Search

Microrheology provides a technique to probe the local viscoelastic properties and dynamics of soft materials at the microscopic level by observing the motion of tracer particles embedded within them. It is divided into passive and active microrheology according to the force exerted on the embedded particles. Particles are driven by thermal fluctuations in passive microrheology, and the linear viscoelasticity of samples can be obtained on the basis of the generalized Stokes-Einstein equation. In active microrheology, tracer particles are controlled by external forces, and measurements can be extended to the nonlinear regime. Microrheology techniques have many advantages such as the need for only small sample amounts and a wider measurable frequency range. In particular, microrheology is able to examine the spatial heterogeneity of samples at the microlevel, which is not possible using traditional rheology. Therefore, microrheology has considerable potential for studying the local mechanical properties and dynamics of soft matter, particularly complex fluids, including solutions, dispersions, and other colloidal systems. Food products such as emulsions, foams, or gels are complex fluids with multiple ingredients and phases. Their macroscopic properties, such as stability and texture, are closely related to the structure and mechanical properties at the microlevel. In this article, the basic principles and methods of microrheology are reviewed, and the latest developments and achievements of microrheology in the field of food science are presented.

It is necessary to control the rheological properties of bolus to prevent aspiration. To know the risk of aspiration for each person with difficulty in mastication and swallowing, it will be effective to use a test fluid which enables doctors to judge the safe range of the viscosity based on videofluorography. Since the knowledge of dominant factors which govern rheology is required, effects of shear rate, cooling rate, concentration of polysaccharides, coexisting seasonings on viscosity and viscoelasticity are overviewed. Since chemical senses are also known to affect the swallowing behavior, the relation between texture and flavor release is described briefly. Mixture of polysaccharides, proteins and fluid gels are overviewed as texture modifiers. Acoustic analysis of swallowing, extrusion method, a falling needle viscometer, tribological study on frictional coefficient of bolus are also described as each method is expected to be a useful tool to understand the complicated aspect of the disorder in mastication and deglutition. Mastication and swallowing of minced foods and model food gels are also described. Finally, the importance of the communication and collaboration between different disciplines is emphasized. Practical Applications Polysaccharides have been used to modify the texture of foods. It is necessary to know how these polysaccharides influence the swallowing behavior to design foods for elderly. Since the texture of foods is influenced by taste, aroma and conversely these are influenced by texture, the knowledge on the relation between texture and flavor release is crucial to manipulate the foods to reduce the risk of aspiration. Some examples which are expected to be helpful to design foods for elderly are shown. [ABSTRACT FROM AUTHOR]

Abstract: 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. [ABSTRACT FROM AUTHOR]

Acid equivalent weight, intrinsic viscosity and FT-IR measurements have demonstrated a polyelectrolyte nature to Lepidium sativum seed extract. The polyelectrolyte nature relates to the carboxyl groups carried by galacturonic acid and glucuronic acid unit. The seed extract exhibited pronounced shear thinning in steady shear rheology and a weak gel type behaviour in dynamic rheology when the concentration is high i.e. > 1%. Such behaviour suggests the ability of L. sativum seed extract to structure a liquid, thus showing the possibility of applying it as a novel thickener and stabiliser in aqueous systems. The characteristic could be due to a strong tendency of molecular association of L. sativum seed extract as found for high M/G ratio galactomannans, and possibly also the enhanced macromolecular entanglement due to relatively rigid chain conformation. Temperature dependence study showed that the rheological properties of L. sativum structured solution is stable against temperature variation. [ABSTRACT FROM AUTHOR]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: Gelation behavior of sodium alginate was investigated in an aqueous system at various CaCO3 doses using two alginate samples of different mannuronate (M)/guluronate (G) ratios but with comparable molecular masses. Macroscopic rheological properties of the polysaccharide were discussed during gelation in relation to microscopic supermolecular structures imaged by atomic force microscopy and Ca2+ binding. At fixed concentrations of the polysaccharide (0.5 w/v%) and glucono-δ-lactone (15mM) as an acidic material, the G-rich sample was higher in elasticity with rod-like molecular assemblies at the highest CaCO3 dose; 15mM, while the M-rich sample was higher in elasticity with network-like molecular assemblies at the lowest CaCO3 dose; 3.75mM. Gelation behavior near the sol-to-gel transition was generally described by the percolation model, except for the M-rich sample at the lowest CaCO3 dose. A critical CaCO3 dose corresponded to 7.5mM at which both alginate samples showed essentially the same gelation kinetics. In an equilibrium state, it was estimated that the G-rich sample was bound to larger amount of Ca2+ at the lowest CaCO3 dose, while the M-rich sample was bound to larger amount of Ca2+ at the highest CaCO3 dose. The amount of bound Ca2+ did not directly relate to elasticity of the system. Based on these results, dominant block structures are suggested for gelation. [Copyright &y& Elsevier]

