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Instrumental characteristics from extensional rheology and tribology for aqueous xanthan gum (XG) and locust bean gum (LBG) solutions were studied in the presence or absence of simulated saliva. Extensional viscosity was calculated from the filament shrinkage behavior using a capillary breakup extensional rheometer, whereas the friction coefficient was measured using a set-up consisting of polydimethylsiloxane substrate and a glass ball bearing on a rotational rheometer. Increase in extensional viscosity was detected immediately after initiation of extensional flow, particularly XG, and also immediately before the filament rupture, particularly LBG. Extensional viscosity tended to decrease with increased addition of simulated saliva for XG, while to increase for LBG. In both cases, effect of cations in the saliva was greater than that of mucin. From the shape of the Stribeck curve (i.e., dependence of the friction coefficient on the entrainment speed) and comparison of the friction coefficient itself, lubricity of XG was greater than that of LBG. Simulated saliva added decreased the friction coefficient for each polysaccharide through functions of cations rather than mucin. Extensional viscosity and tribological measurements revealed mechanical properties of polysaccharide solutions which cannot be determined or quantified by shear viscosity alone.

The influence of the structure formed by the type of hydrocolloids (low-methoxyl pectin, the mixture of xanthan gum, and locust bean gum, and mixture of xanthan gum, and guar gum) and the aeration time (3, 5, 7, and 9 min) on textural properties of freeze-dried gels were investigated. The hardest texture generating the strongest acoustic emission was obtained by freeze-dried pectin gel, characterised by the lowest porosity and the largest pore diameter. Aeration time significantly affected mechanical and acoustic properties of the pectin gel lyophilisate. No effect of gel aeration time on tested characteristics of samples with mixture of hydrocolloids was observed. Strong positive correlations between acoustic energy as well as the maximum force and work and negative ones between porosity and pore diameter indicate that greater resilience and stronger acoustic emission of freeze-dried gels was caused by the reduction of porosity and the increase in the pore size of the material. Practical applications The research is expected to show the phenomenon of structure formation when preparing and freeze-drying gels and explain the influence of the process parameters (time of aeration, the type of hydrocolloids) on the formation of the internal structure and physical properties of a dried product, especially mechanical and acoustic properties. This achievement will contribute to the development of the science of food and human nutrition, especially within the context of the popular research on aerated diet products. The expected result will be the ability to develop a new technology for producing food with a delicate texture, using the phenomenon of sublimation. As a result, designing changes in the structure of freeze-dried fruit gels with a delicate structure will be possible due to the choice of ingredients and aeration parameters in order to develop innovative food characterised by favorable nutritional, health and functional properties, which will be attractive for the consumers.

In this research, simultaneous contribution of konjac-mannan (0.3%), xanthan (0.3%), and tragacanth (0.3%) gums in tomato ketchup was investigated comparing the physicochemical, rheological, texture, and sensory properties with the control sample containing 0.3% xanthan gum. Samples selected through viscosity and syneresis evaluation of the nine prepared samples were analyzed by color, flow behavior, frequency sweep, particle size, texture, and sensory experiments. Results indicated that increasing xanthan concentration did not have any significant effect on the apparent viscosity while considerable improvement was observed in the physical stability of ketchups containing konjac-mannan/xanthan ascribed to smaller particles with larger contact surfaces encouraging gel network formation. Highest a* and a*/b* was observed for konjac-mannan/xanthan (0.075%/0.225%) in which formation of hydrated gel granules of gums intensifies light diffraction due to the decreased particle size. This synergistically formed viscous three-dimensional gel network is responsible for the highest cohesiveness and gumminess of the same sample between the ketchup formulations containing two gums. Organoleptic properties of ketchup samples containing konjac-mannan/xanthan showed no significant difference with the control sample. PRACTICAL APPLICATIONS: Development of modern food technologies along with the lifestyle changes over the past few decades and grown public awareness of the relevance between health and nutrition have considerably increased the consumption of ready meals containing low-fat and fiber-rich functional condiments. Ketchup is a popular sauce thickened with tomato pulp powder, potato or corn starch, modified starch, and severally available hydrocolloids such as carboxymethyl cellulose, xanthan, guar, and locust bean gum. In this research work, mixtures of konjac-mannan and xanthan/tragacanth hydrocolloids are used to produce new ketchups with improved physical and rheological properties and lower prices.

