Dynamic viscoelastic study on the gelation of basil seed gum

Oscillatory measurements were used to investigate the effect of temperature and concentration on the viscoelastic and gelling properties of basil seed gum (BSG). Linear viscoelastic region was determined by strain sweep and it was found in 0.5% strain. Storage modulus (G′) was greater than loss modulus (G″) in all concentrations and they increased by improving BSG concentration. Yield stress value was determined by stress sweep and it increased from 1.40 to 7.47 Pa when BSG concentration increased from 1% to 3%. Frequency sweep showed BSG solution was a typical weak gel, and complex viscosity (η*) had linear correlation with frequency. The effect of temperature on gel forming was investigated during heating (20–90 °C) and cooling (90–20 °C) phases. BSG was characterised as a thermo‐reversible gel and did not have thermal hysteresis. Gelling temperature was raised as BSG concentration was increased. Exhibiting special rheological properties of BSG makes it as a proper synergistic gel, which can be applied in real food systems such as dairy desserts.     

The effect of shear on the rheology and structure of heat‐induced whey protein gels

The influence of mechanical shearing on the small deformation properties and microstructure of heat‐induced whey protein gel has been studied. The viscoelastic properties of these gels at different concentrations of 10% and 20% (w/w) exposed to different shear rates of 0, 50, 100, 200 and 500 s^?1 during gelation were measured using dynamic oscillatory rheometry. The structure of both the shear treated and unsheared gels was then investigated using light microscopy. The results showed that the storage modulus of the gels at both concentrations was increased by increasing the shear rate exposure during gelation while the shear‐treated gels were more elastic and showed frequency‐independent behaviour. As the total protein concentration of the gel increased, the viscoelastic properties of the gels also increased significantly and the gels showed greater elasticity. The gels obtained from the higher shear rate exposure were stronger with higher elastic moduli at both protein concentrations. Images of the gels obtained using light microscopy showed that shearing resulted in phase separation and some aggregation in the structure of the gels at both concentrations. However, the shearing rates applied in this study were not enough to cause aggregation breakdown in the gel network.     

Rheological,thermal and microstructural properties of whey protein isolate‐modified cassava starch mixed gels at different pH values

The objective of this study was to investigate the rheological, thermal and microstructural properties of whey protein isolate (WPI)‐hydroxypropylated cassava starch (HPCS) gels and WPI‐cross‐linked cassava starch (CLCS) gels at different pH values (5.75, 7.00 and 9.00). The rheological results showed that the WPI‐modified starch gels had greater storage modulus (G?) values than the WPI‐native cassava starch gels at pH 5.75 and 7.00. Differential scanning calorimetry curves suggested that the phase transition order of the WPI and modified starch changed as the pH increased. Scanning electron microscopy images showed that the addition of HPCS and CLCS contributed to the formation of a compact microstructure at pH 5.75 and 7.00. A comprehensive analysis showed that the gelling properties of the WPI‐modified starch were affected by the difference between the WPI denaturation temperature and modified starch gelatinisation temperature and by the granular properties of the modified starch during gelatinisation. These results may contribute to the application of WPI‐modified starch mixtures in food preparation.     

α‐Lactalbumin solubilisation from a precipitated whey protein concentrates fraction: pH and calcium concentration effects

The selective precipitation of α‐lactalbumin (α‐La) is the basis for one of the possible methods in whey protein fractionation. Calcium concentration, type of acid added and pH play important roles in α‐La precipitation and on the following resolubilisation. Two washing steps are enough for quantitative removal of β‐lactoglobulin entrapped in the precipitate. α‐La losses are minimised during washing steps (5%) when NaCl is used as washing agent. The most important parameter to control during the resolubilisation step is pH, the maximum amount of the initial re‐dissolved α‐La being 76% when the pH is adjusted to 7.5, CaCl2 concentration is 0.2 m and prior precipitation is carried out adding citric acid. Addition of CaCl2 is not necessary to dissolve α‐La because of the fact that there is enough calcium in the precipitate to join all α‐La; however, its presence improves the solubilisation yield (66% vs. 75%).     

