Influence of selected hydrocolloids on triticale starch rheological properties

The aim of the study was to define the influence of selected nonstarch polysaccharides (guar gum, xanthan gum and arabic gum) on several rheological properties of triticale starch pastes/gels, at constant polysaccharide concentration (6.5 g/100 g). These included pasting characteristics, flow curves at 50 °C and mechanical spectra at 25 °C. It was found that the presence of a gum in a system modified the rheological properties of triticale starch gels/pastes, depending on the type and concentration of the gums. In the case of guar and xanthan gums, higher pasting viscosity was observed and the shear stress was increased compared with native starch. The presence of guar gum reduced the degree of thixotropy hysteresis, negative values for this being found for systems with xanthan in spite of their shear‐thinning behaviour. Systems containing arabic gum displayed lower values of pasting and flow viscosity. The type and concentration of gums added to the polysaccharide influenced the viscoelastic properties of the gels.     

Effect of whey and pea protein blends on the rheological and sensory properties of protein-based systems flavoured with cocoa

Whey and pea protein combined in different proportions (100W:0P, 75W:25P, 50W:50P, 25W:75P, 0W:100P) were used to prepare protein-based systems flavoured with cocoa and containing κ-carrageenan or κ-carrageenan/xanthan gum as thickeners. Steady and dynamic shear rheological properties of samples were measured at 10 °C and sensory differences were evaluated. Protein-based systems exhibited a shear-thinning flow behaviour that was fitted to the simplified Carreau model. Samples showed different viscoelastic properties, ranging from fluid-like to weak gel behaviour. For both types of system (with and without xanthan gum) viscosity, pseudoplasticity and elasticity rose on increasing the pea protein proportion in the blend. The sample with only whey protein obeyed the Cox-Merz rule, while in the rest of the samples complex viscosity was higher than apparent viscosity. Regarding sensory properties, the protein blend ratio mainly affected sample thickness, which rose as pea protein proportion increased. However, at the same time, the chocolate flavour and sweetness decreased and the off-flavour increased.     

Rheological properties of wet foams generated from viscous pseudoplastic fluids

Foams generated from viscous non-Newtonian fluids have received insufficient attention in the literature despite their wide ranging industrial applications. We study the steady shear flow and viscoelastic properties of wet foams generated in a continuous multi rotor-stator pilot-scale device. The foams are generated from viscous pseudoplastic liquids consisting of aqueous solutions of Xanthan gum and caster sugar, and stabilised with a non-ionic food grade surfactant (PGE 55). Rheological measurements were conducted inside a parallel plate geometry on a controlled stress/strain rheometer. The effects of foam microstructural properties as defined by the process parameters (rotor speed, foam air fraction) and liquid composition (Xanthan gum concentration) are elucidated. Simultaneous in-situ visualisation of the foam during shearing revealed for the first time the existence of inward shear-induced radial migration of liquid at high shear rates which is responsible for the time-dependence behaviour of the foams. The foam flow curves were successfully fitted to a generalised dimensionless form of the Carreau-Yasuda model with data for all conditions investigated collapsing approximately on one single curve, which allows prediction of foam apparent viscosity as a function of air volume fraction.     

Steady and dynamic shear rheological properties of extrusion modified fenugreek gum solutions

This study investigated the rheological properties of extrusion modified fenugreek gum solutions (0.5, 1.0, 1.5, and 2.0%, w/v) under steady and dynamic shear conditions. Fenugreek gum was extruded in a twin-screw extruder without an exit die to minimize a decrease in molecular weight of fenugreek gum during extrusion process. Both of the steady and dynamic shear rheological tests revealed that extrusion process did not substantially influence the steady and dynamic shear properties of the gum. The power law model was applied to describe the flow behavior of the extruded gum solutions. The extrusion modified fenugreek gum solutions exhibited a shearthinning flow behavior at 25°C, and the values of consistency index (K) and apparent viscosity (η_a,100) increased with an increase in the gum concentration. The magnitudes of storage modulus (G′) and loss modulus (G″) for the extrusion modified fenugreek gum solutions increased with increasing frequency (ω) and with increasing gum concentration.     