Small amplitude oscillatory shear tests were performed to measure the elastic modulus of 1:1 xanthan–locust bean gum (X/L) mixed gels prepared with different total polymer concentrations (C = 0.1% to 3%). The critical concentration of X/L mixture was determined to be 0.15%. Based on the elasticity exponent (t) values, the concentration–modulus power–law relationship suggested the existence of two concentration regimes – a low concentration regime (0.15 ≤ C ≤ 0.5%) with tlow = 3.88 and a high concentration regime (0.5 ≤ C ≤ 3.0%) with thigh = 1.47. The elastic active network chain of X/L mixed gels was determined by the cascade model, and compared with the similar calculation based on the classical rubber elastic theory. The cascade model clearly showed the existence of nonideality parameter and enthalpic contribution to the X/L mixed gel. Practical applications The concentration dependence at the highest interaction might be useful for developing highly concentrated xanthan and locust bean gum mixture gels. Most studies of xanthan and locust bean gum mixtures focused only on the lower concentration regime. In this study the modulus at a higher concentration increased but eventually saturated.

The use of whey protein concentrate (WPC) for the improvement of physical properties of nonfat fermented milk drink was investigated. Drinks were prepared from nonfat milk powder and WPC at different proportions. Rheological properties, serum separation and particle size of the drinks were measured. The effect of WPC on the physical properties of the drinks was evaluated by comparison with those of commonly used stabilizers, including propylene glycol alginate and locust bean gum. WPC addition caused an increase in the consistency coefficient and thixotropy and a decrease in the particle size of the samples. There was no serum separation in the sample with 2% WPC. Large unstable aggregates were observed in the sample with 3% WPC, which also exhibited the highest serum separation. WPC up to a level of 2% positively influenced the physical properties of nonfat fermented milk drink similar to stabilizers. PRACTICAL APPLICATIONS Fermented milk drinks are consumed especially for their beneficial health effects. Physical properties of fermented milk drinks influence their quality and consumer acceptability. Hydrocolloid stabilizers are used for the improvement of physical properties of fermented milk products. Whey protein concentrates (WPC) with high protein content can be used to substitute hydrocolloid stabilizers. In this study, the effect of the addition of WPC with 75% protein in place of a part of the nonfat milk powder on the physical properties of nonfat fermented milk drink with 6% dry matter was investigated. Use of an appropriate level of WPC was found to be important for obtaining a desirable effect on the physical properties of nonfat fermented milk drink. The effect of WPC was found to be comparable to those of commonly used hydrocolloid stabilizers. Use of WPC also enhances the nutritional value of the product as whey proteins have a high biological value.

Locust bean gum (LBG) solutions and gels were studied in compression, and stress-relaxation was monitored by an Instron universal testing machine (UTM). The strength of the formed gels under freeze-thaw treatment was dependent upon the freezing and thawing rates and the temperature of freezing. LBG solution which froze at a rate of 50C/min was stiffer than those samples which froze at a rate of 1C/min. LBG solution thawed at a rate of 1C/min was stiffer than those samples which were thawed at 10C/min. Very high freezing rates may reduce the size of the formed ice crystals (less disturbance to network formation), while slow thawing may induce the favored gelation. LBG solutions frozen to -60C were stiffer than those frozen to -20C. A short holding time (up to 90 min) at the freezing temperature did not influence the strength of the cryogels. These parameters are important in building products which require a priori knowledge of their texture.

Single compression tests were applied to carrageenan plus locust bean gum model gels (1:1) without sucrose and with 40% added sucrose, and two commercial samples of quince jelly containing high levels of sucrose (55 and 72 °Brix). The samples were glued to the main platform of the texturometer. The tests were performed up to two different levels of compression. Negative area (A adh ), the time that the samples remained adhering to the probe (t adh ), and maximum negative force (F max ) during the decompression stroke were determined. All the parameter values for the commercial samples were greater than those for the model systems. A adh and F max were good indices of adhesiveness. The highest discriminative capacity in detecting sucrose levels of these two parameters was obtained at a low degree of compression; this could be because the samples had not suffered damage to their internal structure. Since the samples had high instantaneous recoverable springiness, the application of automated TPA proved inappropriate for obtaining a measurement of adhesiveness.

