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Two commercial mixers, four-blade (vane) and six-blade, attached to a rheometer were tested to evaluate the viscosity of a chia seed water suspension using radius ratios of 1.4 and 1.2, respectively, in the mixer-in cup systems. Two approaches were proposed to calculate the effective and shear viscosities, power consumption in laminar flow, and Couette analogy. The relationship between the power and Reynolds numbers gives a proportionality constant of 6.27 for the four-blade mixer and 5.19 for the six-blade mixer. The effective viscosity was estimated using the respective constant, measured torque, and angular velocity. Sodium carboxymethylcellulose solutions were used to validate the Couette approach. The shear rate was calculated considering Newtonian and shear-thinning behaviours. The effective viscosity of chia water (10% seeds) varied from 4.46 to 2.43 Pa s for a range of 100–300 rev min−1, while the shear viscosity varied from 3.26 to 1.81 Pa s for a range of 60.1–180.2 s−1. The flow behaviour index was 0.45, and the consistency index was 22.1 Pa sn. Results are useful for quality control purposes and for design calculations. A practical procedure was performed to calculate shear viscosity and shear rate, using the four-blade mixer, helpful for rheological characterization of coarse suspensions.

The objective of this study was to quantify the effect of konjac glucomannan (KGM) on the rheological properties, particle size, and stability of sodium caseinate oil-in-water emulsions, proposed as model emulsions using milk proteins and an alternative thickening hydrocolloid with beneficial properties. Rheology of aqueous phases was investigated since it could contribute to emulsion properties. Liquid-like behaviour was observed in the aqueous phase mixtures, as the KGM rheology; however, emulsions showed solid-like behaviour, associated with a weak emulsion gel network formed by a depletion-flocculation phenomenon. Under flow conditions, the aqueous mixtures showed shear-thinning behaviour and zero-shear viscosity like KGM aqueous solutions, while emulsions at high shear rates were fitted to the Ostwald-de Waele relationship. The instability processes observed were quantified using the time at which clarification began and clarification rate. Emulsions containing 0.75% KGM or higher reduced gravity-induced creaming and phase separation up to 32 days.

Avocado is increasingly utilised for the manufacture of products including purees, concentrates, powders and avocado oil. The design of such processes requires understanding of the rheology, particularly during the puree's transformation. This study characterised the viscoelastic properties at 25 °C of fresh avocado puree resulting from various processing operations including mixing, water dilution, and after sonication treatment. The storage ( G ′) and loss ( G ″) moduli of avocado puree demonstrated a solid-like behaviour irrespective of treatment or dilution, contrary to other food matrices. Avocado puree produced with manual-shearing showed greater G ′ and G ″ than when obtained with a food-processor. Extended shearing through the malaxation operation (mixing and kneading at 49 rpm and 45 °C); or water dilution to 72–94% moisture, diminished both moduli, with an exponential decrease observed in the latter. However, sonication for 5 min with high-power-ultrasound (18 kHz and 40 kHz) or megasonics (MS) (2 MHz) (80–90 kJ kg −1 ) increased G ′ and G ″. The net change in viscoelastic properties due to puree low frequency sonication correlated linearly with moisture content. The influence of processing interventions in avocado puree was demonstrated through rheological methods applicable for avocado process optimisation and product development.

Aqueous systems of agave fructans and sodium caseinate were studied to identify the physical and physicochemical properties of the individual macromolecules and their mixtures. Bulk behavior of agave fructans alone and in mixtures with sodium caseinate systems was similar to that of the density and rheology of monosaccharide solutions. A synergistic surface activity effect was found and attributed to the tendency of agave fructans to associate with sodium caseinate, as was confirmed by the viscosity, zeta potential values and particle size distribution. Their mixture developed properties that make them appealing for applications in foods that are dispersed systems (emulsions and foams) where a large increase in viscosity is not desirable.