It is demanded to supply foods with good quality for all the humans. With the advent of aging society, palatable and healthy foods are required to improve the quality of life and reduce the burden of finance for medical expenditure. Food hydrocolloids can contribute to this demand by versatile functions such as thickening, gelling, stabilising, and emulsifying, controlling texture and flavour release in food processing. Molar mass effects on viscosity and diffusion in liquid foods, and on mechanical and other physical properties of solid and semi-solid foods and films are overviewed. In these functions, the molar mass is one of the key factors, and therefore, the effects of molar mass on various health problems related to noncommunicable diseases or symptoms such as cancer, hyperlipidemia, hyperglycemia, constipation, high blood pressure, knee pain, osteoporosis, cystic fibrosis and dysphagia are described. Understanding these problems only from the viewpoint of molar mass is limited since other structural characteristics, conformation, branching, blockiness in copolymers such as pectin and alginate, degree of substitution as well as the position of the substituents are sometimes the determining factor rather than the molar mass. Nevertheless, comparison of different behaviours and functions in different polymers from the viewpoint of molar mass is expected to be useful to find a common characteristics, which may be helpful to understand the mechanism in other problems. Image 1 • Examples of rheology control by molar mass are shown. • High and low molar mass compounds often show opposite effects. • Effects of lower mass compounds on the properties of food polymers are discussed. • Molar mass effects in physiological function of foods are discussed. • Molar mass effects in flavour release are discussed. [ABSTRACT FROM AUTHOR]

Recently, research interests are growing regarding the formation and mechanisms of amyloid fibrils from plant proteins. This study investigated the fibrillization kinetics and rheological behaviors of panda bean protein isolate (PBPI) at pH 2.0 and 90 °C for various heating times (0–24 h). Results showed that PBPI formed two distinct classes of fibrils after heating for 10 h, including flexible fibril with a contour length of ∼751 nm, and rigid fibril with periodicity of ∼40 nm. The secondary structural changes during fibril formation were monitored by circular dichroism spectroscopy and indicated that β-sheet content increased first (0−12 h) and then decreased (>12 h), which coincided with similar changes in thioflavin T fluorescence. The gel electrophoresis revealed that the polypeptides of PBPI were progressively hydrolyzed upon heating, and the resulting short fragments were involved in fibril formation rather than PBPI monomer. PBPI-derived fibrils showed extremely high viscosity and storage modulus. A plausible molecular mechanism for PBPI fibrillation process was hypothesized, including protein unfolding, hydrolysis, assembly into matured fibrils, and dissociation of the fibrils. The findings provide useful information to manipulate the formation of legume proteins-based fibrils and will benefit future research to explore their potential applications. [Display omitted] • The self-assembling behavior of PBPI was time-dependent at 90 °C and pH 2.0. • PBPI self-assembled into flexible fibril and rigid fibril. • PBPI-derived fibrils possessed extremely high viscosity. • PBPI-derived fibrils showed excellent gelling performances. • PBPI fibrillation included unfolding and hydrolysis, aggregation, and disintegration. [ABSTRACT FROM AUTHOR]