Texture profile analysis and rupture tests, respectively, at a deformation of 5 and 80%, were carried out on commercial kappa-carrageenan gel cylinders (3% w/v concentration) and on mixed gel cylinders (kappa-carrageenan/iota-carrageenan or locust bean gum [LBG], in different proportions), to select the best gel composition as an immobilization matrix for continuous lactic acid fermentations of dairy media. Mixed gel cylinders were soaked in a model system for lactic fermentations consisting of 36 dairy media: milk, whey and whey permeate, with 4 lactate concentrations (5, 20, 35 and 50 g/L of medium), combined with 3 pH values (6.5, 6.0, 5.5). GENUGEL X-0909 n°5180850 was the most resistant of all commercial kappa-carrageenans available; mixing this kappa-carrageenan with LBG in the respective proportions of 2. 75 %/0.25% gave the best rheological properties to the resulting mixed gel. Our study of the impact of fermentation parameters showed that pH has a significant effect on hardness, cohesion and percentage of deformation at rupture in milk (but not in the other 2 media). A pH drop of milk from 6.5 to 5.5 resulted in more brittle gels which may be explained by an increase in the amount of soluble calcium cations. Generally, soaking in milk produced the most brittle gels due to its calcium content, whey produced the hardest gels and whey permeate, the softest. An increase in the ammonium lactate concentration significantly improved hardness, rupture force and percentage of deformation at rupture, while reducing cohesion and resilience: NH 4 + cations would account for this effect. The differences in rheological behaviour of immobilization gel beads during continuous lactic fermentations of milk and whey permeate would be due to the cation content and more specifically to the higher calcium concentration in milk.

A four parameter semi-empirical model has been developed using the fractional derivative (FD) theory, which consists of applying a mathematical operator to a constitutive equation. The Fourier transform approach is used to obtain the analytical function of the derived model. Since a single four parameter model can predict both storage modulus (G') and dynamic viscosity (n ' ), the developed FD model was appropriate in describing the viscoelastic properties of selected food gum dispersions, food gum mixtures and gellan gel. This fractional derivative model shows good simulation capability for selected food gum dispersions (0.5% xanthan gum, 0.5 and 0.75% locust bean gum, and 0.5, 0.75, and 1.0% guar gum), 0.6% gellan gel, and binary mixtures of carrageenan and guar gum, carrageenan and xanthan, as well as guar and xanthan gum.

Mixed gels of K-carrageenan (C) and a galactomannan gum, viz., locust bean (L), tara (T), and guar (G) in ratios of 7:3 and 1:1 (total concentration 1%), were examined for their rheological properties and by a sensory evaluation. Texture, creep and rupture were measured, and the semantic differential method (SD) was employed. K-Carrageenan alone could not form a gel at the concentration of 0.5%, while C-L and C-T but not C-G mixtures in the ratio of 1:1 formed gels. The mixed gels of C-L were hard, very elastic and not perceived as smooth by the sensory evaluation. The values for the gels comprising T were intermediate between the C-L and C-G gels in instrumental measurements and sensory characteristics, indicating that the C-T mixture performed well as an edible gel. This difference is attributed to the synergistic effect between K-carrageenan and the gums.

The rheological behaviour of kappa-carrageenan/galacromannan blends, at ratios ranging from 1/99 to 5/95 in the presence of KCl, was investigated by means of viscosity and oscillatory shear measurements, these experiments were performed at 1% total polymer concentration and at 15C. The results were compared to those of the galactomannans alone (locust bean gum or guar gum). The mixtures exhibited gel-like properties provided the KCl content was high enough to induce stabilisation of the kappa-carrageenan molecules in the helical conformation. This limiting KCl content for gelation was of the order of 0.02% and did not depend upon the kappa-carrageenan concentration under these experimental conditions. The mixtures exhibited similar tendencies overall irrespective of whether the galactomannan was guar gum or locust beam gum

Flow and viscoelastic properties of three thickened systems are presented: aqueous solutions of locust bean gum, of xanthan and a dispersion of a crosslinked waxy corn starch. Creep measurements allow investigations at very low shear rates. The existence of a yield stress is discussed. Flow was observed at low shear rates, but the starch paste exhibited pseudo-yield stress behaviour. Dynamic measurements were performed and the relationships between flow curves and mechanical spectra are discussed.

