Rheological,thermal and structural behavior of poly(ε-caprolactone) and nanoclay blended films

Poly(ε-caprolactone)/nanoclay composite (PCLNC) films were prepared by solvent casting method using a wide range of layered silicate (2.5–10%) and were characterized by different techniques. Nanofiller dispersions in PCL matrix were studied by wide-angle X-ray diffraction (XRD) and transmission electron microscopy (TEM), and results indicated the formation of some intercalated nanostructure of PCLNC. Rheological and thermal properties of PCLNC were measured by parallel-plate oscillatory rheometry and differential scanning calorimetry (DSC), respectively. Rheological study indicated that the predominating liquid-like properties (viscous modulus, G″ > elastic modulus, G′) of neat PCL gradually transformed to solid-like (G′ > G″) behavior after incorporation of clay in the temperature range of 90–120 °C. A plot of G′ vs. G″ provide information on intercalation and microstructure of nanocomposite. Applicability of time–temperature superposition (TTS) principle and van Gurp–Palmen plot (phase angle vs. absolute complex modulus) on rheological data of clay incorporated PCL were employed and found that the results failed to follow the rules. Incorporation of the nanoclay into PCL matrix increased the crystallization temperature (T_c) and melting temperature (T_m) of neat PCL from 28.7 to 32.3 °C and 56.3 to 59.2 °C, respectively due to the nucleating effect, but the glass transition temperature (T_g) (≈−65 °C) was remained unaffected. The decrease in crystallinity with increase in clay concentration was confirmed by both XRD and DSC data.     

Viscoelastic behaviour of heat-treated whey protein concentrate suspensions

The viscoelastic behaviour of heat-treated whey protein concentrate (WPC) suspensions was studied. Suspensions with total protein (TP) content of 5% and 9% w/v prepared from a commercial WPC with 38% w/w protein were treated at two temperatures (72.5 and 77.5 °C) during selected times to obtain 60% of denatured protein content. Unheated WPC suspensions were used as control. Frequency sweeps were performed in the range of 0.01–10 Hz at 20 °C. Mechanical spectra of WPC suspensions were similar to viscoelastic fluids. However, unheated WPC suspensions showed some mechanical characteristics of colloidal crystals, like little dependency of elastic (G′) and viscous (G″) moduli with TP content, solid-like mechanical spectra, and difficulty to flow at low content of TP. At a selected frequency of 1 Hz, viscous modulus was more frequency (ω) dependant on experimental conditions (TP and temperature) than elastic modulus. Mechanical spectra were modelled using power law equations (G′ = aω^x, G″ = bω^y), but only parameters of heat-treated WPC suspensions containing 9% of TP showed temperature dependency. Characteristic relaxation times (τ_c) were calculated as the inverse of the crossover frequency, where G″ = G′. Heat treatments produced a decrease in the extent of the elastic behaviour because heat-treated WPC suspensions presented higher phase angle and smaller τ_c values than unheated WPC suspensions for the same TP content. The τ_c decreased when treatment temperature increased but only in heat-treated WPC suspensions with 5% of TP.     

Study on the rheological properties of heat-induced whey protein isolate-dextran conjugate gel

Effect of glycosylation on the rheological properties of whey protein isolate (WPI) during the heat-induced gelation process was evaluated. Significant changes in browning intensity, free amino groups content and SDS-PAGE profile showed that the conjugate of WPI and dextran (150 kDa) was successfully prepared using the traditional dry-heating treatment. For the conjugate, during the heating and cooling cycle, the curves of G′ and G″ were considerably shifted to lower values and their shapes varied comparing to the corresponding spectra of initial WPI and WPI + dextran mixture. After holding at 25 °C, G' reached a value of about 2200 Pa, only a tenth of the value that obtained in the initial WPI gel. Moreover, frequency sweep measurements revealed that the stiffness of gel was greatly reduced in the conjugate, although a typical elastic gel was still formed. All data showed that the rheological properties of thermal gelation could be modified upon the covalent attachment of dextran.     

