番茄浆料的流变特性研究

对不同浓度(15、18、20和24°Brix)的番茄浆料分别在30、40、50和60℃时的流变学性质进行了研究。结果显示,番茄浆料为假塑体系,屈服应力值的范围比较宽(40-140pa)。通过回归分析,发现数学模型,K=koexp(Ea/RT)和K=Aexp(BC),可以分别用来描述温度和浓度对番茄浆料稠度系数的影响。在实验条件下,实验值能够很好地拟合模型。并且推导出温度和浓度同时对番茄浆粘度影响的方程。利用这些方程,可以预测实际加工中不同温度和不同浓度下番茄浆料的粘度。     

胶体磨处理对鲜枣浆黏度特性的影响

在不同胶体磨处理次数、不同枣浆浓度和不同温度的条件下,考察胶体磨处理对鲜枣浆黏度特性的影响,实验结果表明:鲜枣浆的果肉颗粒随胶体磨处理次数的增加而变小,鲜枣浆的黏度与果肉颗粒的尺寸有密切的关系;胶体磨处理对不同浓度鲜枣浆黏度的影响可以用方程η=K(C)A和η=Kexp(AC)来表示;胶体磨处理对不同温度鲜枣浆黏度的影响可用方程η=K0exp(Ea/RT)来表示.上述结果表明,胶体磨处理条件对控制鲜枣浆的黏度具有重要作用.     

高透光率青梅汁浓缩过程中流变特性的研究

目的:系统研究高透光率青梅汁流变特性及其粘度变化规律。方法:用N DJ-1型旋转粘度计对不同温度和不同浓度下高透光率青梅汁的粘度进行了测定。结果:高透光率青梅汁为牛顿流体。阿累尼乌斯方程和数学模型K=A exp(BC)能分别较好地反映温度对粘度和溶解性固形物含量对粘度的影响。数学模型η=K1exp(Ea/R T+K2C+K3C2)能反映温度、溶解性固形物含量对粘度的综合影响。结论:利用回归方程,可以预测实际生产中不同温度和不同浓度下高透光率青梅汁的粘度。     

超临界CO2萃取番茄籽油

采用超临界CO2萃取技术对番茄籽油进行萃取,经过单因素和优化实验,对不同萃取时间、压力和温度下油的萃取率、脂肪酸组成和品质进行了比较.其中萃取时间和萃取压力对番茄籽油的萃取率影响显著(α=0.05),萃取温度影响较显著(α=0.1).最佳萃取条件为萃取时间2 h、萃取温度50℃、萃取压力30 MPa,萃取率达96.34%.通过气相色谱分析,由超临界CO2萃取得到番茄籽油的主要脂肪酸质量分数分别为棕榈酸(C160)约13%,硬脂酸(C180)约5%,油酸(C181)约22%,亚油酸(C182)约56%,花生酸(C200)约2.8%.通过测定番茄籽油过氧化值、酸价、碘价和皂化价,显示番茄籽油有较好的品质,不同的萃取条件对番茄籽油品质无显著影响.     

热分散处理条件对胶黏物分散与后续去除的影响第2部分 溶解物质、胶体物质和悬浮固形物的产生与去除

通过改变热分散系统的处理温度、齿盘间隙以及进浆浓度,研究了废纸脱墨浆中溶解和胶体物质(DCS)以及悬浮同形物(SS)的含量及其变化,讨论了随后的后浮选过程对这些成分的去除效果.研究结果表明,提高处理温度、减小齿盘间隙或增加进浆浓度,都能使热分散处理后浆料中的DCS含量显著增加,构成DCS的溶解物质(DS)和胶体物质(CS)含量也相应分别增加.在温度为100℃、齿盘间隙为0.3 mm、进浆浓度为30％时,与进入热分散机之前浆料中的含量相比,DCS增加了13.6％ ～ 16.8％,DS增加了5.7％～5.9％,CS增加了60.7％ ～65.3％.然而,热分散之后虽以CS的增加量为多,但浆料中DCS的丰要构成仍是DS.热分散之后浆料水相小的SS含量显著增加,达到了 21.7％ ～26.0％.后浮选过程可以有效去除SS,去除率达到45.2％～46.7％,CS的去除率仅为6.1％～6 8％,浮选过程难以去除DS.     