The influence of sucrose addition and type of salt (NaCl; Morton Lite salt: 50% NaCl and 50% KCl, and Mineral salt: 65% NaCl, 25% KCl and 10% MgSO4) on the rheological properties of O/W emulsions containing locust bean gum was analyzed. Flow curves over the range 0.1 to 100 s−1 and transient flow curves at 0.2 s−1, at 20 and 30C were obtained for 12 different emulsions, containing 30% (w/w) of sunflower oil. The K and n power law parameters and the hysteresis loop area (HL) were evaluated from the flow curve. So were the Hahn parameters from time-dependent stress decay fitting. Rheological behaviour of emulsions was affected by the type of salt and the presence of sucrose. Changes in solvent properties of the continuous phase in the emulsions on the macromolecules present could be responsible for the different behaviour. The ageing effect on flow behaviour parameters and on the hysteresis loop area was also studied. Evolution of rheological parameters during emulsion storage suggests that increase of ionic strength and polar solutes concentration decrease the stabilizing properties of locust bean gum.

Apparent viscosities of guar gum, locust bean gum, and sodium carboxymethylcellulose were measured at shear rates of 16-2620s-1 in water, sucrose, milk, and sucrose/milk solutions. The effect of different heat treatments was also studied. For all solutions, a power law equation described the variation of relative viscosity with shear rate allowing comparison of their non-Newtonian behaviour. With the neutral hydrocolloids, the hydration was limited by the presence of sucrose and milk which reduced the effective length of the polymer molecules. The behaviour of the polyanionic hydrocolloid, Na CMC, although influenced by milk and sucrose separately, was controlled by milk in a milk/sucrose mixture. This is due to milk salts which reduced the intramolecular repulsions along the polyanion and substantially lowered its effective hydrated length.

Flow parameters of 1:1 mixtures of carrageenan-guar and CMC-locust bean gum in the presence of common food ingredients, namely, sugar, salt and proteins, were determined by using a coaxial viscometer. The effect of additives on yield stress, and power law model constants varied depending on the type of ingredient and its concentration, and the nature of the gum. Although, it is interesting to see the flow behavior of gum blends together with the additives in concentrations that are common in food products, it is necessary to study an enormous number of combinations in order to analyze a multicomponent system quantitatively.

Etude de la resistance au cisaillement et de la compressibilite des gels de carraghenanes ainsi que du durcissement lors de l'incorporation de gomme de caroube et d'ions potassium. Comportement des gels dans les milieux de fermentation. On cherche a definir la composition du gel donnant les meilleures proprietes mecaniques. Il existe un minimum de concentration en gomme de caroube, voisin de 5 %, permettant d'obtenir un gel suffisamment ferme

The rheological properties of several samples of guar gum and locust bean gum, characterized by light scattering and intrinsic viscosity measurements, were studied. The flow curves of concentrated solutions were obtained with a cone-plate viscometer and their viscoelastic properties were measured with a concentric hemispheres viscoelastometer. The two flow-units Ree-Eyring model and the Cross equation gave a good fit to the experimental flow curves. The zero shear rate viscosity, and the relaxation time, of the Ree-Eyring model depend mainly on the reduced concentration c[η]. This result, as well as the viscoelastic properties, indicate that entanglements play a dominant role in concentrated solutions. From a practical viewpoint, it is possible to predict the flow curve of a galactomannan solution at any concentration if the intrinsic viscosity of the sample is known. However, there are secondary differences in the flow parameters, mainly in the relaxation time, which are not ascribed to [η]. It is hypothesized that these differences are due to the mean branching degree rather than to the botanical origin. As, in solution, the smoothest galactomannan macromolecules are more probably aggregated than isolated, further work should aim at establishing the relationships between aggregate formation and degree of branching.

The effect of different hydrocolloids on the breaking strength, cohesiveness and rigidity of kappa carrageenan gels was studied using comression tests with the Instron. Instrumental measurements were supplemented with benchtop sensory evaluation of texture by mouth, gel clarity and syneresis. The evaluated hydrocolloids included locust bean gum, iota carrageenan, amidated low methoxyl pectin, xanthan gum, and their selected combinations. Best gels were obtained by using 0.15% kappa carrageenan and 0.85% iota carrageenan, or 0.2% kappa carrageenan, 0.2% locust bean gum and 0.6% amidated LM pectin. Although none duplicated the textural quality of gelatine gels, they represented a wide range of interesting and potentially useful textures.