Effects of fluid shear and temperature on whey protein gels, pure or mixed with xanthan

The effects of shear on whey protein isolate (WPI) gels, pure or mixed with xanthan, have been investigated at pH 5.4 by dynamic oscillatory measurements and light microscopy (LM). The shear was performed on the suspensions under a constant stress of between 0.04 and 2.1 Pa. Various temperature conditions were chosen in order to describe the effects of shear at the different states of aggregation of the WPI. Shear-sensitive aggregation phenomena were already found around 40°C for the pure WPI samples. Continuous shearing during heating from 20 to 40°C, prior to heat treatment at 90°C, resulted in a gel with a storage modulus (G′) half that of the unsheared gel, independent of the shear stress. Continuous shearing during heating from 20 to 76°C resulted in a further decrease in G′. Inhomogeneities arose in networks formed from continuously sheared suspensions during heating from 20 to 50°C and above. Depending on the shear stress and on the heating range of the shear, the networks showed areas of varied compactness and different classes of pores, ranging from 10 to 200 μm. A higher G′, compared to that for the unsheared gel, was found for gels subjected to shear for short periods in the vicinity of the gel point. The presence of xanthan inhibited the aggregation and demixing of the WPI, described as a sterical phenomenon. Under static conditions, the presence of xanthan resulted in a more homogeneous WPI network. Exposing the mixed suspensions to shear generally increased the inhomogeneity of the network structure. Short periods of shearing in the vicinity of the gel point affected the kinetics of the gel formation and resulted in gels with higher G′ values than the unsheared gel. Continuous shearing under stresses below 0.09 Pa, during heating from 20 to 60°C and above, also resulted in gels with an increased G′. Continuous shear under stresses above 0.9 Pa resulted in gels with a decreased G′     

Rheological characteristics of tamarind (Tamarindus indica L.) juice concentrates

The steady-shear and small-amplitude oscillatory rheological properties of tamarind (Tamarindus indica L.) juice concentrate (TJC) were studied in the temperature range of 10-90 °C using a controlled-stress rheometer. Under steady-shear deformation tests, shear stress-shear rate data were adequately fitted to the Herschel-Bulkley and Casson model at lower (10-30 °C) and higher (50−90 °C) temperature range, respectively. The Carreau model was applied to describe the shear-thinning behaviour of the concentrate, and the model parameters estimated empirically showed temperature dependence. Oscillatory shear data of TJC revealed predominating viscous behaviour (G″>G′) at lower frequency range while the elastic modulus predominating over the viscous one (G′>G″) at higher frequency range. The Cox-Merz rule that relates steady shear and dynamic material functions was tested and not followed by most of the temperatures. The specific heat of TJC increased with temperature and the glass transition temperature of the product was found to be −70.74 °C.     

Rheological characterisation of cake batters generated by planetary mixing: Comparison between untreated and heat-treated wheat flours

The rheological behaviour of high ratio cake batters prepared with untreated and heat-treated wheat flours was analysed at different stages of the manufacturing process, namely slurry, (on aeration) foams and (with fat addition) aerated emulsions, featuring air volume fractions up to 0.50. Both steady shear and viscoelastic behaviours were studied. All materials exhibited shear-thinning behaviour at 20 °C over the shear rate range studied (0.07-10 s⁻¹). The generalised Cox-Merz rule could be applied to all samples. Materials prepared with heat-treated flours exhibited greater stability, as indicated by slurry thixotropy and cohesive energy, and the change in apparent viscosity and air content of foams and aerated emulsions on extended mixing. Foams and aerated emulsions showed significant elastic behaviour with G′∼G″. The temperature dependency of aerated emulsions was studied by oscillatory shear testing from 20 to 100 °C and indicated three regimes in temperature dependence: below 40 °C G′and G″ were insensitive to temperature; between 40 and 70 °C the complex viscosity exhibited Arrhenius-type behaviour, while above 70 °C G′ and G″ increased as expected for gelatinisation and foam setting. The weak gel model for foods was used to analyse the latter data sets and confirmed that the gel network generated in aerated emulsions prepared with heat-treated flours was significantly stronger than those made with unheated flours. The differences between flour types were also observed in tests on un- and heat-treated flours obtained from a second and third harvest. The impact of these quantifiable differences in rheology on performance during baking is discussed.     