Defatted wheat gluten proteins were subjected to a thermal process under mildly acidic conditions using 50–250 mM HCl. The degree of deamidation and hydrolysis reached in gluten proteins produced variable water-soluble fractions at neutral pH. When pH shifted from alkaline to acidic ranges, these fractions, in buffered aqueous media, developed different zeta potentials and different association/aggregation states. Interfacial rheological properties of water-soluble peptides were characterized by dilatational rheology at the air–water interface. A pendant drop tensiometer was used to produce harmonic perturbations to obtain the elastic component of the interfacial viscoelasticity modulus. Gluten proteins with the lowest degree of hydrolysis and deamidation, produced peptides with the highest interfacial elastic moduli of adsorbed films at the air–water interface. The mildly acidic treatment produced water-soluble peptides at neutral pH with different molecular weight profiles; a peptide fraction with molecular weight lower than 10 kDa increased with the increasing HCl concentration.

Ultrasound treatment is known to increase the oil extractability in olive and palm oil processes. This work examined the effect of ultrasound conditioning of avocado puree on oil extractability and quality, at low (18+40kHz) and high (2MHz) frequencies, at litre-scale. Other ultrasound parameters evaluated included high frequency effect (0.4, 0.6, and 2MHz; 5min; 90kJ/kg) and sonication time (2.5-10min at 2MHz), without malaxation. Finally, a megasonic post-malaxation intervention was assessed at selected malaxation times (15, 30, and 60min). Both low and high frequency ultrasound treatments of the non-malaxed avocado puree improved extractability by 15-24% additional oil recovery, with the highest extractability achieved after 2MHz treatments, depending on the fruit maturity and oil content. There was no preferential improvement on oil extractability observed across high frequencies, even though extractability increased with sonication time. Ultrasound treatment also showed a positive effect after puree malaxation. Oils obtained from sonicated purees showed peroxide and free fatty acid values below the industrial specification levels and an increase in total phenolic compounds after 2MHz treatment. High frequency ultrasound conditioning of avocado puree can enhance oil separation and potentially decrease the malaxation time in industrial processes without impacting on oil quality.

En este capitulo se revisa la doble funcionalidad de un polisacarido novedoso de origen asiatico, el glucomanano de konjac, por un lado se resumen las aplicaciones tecnologicas y por el otro, las relacionadas con la mejora de salud y reduccion del riesgo de contraer enfermedades. Las propiedades funcionales desde el punto de vista tecnologico estan ligadas con su alta solubilidad y retencion de agua (espesante) o como polisacarido estructurado (gelificante), propiedades que modifican fuertemente su reologia en medio acuoso. Desde el punto de vista nutricional o medicinal, el konjac funciona como una fibra dietetica viscosa, uno de sus principales usos nutraceuticos es disminuir el colesterol, evita tambien la absorcion de algunas grasas y provoca saciedad, siendo un potencial coadyuvante para el control de la obesidad, hiperglucemia (disminuye los niveles de glucosa e insulina), hiperlipidemia e hipercolesterolemia (interfiere en el transporte de colesterol y acidos biliares). Ha sido utilizado contra el estrenimiento, sin embargo, su consumo puede presentar algunos inconvenientes como la produccion de flatulencias o molestias abdominales.

The effect of different concentrations of added sodium caseinate (Na-Cas) and whey protein concentrate (WPC) on the foaming properties of reconstituted skim milk powder (SMP) was studied, to quantify practical applications as additives in aerated foods. Density and viscosity of the samples increased with increasing concentration of SMP or protein. The pH of the fortified products were close to those of the reconstituted SMP at 10%. The surface tension of both reconstituted SMP alone, and that fortified with WPC was higher than that of reconstituted SMP fortified with Na-Cas; these samples also took more time to reach equilibrium. Foaming capacity increased with increased SMP or protein. Despite the low surface tension attained at equilibrium of reconstituted SMP with increasing Na-Cas concentration, foam stability decreased. The kinetics of drainage, Ostwald ripening, and the collapse of bubbles were calculated. The most stable foams were those from reconstituted SMP fortified with WPC.