The functions of low molecular-weight M w polyuronate on the calcium binding and calcium-induced gelation of normal sodium alginate (ALG) have been investigated. Mannuronate- and guluronate-rich fractions were prepared from ALG at two different M w for each. In the mixtures of ALG and each alginate fraction, changes in the relative viscosity of dilute solutions and rheological properties of the gels were examined after calcium addition. In dilute solutions, the mannuronate-rich fractions did not substantially alter the calcium binding behavior of ALG regardless of M w . On the contrary, the guluronate-rich fractions changed the calcium binding behavior of ALG, and more calcium was required for increase in the relative viscosity relating to the formation of egg-box dimers and subsequent aggregations. These results were more evident when M w of guluronate-rich fractions was lower. Gel rheology was also different between the mannuronate- and the guluronate-rich fractions. In the gels, both fractions decreased the storage modulus in the linear viscoelastic regime with increased yield strain, but these effects of the guluronate-rich fractions were greater than the mannuronate-rich fractions when compared at equivalent M w . These functions of the guluronate-rich fractions were quite different from those of low-methoxyl pectin fraction. By using well-characterized polyuronate samples, calcium-induced gelation for the mixture of ALG and each low M w polyuronate was compared on the molecular level. [ABSTRACT FROM AUTHOR]

Mixed gels containing κ-carrageenan, ι-carrageenan, konjac glucomannan and xanthan were investigated. In binary mixtures, the only interactions identified from differential scanning calorimetry were between konjac glucomannan and κ-carrageenan or xanthan. The effect of konjac addition on κ-carrageenan-ι-carrageenan mixed gels was similar to that on κ-carrageenan gels, namely, an initial increase of the elastic modulus was observed up to a certain stoichiometric ratio, followed by a plateau of the elastic modulus and a strong increase of the fracture strain when konjac was added in excess. Addition of xanthan led to maxima and minima of the elastic modulus and fracture strain and stress. Interestingly, characteristic features of the elastic modulus appeared at the same concentration of xanthan added to kappa-carrageenan/konjac glucomannan mixtures with or without iota-carrageenan, indicating that xanthan is present in the kappa-carrageenan/konjac phase and absent from the iota-carrageenan phase. Characteristic features of the fracture properties, however, were shifted to higher concentrations of xanthan when iota-carrageenan was added. We tentatively conclude that xanthan chains that are concentrated in the kappa-carrageenan/konjac phase under quiescent conditions achieve homogeneous distribution under large mechanical deformation. [ABSTRACT FROM AUTHOR]

Abstract: Fourteen commercial LM-pectin samples were investigated in this study. The degree of esterification (DE) varied from 9.6% to 42.0% and the degree of amidation (DA) from 0% to 25%. Chemical and structural characteristics were examined using atomic absorption (AA), dilute solution capillary viscometry, GPC-MALLS and dynamic light scattering. The intrinsic calcium was in the range of 47–1388ppm, the intrinsic viscosity varied from 2.9 to 4.9 (dL/g) and the weight average molecular weight (M w) from 113 to 290 (kDa). Most of the samples had Huggins constants of ∼0.5. However, for samples having acidic pH, Huggins constant values greater than 1, which can be as an indication of aggregation, were obtained. The high Huggins constant value could be reduced to ∼0.5 by the addition of 3M urea, indicating that the aggregation was stabilised by hydrogen bonding. Shear flow viscosity revealed three types of rheological behaviour. Type A showed pronounced shear thinning behaviour, which was reduced by the addition of hydrogen bonding breaking agent urea. Type B with intrinsic Ca of 1mM and pH ∼4 showed two shear thinning regions, with significantly enhanced shear viscosity upon addition of calcium. Type C showed the least aggregation due to its pH ∼4 and low intrinsic Ca, but could be converted to type B upon addition of Ca. The effect of Ca on the rheological behaviour of types B and C was further confirmed by CaCl2 and Ca-chelating agent (EDTA). Temperature affected the molecular conformation of all types and most significantly type A by eliminating the hydrogen bonding. [Copyright &y& Elsevier]