Effects of chitosan molecular weight and degree of deacetylation on the properties of gelatine-based films

The effect of chitosan molecular weight (MW) and degree of deacetylation (DD) on the physicochemical properties of gelatine-based films was studied with the goal of improving the films. Determination of the dynamic viscoelastic properties (elastic modulus G′ and viscous modulus G″) of the film-forming solutions revealed that the interactions between gelatine and chitosan were stronger in the blends made with chitosan of higher molecular weights or higher degrees of deacetylation than the blends made with lower molecular weights or degrees of deacetylation. Fish gelatine films modified with chitosan of higher molecular weights or higher degrees of deacetylation had higher tensile strengths (TS, 72.4 MPa for 550 kDa vs. 62.2 MPa for 200 kDa; 63.2 MPa for 93.6% DD vs. 38.0 MPa for 76.5% DD) and higher glass transition temperatures (T_g, 130 °C for 550 kDa vs. 108 °C for 200 kDa; 108 °C for 93.6% DD vs. 103 °C for 76.5% DD). Fourier transform infrared spectra (FTIR) and X-ray diffraction (XRD) studies indicated that gelatine and chitosan interactions determined the properties of the film. Thus, combining gelatine and chitosan may be a method for improving the physicochemical properties of gelatine films, especially when using chitosan of higher molecular weights and higher degrees of deacetylation.     

Solubilized micellar calcium induced low methoxyl-pectin aggregation during milk acidification

Low methoxyl (LM) pectin was combined with 3-kDa molecular weight cut-off permeates from milk subjected to pH 6.7 to 5 and 7°C or 40°C with the objective of studying the effect of solubilized micellar calcium on viscoelastic properties of LM-pectin-milk mixes. Lowering the pH of skim milk with hydrochloric acid during ultrafiltration gradually promoted permeates to exhibit gel-like behavior when combined with LM-pectin. The onset of the gel-like behavior (G′ > 1) occurred at a higher pH when permeates were obtained from milk filtered at 7°C compared with 40°C. As pH value during ultrafiltration approached 5 and regardless of temperature, G′ for permeate-pectin mixes approached the same values (∼70 Pa) as G′ for skim milk-pectin mixes. In all cases G′ was highly correlated with free calcium concentration (r > 0.95). The gradual acidification of skim milk-LM-pectin using glucono-δ-lactone, promoted a sharp increase in storage modulus as pH approached 5.2 and a maximum G′ increment (ΔG′) at pH ∼4.9. From pH 4.9 to 4, G′ continued to increase but at smaller increments. It was concluded that LM-pectin-casein micelle interaction in milk is a 2-step process: 1) solubilized micellar calcium dependent pectin-pectin interaction as pH approaches 5.0 to 4.9, and 2) pectin-casein micelle interaction in the 5.0-4.9 to 4.0 pH range.     

