Associative and segregative interactions between gelatin and low-methoxy pectin: Part 2—co-gelation in the presence of Ca

The effect of segregative interactions with gelatin (type B; pI=4.9; 0–10 wt%) on the networks formed by low-methoxy pectin on cooling in the presence of stoichiometric Ca²⁺ at pH 3.9 has been investigated by rheological measurements under low-amplitude oscillatory shear. Samples were prepared and loaded at 85 °C, cooled (1 °C/min) to 5 °C, held for 100 min, and re-heated (1 °C/min) to 85 °C, with measurement of storage and loss moduli (G′ and G″) at 10 rad s⁻¹ and 2% strain. The final values of G′ at 5 °C for mixtures prepared at the same pH without Ca²⁺ were virtually identical to those observed for the same concentrations (0.5–10.0 wt%) of gelatin alone, consistent with the conclusion from the preceding paper that electrostatic (associative) interactions between the two polymers become significant only at pH values below 3.9. Increases in moduli on cooling in the presence of Ca²⁺ occurred in two discrete steps, the first coincident with gelation of calcium pectinate alone and the second with gelation of gelatin. Both processes were fully reversible on heating, but displaced to higher temperature (by 10 °C), as was also observed for the individual components. The magnitude of the changes occurring over the temperature range of the gelatin sol–gel and gel–sol transitions demonstrates that the gelatin component forms a continuous network; survival of gel structure after completion of gelatin melting shows that the calcium pectinate network is also continuous (i.e. that the co-gel is bicontinuous). On progressive incorporation of NaCl (to induce phase separation before, or during, pectin gelation) the second melting process, coincident with loss of calcium pectinate gel structure, was progressively abolished, indicating conversion to a gelatin-continuous network with dispersed particles of calcium pectinate. These qualitative conclusions are supported by quantitative analyses reported in the following paper.     

Influence of complexing carboxymethylcellulose on the thermostability and gelation of α-lactalbumin and β-lactoglobulin

Thermostability and gelation of the main proteins of whey, α-lactalbumin (α-lac) and β-lactoglobulin (β-lg) recovered by selective complexation with carboxymethylcellulose (CMC) was studied to evaluate its functionality in food systems. Their behavior was compared to the non-complexed proteins. Both complexes showed a maximum stability at pH 4, that is close to the pH of obtention of β-lg/CMC coacervate (pH 4) and α-lac/CMC coacervate (pH 3.2). Protein complexation increased the thermostability of β-lg by approximately 6–8 °C and that of α-lac by approximately 26 °C due to immobilization of protein molecules in a complex, mainly by electrostatic interactions and because of different amounts of bound polysaccharide. The denaturation enthalpy of complexed proteins markedly decreased as compared to free proteins. Storage modulus (G′) and loss modulus (G″) were recorded to reflect the structure development during heating β-lg/CMC and α-lac/CMC complexes at different pH values. β-lg/CMC complex at 20 wt% was a viscoelastic liquid at pH values within 2 and 8 but upon heating turned to a particulate viscoelastic gel. However, α-lac/CMC complex formed before heating opaque, large visible white particulate aggregates that sticked together to give a solid viscoelastic structure that was not further modified by thermal processing.     

Rheology and granule size distributions of corn starch dispersions from two genotypes and grown in four regions

Starch was extracted from corn of two genotypes (Clint and P3730) grown during the 1997 season in four regions in New Zealand and Australia. The granule size distributions in unheated and heated (80°C, 2–120 min) 2.6% starch dispersions (STDs) were different. Most of the heated STDs exhibited shear-thinning behavior, but dispersions of a Clint starch exhibited shear-thickening behavior at shear rates >300 s⁻¹. The power law consistency coefficient of the STDs increased, but their flow behavior index decreased with heating time. Values of the consistency coefficient of all the STDs were found to be related to the cube of the mean granule diameter. Frequency versus storage modulus (G′) data of a 5% Clint STD heated at 80°C, 30 min, showed increase in G′ with ω in a convex down manner, while the other STDs showed typical increase in a convex up manner.     