In the present work, the rheological properties of model boli were analysed based on the granular matter physics. Polysaccharide microgels mixed with artificial saliva were prepared as model boli. The storage modulus G ′ of alginate gel beads increased and then decreased with increasing content of artificial saliva. Surface of alginate gel beads prepared by dripping into calcium chloride solution were wiped to remove the moisture to mimic the oral condition of the Sjögren's syndrome. G ′ decreased monotonically with increasing artificial saliva beyond a certain amount of the added saliva, which is similar to the widely observed characteristic of wet granular materials. Although the analysis is limited to a model bolus at a certain stage of oral processing mimicked by instrumentally prepared microgels of uniform size and shape, it revealed some fundamental aspects highlighting the implication of a wet granular matter as a useful concept for further understanding of the bolus rheology. [Display omitted] • Polysaccharide microgels were prepared and mixed with artificial saliva. • Elastic modulus of a microgel was measured using Hertz theory. • Storage modulus of microgels increased and decreased with increasing saliva. • Smaller alginate microgels showed a peak modulus at a lower saliva content. [ABSTRACT FROM AUTHOR]

The number of persons with difficulty in mastication and swallowing is increasing and causes a social problem. Commercially available soft gels for disadvantaged persons are known to be crushed between the tongue and the hard palate, but the detailed mechanism is not well understood. After reviewing the safety and difficulty in eating, the significance of the tongue pressure is discussed. To avoid the complexity of the simultaneous action of the teeth and the tongue, squeezing with the tongue without teeth is studied. Squeezing of gels with different deformabilities between the tongue and palate is analyzed using an ultrathin sensor, and compared with the in vitro test using an artificial tongue and panellists' judgements of the strategy change from tongue-palate compression to chewing. It was clarified that the work of the tongue just before swallowing depends not only on the initial mechanical properties of foods but also on the oral processing before the swallowing. This poses a question on the prevailing view that the final mechanical properties just before swallow does not depend on the initial mechanical properties of ingested foods. The transition of the strategy from the tongue-palate squeezing to the teeth chewing was shown to be determined using an artificial tongue compression approach in combination with sensory evaluation to select the strategy. These findings can be a basis for understanding better the conditions necessary for designing food gels. The tangential force during squeezing should be analyzed in the future. • Food oral processing and difficulty in eating are overviewed. • Tongue pressure measurement is shown useful in the analysis of tongue-palate squeezing. • Change of mechanical properties of food gels during tongue-palate squeezing is clarified. • Tongue-palate squeezing has some limitation for bolus formation with increasing gel strength. • Transition from tongue-palate squeezing to chewing can be predicted by a simulation. [ABSTRACT FROM AUTHOR]

Abstract In this study, the influence of Persian gum (PG) on the properties of whey protein concentrate (WPC) emulsion gel prepared through cold set gelation method (incorporation of CaCl 2) was investigated. The mean droplet size of emulsions was analyzed prior to gelation and the emulsion gel samples were characterized by rheological studies, scanning electron microscopy (SEM) and water holding capacity (WHC) measurement. Results showed PG affected the droplet size of the initial emulsions and the matrix of gel systems. Emulsions containing 0.3% w/w PG revealed higher heat stability compared to the control. A viscoelastic behavior was observed for all emulsion gels with G′ being greater than G″ over the whole frequency range tested. Increasing the concentration of PG led to a change in the gel structure at pH 7. SEM images exhibited that PG at 0.3% w/w gave rise to an ordered honeycomb-like microstructure with an interconnected porous matrix of thin walls. In contrast, adding 0.6% w/w PG resulted in a non-uniform network with large pores of thick and rough walls and reduced the WHC. These findings suggest the viscoelastic properties and microstructure of WPC emulsion gel can be tailored by adjusting PG concentration for food formulations. Highlights • The structure-to-function properties of WPC emulsion gels containing PG were assessed. • The size of emulsion droplets and the structure of whey protein concentrate gel were influenced by Persian gum. • 0.3% w/w PG provided better WHC and ordered continuous microstructure in the system. • Microstructure and rheological properties of whey protein concentrate emulsion gels varied by Persian gum concentration. [ABSTRACT FROM AUTHOR]

