Boer(MGAB)、修正Halsey(MHAE)、修正Oswin(MOE)为适合的等温线拟合方程,采用多项式EMC方程分析马铃薯全粉的安全储运最大允许的含水率,在25℃、RH60%条件下,绝对安全水分是10.05%;在25℃、RH 70%条件,相对安全水分是12.64%。采用MHAE分析马铃薯全粉水分吸附等热,随着含水率增加到17.5%,马铃薯全粉水分吸附等热则以抛物线形式快速地减少,之后随着含水率增加,水分吸附等热则减少缓慢。在含水率22%,马铃薯全粉水分吸附等热接近纯水的吸附等热。     

颗粒饲料平衡含水率的试验研究

颗粒饲料的解吸和吸湿平衡含水率是研究颗粒饲料冷却干燥机理、冷却器设计、安全贮藏的重要参数。应用静态法测定了颗粒饲料在不同温度及相对湿度下的解吸和吸湿平衡含水率。分析了温度、相对湿度对颗粒饲料平衡含水率的影响，并对试验结果进行了回归分析，得出了描述颗粒饲料解吸和吸湿平衡含水率数学模型。     

甘蓝型油菜籽的吸湿特性及其数学模型

油菜籽的吸湿特性影响油菜籽的收储工艺和储藏品质,为了给甘蓝型油菜籽收储工艺和管理提供基础依据,本文实验研究了甘蓝型油菜籽在温度为0~30℃,相对湿度为32%~88%的条件下的吸湿特性,比较了7种数学模型在甘蓝型油菜籽吸湿过程的适用性。结果表明:甘蓝型油菜籽的吸湿性受温度和相对湿度的影响很大,温度越高,达到吸湿平衡所需要的时间越短,相对湿度越大,平衡含水率值越大,达到吸湿平衡的时间越长;Peleg模型的相关系数为0.999,卡方为0.154和均方根误差为0.160,是描述油菜籽吸湿特性的最佳数学模型;随着温度的升高,甘蓝型油菜籽的临界相对湿度增大,降低储藏温度,可以有效降低油菜籽的的临界相对湿度;随着平衡含水率的增加,甘蓝型油菜籽的净等量吸湿热指数递减。     

罗非鱼鱼肉的解吸平衡规律研究

罗非鱼鱼肉的解吸平衡含水率不但决定给定干燥条件下所能达到的最低水分,且直接影响干燥速度,本文采用静态称重法研究了罗非鱼鱼肉在不同温度(40℃～60℃)和不同相对湿度(11.0～84.0%)条件下的解吸平衡含水率的变化规律,比较了罗非鱼背部和腹部肌肉在恒温60℃和不同湿度下的解吸平衡含水率的差异,分析了温、湿度对鱼肉的平衡含水率的影响,并对试验测定的结果进行了回归分析,得出Chung-Pfost模型最适宜描述罗非鱼鱼肉的平衡含水率变化。     

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).     

Adsorption isotherms for red chilli (Capsicum annum L.)

The adsorption equilibrium moisture contents for red chilli were determined experimentally in relative humidity range of 11–97% at the temperatures of 20, 30, 40, and 50°C. Six equilibrium moisture content models were fitted to the experimental data. The modified Oswin model was the best fitted equation for relative humidity range of 11–97% for the adsorption data of red chilli.     

Moisture desorption isotherms of medium-grain rough rice

Moisture desorption isotherms (EMC/ERH) of medium-grain rough rice (Japonica variety) were determined using a constant environment chamber for various combinations of air temperature (11.8-51.0 degrees C) and relative humidity (37.1-89.7%). The initial moisture contents were in the range of 24.7-41.6% dry basis. A thin-layer technique was used to achieve uniform drying. Each test was continued until the moisture content change in 24h was less than 0.1% dry basis. The final moisture content was considered as the dynamic equilibrium moisture content. Four three-parameter EMC/ERH equations, the modified Henderson, modified Chung-Pfost, modified Oswin and modified Halsey equations, were compared for their ability to fit the experimental EMC/ERH data. The residual sum of squares (RSS) and standard error of estimate (SEE) were adopted as the criteria to evaluate the fitting performance of the models. The modified Chung-Pfost equation was identified as the most appropriate equation for representing the EMC/ERH desorption isotherms of rough rice. Coefficients for equilibrium moisture content as a function of equilibrium relative humidity and temperature are given. The EMC/ERH data obtained in this study agreed well with previously published data. However the average isotherm, combining desorption and adsorption data, of ASAE does not predict the desorption EMC of rough rice accurately.     