Dielectric properties of soybean protein isolate dispersions as a function of concentration, temperature and pH

Dielectric properties of commercial soy protein isolate (SPI) dispersions were measured over the frequency range of 200-2500 MHz by the open-ended coaxial probe method using a network analyzer as a function of concentration (5, 10 and 15 g/100 g water), temperature (20-90 °C) and pH (4.5, 6.6 and 10). Results indicated that the dielectric constant (ε′) decreased with temperature (except at 90 °C) and frequency while increased with concentration. The loss factor (ε″) increased with frequency and concentration; however, temperature showed mixed effect. Both ε′ and ε″ data were related to frequency using a polynomial model. The significant change in ε′ and ε″ at 90 °C was a result of protein denaturation which was identified by differential scanning calorimetry (DSC). Change in the association/dissociation behavior of SPI dispersions due to electrostatic attraction/repulsion among protein molecules on heating as a function of pH was assumed to be responsible for the significant increase in dielectric parameters. Penetration depth (D_p) was estimated under various conditions and it decreased with an increase in frequency, concentration, temperature and pH. The minimum D_p was found at alkaline pH at a temperature of 90 °C and frequency of 2450 MHz.     

Moisture content in honey determination with a shear ultrasonic reflectometer

An ultrasonic method, based on the measurement of the complex reflection coefficient at an interface (elastic material)/(viscoelastic material) has been developed for shear waves and an operating frequency of 10 MHz. With this technique, the dynamic elastic moduli G′ and G′′ can be obtained with a high accuracy. For various honeys and moisture contents we show that the temperature for which (G′′/G′) = 1 undergoes an important variation (25–3 °C) for moisture contents ranging from 15% to 20%. With this technique one can distinguish two honeys with moisture contents difference less than 0.2%. Regarding the high sensitivity of the method, considering the fact that ultrasonic waves can propagate through optically opaque materials and is a nondestructive approach, we propose a discussion about the application of this technique for honey quality control.     

Dynamic rheological and thermal study of the heat-induced gelation of tomato-seed proteins

The structural aspects of proteins prepared from tomato seeds were studied by dynamic rheology, modulated differential scanning calorimetry (MDSC) and Fourier transform infrared (FTIR) spectroscopy. The critical gel point was determined from storage (G’) and loss (G”) moduli as functions of time and frequency. The findings indicate that tomato-seed proteins can create gels during heat treatment at 90–95 °C. Mechanical spectra of the tomato-seed protein gels were classified as weak gels based on the frequency sweep, complex viscosity (η∗) and tan δ results. Moreover, G’ and G” changes were found to be dependent on both concentration and frequency. MDSC showed two peaks, with gelation temperatures (T_d) of 70 and 87 °C, which we attribute to starch and globular protein fractions, respectively. The FTIR spectra show an increase in the absorbance of amides I and II after increasing the solid content from 1 to 10% w/w, indicating mostly β-sheet and α-helical conformations.     

Casein glycomacropeptide pH-driven self-assembly and gelation upon heating

Casein glycomacropeptide (CMP) found in cheese whey is a C-terminal hydrophilic glycopeptide released from κ-casein by the action of chymosin during cheese making. In a previous work a self-assembly model for CMP at room temperature was proposed, involving a first step of hydrophobic assembly followed by a second step of electrostatic interactions which occurs below pH 4.5. The objective of the present work was to study, by dynamic light scattering (DLS), the effect of heating (35–85 °C) on the pH-driven CMP self-assembly and its impact on the dynamics of CMP gelation. The concentration of CMP was 3% w/w for DLS and 12% w/w for rheological measurements. The solutions at pH 4.5 and 6.5 did not show any change in the particle size distributions upon heating. In contrast the solutions at pH lower than 4.5 that showed electrostatic self-assembly at room temperature were affected by heating. The mean diameter of assembled CMP increased by decreasing pH. For all solutions with pH lower than 4.5, the particle size did not change on cooling, suggesting that the assembled CMP forms formed during heating were stable. The gel point determined as G′–G″ crossover, occurred in all systems at 70 °C, but at different times. The rate of self-assembly determined by DLS as well as the rate of gelation increased with increasing temperature and decreasing pH from 4 to 2. Increasing temperature and decreasing pH, the first step of CMP self-assembly by hydrophobic interactions is speed out. All the self-assembled structures and the gels formed at different temperatures were pH-reversible but did not revert to the initial size (monomer) but to associated forms that correspond mainly to CMP dimers.     