Changes induced by addition of calcium chloride in particle size distribution and electrokinetic potential were determined in sodium caseinate/sodium alginate mixtures dissolved in water or acetate buffer at ambient temperature. Rheological properties of aqueous mixtures and respective oil-in-water emulsions (30% oil w/w) were evaluated using a low-stress rheometer. Stability and particle diameter of emulsions were measured. Caseinate and alginate solutions were negatively charged and showed negative electrokinetic potential; however values of mixtures were between those of the values for the individual hydrocolloids. When calcium ions were added the electrokinetic potential diminished while the negative charge was preserved. Aqueous mixtures of caseinate and alginate showed average particles size between of those of caseinate or alginate samples. We observed low viscosity values and Newtonian behavior for both caseinate (1 and 2%) and alginate (0.1%). Addition of 5 mM CaCl 2 to alginate solutions induced shear-thinning behavior as well as the development of viscoelasticity. Both the viscosity and the elastic modulus of these polysaccharide solutions were attenuated by the presence of protein or dispersed oil in mixtures or emulsions, respectively. High average particle diameter of emulsions prepared was obtained (close to 10 μm), however, stability of emulsions was possible only with the addition of CaCl 2 to the mixtures, in both water and acetate buffer. In these cases elastic behavior predominated to viscosity in the formation of emulsions, confirming the prevalence of aqueous phase rheology on emulsions.

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

The effect of two hydrocolloids, the overall composition and stirring rate of a confectionery semi-liquid syrup model, were studied by means of the measure of rheological properties, instrumental texture evaluation and turbidity. A syrup model was made with sucrose, high fructose corn syrup, gum (dextran or carrageenan), citric acid and water. An experimental design based on Taguchi’s method was employed to evaluate the influence of sugar concentration, gum type, gum concentration, citric acid concentration and stirring rate. An analysis of variance was performed. From all evaluated properties (except turbidity), °Brix was the factor that showed the maximum influence, with higher values on textural properties (adhesive force, cohesive work and stringiness). The gum type had influence over viscosity, hardness, adhesive force and turbidity. The Newtonian behavior predominated in the syrups and viscosity of samples was affected by the variables studied. The mean values of viscosity, hardness and adhesive force for all samples with carrageenan were higher than those obtained with dextran (at both °Brix levels).

This work discusses physicochemical properties (particle size distribution, electrokinetic potential, interfacial tension) and rheological responses of oil-in-water emulsions prepared with 30% sunflower oil and different sodium caseinate/gellan gum mixtures, at pH 5.4 and 25 °C. The characteristics of caseinate, gellan gum, and caseinate/gellan mixture solutions were studied first. They showed low viscosity values and almost Newtonian behavior. Addition of 5 mM CaCl2 to the gellan solutions induced shear-thinning behavior, as well as the development of viscoelasticity. Both the viscosity and the elastic modulus of polysaccharide solutions were attenuated by the presence of protein. Emulsions without gellan in the aqueous phase were almost Newtonian, with relatively low viscosity values. When gellan concentration was 0.03% or higher, shear-thinning behavior and viscoelasticity were observed; these effects were negatively influenced by the addition of CaCl2. Casein-covered oil droplets are dispersed in the background matrix formed by the polysaccharide and casein aggregates (filler particles). The emulsion is thus stabilized against both flocculation and creaming, while the rheological behavior strongly depends on the structural state of the polysaccharide. The interaction between caseinate and gellan appears to be the key factor to understand the resulting macroscopic behavior.

