Rheological Properties of High-Methoxyl Pectin and Locust Bean Gum Solutions in Steady Shear

The Cross and Carreau flow models described well the shear rate-apparent viscosity data. The coil overlap parameter, c[η], correlated well with the zero-shear rate specific viscosities of these mixtures. Experimental values of intrinsic viscosities of the mixtures were in good agreement with the prediction based on an additive model of the individual contributions of the gums. From the results obtained for the mixtures of both polysaccharide solutions at similar viscosity, pH and ionic strength, no significant interactions were detected. Hypotheses for this lack of polymer interaction were developed. Results with such model systems are useful in understanding the relation of composition to the properties of complex food systems.     

Dynamic Rheological Measurement of Structure Development in High-methoxyl Pectin/Fructose Gels

Incipient structure development (SD) in 65% fructose—0.5, 0.75, and 1% high—methoxyl (HM) pectin gels (pH 2.7) being cooled (50–10°C) were measured in terms of dynamic viscosity (η*) at 1Hz. SD rates (poise/min) were higher at lower temperatures, higher pectin concentrations, and when pectin was hydrated for 16 hr. Below the gel temperature, SD rates in 1% gel followed the Flory-Weaver model. SD in stored 0.5% gels during 22 days was strongly affected by storage temperature (2–38°C) and pH. SD rates in pH 2.7 gels were positive above, but negative below 18°C.     

商业橘皮果胶与大豆果胶流变性质的比较

通过流变学方法对商业橘皮果胶及大豆果胶溶液黏度及凝胶过程进行分析。结果表明：相同条件下,商业橘皮果胶的黏度高于大豆果胶;在形成凝胶过程中,商业橘皮果胶凝胶体系储能模量要远高于大豆果胶。果胶质量浓度为2 g/100 mL、蔗糖添加量为55、60 g/100 mL,葡萄糖酸内酯（D-glucono-δ-lactone,GDL）添加量为3、4 g/100 mL的商业橘皮果胶与相同条件下的大豆果胶储能模量差异不大;通过加入蔗糖及GDL或提高大豆果胶质量浓度,可明显提高大豆果胶凝胶体系的储能模量,增加大豆果胶的凝胶强度。     

pH值对低酯果胶/酪蛋白酸钠复合体系流变及结构特性的影响

为研究pH值对低酯果胶/酪蛋白酸钠复合体系流变及结构特性的影响,分别在不同酸性条件下（pH 3.0、3.5、4.0、4.5、5.0、5.5）对复合体系的静态剪切及动态黏弹流变特性、Zeta电位、粒径、浊度、微观结构进行测定。结果表明：复合体系流变特性呈两段式变化,在pH 3.0～4.0时,随pH值的增大,复合体系流体指数n和tanδ均增大,稠度系数K减少;在pH 4.5～5.5时,体系n和tanδ骤减后继续增加,且增加程度更大,K骤增后继续减少。复合体系Zeta电位值随着pH值的增大而降低。Zeta电位值在pH 3.0～4.0时为正,在pH 4.5～5.5时为负。复合体系粒径和浊度值均随着pH值的增大呈先增大后减小的趋势,在pH 4.5时达到最大。随着pH值的降低,复合体系微观结构由杂乱变得细密。在pH 3.0～4.0时,体系以低酯果胶附着在酪蛋白表面结构为主;在pH 4.5～5.5时,体系中低酯果胶的网状结构更明显。因此,pH值的变化会改变复合体系的流变及结构特性,从而影响体系的稳定性。     

Rheology and Relationship among Rheological Parameters of Cross-Linked Waxy Maize Starch Dispersions Heated in Fructose Solutions

ABSTRACT: Dispersions of 5% cross‐linked waxy maize starch heated in Newtonian aqueous fructose solutions, 0 to 600 g per kg, exhibited either thixotropic or antithixotropic flow behavior, and viscoelastic behavior. The mean starch granule dia in the dispersions changed slightly with fructose content. Values of G' of the dispersions were higher than those of G', reflecting gel‐like behavior of the dispersions. Values of the first normal stress coefficient predicted from dynamic rheological and apparent viscosity data based on the Goddard‐Miller model were in reasonable agreement with experimental values.     