The effect of pH,salts and sugars on the rheological properties of cress seed (Lepidium sativum) gum

Effect of shear rate (15–600 s^?1), gum concentration (1–2%), pH (3–9), sucrose (10–40%), lactose (5–15%), NaCl (100–300 mm ) and CaCl₂ (5–50 mm ) was evaluated on apparent viscosity (η_a), flow behaviour index (n), consistency coefficient (K) and yield stress (τ₀) indices of cress seed gum (CSG) solutions. Different rheological models were used to fit the experimental data, although the Herschel–Bulkley model was found the best model. An increase in gum concentration led to an increase in τ₀, η_a, and k and a decrease in n values. The addition of salts lowered the k value; however, the n value showed slight significant change. The presence of sugar resulted in the enhancement of n, k, τ₀ and η_ap values. The existence of yield stress and pseudoplastic behaviour of CSG, its stability against salts, wide range of pH and synergic effect of sugar make it a good thickener and stabiliser in food formulations.     

Development of low‐fat sausages using basil seed gum (Ocimum bacilicum L.) and gelatin as a fat replacer

This research was performed to evaluate the rheological properties of myofibrillar protein gels (MPs) with basil seed gum (BSG) alone or in combination with gelatin (0.25%, 0.5%), and to determine the physicochemical properties of low‐fat sausages (LFSs) manufactured with BSG alone (0.5%) or combined with gelatin (0.25%). Viscosity and cooking yields (%) of MPs with BSG alone or in combination with gelatin were higher than those of the control. However, gel strength of MPs with the combination of BSG and gelatin (0.25%) was higher than that with BSG alone. The combination of BSG and gelatin produced a more stable and denser structure than control or BSG alone. In the LFSs, the addition of BSG reduced the percentages of expressible moisture and cooking loss, and the combination of the BSG and gelatin improved gumminess and cohesiveness compared to BSG alone. The use of BSG as a water binding agent and gelatin to improve gel formation will be considered as fat replacer for the manufacture of low‐fat comminuted sausages.     

乳清分离蛋白-黄原胶复合乳化剂制备南瓜籽油O/W型乳液及其稳定性北大核心CSCD

为提高南瓜籽油(PSO)的稳定性,以及提高由单一乳清分离蛋白(WPI)作为乳化剂制备的水包油(O/W)型乳液的稳定性,制备了黄原胶(XG)与乳清分离蛋白协同稳定的南瓜籽油O/W型乳液,探究了黄原胶添加量及添加顺序对乳液性质及其稳定性的影响。结果表明:黄原胶质量浓度为2.0 mg/mL时,乳液平均粒径最小,为(10.53±0.06)μm,而ζ-电位绝对值最大,为(37.92±0.61)mV,乳液稳定性最好;黄原胶添加顺序不同,乳液稳定性有所差别,其中乳液WPI-PSO-XG(乳清分离蛋白与南瓜籽油乳化得粗乳液,再加黄原胶二次分散得到的乳液)的物理和化学稳定性最好;加速氧化实验显示,乳液的过氧化值(POV)及硫代巴比妥酸反应物(TBARS)值均低于南瓜籽油,其中乳液WPI-PSO-XG的POV和TBARS值最低,与南瓜籽油相比,分别降低了16.13 mmol/kg和17.63μmol/L,表现出良好的氧化稳定性。说明南瓜籽油与乳清分离蛋白制备成初乳液,再加入黄原胶,可使乳液稳定性提高。     

Effects of β‐glucans on properties of soya bean protein isolate thermal gels

The effects of concentration and molecular weight of oat β‐glucans on properties of soya bean protein isolate (SPI) thermal gels prepared by heating at 90℃for 30 min were investigated. Compared with control (free of β‐glucan) formulations, the presence of β‐glucans (0.5–1.5%, w/v) largely enhanced storage modulus (G′) and texture properties of SPI (12%, w/v) thermal gels measured by dynamic oscillatory rheometry and texture profile analysis, which were developed as increasing β‐glucan concentration and molecular weight. It is possible that β‐glucans could cause the formation of protein aggregates to produce gels through hydrophobic interactions. Mixed gel systems at low ionic strength showed higher G′ resulting from the lower denaturation temperature of SPI, which was beneficial to the formation of gel structure. In addition, although adding a certain amount of β‐glucan into SPI reduced water‐holding capacity of mixed gels, high molecular weight of β‐glucan improved their water‐holding capacity compared to control formulations attributed to the improvement of the structural integrity of the mixed gel network.     