Millimetric particles suspended in four different fluids were sheared and video-recorded using a controlled-stress rheometer with a four-blade vane-in-a-large-cup. Experimental situations where the suspension next to the vane moves as a solid cylinder, i.e., where the Couette analogy can be applied, were determined. Velocity fields were measured by particle image velocimetry (PIV) in various suspensions: resin particles in oil (creamed particles), resin particles in water (settled particles), acetate particles in glycerin, and uniformly suspended gelatin particles in a commercial beverage. Data were expressed in terms of the Reynolds number calculated from experimental angular velocity measurements. The suspensions revealed flow patterns which include a considerable amount of vortices initially originating close to the millimetric-size particle bed and thereafter distributing and spreading within the large-baffled-cup. Flow characterization with a vane-in-a-large-cup was only possible for acetate particles in glycerin undergoing laminar flow, as verified by PIV and magnitude of the Reynolds number. Average shear stress and shear rate values were calculated and results for the suspension viscosity were in agreement to those predicted by the model of Happel (Viscosity of suspensions of uniform spheres. Journal of Applied Physics , 1957, 28 (11), 1288–1292).

The rheological behavior of six different commercial brands of Mexican sauces was studied. The sauces were considered to be homogeneous with fine particles (“Barbecue”, “Chipotle” and “Valentina”) and heterogeneous with coarse particles (“Taquera”, “Ranchera” and “Verde Bufalo”). The conventional concentric cylinders geometry was used to validate the non-conventional vane-in-cup system. Two containers were tested for the vane-in-cup; a small cup (cup/bob radius ratio = 1.06) and a large cup (cup/bob radius ratio = 2). Rheological parameters were calculated using the Couette–Searle analogy, considering a non-Newtonian behavior and a large cup. The large cup contained eight baffles to avoid slippage at the wall. Homogeneous sauces with fine particles were examined in all fixtures, while the heterogeneous containing coarse particles, only in the vane-in-large cup. All sauces exhibited a shear-thinning behavior that could be correlated by the power-law model. Several shear stress and shear rate factors proposed in the literature for large gaps and power-law models were compared to the average shear factors proposed in this study. The method proposed here was proved to be an alternative to characterize the flow properties of coarse particles suspensions in a vane-in-a-large cup rheometer.

The calculation of head loss in valves and fittings is highly important to design food engineering processes under several pumping conditions. Nevertheless, there are few data reported to predict pressure loss in accessories for non-Newtonian fluids in laminar flow, usually observed in many viscous fluid foods. In this study, experimental data of pressure drops as a function of the generalized Reynolds number were obtained to determine the resistance or friction loss coefficient (k f ) of power-law fluids while pumped through 1-in, diameter stainless steel valves (butterfly and globe), and an assembly of four 90° bends. Aqueous dispersions of carboxymethylcellulose were used as a model of a shear thinning fluid. Results showed that for all the accessories evaluated, the k, values hold an inverse function with the generalized Reynolds, using the classical log-log plot. Results are in agreement with data reported in the literature for Newtonian and power-law fluids. The correlations obtained in this study were compared with results in previous works and they were found to be within the range reported.

The objective of this study was to characterize the flow behavior of a solid-liquid food model which imitates Mexican sauces. The model food suspension consisted of seeds suspended in a shear-thinning fluid (Avicel and Xanthan gum). The effects of size and particle concentration were investigated using a traditional disc geometry in wide gap (spindle), and a ribbon adapted to a rotational viscometer. The effect of particle size was evaluated in a tube viscometer. Power-law parameters and apparent viscosity were estimated in the shear range of each viscometer. The experimental apparent viscosity showed good agreement with predictions obtained using a theoretical expression of relative viscosity for uniform spheres. In all the viscometers investigated, shear-thinning behavior of the suspension was observed, as the aqueous phase, due to low interactions among particles. The ribbon geometry appears to be the best option for flow characterization of food suspensions containing coarse disc shaped particles.