番茄沙司货架寿命动力学模型研究

研究在不同贮藏温度下,添加茴香精油、苯甲酸钠及未添加防腐剂的3种番茄沙司的菌落总数随贮藏时间的变化规律,并建立番茄沙司货架寿命的动力学模型,以预测3种番茄沙司在贮藏过程中的货架寿命。结果表明:阿伦尼乌斯(Arrhenius)方程和一级化学反应动力学方程相关系数均大于0.9000,在预测货架寿命上具有较高的拟合度。在301~318K温度范围内,可以用一级化学反应动力模型来预测番茄沙司的货架寿命。3种番茄沙司的货架寿命动力学模型分别为A=50e(1.3422e-11950/RT)t,A=50e(1.2810e-11300/RT)t,A=50e(0.921e-7830/RT)t。     

分离高温盐的工艺条件研究

文章利用不同温度下Na ,K ∥Cl-,SO2 -4 —H2 O四元体系相图 ,对通过物理方法分离高温盐中一水硫酸镁和氯化钠的工艺条件进行了分析。得出当循环母液和高温盐配成的浆料温度超过 5 5℃ ,浆料液体中氯化镁达到一定浓度时 ,才能分离出纯净的一水硫酸镁和氯化钠。     

臭氧对聚酯浆料的降解性能

聚酯浆料是一种新型的纺织浆料,对涤纶的黏附性能优异,但退浆性能差。采用O_3氧化法对聚酯浆料进行降解,明确聚酯浆料的初始浓度、pH、反应温度、O_3通入速率对其降解效果的影响,并借助傅里叶变换红外光谱仪和气质联用仪对其降解产物进行初步分析。结果表明:聚酯浆料的初始浓度越大,降解率越低,但降解量增大;碱性条件有利于O_3对聚酯浆料的降解;20～30℃时,升高温度可以提高降解率,30～50℃时,升高温度对降解率的提高影响不大,温度升高到60℃,降解率降低;O_3通入速率在6.0～11.4 g/h时,增大O_3通入速率可以提高聚酯浆料的降解率,但是通入速率增加至13.2 g/h,降解率降低。通过分析红外光谱图、气质联用色谱图,结合叔丁醇(TBA)对聚酯浆料降解率的影响,明确了·OH在O_3降解聚酯浆料中起主要作用,聚酯大分子链在·OH的作用下发生断裂,最终生成醛、酮、羧酸等低分子质量化合物。     

能斯特分配定律教学中的几个问题

本文讨论了能斯特分配定律的热力学基础与有离解和■合现象的液～液分配平衡.由化学平衡导得了分配系数的一般表达式为:K=C_w(1-x)/■[c_8(1-y)]~(1/2),而K=C_w/C_y~(1/2)仅在特定条件下才成立;对于在两相中都有??合现象的体系,其一般表达式为K'=[c■(1-y_1)■~(1/m)/[c_l~(β)(1-y_2)]~(1/n).同样,K'=[c_i~(a)]~(1/m)/[c_1~((β))]~(1/n)也仅在特定条件下成立.证明了K和K'实际上是一个组合平衡常数,它并不表示溶质在两相中的真实浓度比值.对于上述体系,若给出溶质在两相中的总浓度,则可以用图解法求能斯特分配系数.最后,讨论了热力学分配系数随温度和压力的变化.     