Effect of heating temperature,pH, concentration and starch/whey protein ratio on the viscoelastic properties of corn starch/whey protein mixed gels

The viscoelastic properties of corn starch (CS) gels were more dependent on heating temperature, while the properties of whey protein isolate (WPI) gels were more dependent on pH. Thus heating temperature (75, 85, 95 °C) and pH (5, 7, 9) were varied to obtain a series of mixed gels with interesting viscoelastic properties. WPI gels showed extensive stress relaxation (SR) indicative of a highly transient network structure, while CS gels relaxed very little in 2000 s. Based on SR results, it appeared that CS/WPI mixed gels with 25 and 50% CS formed compatible network structures at 15% total solids only at pH 9. This supposition was supported by SEM microstructures obtained for dehydrated gels and a synergistic increase in the large‐strain fracture stress for these gels. Some synergy was also found for mixed gels at 30% total solids at pH 9, while at pH 7 the mixed gels seemed to contain separate additive WPI and CS networks unlike the case for pH 7 at 15% total solids. In both cases (15 and 30% total solids) the degree of elasticity of the mixed gels decreased as the WPI content increased. Mixed gels (CS:WPI = 0.5) at pH 9 showed increased fracture stress and fracture strain relative to the same gels at pH 7. This suggests that a unique chemical compatibility exists at pH 9 and results in gels that combine the elasticity of CS and the internal stress dissipation of WPI. © 2001 Society of Chemical Industry     

Stability of protein‐stabilised β‐carotene nanodispersions against heating,salts and pH

BACKGROUND: Milk proteins are used in a wide range of formulated food emulsions. The stability of food emulsions depends on their ingredients and processing conditions. In this work, β‐carotene nanodispersions were prepared with selected milk‐protein products using solvent‐displacement method. The objective of this work was to evaluate the stability of these nanodispersions against heating, salts and pH. RESULTS: Sodium caseinate (SC)‐stabilised nanodispersions possessed the smallest mean particle size of 17 nm, while those prepared with whey‐protein products resulted in larger mean particle sizes (45–127 nm). Formation of large particles (mean particle size of 300 nm) started after 1 h of heating at 60 °C in nanodispersions prepared with SC. More drastic particle size changes were observed in nanodispersions prepared with whey protein concentrate and whey protein isolate. The SC‐stabilised nanodispersions were fairly stable against Na⁺ ions at concentrations below 100 mmol L^?1, but drastic aggregation occurred in ≥ 50 mmol L^?1 CaCl₂ solutions. Aggregation was also observed in whey protein‐stabilised nanodispersions after the addition of NaCl and CaCl₂ solutions. All sample exhibited the smallest mean particle size at neutral pH, but large aggregates were formed at both ends of extreme pH and at pH around the isoelectric point of the proteins. CONCLUSION: The nanodispersions prepared with SC were generally more stable against thermal processing, ionic strength and pH, compared to those prepared with whey proteins. The stable β‐carotene nanodispersions showed a good potential for industrial applications. Copyright © 2008 Society of Chemical Industry     

Influence of tragacanth gum exudates from specie of Astragalus gossypinus on rheological and physical properties of whey protein isolate stabilised emulsions

The aim of this work was to investigate the effects of Iranian tragacanth gum (Astragalus gossypinus) (0.5, 1 wt.%), Whey protein isolate (WPI) (2, 4 wt.%) and acid oleic‐phase volume fraction (5, 10% v/v) on droplet size distribution, creaming index and rheological properties of emulsions with various compositions. Rheological investigations showed that both loss and storage modules increased with gum and oil contents. However, the viscoelastic behaviour was mainly governed by the gum concentration. Delta degree (storage and loss modules ratio) increased with frequency indicated that liquid like viscose behaviour dominates over solid like elastic behaviour. The shear‐thinning behaviour of all dispersions was successfully modelled with power law and Ellis models and Ellis model was founded as the better model to describe the flow behaviour of dispersions. Droplet size distribution was measured by light scattering; microscopic observations revealed a flocculated system. Increase in gum, WPI and oil contents resulted in decrease in creaming index of emulsions with dominant effect of gum concentration.     