Effect of temperature and cross-linking density on rheology of chemical cross-linked guar gum at the gel point

The evolution of viscoelasticity within a solution of guar gum (GG) in the presence of an excess of cross-linker (glutaraldehyde, Ga) has been monitored, at different temperatures (7, 15, 25 and 37 °C), evaluating the sol–gel transition by means of dynamic mechanical experiments. Furthermore, at 25 °C, the samples were characterized as a function of the different amounts of cross-linker. The gelation time of the systems, evaluated with the loss tangent, decreased with increasing temperature and, at a fixed temperature (25 °C), decreased with increasing cross-linker concentration. At the gel point a power-law frequency dependence of the dynamic storage modulus (G′≈ωⁿ) and loss modulus (G″≈ωⁿ) was observed. The value of n, evaluated according to three different methods (n_slope, considering the parallelism of the two moduli, n_tan, from the frequency-independence of tan δ, and from the crossing point between the apparent exponents of G′ and G″, n_app), decreases with increasing cross-linking densities and with increasing temperature. The fractal dimension (d_f) was determined for the incipient GG/Ga hydrogels. The value of d_f increases with increasing cross-linker concentration and decreases with increasing temperature. This trend of d_f suggests a more “tight” structure of the network at higher cross-linking densities and at lower temperatures. The activation energy (E_a) of the chemical reaction between GG and Ga was estimated: the experimental value was close to those obtained in the case of similar chemical reactions among polymers and different kinds of cross-linkers.     

Effects of the concentration of insoluble calcium phosphate associated with casein micelles on the functionality of directly acidified cheese

Directly acidified cheeses with different insoluble Ca (INS Ca) contents were made to test the hypothesis that the removal of INS Ca from casein micelles (CM) would directly contribute to the softening and flow behavior of cheese at high temperature. Skim milk was directly acidified with dilute lactic acid to pH values of 6.0, 5.8, 5.6, or 5.4 to remove INS Ca (pH trial). Lowering milk pH also reduced protein charge repulsion, which could influence melt. In a second treatment, EDTA (0, 2, 4, or 6 mM) was added to skim milk that was subsequently acidified to pH 6.0 (EDTA trial). Both types of milks were then made into directly acidified cheese. Cheese properties were determined at approximately 10 h after pressing to reduce possible confounding effects of proteolysis. The INS Ca content was determined by the acid-base titration method. Dynamic low-amplitude oscillatory rheology was used to measure the viscoelastic properties of cheese during heating from 5 to 80°C. The composition of all cheeses was as similar as possible, with cheese-making procedures being modified to obtain similar moisture contents (∼55%). Insoluble Ca contents of cheeses significantly decreased with a reduction in pH or with the addition of EDTA to skim milk. The pH values of cheeses in the pH trial varied, but all cheeses in the EDTA trial had similar pH values (∼5.73). In the pH trial, the reduction in cheese pH and consequent decrease in INS Ca content resulted in a reduction in the G′ values of cheeses at 20°C. In contrast, the G′ values at 20°C in cheeses from the EDTA trial increased with EDTA addition up to 4 mM EDTA. The G′ values at 70°C of cheeses from the pH trial decreased with a decrease in cheese pH, and a similar decrease was observed in the G′ values of cheese from the EDTA trial with an increase in EDTA concentration even though these cheeses had a similar pH value. In both trials, loss tangent (LT) values increased with temperatures >30°C and reached a maximum at approximately 70°C. In the pH trial, LT values at 70°C increased from 1.50 to 4.24 with a decrease in cheese pH from 5.78 to 5.21. The LT values increased from 1.43 to 3.23 with an increase in the concentration of added EDTA from 0 to 6 mM. In the EDTA trial, the decrease in G′ and increase in LT values at 70°C were due to the reduction in INS Ca content, because the pH values of these cheeses were the same. It can be concluded that the loss of INS Ca increases the melting in cheeses that have the same pH and gross chemical composition, and removal of INS Ca can even make cheese at high pH (∼5.73) exhibit reasonable melt characteristics.     