The aim of this study was to measure the pressure drops of a solid-liquid food model and to compare pressure drop estimations obtained from proposed correlations for asymmetric distributed suspensions in a horizontal pipe. The model food suspension consisted of alginate spheres suspended in a Newtonian sugar syrup of medium viscosity. The suspension was pumped into a horizontal pipe and measurements for three different sphere diameters and solid-phase concentrations were carried out. Particle velocity, necessary for pressure drop estimations, was predicted using the Eulerian approach, which assumed solid and liquid phases as continuous. Considerations taken were: one dimensional flow of fluid and particles, drag force acting on the particles and constant pressure drop. The momentum equations were solved by the fourth order Runge-Kutta method. Predicted particle velocities showed a retarded parabolic profile compared to the fluid. Drag expressions used, considerably influenced the predicted particle velocities. Estimated pressure drops for the suspensions using the predicted particle velocities agreed with the experimental pressure drops when the tube-particle diameter ratio was higher than 5.8.

An exopolysaccharide producer, Beijerinckia sp. was isolated and identified from a sample of soil. A sample of 10.3 g (dry weight) of polysaccharide/L was obtained by fermentation on liquid Czapek culture media supplemented with yeast extract. The functionality of the biopolymer was characterized for its potential use by the food industry. It showed shear thinning behaviour (pseudoplastic). The effects of concentration, temperature and pH were evaluated; almost all of the salts had no effect on rheological parameters of the power law model. There was a linear rela tionship between the percent of remaining emulsion after centrifugation and the polysaccharide biopolymer concentration, demonstrating the stabilizing effect of biopolymer on the emulsion. In contrast, the biopolymer was not able to form a gel under various pH and temperature condi tions, or with the addition of ions.

This work discusses rheological and physicochemical properties of sodium caseinate and gum arabic, in aqueous media (25 °C). All the systems showed low viscosity values and Newtonian behaviour in the shear rate range studied. From particle size distribution, a limited thermodynamic compatibility was observed since hydrocolloids mixtures showed particles size between the values from the systems alone. Interfacial tension measurements at equilibrium at the air-water interface, revealed that the binding affinity of arabic to the air water interface is very low compared to that of caseinate. The adsorption critical concentration could be deduced as a function of aqueous solutions composition. In competitive adsorption experiments involving simultaneous adsorption of the hydrocolloids from a bulk mixture, sodium caseinate displaced gum arabic from the interface at both polysaccharide concentrations, changing the adsorption critical concentration.

Texture profile analysis (TPA) of stirred and set cultured milk were evaluated, using an exopolysaccharide producing strain of Lactobacillus delbrueckii subsp. bulgaricus (NCFB 2772) and a protein enriched substrate (retentate). In both cases, samples were compared respectively with a nonropy strain (NCFB 1489) and reconstituted skim milk substrate. The retentate fermented products were firmer in comparison with skim milk products, both at 10% of total solids. A loss of structure occurred when the retentate products were stirred causing a nine-fold decrease in hardness, whereas in cultured milk products the loss was of around three-fold. The main differences were found in adhesiveness and fracture characteristics. Set retentate ropy product was five times more adhesive than the nonropy one, whereas in stirred retentate and set skim milk products the difference was two-fold. No differences in adhesiveness were detected when skim milk products were stirred using either strain. The fracture force on ropy retentate samples increased after fracture while the nonropy ones showed a decrease, implying more structural breakdown in the latter. On set products, cohesiveness increased slightly due to the ropy strain. Changes in texture observed between ropy and nonropy strains can be attributed to exopolysaccharide attachment to the casein matrix being increased when the protein content is higher. Le sujet de cette etude est d'evaluer la difference entre des laits fermentes brasses ou non, en determinant la contribution de souches de lactobacillus delbrueckii subsp. Bulgaricus NCFB 2772, productrices d'exopolysaccharides, sur la consistance particuliere de lait ecreme fermente et de retentat d'ultrafiltration de lait et en comparant les souches productrices aux souches non productrices. Elle etudie en particulier l'interaction entre ces polysaccharides et les proteines laitieres conduisant a un effet synergique.