海藻酸钠/阿拉伯树胶混合可食性膜液的流变性能

为了探讨海藻酸钠/阿拉伯树胶混合膜液流变特性,利用Discovery HR-2型流变仪,研究海藻酸钠浓度、阿拉伯树胶浓度、增塑剂浓度和测试温度对海藻酸钠基成膜液体系的流变性的影响。结果表明:成膜液均属于非牛顿假塑性流体,具有剪切变稀性质,流变特性均符合Ostwald-de-Waele幂律方程,且流动指数与稠度系数的变化均受到海藻酸钠浓度、阿拉伯树胶浓度、增塑剂浓度和测试温度不同程度的影响。     

印花用瓜耳豆胶糊料流变性能研究

研究了瓜耳豆胶溶液的流变性能.通过固体质量分数对瓜耳豆胶溶液表观粘度的影响以及粘温特性、小幅振荡剪切应力扫描和频率扫描实验,金属离子及化学试剂对瓜耳豆胶溶液粘弹性能的影响试验,确定了溶液体系的流变性参数.结果表明:瓜耳豆胶溶液的表观粘度随固体质量分数的增加而增大,随温度的升高而明显下降.从小幅振荡剪切应力扫描、频率扫描实验得出:随着温度升高,储能模量、耗能模量变小,而随着金属离子的添加,储能模量、耗能模量变大.     

Rheological behaviour of tamarind seed gum in aqueous solutions

Tamarind seed gum as seed polysaccharide from Tamarindus indica L. has been characterized for physicochemical and rheological properties in the present work. The structural analysis determined the presence of glucose:xylose:galactose in a molar ratio of 2.61:1.43:1.The Huggins and Kraemer plots obtained by capillary viscometry gave an intrinsic viscosity of 4.7 dl g⁻¹ and the viscosity average molecular mass was calculated to be 9.18 × 10⁵ g mol⁻¹ using the Mark-Houwink relationship. The steady shear and dynamic viscoelasticity properties of tamarind seed gum in aqueous solutions at different concentrations were investigated at 20 °C using a Haake Rheometer RS75. The tamarind seed gum solutions clearly exhibited shear-thinning flow behaviour at high shear rate and Newtonian region occurred at low shear rate range, however, at higher concentrations, pronounced shear thinning was observed. The value of zero shear viscosity (η₀) was estimated by fitting Cross and Carreau models. The specific viscosity at zero shear rate (η_sp0) was plotted against the coil overlap parameter (C[η]) and the slopes of the lines in the dilute and semi-dilute regions were found to be ∼2.2 and 4.3, respectively. The value of the critical concentration (C^∗) was about 4.23/[η]. While, the mechanical spectra in the linear viscoelastic region of tamarind seed gum solutions showed the typical shape for macromolecular solutions. Plots of η versus γ and η^∗ versus ω were superimposable and hence obey the Cox-Merz rule.     

Rheological study of gum arabic solutions: Interpretation based on molecular self-association

This study deals with the rheological properties of aqueous solutions of gum arabic, the complex arabinogalactan polysaccharide containing about 2% protein. The flow behavior of control gum and a matured gum (EM2), which have different molecular associations, was investigated at different concentrations in water and added urea (6M) by rheological and dynamic light scattering methods. The influence of molecular association on rheological behavior of gum arabic solutions was studied. It was found that though Newtonian behavior was observed across a wide range of concentrations and at high shear rates, gum arabic solutions showed a pronounced shear thinning in low shear rate ranges. The maximum difference in viscosity between shear rate increasing and decreasing processes was observed at 6% for both control gum and EM2 in water, and at 3% for control gum and 9% for EM2 in urea solutions. The results demonstrated macromolecular association of gum arabic occurring in the solutions, and the observed time-dependent flow behavior reflected microstructural breakdown and re-building in the systems. This phenomenon was understood in view of the relationship between rheological properties and microstructural characteristics. A model was presented to interpret the rheological behavior, which is attributed to the occurrence of shear-induced breakdown and re-formation of gum arabic aggregates.     