Frequency- and temperature-dependent dielectric properties of fruit juices associated with pasteurization by dielectric heating

Dielectric properties of apple, pear, orange, grape and pineapple juices were studied from 20 to 4500 MHz at 15-95 °C. The dielectric constants ε^′ of fruit juices decreased as frequency increased. The loss factors ε^″ decreased with increasing frequency to a minimum between about 1000 and 3000 MHz, depending on temperature, and then increased as frequency increased. The frequency of that turning point increased, whereas the minimum ε^″ decreased with increasing temperature. The ε^″ values increased with increasing temperature below about 1000 MHz, and decreased with increasing temperature above 3000 MHz. Dielectric constants decreased consistently and linearly with increasing temperature. Linear or polynomial correlations for the dependence of dielectric properties on temperature were developed. The power penetration depth of all fruit juices decreased with increasing frequency. The depth decreased as temperature increased at lower frequencies and increased with temperature above 3000 MHz. The dielectric properties obtained in the study provide important parameters for juice pasteurization by dielectric heating.     

The impact of concentration,temperature and pH on dynamic rheology of psyllium gels

Structural aspects of the psyllium gum prepared from the seed husk of the plant of Plantago ovata Forsk was characterized by dynamic rheology and microscopy. Dynamic rheological properties of psyllium gel in the linear viscoelastic region, as a function of concentration (2, 2.5 and 3% w/w), temperature (5–95 °C) and pH (2.5–10) were investigated. Mechanical spectra of the psyllium gels were obtained by frequency sweep measurement classified into that of weak gels because G′ was larger than G″ throughout the tested frequency range and the separation of the two moduli (tan δ) was greater than 0.1. The phase angle increased with temperature and a peak associated with gel melting appeared at about 40 °C. All gels at different pH presented a typical weak gel spectrum. Scanning electron microscopy showed porous structures with different pore-size distribution for psyllium gels under different conditions in terms of concentration, pH and temperature.     

Physical properties of acid milk gels prepared at 37°C up to gelation but at different incubation temperatures for the remainder of fermentation

We investigated the effect of altering temperature immediately after gels were formed at 37°C. We defined instrumentally measurable gelation (IMG) as the point at which gels had a storage modulus (G′) ≥5 Pa. Gels were made at constant incubation temperature (IT) of 37°C up to IMG, and then cooled to 30 or 33.5, or heated to 40.5 or 44°C, at a rate of 1°C/min and maintained at those temperatures until pH 4.6. Control gel was made at 37°C (i.e., no temperature change during gelation/gel development). Gel formation was monitored using small strain dynamic oscillatory rheology, and the resulting structure and physical properties at pH 4.6 were studied by fluorescence microscopy, large deformation rheology, whey separation (WS), and permeability (B). A single strain of Streptococcus thermophilus was used to avoid variations in the ratios of strains that could have resulted from changes in temperature during fermentation. Total time required to reach pH 4.6 was similar for samples made at constant IT of 37°C or by cooling after IMG from 37 to either 30 or 33.5°C, but gels heated to 40 or 44°C needed less time to reach pH 4.6. Cooling gels after IMG resulted in an increase in G′ values at pH 4.6, a decrease in LT_max, WS, and B, and an increase in the area of protein aggregates of micrographs compared with the control gel made at constant IT of 37°C. Heating gels after IMG resulted in a decrease in G′ values at pH 4.6 and an increase in LT_max values and WS. The physical properties of acid milk gels were dominated by the temperature profile during the gel-strengthening phase that occurs after IMG. This study indicates that the final properties of yogurt greatly depend on the environmental conditions (e.g., temperature, time/rate of pH change) experienced by the casein particles/clusters during the critical early gel development phase when bonding between and within particles is still labile. Cooling of gels may encourage inter-cluster strand formation, whereas heating of gels may promote intra-cluster fusion and the breakage of strands between clusters.     