基于绿熟番茄果实L* 值的番茄红素含量预测模型建立

为了研究绿熟番茄果实贮藏期间颜色和番茄红素含量变化的关系,通过不同温度下的贮藏实验研究基于果实明度(L* 值)的番茄红素含量预测模型。将绿熟番茄果实贮藏在283.15、288.15、298.15K 条件下,测定了果实L* 值和番茄红素含量的变化。采用指数函数和Gomportz 函数分别对不同贮藏温度下番茄果实L* 值和番茄红素含量进行曲线拟合,建立了果实L* 值和番茄红素含量与贮藏时间和贮藏温度之间的动力学模型。实验表明,指数函数和Gomportz 函数分别对番茄果实L* 值和番茄红素含量的变化具有较高的拟合精度(R2 ＞ 0.95)。在Arrhenius 动力学方程基础上得到绿熟番茄果实贮藏期间L* 值和番茄红素含量变化的活化能(Ea)分别为48.09kJ/mol 和67.06kJ/mol,复相关系数分别为0.9644 和0.9815。建立的基于果实L* 值变化的番茄红素含量的预测模型所获得的番茄红素预测值与实测值之间的平均相对误差为8.74%,小于10%。这表明,在283.15～298.15K(10～25℃)的贮藏温度范围内,可根据番茄果实采后L* 值的变化对番茄红素的含量进行预测。     

浓缩葡萄汁流变特性研究

本文对不同浓度的浓缩葡萄汁在不同温度下的流变学特性进行研究。结果表明:在本文研究的温度和浓度范围内,浓缩葡萄汁属于牛顿流体;通过回归分析,分别给出了温度的变化和浓度的变化对粘度影响的关系式以及温度和浓度对粘度综合影响的方程式,方程的建立可利用来预测实际加工过程一定温度和浓度范围内浓缩葡萄汁的粘度。     

浓缩石榴汁流变特性研究

研究了不同浓度的石榴汁在不同温度下的流变特性。结果表明:在实验范围内,石榴汁表现为胀塑性流体,通过回归分析,温度对表观粘度的影响可以用Arrhenius方程表示,浓度对表观粘度的影响可以用指数方程更好地表示,并推导出温度和浓度对表观粘度综合影响的方程式。该方程的建立可以用来预测实际加工过程中一定温度和浓度时石榴汁的表观粘度。     

EFFECT OF TEMPERATURE ON VISCOSITY OF FRUIT JUICES AND PUREES

SUMMARY: The viscosities of selected fruit juices and purees were measured with a coaxial-cylinder viscometer in the temperature range 20–70°C. Depectinized apple juice and Concord grape juice were Newtonian fluids at all concentrations and their viscosity decreased considerably at higher temperatures. Cloudy apple and orange juices changed from Newtonian to pseudoplastic at concentrations higher than 50 and 20° Brix. respectively. Temperature had a smaller effect on viscosity of cloudy juices than of clear juices. The apparent viscosity of fruit purees (pseudoplastic fluids) decreased slightly at higher temperatures. The activation energy for flow increased with the juice concentration and decreased with the presence of suspended particles in the fruit product. The data and conclusions are useful in the design and operation of efficient food-processing equipment.     

Rheology of supersaturated sucrose solutions

Sucrose solutions, with concentrations near or superior to saturation, present high potentialities for the candy and pastry industries. Creep measurements under small stresses were done to obtain the rheological properties of highly concentrated sucrose solutions, since such solutions could be in a metastable state and tend to crystallise. The viscosities of these solutions, from 70.0% to 85.2% (w/w), were determined experimentally at different temperatures, from 0 to 90 °C. The temperature dependence of viscosity was studied using experimental and published data for, respectively, high and low concentrations (<70% (w/w)). Results showed that the Arrhenius model describes better the temperature dependence of viscosity for concentrations under saturation and in the high concentration regime the WLF model had a better predicting ability. The effect of concentration on viscosity was observed and included in the Arrhenius and WLF models’ parameters. The proposed models were able to successfully describe the data in the corresponding concentration range. These results can be used in predicting the viscosities of syrups for either process design or new products formulation.     

RHEOLOGICAL PROPERTIES AND FLUID DYNAMICS OF COFFEE EXTRACT

The rheological behavior of coffee extract with different water contents (49 to 90%) was studied at a wide range of temperatures (274 to 365 K) using a concentric cylinder rheometer. The flow curves followed different models depending on the concentration and temperature level. Newtonian behavior was observed at high values of water content and temperature, changing to power law as these values were decreased. The Newtonian viscosity as well as the consistency and behavior index could be well correlated by functions simultaneously dependent on temperature and water content. The rheological parameters, together with experimental values of pressure loss in tube flow, were used to calculate friction factors. These showed to be in good agreement with those resulting from classical theoretical and empirical equations, thus confirming the reliability of the rheological measurements.     