Rheological and equilibrium properties of milk proteins and tara gum mixtures

The stability of aqueous purified tara gum (TG) mixtures with sodium caseinate (NaCas) and whey protein concentrate (WPC) was investigated. Phase diagram of TG–milk proteins mixtures was obtained by measuring the sedimented fraction or the rheological parameters. The rheological behaviour was also evaluated as function of NaCas and WPC concentration, considering the zero-shear rate viscosity and the relaxation time as response variables. The rheological parameters were determined by rotational rheometry. The studied solutions presented a meta-stable condition provided by the increase in viscosity, while mixtures with NaCas at low TG concentrations sedimentation by volume exclusion occurred. The rheological behaviour of NaCas and WPC aqueous solutions approached the Newtonian and shear-thickening model, respectively. The mixtures with TG showed a pseudoplastic behaviour, approaching the Cross model. The results indicated interaction between TG and the studied proteins, expressed by an increase of zero-shear viscosity and the relaxation time at higher gum concentration.     

Rheological properties of gum arabic solution: From Newtonianism to thixotropy

The influence of molecular association on the rheological behavior of gum arabic solution was studied. Using time-dependence of transient shear stress a reversible molecular association could be arrested and the thixotropy of gum arabic solution was interpreted. The structural breakdown, buildup and the effect of shear history due to molecular association could be related using the Casson’s equation. Stress jump measurements distinguished the effect of molecular association on the elastic and viscous contributions of shear stress. An elastic-like contribution dominated at low shear rates whereas the viscous component became important at high shear rates. The elastic contribution was strongly affected by the molecular association of gum arabic, with increased molecular association contributing to a larger elastic contribution. The elastic and viscous contributions were also investigated in transient flow. Both of the contributions increased with rest time, indicating a buildup of molecular association. With increasing the rest time the elastic contribution increased much faster than the viscous contribution to the total stress.     

黄原胶流变学特性的研究

分别研究了黄原胶浓度、温度、热处理时间、pH值、抗氧化剂VC、氧化剂H2O2、金属离子以及大豆分离蛋白对黄原胶黏度的影响.实验结果表明,随着黄原胶浓度的增大,黏度增大直至基本不变;温度、热处理时间使其黏度稍微有所下降:pH值为6.0时,黏度最大;抗氧化剂VC、氧化剂H2O2使黏度降低;随着金属离子Na+、Fe2+浓度的增大,黄原胶黏度呈下降变化;大豆分离蛋白使黄原胶黏度有所增加.     

Rheological properties of emulsions containing milk proteins mixed with xanthan gum

Oil in water emulsions (30% w/w) containing mixtures of milk proteins with xanthan gum were rheologically characterized at ambient temperature and the evolution of their properties was measured during a month under cold storage. The milk proteins used were sodium caseinate and whey concentrate at 2% mixed with xanthan gum at 0.3% or 0.5%. Emulsions properties were compared to those of respective aqueous systems and in general showed same rheological behaviour as their respective aqueous system, however, emulsions presented higher consistency index, due to oil droplets concentration. The flow behaviour index showed a small variation, increasing its value slightly. The consistency of emulsions with xanthan was similar, independently of the milk protein used, confirming that xanthan rheology predominates on emulsion rheology.     

Rheological properties of Cedrela odorata gum exudate aqueous dispersions

Rheological studies of Cedrela odorata gum aqueous dispersions demonstrated viscoelastic properties. Mechanical spectra derived from small amplitude oscillatory shear (SAOS) results support the onset of gel-like structure at given conditions (10% w/v, 20 °C). The increase in the storage and loss moduli, along with the drop in their frequency dependence, observed at higher gum concentrations, indicates a slower relaxation mechanism, which may be related to the increasing number and structural complexity of transient junction zones among macromolecules. The transition from gel-like to sol-like structure, at higher temperature, was detected from SAOS results. The flow behaviour of the aqueous gum dispersions under steady shear is highly non-Newtonian and can be modelled by the Sisko equation. The Cox–Merz rule was found to fail at critical gum concentration for the onset of gel-like behaviour and also at a temperature slightly above the gel–sol transition. C. odorata gum aqueous dispersions may have interesting applications as stabilisers of emulsions and suspensions on account of their rheological behaviour.     