Microstructure and elastic modulus of mixed gels of gelatin + oxidized starch: Effect of pH

The microstructure and elastic shear modulus of cold-set gels formed from high-sugar aqueous mixtures of gelatin (7 wt%) + oxidized starch (0-6 wt%) were investigated as a function of pH. Samples prepared at 90 °C, with citric acid added to adjust the pH, were rapidly quenched to ∼1 °C, subjected to a standard thermal treatment (40 °C for 10 min), and then investigated by confocal microscopy and small-deformation rheology at 24 °C. Under ‘natural’ conditions of pH ≈ 5.2 (no citric acid addition), the samples exhibited phase separation with a characteristic spinodal-type morphology. The spatial extent of the structural heterogeneity, expressed by a single length-scale parameter, was found to increase with starch concentration. Gradual acidification led to a reduction in this length-scale parameter, leading to complete inhibition of phase separation below a certain characteristic pH value in the range 4.5-4.9 (depending on starch content). Over the investigated pH range, the effect of starch addition was to reduce the storage modulus of the resulting gel. This reduction was more pronounced for the phase-separated samples. The pH of maximum rigidity was found to decrease from pH_max ≈ 4.6 for 0 wt% starch to pH_max ≈ 4.2 for 6 wt% starch. Taken all together, these observations can be understood in terms of the effects of pH on the cross-linking behaviour of the gelatin and the nature of the gelatin-starch electrostatic interactions. The microscopy results are consistent with a transition in behaviour from thermodynamic incompatibility (segregative interactions) at high pH to soluble complexation (associative interactions) at low pH.     

添加黄原胶的纯胶乳液稳定性及流变特性研究

通过对添加黄原胶(XG)的纯胶乳液粒径、稳定动力学参数、静态和动态流变特性的考察,探讨不同含量XG导致纯胶乳液失稳及致稳的机理,并制备出具有长期贮藏稳定性的纯胶乳液。研究发现,含0.1%、0.2%XG的纯胶乳液较易发生排斥絮凝,稳定性分析结果显示未添加XG的纯胶乳液30 d内的稳定性系数(SI)较低,90 d后底部背散射光强度(BS)降低,而含0.5%XG的纯胶乳液90 d内稳定性较好;流变特性检测结果表明随着XG含量的增加,纯胶乳液的表观黏度增加,流动性指数(n)由0.939降为0.414,触变环变大,体系的假塑性增强,含0.5%XG的纯胶乳液贮能模量(G')大于耗能模量(G″)且δ值小于45°,形成弱凝胶结构,具有长期贮藏稳定性。     

Structure and rheology of the κ-carrageenan/locust bean gum gels

The structure and interaction of κ-carrageenan and locust bean gum (LBG) has been studied using rheology, cryo-SEM, conductivity and syneresis characterization. The rheological behaviour of the binary system has been characterized using both compression and shear measurements. Elimination of slip in the shear measurements yields G′ values of the order 10,000–30,000 Pa for a 1% κ-carrageenan gel in 0–0.2 M added KCl. These values are higher than previously reported. No synergistic peak was found with the addition of LBG as has been previously reported. The measured modulii for these gels yields a Poisson's ratio of 0.5. Compression rupture stress and strain were also monitored. The rupture measurements do show a synergistic peak indicating that the interaction does occur and is important at high strain amplitudes. The gel points as determined by conductivity for these systems show a decrease in temperature with increasing LBG concentration, which is consistent with rheological measurements. Syneresis results are reported for the range of κ-carrageenan/LBG ratios. The syneresis shown by the mixtures is the same as that shown by the same concentration of κ-carrageenan. Structures of the gels as determined by cryo-SEM are also reported. Characteristic length scales in these systems are of the order of tens of microns and show little change with LBG concentration. The reduction in the characteristic length scale with increasing LBG concentration is discussed in terms of the rheological behaviour.