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     

Steady and dynamic shear rheology of starches from different oat cultivars in relation to their physicochemical and structural properties

Starches isolated from eight oat cultivars were tested for their physicochemical, structural, and rheological properties. The isolated starches had low levels of ash and nitrogen contents with amylose ranging from 21.8 to 32.3 g/100 g. The amount of water released from starch gels decreased significantly (p < 0.05) with increase in freeze thaw cycle. The scanning electron micrographs revealed the presence of polygonal to irregularly shaped starch granules. All the starches exhibited A-type X-Ray diffraction pattern typically characteristic of cereal starches. The rheological properties of pastes were well described by the Herschel-Bulkley model at a shear rate of 0–100 s^?1 (R² > 0.99). The starch pastes behaved like a pseudoplastic fluid and exhibited shear thinning fluid characteristics with values of flow behaviour index considerably less than 1. Both the storage and loss moduli of the pastes increased sharply initially and then dropped after reaching the gelatinization peak. The magnitude of the dynamic rheological parameters varied significantly (p < 0.05) between the cultivars. All the starch pastes were highly elastic than viscous as evidenced by the lower tan δ values. Structure property relationships were established between starches using principal component analysis.     

Microstructure and rheological properties of psyllium polysaccharide gel

The strong gelling property of psyllium polysaccharides is closely related to its health benefits and applications, such as use as a binding agent in the landscape industry. However, information about gelling properties of psyllium polysaccharides is very limited. To explore the gel properties of psyllium, the alkaline extracted gel fraction (AEG) of psyllium polysaccharides was studied in this investigation. The rheological and low-temperature electron microscopy methods including cryo-scanning electron microscopy (Cryo-SEM) and freeze-substitution for transmission electron microscopy (TEM) were used to investigate Ca²⁺ influence on the gel properties of AEG. AEG formed a weak gel with a fibrous appearance. AEG did not have a sharp melting point and exhibited no thermal hysteresis during heating and cooling procedure. The origin of this gelling behaviour was due to the fibrillar gel structure of psyllium polysaccharide. It was found that Ca²⁺ had a significant influence on the gel properties and microstructure. Elastic modulus G′ of gel increased as Ca²⁺ concentration increased. Critical strain S at first increased and then decreased as Ca²⁺ concentration increased. AEG gel became more resistant to temperature change on addition of Ca²⁺. Psyllium gel changed to aggregated gel with added Ca²⁺. The strands of gel appeared thicker and the density of the junction zone increased with increasing Ca²⁺ concentration as revealed by SEM and TEM. The changing bulk gelling properties of psyllium polysaccharide by adding Ca²⁺ was attributed to the change in gel structure.     

Swallowing profiles of food polysaccharide gels in relation to bolus rheology

Swallowing profiles of food polysaccharide gels were investigated in relation to bolus rheology. Polysaccharide gel from either gellan gum or a mixture of gellan gum and psyllium seed gum was used as a model food. Acoustic analysis and sensory evaluation were carried out to investigate the swallowing profiles using the same human subjects. Model bolus was prepared through instrumental mastication using a mechanical simulator to mimic the action of the human jaw in the presence or absence of artificial saliva and was subjected to dynamic viscoelasticity measurements to investigate the rheological properties. Bolus from the binary gel was shorter in time required to transfer through the pharyngeal phase due to mass flow and was scored higher in sensory perceived cohesiveness (bolus forming) than that from gellan gum gel. Model bolus from the binary gel showed a rheologically weak gel (or structured fluid) behavior and was higher in structural homogeneity than that from gellan gum gel. Also, dynamic viscoelasticity parameters of the binary gel were less dependent on the addition level of saliva. Results indicate that the viscoelasticity balance is a key for texture design of dysphagia foods in relation to the saliva miscibility.     

Effect of heating temperature and sodium chloride concentration on ultrastructure and texture of gels made from giant squid (Dosidicus gigas) with addition of starch,l-carrageenan and egg white

This paper seeks to compare the ultrastructure of gels made from frozen muscle of giant squid (Dosidicus gigas) at various temperatures with a number of different rheological parameters, with reference to a variety of added ingredients (non-muscle proteins and hydrocolloids) and to NaCl concentration. Interesting data on gel rheological properties were found where formulae containedl-carrageenan, starch and egg white, with a low salt concentration (1.5%). This seems to be because carrageenan forms an independent network which supports the principal structure formed by the fish protein; starch is incorporated into the network and retains water; and egg white forms a supplementary network which helps to improve rheological properties.     