Steady-shear flow of semidilute guar gum solutions with sucrose, glucose and sodium chloride at different temperatures

Steady-shear flow curves of aqueous solutions of guar gum at 0.22% at different temperatures (5-65 °C), guar gum (0.22%) with sugars (sucrose or glucose) at different sugar/water ratio (0.10, 0.20 and 0.40) at 5 °C, guar-sugar (at 0.40 sugar/water ratio) at different temperatures (5-65 °C) and guar gum and guar-sucrose (0.40 sucrose/water ratio) with NaCl (1%) at 5 °C, were determined using a controlled-stress rheometer over a wide range of shear rate (1-1000 s⁻¹). Apparent viscosity increased with decreasing temperature and increasing sugar content independent of sugar type. Synergic effect on apparent viscosity due to sugar addition was found and was correlated with sugar content. Salt addition decreased slightly the apparent viscosity and increased the shear-thinning behaviour of the guar gum solution. Steady-shear flow curves were satisfactorily described by the Cross model. Semi-empirical correlations of Cross model parameters with sugar content and temperature were obtained.     

魔芋胶溶液浓度对其流变学特性的影响研究

配制质量分数为0.1~1.0%的魔芋胶溶液,通过稳态流动、应变扫描、频率扫描以及动态粘弹性温度扫描、动态粘度温度扫描,观察不同溶液浓度对粘度特性随剪切速率及温度的变化情况,粘弹性随应变、频率及温度的变化,以及考察模量频率相交点、松驰时间等与结构特性相关的各因素。试验结果表明：在1%浓度范围内,魔芋胶溶液的零剪切粘度、粘度、剪切稀化指数、特征松驰时间及弹性模量、粘性模量、损耗正切与浓度之间存在高度的相关性。另外,浓度的改变影响频率扫描中G’=G’’时交点处频率、模量及松驰时间,亦影响动态粘弹性温度扫描中凝胶-溶胶转换时温度的高低与模量的大小。     

增稠剂对酸奶质地的影响研究

对酸奶的硬度、黏度、凝聚性、保水性进行测定，研究了不同增稠剂对酸奶质地和感官特性的影响。结果表明。果胶、明胶、耐酸CMC、海藻酸钠分别提高了酸奶的黏度，而槐豆胶、瓜尔豆胶、魔芋胶则相反；只有果胶和明胶提高了酸奶的保水力；果胶、明胶时酸奶质地的影响随着浓度的增加而增加。统计结果表明，当增稠剂添加量为0．1％时，不同增稠剂对酸奶的质地存在显著影响；同时．增稠荆浓度对酸奶质地的影响也显著。     

两种皂荚多糖胶流变性质的表征

采用Brookfield 流变仪研究在不同加热时间、温度、pH 值以及盐和糖质量浓度等条件下两种不同形状皂荚豆中多糖胶的流变性质。结果表明：皂荚豆胶是一种假塑性流体,测得的剪切速率和相应的剪切应力的关系符合Power-law 模型,圆皂荚豆胶具有较高的黏度,且假塑性明显高于扁皂荚豆胶。在80℃条件下加热1h 可使皂荚豆胶完全水合,胶液黏度随温度的上升而下降。在pH2～11 范围内,皂荚豆胶比较稳定,但过酸或过碱会导致黏度的下降。皂荚豆胶的黏度随NaCl 质量浓度的上升而下降,随白砂糖质量浓度的上升而略微升高。与扁皂荚豆胶相比,NaCl 对圆皂荚豆胶的降黏作用较为明显。     

Effects of guar gum and arabic gum on the physicochemical,sensory and flow behaviour characteristics of frozen yoghurt

This study investigated the effect of guar gum and arabic gum on physicochemical, sensory and flow behaviour properties of frozen yoghurt. The results indicated that gums significantly affected the viscosity, overrun and melting rate of frozen yoghurt. The highest overrun value was observed in sample containing 0.5% arabic gum. Frozen yoghurt containing 0.3% guar gum had the highest viscosity. The longest first dripping time was observed in sample containing 0.5% arabic gum. Flow behaviour of samples showed that all frozen yoghurts exhibited shear thinning behaviour. Guar gum at a concentration of 0.2% and arabic gum at a concentration of 0.5% presented the best total acceptability. The results of this study revealed that the frozen yoghurt produced with arabic gum had the better overall sensory and physicochemical characteristics.     