In recent decades, microbial synthesis of polysaccharides with special functional properties has attracted increasing attention. This work reported a novel exopolysaccharide (EPS)-producing strain, Klebsiella sp. PHRC1.001 isolated from activated sludge. Physicochemical, rheological, emulsifying and toxicological properties of the obtained EPS were characterized. The EPS was mainly composed of d -glucose and l -arabinose, and was found to exist in aqueous solution in a nano-particulated form (∼50 nm in diameter) with a strong tendency of aggregation. Rheological analysis showed that the EPS aqueous solution was a typical pseudoplastic fluid at higher concentration and could form weak gel upon alkaline treatment followed by neutralization. The EPS exhibited excellent emulsifying properties in stabilizing oil-in-water emulsions presumably by a Pickering mechanism owing to its nanoparticle structure. Acute toxicity test showed that 1.8 g EPS per kg of body weight caused no toxic effect on mice. PHRC1.001 EPS has the potential to be a novel industrial polysaccharide. [ABSTRACT FROM AUTHOR]

The risk of dysphagia in the elderly has gradually become a social problem. An important strategy is to modify the food texture to reduce aspiration risk. Microgel, a structured fluid usually prepared by Couette flow and jacketed stirring, has attracted much attention due to its unique rheological properties and complex microstructure. This study proposed a continuous production process of agar structured fluid through pipe wall laminar shear. The rheological properties and particle size distribution of the agar microgel were characterized. The morphology of microgel and its interaction with water molecules were examined through scanning electron microscopy (SEM) and low-field nuclear magnetic resonance (LF-NMR), and some positive feedback examples were obtained through the videofluorographic swallowing study (VFSS). A molecular model was proposed in which agar microgel is a supramolecular structure with a multidomain weak interaction, whose "hairy" structure is the site of domain-domain interaction. Agar microgel as a structured fluid can achieve higher yield stress and elastic modulus at the same concentration compared to xanthan gum solution, which is expected to be the next cost-effective and age-appropriate pre-thickened diet for older adults with dysphagia. [Display omitted] • A novel preparation method to obtain agar microgel with high efficiency is proposed. • The molecular model of agar microgel formation is developed. • The agar microgel is considered a multi-domain weak interaction supramolecular structure. • It deepened the understanding of the "hairy" structure, which is the site of domain-domain interaction. • The agar microgel is expected to become a new member of the dysphagia diet family. [ABSTRACT FROM AUTHOR]

[Display omitted] • Edible oleogels was fabricated using soy fiber particles (SFP) with water as the second fluid. • SFP oleogels with modulated properties can be obtained by particle size, particle content and the second fluid content. • Similar properties of bread made with edible oleogels was observed in comparison with using commercial butter. Oleogels containing less saturated and trans -fats were considered as an ideal option to replace the solid fats in foods. In this research, oleogel was fabricated by dispersing soy fiber particles (SFP) in soy oil, and further it was used in bread preparation. Effect of the particle size, particle content and the second fluid content on the formation of oleogels were evaluated, based on the appearance and rheological properties. Results showed that the suspension of SFP in soy oil (24%, w/w) could be transformed into gel-like state, upon the addition of the second fluid. The SFP based networks were dominated by the capillary force which was originated from the second fluid. The rheological properties and yield stress of the oleogels could be modulated by particle size and particle content of SFP in oil phase, as well as the second fluid content in the system. When the oleogels were applicated in bread preparation, a layered structure could be formed in the bread, indicating the possibility of replacing the solid fats in bakery products by our oleogels. Our results offered a feasibility approach for oil structuring with natural raw materials, and developed a new approach to replace the solid fats in foods. [ABSTRACT FROM AUTHOR]