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.     

A mean moisture content-equilibrium relative humidity relationship for nine varieties of wheat

A mean moisture content-equilibrium relative humidity relationship for nine varieties of wheat at 25°C is presented, for which the curves were fitted by eye. The mean safe storage moisture content in equilibrium with 70% relative humidity (r.h.) for all the wheat varieties adsorbing moisture was 14.7% (wet weight basis) but if varietal differences and errors in measurement are taken into account, the moisture content of stored wheat may need to be as low as 13% to be safe from attack by mites. The hysteresis between adsorption and desorption reached a maximum of 0.7% moisture content at 40–50% r.h. Hysteresis was found to be statistically significant up to 75% r.h. Equilibrium moisture contents were calculated from data transformed using the Chung and Pfost equation and compared with the measured moisture contents.     

玉米吸湿特性及其等温线类型研究

对测定的我国16个玉米品种的水分吸着等温线数据,采用9个水分吸着方程进行拟合,并根据修正4-参数Guggenheim-Anderson-de Boer方程(4-MGAB)派生的指标划分等温线类型。结果表明,CAE、修正Chung-Pfost(MCPE)、Strohman-Yoerger(STYE)、Brunauer-Emmett-Teller(BET)、3-MGAB、4-MGAB、修正Henderson(MHE)及修正的Oswin(MOE)方程均适合拟合测定的玉米水分吸着等温线,而Modi-fied Halsey(MHAE)不适合。MCPE和CAE被认为是玉米较佳水分吸着方程,方程参数MCPE的C1和C2、CAE的b1在不同玉米品种之间、黄玉米和白玉米之间差异不明显。但是,同一玉米品种吸附等温线的方程参数不同于解吸等温线的对应方程参数。另外,根据D10、Rfi、awn、X4指标判断玉米水分吸着等温线类型,16个玉米品种的吸附和解吸等温线均属于S型等温线(Ⅱ)。结果表明玉米水分吸附与解吸的MCPE和CAE方程参数可用于玉米收获后干燥及储藏通风操作。     

Moisture sorption and thermodynamic properties of cassava starch and soy protein concentrate based edible films

Moisture sorption isotherms and thermodynamic properties of cassava starch and soy protein concentrate–based edible films were investigated. Equilibrium moisture content was determined at various temperatures (10, 20, 30 and 40 °C) and relative humidities (17–83%) using gravimetric method, and the results were analysed using four sorption isotherm models. The equilibrium moisture of edible films (both adsorption and desorption modes) decreased with soy protein concentrate addition and temperature at constant water activity. The monolayer moisture content values of cassava starch–soy protein concentrate edible films decreased with increase in temperature and soy protein level. GAB and Oswin models (%RMS ≤10) best described the isotherms of the biofilms with the monolayer moisture contents, isosteric enthalpy and entropy higher for adsorption with significant kinetic compensations. The moisture sorption and thermodynamic properties of cassava starch–soy protein concentrate edible films showed that they are suitable for packaging applications.     

The moisture content-equilibrium relative humidity relationship of rice bran at different temperatures

The moisture content/equilibrium relative humidity relationships at 15, 25 and 35°C, for unextracted rice brans from Burma and Tanzania, unextracted bran from a South African parboiled rice, and a pelleted extracted rice bran from India, are presented and discussed. The relationships differed in shape and position of the curves, and in the magnitude of hysteresis between adsorption and desorption. The equilibrium moisture contents at 65% r.h. and below, of Burmese, Tanzanian and Indian brans were in reverse order of their fibre and ash contents. These moisture contents did not decrease consistently with oil content as they did for those cereal grains and oil-seeds previously investigated. The hysteresis for the parboiled bran was less, and the equilibrium moisture content was generally lower than for the other brans.