RHEOLOGICAL PROPERTIES AND APPLICATIONS OF MESQUITE TREE (PROSOPIS JULIFLORA) GUM. 1. RHEOLOGICAL PROPERTIES OF AQUEOUS MESQUITE GUM SOLUTIONS

The viscosities of aqueous mesquite gum solutions were measured at gum concentrations extending to 16.7% (w/v). Very dilute solutions exhibited typical polyelectrolyte behavior with respect to the influence of gum concentration on the reduced viscosity in the absence and presence of electrolyte. Shear thickening was exhibited at concentrations of 1–16.67% (w/v) when the shear rate exceeded ∼100 s⁻¹, whereas shear thinning was exhibited at lower shear rates. Shear thickening was attributed to configurational changes in the gum molecules at high shear rates. Electrolytes (0.1N NaCl and 0.1N CaCl₂) reduced the viscosity of concentrated solutions at high shear rates to a larger extent than increasing the pH. Charge screening by electrolyte permits the gum molecules to assume a more compact configuration.     

Rheological properties of aqueous blends of high purity barley β-glucan with high purity commercial food gums

Rheological properties such as flow behaviour, viscosity, viscoelasticity, and thixotropy of solutions of β-glucan purified from barley fibre concentrate and twelve commonly used food gums, alone and in combinations, were characterised using an oscillatory rheometer. Pure gums and gum combinations were evaluated at 0.5% and 0.75% (w/w) total gum concentration in aqueous medium, whereas the β-glucan/gum ratios were kept at 90/10 or 80/20 (w/w). Viscosity synergism was observed for β-glucan solutions in combination with xanthan, iota-carageenan, and carboxymethyl cellulose. However, barley β-glucan blends with lambda-carageenan, Konjac, high- and low-methoxyl pectin, microcrystalline cellulose, alginate, and gum arabic showed marked lowering of the viscosity compared to β-glucan alone. In addition, β-glucan/xanthan gum blends demonstrated improved shear tolerance compared to xanthan dispersions alone, and soft gel transformation. Non-thixotropic behaviour was observed for 0.5 and 0.75% (w/w) β-glucan dispersions and its gum combinations. None of the gum combinations studied demonstrated thixotropy.     

Carboxymethyl derivatives of flaxseed (Linum usitatissimum L.) gum: characterisation and solution rheology

Carboxymethyl ether moieties were introduced to flaxseed (Linum usitatissimum L.) gum (FG) by reacting gum with monochloroacetic acid (MCA). Effects of ether forming reaction conditions, temperature, NaOH concentration and molar ratio of FG (anhydroxylose equivalent) to MCA, on the degree of substitution (DS) were investigated. Treatment at 70 °C, with 7.0 m NaOH, and molar ratio of MCA to FG of 10:1 over 3 h produced a polysaccharide with a DS of 0.824 ± 0.012. Both surface morphology and thermal behaviour were modified. Solutions of FG (0.5–4.0%, w/v) exhibited shear‐thinning behaviour where viscosity decreased with decreased FG concentration. After carboxymethylation, modified polymer solutions also exhibited shear‐thinning behaviour, where dynamic viscosity was lower than that of native FG solutions at the same concentration. The dynamic viscosities were lower for solutions of modified FG with higher DS and also lower for solutions made at lower FG concentrations (0.5–4.0%, w/v). A more liquid‐like behaviour with increasing FG DS was indicated as storage modulus G′ and loss modulus G″ decreased and became more frequency dependent. The substitution of hydroxyl groups with carboxymethyl groups suppressed entanglement between FG polysaccharide chains by reducing intermolecular association.     

Rheological behaviour of β-glucan preparations from oat products

The cereal dietary fibre β-glucan has outstanding functional and nutritional properties, because of its viscosity in aqueous systems and in the intestinal tract. The rheological behaviour of β-glucan (concentrations: 2% and 4%) isolated from extruded and autoclaved oat meal and from oat bran was evaluated using oscillatory and rheological measurements. In frequency sweep, the storage and loss moduli G′ and G″ of β-glucan preparations from extruded meal and from bran increased continuously with increasing frequency, showing a dominantly viscous behaviour. With increasing frequency, the elastic properties improved. β-Glucan from autoclaved meal also showed elastic behaviour. With the exception of β-glucan from autoclaved meal, G′ and G″ were not influenced by deformation in the amplitude sweep. Complex viscosities decreased with frequency (in all samples) and were independent of deformation (in extruded meal and bran). In shear experiments, β-glucan solutions were structurally viscous non-Newtonian solutions with rheostable behaviour. β-Glucan (2%) from bran had the highest and that from autoclaved meal had the lowest apparent and process viscosities. Fluid dynamic parameters may influence the flow, diffusion or transport behaviour of β-glucan during digestion processes in the small intestine, but the influence of the viscous behaviour is limited.     