Mechanical, water vapor barrier and thermal properties of gelatin based edible films

Edible films are thin materials based on a biopolymer. The objectives of this work were to determine the water vapor permeability and the mechanical and thermal properties of edible films based on bovine hide and pigskin gelatins. These films were prepared with 1 g of gelatin/100 ml of water; 15–65 g sorbitol/100 g gelatin; and at natural pH. The samples were conditioned at 58% relative humidity and 22°C for 4 days before testing. The mechanical properties were determined by the puncture test and the water vapor permeability by gravimetric method at 22°C. For DSC analysis, samples were conditioned over silica gel for 3 weeks. Samples (10 mg) were heated at 5°C/min, between −150 and 150°C in a DSC TA 2010. A second scan was run after cell cooling with liquid nitrogen. As expected, the puncture force decreased and the puncture deformation and water vapor permeability increased with the sorbitol content. The origin of gelatin was important only above 25 g sorbitol/100 g gelatin. The DSC traces obtained in the first scan of samples with 15–35 g sorbitol/100 g gelatin, showed a well visible glass transition followed by a sol–gel transition. However, with the increase of sorbitol concentration, the glass transition became broader, typical of the system presenting a phase separation. The model of Couchman and Karazs for ternary system, was used to predict the Tg values as a function of sorbitol concentration.     

Crystalline stability of self-assembled fibrillar networks of 12-hydroxystearic acid in edible oils

The stability of organogels differs based on the organogelator concentration, storage temperature, and solvent type. Organogel post-crystallization annealing was monitored at 5 °C, 15 °C, 20 °C or 30 °C for up to 1 month. Gels, stored at 5 °C, had highly immobilized oil, as judged from large T₂ relaxation peaks at 50–70 ms determined by pulsed nuclear magnetic resonance (pNMR) and visual observations. When the gels were stored at 30 °C, the 50–70 ms T₂ relaxation peak shifted to longer relaxation times, indicating that the oil was more mobile than at 5 °C. Along with the increase in syneresis at 30 °C, the 12HSA network’s crystallinity was also greater, having fewer inclusions of liquid oil, as determined by pNMR. The highly branched network observed at 5 °C changed more in time with regards to crystallinity although it entrained the oil to a much greater extent than the gels stored at 30 °C.     

Effect of surface-active stabilizers on the surface properties of coconut milk emulsions

Previously we have demonstrated improved stability of coconut milk emulsions homogenized with various surface-active stabilizers, i.e., 1 wt% sodium caseinate, whey protein isolate (WPI), sodium dodecyl sulfate (SDS), or polyoxyethylene sorbitan monolaurate (Tween 20) [Tangsuphoom, N., & Coupland, J. N. (2008). Effect of surface-active stabilizers on the microstructure and stability of coconut milk emulsions. Food Hydrocolloids, 22(7), 1233–1242]. This study examines the changes in bulk and microstructural properties of those emulsions following thermal treatments normally used to preserve coconut milk products (i.e., −20 °C, −10 °C, 5 °C, 70 °C, 90 °C, and 120 °C). Calorimetric methods were used to determine the destabilization of emulsions and the denaturation of coconut and surface-active proteins. Homogenized coconut milk prepared without additives was destabilized by freeze–thaw, (−20 °C and −10 °C) but not by chilling (5 °C). Samples homogenized with proteins were not affected by low temperature treatments while those prepared with surfactants were stable to chilling but partially or fully coalesced following freeze–thaw. Homogenized coconut milk prepared without additives coalesced and flocculated after being heated at 90 °C or 120 °C for 1 h in due to the denaturation and subsequent aggregation of coconut proteins. Samples emulsified with caseinate were not affected by heat treatments while those prepared with WPI showed extensive coalescence and phase separation after being treated at 90 °C or 120 °C. Samples prepared with SDS were stable to heating but those prepared with Tween 20 completely destabilized by heating at 120 °C.     