Rheological properties of cereal starch gels and Mesona Blumes gum mixtures

The effect of Mesona Blumes gum (MBG) was examined on steady and dynamic shear of MBG/rice starch and MBG/wheat starch gels. In addition, stress relaxation and creep tests were performed for two types of cereal starch gels. The flow curves of both MBG/starch gels exhibited pseudoplastic behavior at shear rates between 0.01 and 10 s⁻¹, and the data were fitted into the power law model (R² = 0.91–0.98). Dynamic mechanical spectrum showed that all gels were strong gels in frequency between 0.1 and 10 Hz. Stress relaxation data at different strains indicated a strain‐softening phenomenon for both gels. Data were fitted into Maxwell model (R² = 0.91–0.98). Creep curves were conducted at the shear stress 6.4 Pa within linear viscoelastic region of both MBG/starch gels. Data were fitted into Burgers model (R² = 0.91–0.98). Apparent viscosity η, storage moduli G′, equilibrium stress relaxation modulus G_e and zero apparent viscosity η₀ of MBG/rice starch gels decreased in the following order: 6/0>6/0.5>6/0.35>6/0.1 (starch/gum w/w). Whereas η, G′, G_e, and η₀ of MBG/wheat starch gels increased gradually along side the increase of MBG contents. The stress relaxation time λ of MBG/rice starch gels increased in the following order: 6/0<6/0.5<6/0.35<6/0.1 (starch/gum w/w) while λ of MBG/wheat starch gels decreased gradually with the increase of MBG level. The influence of MBG on two examined cereal starch is totally opposite.     

Rheological properties of whey protein isolate stabilized emulsions with pectin and guar gum

Dynamic oscillatory and steady-shear rheological tests were carried out to evaluate the rheological properties of whey protein isolate (WPI) stabilized emulsions with and without hydrocolloids (pectin and guar gum) at pH 7.0. Viscosity and also consistency index of emulsions increased with hydrocolloid concentration. At γ = 20 s⁻¹, the value of viscosity of the emulsion with 0.5% (w/v) pectin was about fivefold higher than that of the emulsion without pectin. Flow curves were analyzed using power law model through a fitting procedure. Flow behaviour index of all emulsions except for containing 0.5% (w/v) guar gum was approximately in the range of 0.9–1.0, which corresponds to near-Newtonian behaviour. The shear thinning behaviour of emulsions containing 0.5% (w/w) guar gum was confirmed by flow behaviour index, n, of 0.396. Both storage (G′) and loss modulus (G″) increased with an increase in frequency. Emulsions behaved like a liquid with G″ > G′ at lower frequencies; and like an elastic solid with G′ > G″ at higher frequencies. Effect of guar gum was more pronounced on dynamic properties. Phase angle values decreased from 89 to <10° with increasing frequency and indicated the viscoelasticity of WPI-stabilized emulsions with and without pectin/guar gum.     

低酰基结冷胶流变行为研究

研究了浓度、温度、剪切速率、pH和离子浓度对低酰基结冷胶流变行为的影响。结果表明,低酰基结冷胶为典型的切力变稀流体,其表观黏度和剪切速率的关系符合幂律方程。在同一剪切速率下,表观黏度随温度的升高而降低。在同一温度下,结冷胶溶液的表观黏度则随着剪切速率的增加而减小。低酰基结冷胶凝胶强度随着Ca2+和Na+浓度的增加出现先增大后减小的趋势,相对于Na+而言,Ca2+形成的凝胶强度更高,且用量更少。     

Physical properties and applications of aqueous solutions of Albizia zygia gum

Some physical properties of aqueous solutions of African Albizia zygia (D.C.) Macbride have been evaluated. Approximately 80% of the gum is soluble in the cold with the remainder dispersed as fine particles of gel. pH titration of the gum indicates one acid group, pK_a = 3.8, for every three monosaccharide units. Solutions of the gum exhibit typical polyelectrolyte behaviour. The viscosity of the solutions increases with concentration but above 1.5% the solutions exhibit shear-thinning. The viscosity of an ice cream mix containing the gum and the properties of the resultant ice cream are compared with standard mixes.     

Rheological properties and gel strength of Phaseolus lunatus protein/carboxymethylated flamboyant gum systems

The rheological behaviour and gel strength of hydrocolloid mixture systems (HMSs) of carboxymethylated flamboyant gum (CFG) with protein hydrolysates (PHs) of Phaseolus lunatus were examined to evaluate the influence of the protein/polysaccharide ratio (2:1 and 3:1), pH (3 and 9) and concentration of solids, according to a 2³ factorial design. The protein concentrate of P. lunatus was hydrolysed with pepsin–pancreatin enzymes. The flow curve results were fitted to the Ostwald–de Waele model. The flow behaviour index (0.66–0.78) for all conditions studied was indicative of the shear‐thinning behaviour. For the HMS, the consistency index (k) values ranged from 0.4 Pa sⁿ to 1.2 Pa sⁿ. The analyses of variance showed that the ratio of PH/CFG and pH were the main variables that had significant effect on k values (P < 0.05). Only PH system presented a weak gel‐like viscoelastic behaviour. Both functional properties were affected by the protein degree of hydrolysis (DH).     