Rheological properties of acid-induced soy protein-stabilized emulsion gels in the absence and presence of N-ethylmaleimide

The storage modulus (G′) and fracture properties of the non-treated and NEM-treated emulsion gels were investigated in the absence and presence of unadsorbed soy protein aggregates (USPA). In the absence of USPA, a decrease in the G′ of emulsion gels was observed after NEM treatment. However, in the presence of USPA, the addition of NEM only slightly decreased the G′ (p < 0.05). For both non-treated and NEM-treated emulsions, a ∼63-folds higher G′ value was obtained after the USPA addition. These results revealed the presence of sulphydryl group – disulfide bond interchange reactions at ambient temperature and under acidic conditions. In the absence of USPA, the sulphydryl group – disulfide bond interchange reactions was the main interactions responsible for the higher G′ values of non-treated emulsion gels, but for the emulsions with USPA presented, the large quantity of non-covalent interactions (e.g. hydrophobic group & hydrogen bonds) is the main interactions responsible for the aggregation and gelation of emulsion droplets. In the presence of USPA, the sulphydryl group – disulfide bond interchange reactions formed in the non-treated emulsion gels did not increase the final G′ but increased the stability of network. A power law relation was observed between the USPA concentration and the final G′, as well as between the oil volume fraction and the fracture stress/strain.     

The effects of xanthan conformation and sucrose concentration on the rheological properties of acidified sodium caseinate–xanthan gels

Xanthan solution transitions caused by annealing at different temperatures were studied by oscillatory rheology. The rheological behaviour of solutions evaluated at 10 °C showed different irreversible xanthan transitions, depending on the annealing temperature. The effect of xanthan conformation and caseinate, xanthan and sucrose concentrations on the mechanical and stress relaxation properties of acidified dairy gels were also investigated. Xanthan transitions produced different structural characteristics in mixed gels, as observed by their relaxation time and residual stress. The amount of sucrose played an important role in the network formation of gels and on the final elasticity. Intermediate concentrations of sucrose yielded gels that were finer than those obtained with low sucrose content, whereas at high amounts of this co-solute, the gels became more fragile. This quadratic effect of sucrose occurred at lower sucrose contents than in protein–sucrose or polysaccharide–sucrose systems. The mechanical properties at equilibrium were affected only by the strength of the interactions between caseinate and xanthan.     

Development and characterization of a novel biodegradable edible film obtained from psyllium seed (Plantago ovata Forsk)

In this study, the physical, thermal and mechanical properties of a novel edible film based on psyllium hydrocolloid (PH) were investigated. PH films were prepared by incorporation of three levels of glycerol (15%, 25%, and 35% w/w). As glycerol concentration increased, water vapor permeability (WVP), percent of elongation (E%) and water solubility of PH films increased whilst, tensile strength (TS), surface hydrophobicity and glass transition point (T_g) decreased significantly. At the level of 15% (W/W) of glycerol, PH films showed the lowest WVP values (1.16 × 10⁻¹⁰ g H₂O m⁻² s⁻¹ MPa⁻¹), E% (24.57%) and water solubility (47.69%) and the highest values for TS (14.31 MPa), water contact angle (84.47°) and T_g (175.2 °C). By increasing glycerol concentration, PH films became slightly greenish and yellowish in color but still transparent in appearance. This study revealed that the psyllium hydrocolloid had a good potential to be used in producing edible films with interesting specifications.     

The effects of psyllium supplementation on body weight,body mass index and waist circumference in adults: A systematic review and dose-response meta-analysis of randomized controlled trials

Abstract

Background: Previous studies reported inconsistent findings regarding the effects of psyllium supplementation on obesity measures. This systematic review and meta-analysis was performed to summarize data from available randomized clinical trials (RCTs) on the effect of psyllium supplementation on body weight, body mass index (BMI), and waist circumference (WC) in adults.

Methods: PubMed, SCOPUS, Cochrane Library, and Google Scholar were searched to identify relevant articles up to August 2018. The effect sizes were presented as weighted mean difference (WMD) and 95% confidence intervals (CI) by using random effects model. To detect dose-response relationships, we used fractional polynomial modeling.

Results: A total of 22 RCTs were included. Meta-analysis did not find any significant effect of psyllium supplementation on body weight (MD: ?0.28?kg, 95% CI: ?0.78, 0.21, p?=?0.268), BMI (MD: ?0.19?kg/m², 95% CI: ?0.55, 0.15, p?=?0.27) and WC (MD: ?1.2?cm, 95% CI: ?2.6, 0.2, p?=?0.09). Subgroup analysis showed that psyllium dosage, kind of psyllium administration, duration of trial, study design, sample size, and gender were potential sources of heterogeneity. Moreover, there was nonlinear association between duration of psyllium consumption, BMI and WC.

Conclusion: Psyllium supplementation does not reduce body weight, BMI, and WC significantly.     