Time-independent and time-dependent rheological characterization of vegetable-based infant purees

Flow behavior of vegetable-based infant purees was analyzed at different temperatures (5–65 °C) giving particular attention to their time-dependent properties in a shear rate range (5–200 s⁻¹). Power law model parameters describing flow behavior of samples depended on kind of infant puree, its water content and measurement temperature. Arrhenius model was used to explain temperature effect on apparent viscosity at 50 s⁻¹. Infant purees exhibited thixotropic behavior for all temperatures tested. For the same temperature, differences in hysteresis loop magnitudes were observed among purees, being more noticeable at lower temperatures. Two models were used to describe the time-dependent behavior, namely Weltman model, and second-order structural kinetic model. For all infant purees, the initial shear stress and the extent of thixotropy increased and decreased significantly with increases in shear rate and temperature. The breakdown rate of puree associations also accelerated at higher shear rates, but no trend was observed with temperature.     

Rheological behaviour of tomato concentrate (Hot Break and Cold Break)

Knowledge of the rheological properties of agricultural products undergoing industrial transformation is of great importance in the design of industrial equipment in which these changes take place and as an index of quality of the finished products.The rheological behaviour of two samples of tomato concentrate (from the same tomato lot) which were treated, during industrial processing, by two different procedures — ‘Hot Break’ and ‘Cold Break’ — have been studied.Using a rotational viscometer the rheological curves of both concentrate samples were obtained at different concentration and temperature conditions, the corresponding values of K (consistency coefficient) and n (flow behaviour index) indicating a typically pseudoplastic behaviour. From the experimental results, the influence of using variable values of n and K has been studied.Finally, equations were derived to represent the apparent viscosity of tomato concentrate at any concentration and temperature within the range investigated.‘Hot Break’ samples showed (at the same temperature and concentration) higher μ_a and K values and lower n values than ‘Cold Break’ samples, which fully agrees with the logical deductions if it is taken into account that during the ‘Hot Break’ process enzymic inactivation occurs which prevents pectin degradation whereas in the ‘Cold Break’ process, enzymes are not inactivated, allowing the pectins present in the ground tomato to be degraded.     

FLOW PROPERTIES OF BABACO (CARICA PENTAGONA) PUREES AND CONCENTRATES

A power law model describes adequately the rheological behaviour of Babaco purees and concentrates while a Herschel-Bulkley model describes concentrates only. A single equation η_a=α x cβ x exp (E_a/RT), combining the effects of temperature and concentration on apparent viscosity (η_a100), was used to describe rheological behaviour.     

Kinematic Viscosity of Ternary Aqueous Solutions of Ethanol and Sucrose

A capillary viscosimeter was used to measure the kinematic viscosity data of aqueous solutions of ethanol and sucrose at several temperatures (from 20 up to 45°C) and concentrations (from 5% up to 95.11% w/w ethanol concentration with variable sucrose concentrations as a function of its solubility). Two models were proposed for fitting the experimental data (one for water/ethanol and another for water/ethanol/sucrose solutions). These models were based in pre-existing equations like Redlich-Kister and Torok-Rard-Miller (for dependency on concentration), and also Vogel-Fulcher-Tamman (for dependency on temperature). The estimated values by these two models gave low deviations from the experimental data for binary and ternary mixtures.     

Color Changes of Tomato Purees During Storage at Freezing Temperatures

ABSTRACT: The changes in color of unblanched and blanched tomato purees during storage at −7 and −18 °C were studied. They showed the typical sigmoidal-shape of radical reactions and were well described by the Logistic equation (R > 0.95; P < 10⁻³). After an initial induction time, a progressive increase in the bleaching rate was found for both unblanched and blanched frozen tomato purees. The color changes for the unblanched sample were statistically higher than those for the heated one. In the former case, the bleaching of carotenoids was attributed to both chemical and enzyme-catalyzed oxidation reactions. The effect of storage temperatures on color changes was appreciable only in the case of the unblanched tomato samples.