Hydrocolloids and Rheology: Regulation of Visco-elastic Characteristics of Waxy Rice Starch in Mixtures with Galactomannans

Texture and sensory properties of starch solutions or gels, resp., can be influenced by regulating the visco-elastic properties that cannot be adjusted by simply varying the waxy rice starch concentration. Therefore, the hydrocolloid galactomannans guar gum and locust bean gum were used for addition. A total polymer concentration of c = 5% was maintained through all tests, the hydrocolloid fractions varied (c_HK = 0.5%, 1%, 2%). The mixtures were entirely decomposed in an autoclave at 130°C resulting in an almost complete destruction of the granular starch structure. With rheomechanical oscillation measurements in the linear-visco-elastic range the influence of the galactomannans onto viscosity yield and visco-elasticity was determined quantitatively. It was found that the influence on the viscosity is depending on the deformation rate. At low frequencies and with increasing galactomannan fraction the viscosity decreases, while above a critical frequency ω_kr an increase in viscosity could be detected compared to pure starch. The mixtures also displayed an increase in viscous fractions versus elastic fractions compared to pure starch. With increasing galactomannan fraction, the ratio storage modulus/loss modulus is reduced continuously from G′:G″ > 10 (definitely mainly elastic) to G′:G″ = 1 with simultaneously decreasing influence of the frequency. Based on the presented data and knowledge on solution structure of the individual components, a model for describing network structures in mixtures was developed. Changes in viscous-elastic properties are based on a thermodynamic incompatibility between starch and galactomannan fractions. The mixtures contain mixed network structures, with waxy rice starch (permanent network points) and galactomannans (temporary network points) contributing individually and characteristically to the resulting flow behaviour.     

Effects of pectin and guar gum on creaming stability, microstructure and rheology of egg yolk plasma-stabilized emulsions

The influence of pectin and guar gum on the creaming stability, microstructure and rheological properties of 1.0% (w/v) egg yolk plasma (EYP)-stabilized 25.0% (v/v) soybean oil-in-water emulsions was studied at pH 7.0. Addition of pectin/guar gum decreased creaming percentage, and no creaming was detected in the presence of 0.5% (w/v) pectin/guar gum as a result of increasing viscosity. At the end of 10 h, creaming percentage decreased from 61 to 57% with the addition of 0.05% (w/v) guar gum and to 39% with the addition of 0.2% (w/v) guar gum. Microscopic observations represented the droplet aggregation arising from the presence of nonabsorbing biopolymers. At \mathop g^. \mathop \gamma \limits^{.}  = 10 s⁻¹, a tenfold increase in viscosity was observed in the presence of 0.5% (w/v) guar gum compared to the presence of 0.1% guar gum due to the thickening effect of polysaccharide. Increasing gum concentrations enhanced the viscosity and hence the consistency index. All emulsions, except for those containing 0.5% (w/v) guar gum, reflect the near-Newtonian behaviour with flow behaviour index, n, of 0.9–1.0. All emulsions exhibited a liquid-like behaviour at low frequencies (<7.0 Hz) where G″ values were higher than G′. Both G′ and G″ showed a frequency dependency and these two moduli crossed each other at higher frequencies (>7.0 Hz), G′ became greater than G″ and the system behaved like an elastic solid. Addition of pectin at all levels cause no significant change in G′ and G″ values, whereas addition of guar gum, especially at a concentration of 0.5% (w/v), significantly improved these values.     