Applicability of time-temperature superposition principle: Dynamic rheology of mung bean starch blended with sodium chloride and sucrose - Part 2

Dynamic rheological characteristics of mung bean starch individually and blending with sodium chloride (5-10%) and sucrose (5-10%) in aqueous medium were studied isothermally (70-95 °C). The elastic modulus (G′) of each dispersion was significantly higher than viscous modulus (G″) and showed a predominant solid-like property. Each ingredient affected the rheological behavior differently. Incorporation of sugar increased the gel rigidity, whereas sodium chloride-starch blend lowered the gel strength as function of concentration. The empirical principle of time-temperature superposition (TTS) was examined to bring experimental dynamic rheological data at various temperatures together into single master curves at a reference temperature of 80 °C. The complex viscosity (η^∗) master curve was obtained for the blends with slight deviation. The elastic modulus superposition (G′-ω) has been found to fail in the studied temperature regime. The failure of TTS was believed to be happened due to complex starch-additive-water matrix formation, temperature response of individual components and phase change during gelatinization of starch.     

Conformational changes and dynamic rheological properties of fish sarcoplasmic proteins treated at various pHs

The conformational changes and rheological properties of soluble sarcoplasmic proteins isolated from striped catfish (Pangasius hypophthalmus), treated at various pHs (2–12), were investigated. Isoelectric point of striped catfish sarcoplasmic proteins was determined to be pH 5. SDS–PAGE of sarcoplasmic proteins treated at various pHs, showed molecular masses ranging from 11 to 97 kDa. Most sarcoplasmic proteins, regardless of treated pHs, showed a molecular mass of 43 kDa. A decrease in total sulfhydryl content was observed when the pH was shifted away from 6, indicating disulfide formation at pH lower and higher than 6. Gradual increases of S₀-ANS and S₀-PRODAN were observed as pH increased from 6 to 12, indicating the unfolding of sarcoplasmic proteins during alkaline extraction. DSC thermograms of sarcoplasmic proteins treated at pH 5–9 exhibited an exothermic transition peak, probably due to disulfide bond formation, and/or hydrophobic interactions, which was highly related to the onset temperature of G′ rising. Gel network formation of sarcoplasmic proteins did not take place at extreme pHs (<4 or >9) where proteins were highly charged while the viscoelastic properties of sarcoplasmic proteins were observed at pH 5.5–9. The highest G′ value at 90 °C was observed at pH 5.5 and 8 (P ? 0.05). The gel point, a temperature at which G′ = G″, increased to higher temperature as pH was shifted away from 7.     

Rheological properties of Salecan as a new source of thickening agent

Salecan is a novel soluble glucan produced by Agrobacterium sp. ZX09, displaying the ability to inhibit pancreatic amylase and reduce postprandial glucose. The research here provides an investigation of the rheological properties of Salecan solution over a wide range of shear rate (0.001–1000 s⁻¹), frequency (0.1–100 rad/s), concentrations (0.3%, 0.5%, 1.0% and 1.5%), temperature (5–95 °C) and pH (1.0–13.0). The power law model well described the rheological behavior of the solutions, in the shear-thinning region, with high determination coefficients, R². Salecan solutions showed a non-Newtonian viscosity behavior at all concentrations and temperatures. The solutions exhibited excellent stability below 55 °C. Viscosities were not affected after being frozen (−20 °C). Over a wide pH range from 6.0 to 12.0, the viscosity almost kept invariant. With increasing frequency, the storage and loss moduli G′ and G″ of Salecan solution increased and complex viscosities decreased continuously, which showed an elastic behaviour. All data indicated that Salecan has excellent rheological properties and could be utilized in food industry as a new source of thickening agent.