柠檬皮高酯果胶的分步提取及表征

本研究采用草酸对柠檬皮进行分步提取,得到两种不同性能的高酯果胶(HMP-1、HMP-2),系统地探究了提取条件HMP-1和HMP-2得率和黏度的影响,对HMP-1、HMP-2进行物化性质表征,并通过原子力显微镜(AFM)进行微观结构观察。实验结果表明,在料液比1:20,pH 1.7,70℃1.5 h的反应条件下,HMP-1得率为19.22%,1%溶液的黏度为104.55 mPa·s,分子量为550.4 ku,酯化度为75.22%,胶凝度为218.24°SAG,在酪蛋白等电点附近具有较高的电位绝对值;在料液比1:10,pH 1.7,80℃1.5 h的反应条件下,HMP-2的得率为9.74%,1%溶液的黏度为49.23 mPa·s,分子量为424.7 ku,酯化度为64.34%,胶凝度为171.12°SAG。AFM结果表明,HMP-1呈现较长的线性形态,HMP-2则呈现较为分散、细碎的状态。本研究实现了柠檬皮果胶的分步提取,得到不同类型的果胶,有助于果胶的多元化发展及精准应用。     

Measurement of Gelpoint Temperature and Modulus of Pectin Gels

Methods which permit the measurement of gelpoint (setting) temperature (T_gel) and rigidity modulus (G) of pectin gels were improved. Gel development on cooling was determined with an oscillatory pressure testing device capable of detecting a modulus as low as 3 Pa and strain values no greater than 5∞10^?3. Sample was set in a glass “U” tube during pressure oscillatory assay for T_gel determination, and transferred after gelling in the same tube for G modulus determination with modified Saunders-Ward apparatus. Results confirmed rheological behavior reported for these kinds of gels and compared favorably with small amplitude oscillatory measurements performed with a stress controlled rheometer using cone and plate (4°, dia = 4 cm) geometry at different frequencies (0.5 to 1.5 Hz) and cooling rates (1 to 3°C/min).     

低酯桔皮果胶凝胶的动力学分析及分形研究

本实验通过流变学方法研究了酰胺化桔皮果胶的胶凝性质并进行相关的动力学分析。首先探讨了在冷却过程中果胶浓度及pH值对体系弹性模量及凝胶形成速度的影响;然后对果胶溶液在冷却过程中形成的凝胶进行了分形研究,采用两种模型进行相关运算并得到了相同的分维数但表征了不同的凝胶体系。     

猕猴桃果胶的黏度特性与流变性分析

采用冷冻干燥和热风干燥方法制备出猕猴桃果胶(kiwifruit pectin,KP),得到KP1和KP2两种成分,二者的pH值分别为3.16和3.39,主要含有半乳糖醛酸。以羧甲基纤维素钠(carboxy methyl cellulose-Na,CMC-Na)为参照系,采用MCR301旋转流变仪研究4因素(pH值、质量浓度、温度和剪切速率)对KP溶液流变性的影响。结果表明,KP1和KP2溶液黏度较低,在1.0 m Pa·s上下,溶液pH值和质量浓度对其影响有限。研究KP1和KP2溶液黏度与温度倒数1/T间的对数关系并观测到,10~30℃区间内其黏度随温度升高而下降,与CMC-Na溶液黏度变化相似。但40~50℃时其溶液黏度和流动性不完全遵循Arrhenius方程,究其原因,KP1和KP2活化能Ea分别为10.075 kJ/mol和4.510 kJ/mol,它们对温度的敏感性低,而导致其黏度和流动性发生改变。幂律方程对KP1和KP2溶液黏度和剪切速率的关系拟合,二者流动指数n均小于1,符合幂律定律对非牛顿流体特征的解释。因此,KP1和KP2溶液具有较典型的剪切稀化现象和流变性,可归属于非牛顿流体。但KP是一种低黏度果胶,故Arrhenius方程不能有效诠释KP溶液黏度与温度变化的规律。     