[Display omitted] • Twelve legume proteins were classified into high, medium and low gel strength. • Phaseolin-rich BKPI, SKPI and PDPI formed high-strength gel regardless of pH. • Gel strength at pH 3.0 was significantly affected by electrostatic interactions. • Gel strength at pH 7.0 was significantly affected by hydrogen bonds. • Gel strength was negatively correlated with the non-network proteins content in gel. This study aimed to investigate the rheological and textural properties of heat-induced gels from twelve legume protein isolates at pH 3.0 and 7.0, including black kidney bean (BKPI), speckled kidney bean (SKPI), panda bean (PDPI), cowpea (CPPI), mung bean (MPI), adzuki bean (API), rice bean (RPI), black soybean (BPI), soybean (SPI), chickpea (CPI), broad bean (BRPI) and pea (PPI). SDS-PAGE revealed that 7S globulin was prominent protein in BKPI, SKPI, PDPI, CPPI, MPI, API and RPI, the main protein fraction of CPI was 11S globulin, and BPI, SPI, BRPI and PPI contained both 7S and 11S globulins as major components. Based on the gel's Power Law constant (K') and hardness, twelve legume proteins were divided into three categories with high, medium and low gel strength. BKPI, SKPI and PDPI with Phaseolin being the major protein fraction showed high gel strength regardless of pH. Electrostatic interactions, hydrophobic interactions and hydrogen bonds were the most important intermolecular forces in the formation of legume protein gel networks, of which gel strength at pH 3.0 and pH 7.0 was significantly affected by electrostatic interactions and hydrogen bonds, respectively. Moreover, gel strength was also remarkably negatively influenced by the non-network proteins. SEM observation indicated that the microstructure of gels at pH 7.0 was denser and more homogeneous than that at pH 3.0, leading to better water holding capacity. These findings would be of great importance for understanding the differences in legume protein gels, and also laid the scientific support for expanding applications of legume proteins in gel-based foods. [ABSTRACT FROM AUTHOR]

The gelation of β-lactoglobulin (BLG) and its fibrils was investigated in the presence of dithiothreitol (DTT) and transglutaminase (TGase). BLG fibrils were prepared by heating BLG at 80 °C and pH 2 for 10 h and then adjusting to pH 7. The structure of fibrils was observed by atomic force microscopy. The small and large amplitude oscillatory measurements were done to examine the gelation process and to get more insight into gel properties. It was shown that TGase alone could induce gelation for fibrillar BLG although it could not for non-fibrillar BLG. TGase could cross-link BLG fibrils to form a gel at very low protein concentration in comparison with other protein gels, and enhance the network formation of both non-fibrillar and fibrillar BLG in the presence of DTT. The scanning electron microscopic observation revealed that TGase increased the network density for non-fibrillar gels while it made network strands thicker for fibrillar gels. [ABSTRACT FROM AUTHOR]

This study characterized the shear and extensional rheology properties of whey protein fibril (WPF) dispersions under different heating times (1, 2, 4, 8, and 16 h), fibril lengths obtained from mechanical stirring times (2, 4, 6, and 8 h), and pH values (2.0, 3.5, 7.0, and 9.0). The WPF dispersions in the steady shear flow, exhibited shear-thinning and the dominant elastic behavior. The WPF dispersions' apparent extensional viscosity and characteristic relaxation times increased as the heating time was extended, and the strain hardening occurred after heating for 8 h. Fibril length had no significant impact on the WPF dispersions' shear rheology properties but greatly influenced their extensional flow behaviors, including the decreased break-up time and relaxation time of the filament after decreasing fibril length. The WPF dispersions at pH 3.5 showed the highest break-up time and relaxation time. In light of fibril entanglement and association in the strong flow field, these results provide a useful guideline for WPF applications in the food industry. [Display omitted] • The shear and extensional rheology properties of WPF dispersions were compared. • Effects of heating time, fibrils length and pH on the rheology were investigated. • Extensional flow was more sensitive to WPF dispersions alteration than shear flow. [ABSTRACT FROM AUTHOR]