Rheological and microstructural properties of rennet-induced milk protein gels formed with Orchis anatolica gum

The effects of Orchis anatolica gum (OaG) on the structural and rheological properties of rennet-induced milk protein gels were investigated. OaG, at 0–0.15%, was added to reconstituted skim milk solutions of identical pH (6.60) and protein content (3.5%). Analyses included dynamic low amplitude oscillatory rheology, forced syneresis (FS) and confocal laser scanning microscopy (CLSM). Addition of 0.10% OaG to reconstituted skim milk solutions decreased the gelation time from 20.2 to 13.4 min, increased the gel firmness from 12.8 to 22.2 Pa and increased FS from 24.4 to 40.7% at 60 min. OaG affected formation of milk protein gel structure by increasing viscosity of the aqueous phase and inducing phase separation, with the balance of these effects dependant on the concentration of OaG. These insights on thermodynamic compatibility between OaG and milk proteins could provide unique functional properties to milk protein gels and facilitate innovation in cheese product development.     

Rheological properties of selected hydrocolloids as a function of concentration and temperature

In this study, rheological properties of several food hydrocolloids (carrageenan, pectin, gelatin, starch and xanthan) were evaluated using a rotational viscometer at three concentrations (1–6%, depending on the type of hydrocolloid) and four temperatures (20, 40, 60 and 80°C). Samples were subjected to a programmed shear rate increasing linearly from 0 to 300 s⁻¹ in 3 min, followed by a steady shear at 300 s⁻¹ for 10 min and finally a linearly decreasing shear rate from 300 s⁻¹ to 0 in 3 min. Experiments were performed in duplicate. In general, the power law model fitted most of the experimental results. Xanthan gum and carrageenan (at 20^oC) were exceptions, characterized by a yield stress and hence the rheograms were fitted with the Herschel-Bulkley model. Furthermore, gelatin showed a Newtonian behavior. Three models (power, exponential and polynomial) were used to evaluate the concentration effect on apparent viscosity. Arrhenius model was used to describe the temperature effect. Among the samples, carrageenan showed the most temperature dependency and xanthan gum, the least.     

葫芦巴胶改善吞咽障碍者饮水安全性的流变学研究

参照美国吞咽障碍膳食标准,以样品的 η50黏度为分类依据,将葫芦巴胶制备成黏度分别为180 cP(花蜜型)、1000 cP(蜂蜜型)和2500 cP(布丁型)的增稠流体,对其流变学性质进行研究,并评价葫芦巴胶用于改善吞咽障碍者的饮水安全性.结果表明,溶解温度是葫芦巴胶流变性质能否满足改善饮水安全性要求的关键.80℃制备...     

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.     

Rheological and physical characterization of film-forming solutions and edible films from tapioca starch/decolorized hsian-tsao leaf gum

Rheological properties of the film-forming solutions of tapioca starch/decolorized hsian-tsao leaf gum (dHG) as well as the structural properties and viscoelasticity of the resulting films were characterized as a function of dHG and glycerol concentrations. As compared to film-forming solutions with tapioca starch alone, the apparent viscosity, storage modulus and loss modulus of starch/dHG film-forming solutions increased, and tan δ decreased with increasing dHG. After casting of the film-forming solutions, all starch/dHG films showed relatively low opacity values. SEM and X-ray diffraction analysis revealed that all starch/dHG films exhibited homogeneous and highly amorphous structure. The extensional creep compliance of starch/dHG films increased with increasing glycerol concentration, implying weaker mechanical strength and higher mobility of polymer chains by the plasticizing effect of glycerol. However, addition of dHG pronouncedly increased the mechanical and elastic properties of tapioca starch films as evidenced by a decrease in extensional creep compliance and retardation time. Such results implied that dHG may possibly modify the network structure of tapioca starch film.