Physicochemical,Rheological, and Thermal Properties of Six Types of Honey from Various Floral Origins in Tunisia

The present study was undertaken to determine the physicochemical, rheological, and thermal properties of six types of Tunisian honey samples from various floral origins (eucalyptus, orange, thyme, mint, rosemary, and horehound). All the honey samples exhibited non-Newtonian behavior at a shear rate ranging between 0.01 and 500 s^–1, with the highest levels of viscosity (µ) being observed for thyme, followed by eucalyptus, rosemary, mint, orange, and horehound honeys, respectively. The effect of temperature on the dynamic viscosity of the samples followed an Arrhenius-like pattern, with activation energy values ranging from 21.23 to 34.91 kJ/mol. The results from oscillatory rheology analysis also revealed that the loss modulus predominated over the storage one in the whole frequency range. As determined by differential scanning calorimetry, the glass transition (T_g) and melting temperatures of the Tunisian honey samples varied between –41.55 and –47.06 °C and between 197.9 and 221.1°C depending on their sugar compositions, respectively.     

Preparation and swelling properties of a pH‐sensitive superabsorbent hydrogel based on psyllium gum

A series of natural polymer‐based superabsorbent hydrogels were prepared by free radical graft copolymerization of partially neutralized acrylic acid (AA) onto psyllium gum (PSY) in aqueous solution, using ammonium persulfate (APS) as the initiator, and N,N′‐methylenebisacrylamide (MBA) as the crosslinker. Fourier transform infrared spectroscopy (FTIR) confirmed that AA monomers have been grafted onto PSY macromolecular chains. The swelling properties of the hydrogels in various saline and pH solutions were investigated, and the swelling kinetics and reswelling ability of the hydrogels were also evaluated systematically. The hydrogels showed excellent responsive properties and reversible On‐Off switching characteristics in various pH buffer solutions, which render the hydrogels available as a candidate for drug delivery system.     

Effects of concentration and temperature on carboxymethylcellulose rheology

The rheological properties of 0.5 to 2.0% carboxymethycellulose (CMC) solutions were measured at 30–90°C with a computer controlled rotational viscometer in a linearly increasing and decreasing three-cycle shearing sequence. CMC solutions showed power-law flow behaviour and rheological properties were significantly ( P < 0.01) influenced by both temperature and concentration. an empirical model was developed to relate the power-law parameters to both concentration and temperature.     

Effect of the type of fat on rheology,functional properties and sensory acceptance of spreadable cheese analogue

The objective of this work was to evaluate the effect of different types of fat (butter oil, partially hydrogenated soybean fat and soybean oil) on the functionality, rheology and sensory acceptance of spreadable cheese analogues. Analogues made with partially hydrogenated soybean fat or soybean oil in substitution to butter oil presented lower fat globule size. As a consequence, these analogues showed lower melting, lower spreadability, higher hardness and higher values for the elastic and viscous moduli than cheese made with butter oil. Despite not managing to imitate the flavour of the traditional cheese, the analogue made with partially hydrogenated soybean fat showed good sensory acceptance.     

Effects of vegetable oils on gel properties of surimi gels

The objective of this study was to determine effects of vegetable oils (soybean, peanut, corn, and rap oils) on the textural, color, microstructural, sensory and rheological properties of surimi gels. As the vegetable oil concentration increased in surimi gels, breaking force of gels was decreased (P < 0.05), while expressible water and whiteness values were increased (P < 0.05). Surimi gels with peanut oil had higher breaking force values, comparing to those with other vegetable oils. Transmission electron microscope shows the similar-size droplets of peanut oil and corn oil in surimi gels. Sensory evaluation indicated that fish balls with 10 g/kg vegetable oils were accepted in term of taste, color and overall likeness by the panelists. Storage modulus (G′) and loss modulus (G″) decreased along with increasing vegetable oil concentration. Results demonstrated that vegetable oils could be used potentially to modify the qualities of surimi-based products, such as color and taste.     

Characterization of commercial Spanish hummus formulation: Nutritional composition,rheology, and structure

Nutritional composition, rheological behavior, and structure of a commercial Spanish hummus were analyzed. The hummus is “high in fiber,” and Fe (1.9 ± 0.02 mg/100 g), Ca (65.7 ± 10.9 mg/100 g), Mg (66.8 ± 1.0 mg/100 g), P (164.9 ± 4.6 mg/100 g), and especially, K (250.7 ± 11.6 mg/100 g) are present in it. The hummus, with dispersion index of 4.14, behaved like a weak gel and exhibited hysteresis loops, and the Herschel-Bulkley model described its steady time-independent flow behavior. Complex viscosity and apparent viscosity at similar frequency and shear rate failed to follow the Cox-Merz rule.     

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 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.     

外源添加物和辅助加工技术对鱼糜凝胶动态流变中温度扫描的影响

综述了不同外源添加物及新型辅助加工技术对鱼糜凝胶过程储能和损耗模量的影响,从动态流变学角度,阐述鱼糜凝胶形成的机制,并展望了辅助加工技术和新型外源添加物在改善鱼糜凝胶性能和低盐鱼糜制品质地等方面的潜力。