The modulatory effect of oligoguluronate (GB) on the gelation of macromolecular alginate (ALG) was investigated by means of dynamic oscillatory rheology, fluorescence and AFM measurements. An inhibitory effect in the range of 0.25 < R (Ca/G) < 0.60 and a promotive effect in the range of R > 0.60, were quantified. The two effects are thought to be associated with the different molecular events that dominate the gelation of alginate, namely, egg-box dimerization and lateral aggregation. Quantitative analysis indicates a competitive binding rather than a screening binding during egg-box dimerization, which is responsible for the inhibitory effect in the lower Ca concentration regime. On the other hand, in the higher Ca concentration regime where alginate gelation is predominated by chain lateral aggregation, the dimers formed by GB could act as a binder to enhance the aggregation of alginate dimers, resulting in a promotive effect on alginate gelation. The results are consistent with the microstructures observed by AFM. [ABSTRACT FROM AUTHOR]

The effect of sucrose addition prior to or following the dissolution of agar on sucrose release from 1 wt% agar gels was studied. The order of addition was found to affect the fracture stress, fracture strain and sucrose release ratio. At sucrose concentrations below 30%, the rheology (fracture stress and strain) and structure of the gels did not depend on the order of addition of sucrose and agar. At sucrose concentrations >40%, however, the network structure of gels where sucrose was dissolved before agar addition was weaker than that of gels where sucrose was added after agar dissolution. The weaker network structure resulted in lower fracture stress and strain values. For gels prepared by adding agar to sucrose solutions, both fracture stress and strain decreased with increasing sucrose concentration in the range 40–55%. The decrease in fracture stress and strain led to an increase in the sucrose release ratio. The sucrose release ratio decreased monotonously with increasing concentration of sucrose when agar was dissolved prior to sucrose addition. The findings are discussed in relation to recent publications on gel inhomogeneity. [ABSTRACT FROM AUTHOR]

The effect of sucrose and agar concentrations on sucrose release from agar gels was investigated. It was found that the sucrose release ratio decreased with increasing sucrose concentration and with increasing fracture stress, which is consistent with previous findings. High correlation was found between the fracture stress, sucrose concentration and the sucrose release ratio. The total amount of sucrose released showed a maximum at a certain sucrose concentration, indicating that sucrose addition to enhance sweetness intensity may be ineffective or even counterproductive beyond a certain limit. [ABSTRACT FROM AUTHOR]

• PDPI showed good foaming and emulsifying properties. • PDPI formed high-strength gels at pH 3.0, 7.0 and 9.0. • PDPI possessed more superior amino acid composition than SPI and PPI. • PDPI had excellent protein efficiency ratio. Panda bean protein isolate (PDPI), a legume-protein with Chinese characteristics, was investigated as an alternative potential food protein source. The physicochemical characteristics, functional properties and amino-acid composition of PDPI were determined and compared with soybean (SPI) and pea protein isolate (PPI). Results showed that PDPI was rich in phaseolin (mainly 7S vicilin), and its molecular weight was lower than that of SPI and PPI which were rich in legumin and vicilin. In comparison to SPI and PPI, PDPI showed the lowest solubility, surface-charge and surface-tension at pH 3.0, 7.0 and 9.0, but it exhibited comparable or even superior functionalities, especially in emulsifying and foaming abilities, gelling behaviour, rheological and textural properties. Moreover, the amino-acid composition and protein efficiency ratio of PDPI were excellent. The knowledge gained in the study is expected to provide reliable scientific science data for the potential application of PDPI in the food industry. [ABSTRACT FROM AUTHOR]

Abstract: The seeds of Lepidium sativum (Garden Cress) were selected as a new source of hydrocolloid and its chemical composition and molecular parameters were determined. The macromolecular component of the extract had a molecular weight of 540 kDa, and was nearly as rigid as xanthan with regard to chain conformation. The main rheological features were investigated as a function of shear rate, concentration and temperature. The extract exhibited strong shear-thinning behaviour, which was even more pronounced than for xanthan. An increase in concentration or temperature led to an increase in pseudoplasticity. The Arrhenius model was applied to the temperature dependence of viscosity, and the activation energy (Ea ) was found to decrease with increasing concentration. The extract solutions showed thixotropic behaviour at all the concentrations and temperatures studied, and the first-order stress decay model with a non-zero equilibrium stress fairly described the time-dependent behaviour. The rheological characteristics found indicated a potential application of the extract as a novel thickener. [Copyright &y& Elsevier]