破碎温度对番茄浆流变性质与果胶分子结构的影响

对在不同破碎温度下所得番茄浆的动态流变性质以及果胶物质相对分子质量的分布和大小进行了研究.结果表明随着破碎温度的增加,番茄浆中果胶物质的平均相对分子质量增加.但当破碎温度为90℃时,果胶物质的平均相对分子质量却有所下降.在80℃和85℃破碎时,番茄浆具有相当大的贮能模量,而在75℃和90℃破碎时,贮能模量值较小.贮能模量值对振荡频率具有一定的依赖性,故番茄浆表现出弱凝胶特性.贮能模量G′和损耗模量G″交汇点的位置随着破碎温度的升高向低频区移动.这说明破碎温度越高,大分子物质被保留得愈多,体系呈较强的弹性;破碎温度越低,体系中大分子物质被保留得越少,体系呈较强的粘性.     

低甲氧基果胶的胶凝机理及防止预凝胶形成的措施

对低甲氧基果胶的胶凝机理及影响胶凝的主要因素———pH值、可溶性固形物含量、钙离子浓度进行了探讨 ,并针对低甲氧基果胶应用中产生的降低产品质量的预凝胶问题进行了讨论 ,为分析低甲氧基果胶应用中的问题提供了依据 ,并提出了一些防止预凝胶形成的措施。     

Rheological Properties of Renneted Reconstituted Milk Gels by Piezoelectric Viscoprocess: Effects of Temperature and Calcium Phosphate

Scanning electron microscopy (SEM) and rheology and permeability were used to evaluate effects of clotting temperature and calcium phosphate on reneted reconstituted milk gels, especially microstructure and permeability. Dynamic measurements with a piezoelectric Viscoprocess determined rheological properties of curd after various times of renneting. An increase in clotting temperature accelerated specific rennet action and gel formation; maximum stiffness was reached faster but its value was weaker. Addition of calcium phosphate increased rate of gel formation. Maximum stiffness was reached faster but its value was not changed. Gel microstructure was not very different but its permeability coefficient decreased.     

超声辅助柠檬酸提取百香果果皮高酯果胶及其理化性质分析

为开发优质果胶资源,利用超声辅助柠檬酸法从百香果果皮中提取高酯果胶,采用单因素实验探讨了料液比、pH、提取时间、超声功率对果胶得率的影响,应用正交试验确定果胶的最优提取工艺,并对其理化性质进行比较分析.结果表明,提取过程中各因素对果胶得率的影响大小为:提取时间＞料液比＞ pH ＞超声功率;最佳提取工艺为:料液比1∶40...     

Rheological Properties of Sonicated Guar,Xanthan and Pectin Dispersions

The influence of high intensity ultrasound on the rheological characteristics of guar, xanthan, and pectin dispersions was investigated. Guar 1%, xanthan 1% and pectin 2% (w/v) dispersions were sonicated at varying intensity levels of 3.7, 6.3, 8.1, and 10.1 W/cm² for 5 min at 25^oC. Significant differences were observed in the rheological characteristics of each sonicated hydrocolloid dispersion studied. Sonication affected the consistency index (k), flow behaviour index (n) and complex power law constants (a and b). No recovery was observed in the structure breakdown after a 24-h storage period. Changes in the rheological properties of guar and pectin dispersions were significantly higher than that of xanthan dispersions.     

Kinetics of Tomato Pectin Methylesterase Inactivation by Temperature and High Pressure

ABSTRACT: In this study we investigated the inactivation of endogenous pectin methylesterase (PME) in tomato juice during combined high-hydrostatic pressure (ambient to 800 MPa) and moderate temperature (60 to 75 °C) treatments under isobaric and isothermal processing conditions. PME inactivation rates increased with increasing processing temperature, with the highest rate obtained during processing at 75 °C and ambient pressure. Inactivation rates were dramatically reduced as soon as processing pressure was raised. High inactivation rates were again attained when processing pressure exceeded a value of about 700 MPa. Such a behavior was described by considering two parallel mechanisms of inactivation, each one following first order kinetics with its own kinetic parameters.     