κ-卡拉胶与魔芋胶复配胶的流变性能及其微观结构研究

研究κ-卡拉胶与魔芋胶(质量比为5.5:4.5)复配胶的流变特性,考察剪切速率、振动频率和温度等对复配胶流变特性的影响。研究结果表明:30℃时复配胶的储能模量G′高于κ-卡拉胶和魔芋胶单体胶的储能模量G′,其损耗模量G"低于κ-卡拉胶的损耗模量G",复配胶的凝胶性质更加明显。随着温度的升高,复配胶体系的G′始终大于G",具有典型黏弹性流体的特性。结构分析表明κ-卡拉胶与魔芋胶之间具有较好的协同作用,通过分子间氢键形成了以κ-卡拉胶网络结构为主,魔芋胶穿插其中的交联网络体系。     

Pectin and Raspberry Concentrate Effects on the Rheology of Stirred Commercial Yogurt

The influence of pectin (0.0–0.5%) and raspberry concentrate (64°B; 0–10%) on the rheological characteristics of commercial stirred yogurt was evaluated using a computer-controlled rotational viscometer. All upward flow curves (shear rate vs shear stress) followed the Herschel-Bulkley model while downward curves showed a linear relationship. The consistency coefficient (upward flow) and apparent viscosity (downward flow) showed a continuously increasing trend with increasing pectin and raspberry concentrate. The rheology of flavored yogurt could be fabricated by post-incubation mixing of stirred yogurt with pectin and raspberry concentrate.     

Flow properties of fruit fillings

The flow properties of the fluid portion of fruit fillings were assessed to investigate the effects of gums. Results indicated that the shear rate–shear stress relations of the fluid portion of commercial fruit fillings and the model fillings made of waxy corn starch, fructose, citrate buffer, and a gum which could be guar gum, locust bean gum, CMC, xanthan gum or κ-carrageenan, fit well into the Herschel–Bulkley equation for pseudoplastic fluids. The fluid portion of the commercial fruit fillings was characterized with a yield stress between 39–51 Pa, a consistency index between 52–104 Pa·sⁿ, and a flow index (n) around 0.4. In addition, the shear rate–shear stress relations could be fitted into a modified Herschel–Bulkley equation with a flow index fixed at 0.4. Addition of guar gum, locust bean gum and CMC increased while xanthan gum and κ-carrageenan decreased the consistency and flow indices in the modified Herschel–Bulkley equation. The effect of gum addition on the apparent viscosity of model fillings varies with the type of gum, amount of addition, and shear rate.     

Comparison of Steady Shear and Dynamic Viscoelastic Properties of Guar and Karaya Gums

Steady shear and small amplitude dynamic viscoelastic properties of suspensions of guar gum and gum karaya in the range of shear rates/frequencies between 0.1 and 100 set⁻¹ were compared. For all concentrations of guar at small shear rates/frequencies steady viscosity (η) is equal to dynamic viscosity (η^′) when corresponding shear rates and frequencies are equal. At large shear rates, steady viscosity (η) is equal to complex viscosity (η*); primary normal stress coefficient (ψ₁) is approximately equal to (2η″/ω). For gum karaya, it was shown that (η″/ω) is nonlinearly related to primary normal stress coefficient (ψ₁) and dynamic viscosity (η′) is nonlinearly related to steady viscosity (η).     

梨膏的流变学特性及其影响因素

目的 考察人为加糖、加胶后梨膏触变性及黏度的变化。方法 以鸭梨为实验材料,通过真空浓缩方式制备鸭梨膏,采用HR-10型流变仪对其流体类型、黏度、触变性进行测定。结果 鸭梨膏属于非牛顿流体,具体细分为无限接近牛顿流体的假塑性流体,具有剪切稀化特性和正触变特性;损耗模量G″总是大于储能模量G’,表现出液体黏性性质;剪切速率与剪切力变化关系符合PowerLaw方程,拟合效果良好(r2>0.99);温度显著影响梨膏黏度,黏度随温度升高而降低,二者关系符合Arrhenius方程,拟合效果良好(r2>0.99);可溶性固形物含量(solublesolidscontent,SSC)对黏度的影响符合指数函数关系,模型拟合效果良好(r2>0.99);SSC以及人为加糖、加胶处理对梨膏触变性、黏度影响显著(P<0.05),黏度随SSC的升高而增强,人为加胶、加糖加胶会导致梨膏黏度显著升高(P<0.05);触变性随SSC的升高而增强,同时人为加糖、加胶、加糖加胶处理会导致梨膏触变性显著减弱(P<0.05)。结论 人为添加糖、胶会导致梨膏的流变学特性发生改变。本研究可为工业...