正交试验优化向日葵盘果胶的提取和基本分析

研究向日葵盘果胶(SFHP)的提取工艺。通过单因素试验,比较酸化水、0.75%六偏磷酸钠、0.5%乙二胺四乙酸二钠、0.5%草酸-草酸铵、0.5%草酸和0.5%草酸铵6种提取剂的提取效果,确定较优的提取剂种类。选择pH值、提取温度、提取时间和提取固液比为主要工艺参数,通过正交试验,确定较优的提取参数组合:pH3.50、提取时间45min、提取温度85℃、固液比1:30(g/mL)。在此条件下,向日葵盘果胶得率为20.9%(以半乳糖醛酸计)。采用高效尺寸排阻色谱-多角度激光散射检测器(HPSEC-MALLS)和高效阴离子交换色谱-脉冲安培检测器(HPAEC-PAD)测定了向日葵盘果胶的分子质量和单糖组成。结果表明,向日葵盘果胶的分子质量高于柑橘果胶,半乳糖醛酸为最主要单糖成分,占单糖总量的82.1%,鼠李糖为次要成分,仅占单糖总量的9.1%。     

两种不同质地的莲藕碱溶性果胶组分热降解规律及流变学差异

选择两种不同质地的莲藕作为材料,研究其碱溶性果胶（sodium carbonate-soluble pectin fraction,NSF）的热降解差异及其与流变的关系。对碳酸钠提取的NSF进行不同温度处理,通过一级结构和纳米微观结构观察和分析发现,沔城藕（粉藕）的NSF热降解程度大于芦林湖藕（脆藕）;芦林湖藕NSF链呈星型状（长支链）而沔城藕NSF链大多呈短直链,两者经加热后均出现链长变短、链高降低、分支度减小的现象;流变学结果表明两种NSF的黏稠度经热处理后均明显降低,沔城藕的NSF假塑性略有增加而芦林湖藕NSF假塑性减小。结合结构分析与流变学结果分析得到果胶链的长度、高度与黏稠度呈正相关;分支度和不同长度的链长所占百分比（分子质量分布）是导致其假塑性不同的重要原因。因此,NSF的结构与流变学特性密切相关,同时也说明NSF的热降解差异与两种藕质地差异存在关联。本研究为NSF的热降解与果蔬质构（加工、成熟度）之间的关系提供了一定理论依据。     

微波降解果胶对其流变性质的影响及动力学

对不同质量浓度(0.5、1.0、1.5、2.0 g/100 m L)的果胶溶液微波处理不同时间(0、1、3、5、8、15、20、30 min)后的流变性质及动力学进行考察。结果表明,随着果胶溶液质量浓度降低、微波处理时间延长、剪切速率增大,样品的表观黏度和特性黏度[η]均降低。用牛顿幂律方程描述溶液的流体行为,果胶溶液是剪切稀化的假塑性非牛顿流体,在低质量浓度时,微波处理对溶液的流体行为影响最大。根据特性黏度对样品进行反应动力学拟合,发现果胶的微波降解遵循反应一级动力学,在质量浓度0.5 g/100 m L时降解速率最快,质量浓度1.5 g/100 m L时降解速率最慢。经与沸水浴无微波的空白组对比,发现微波降解果胶的过程还存在非热效应。     

超高压与重组果胶甲酯酶抑制剂联合应用对鲜榨橙汁果胶甲酯酶活性及品质的影响

为了探究超高压与重组果胶甲酯酶抑制剂(recombinant pectin methylesterase inhibitor,rPMEI)联合处理对鲜榨橙汁中果胶甲酯酶(pectin methylesterase,PME)活性及品质的影响,研究了超高压(400、500和600 MPa,5 min,20 ℃)与重组果胶甲酯酶抑制剂对橙汁微生物、PME酶活、色泽和V_C含量的影响。结果表明:超高压处理条件为500 MPa/5 min,rPMEI添加浓度为0.06 mg/mL时,橙汁中的菌落总数、霉菌与酵母菌数均能达到农业行业标准《NY/T 434-2016绿色食品、果蔬汁饮料》所规定的要求,同时PME被完全钝化;橙汁色泽变化显著小于热处理组(ΔE^*=1.22<2.26);V_C保留率为85.1%,显著高于热处理组(保留率=8.33%)。