Temperature dependence of the formation and melting of pectin–Ca networks: a rheological study

Small deformation dynamic rheometry was used to characterise the calcium-induced gelation of low-methoxyl pectins, at two different pH values. The gelation kinetics was interpreted with basis on the change of the storage modulus with time, taken as a measure of changes in cross-linking density within the pectin–calcium network. The temperature influence on the rate of gel formation and ageing was evaluated, as well as the temperature sensitivity of the cured gels. The formation and the softening/melting of pectin–calcium networks were also studied under non-isothermal conditions. The structural diversity of the two pectin samples had a great influence on the gelation kinetics and thermal behaviour of these pectin–calcium networks, due to differences in the steric arrangement or environment and/or availability of the chelating groups. An association mechanism is suggested to predominate under conditions of low availability of dissociated carboxylic groups, due to a low pH, higher degree of methylation, or steric constraints introduced by acetylation or neutral side chains, different from the classical ‘egg-box’ model, and where non-ionic hydrogen bonding and hydrophobic interactions may co-exist and cooperate with coordinative binding of calcium-ions.     

Whey protein concentrate/λ-carrageenan systems: Effect of processing parameters on the dynamics of gelation and gel properties

The thermal characteristics, dynamics of gelation and gel properties of commercial whey protein concentrate (WPC), WPC/λ-carrageenan (λ-C) mixtures (M) and WPC/λ-C spray-dried mixtures (DM) have been characterized. In a second stage, the effect of the gelling variables (T, pH, total solid content) on gelation and textural properties of DM was evaluated through a Doehlert uniform shell design.The presence of λ-C either in mixtures (M) or in DM promoted the WPC gelation at lower concentration (8%). M showed higher rates of formation and better gel properties (higher hardness, adhesiveness, springiness and cohesiveness) than DM.Nevertheless, when the effects of pH (6.0–7.0), heating temperature (75–90 °C) and total solid content (12–20 wt%) on gelation dynamics and gel properties of DM were studied, gels with a wide range of rheological and textural properties were obtained. While pH did not affect the gelation dynamics, it had some effect on rheological and textural properties. Total solid content and heating temperature were the most important variables for the dynamics of gelation (gelation rate (1/t_gel), gelation temperature (T_gel), rate constant of gel structure development (k_G), elastic modulus after cooling (G′_c) and textural parameters (hardness, springiness and cohesiveness).     

Gelation mechanism and network structure of mixed solution of low- and high-acyl gellan studied by dynamic viscoelasticity, CD and NMR measurements

The gelation mechanism and the change of the network structure during cooling of the mixed solution of high-acyl (HA) and low-acyl (LA) gellan (containing 0.5% HA gellan and 0.5% LA gellan; hereafter called “mixed solution”) were elucidated on the basis of the results of dynamic viscoelasticity, circular dichroism (CD), and NMR measurements, which provide information about the network formation, the structural change due to random coil-double helix (C–H) transition, and the chain mobility of gellan, respectively. It was demonstrated that HA gellan chains in the mixed solution underwent C–H transition individually to form a network structure at the transition temperature for 1% HA gellan solution (75 °C), where storage modulus G′ and loss modulus G″ were steeply increased and the chain mobility of the HA gellan was restricted. The structural change of the HA gellan chains proceeded gradually with further cooling. At 25 °C, which is the C–H transition temperature for 1% LA gellan solution, LA gellan chains in the mixed solution formed a double helix, where G′ and G″ were slightly increased and the chain mobility of LA gellan was restricted. The results suggest that the double helix formation involves only the same kind of gellan chains even in the mixed solution, and that LA gellan chains decrease the mobility and promote the double helix formation of HA gellan chains, and vice versa.     

Effect of addition of selected solid cosolutes on viscoelastic properties of model processed cheese containing pectin

The aim of this study was to investigate the effect of various selected solid low-molecular cosolutes (d-glucose, d-fructose, d-galactose, lactose, saccharose; target concentrations in samples 1% w/w) on viscoelastic properties of model processed cheese (40% w/w dry matter and 50% w/w fat in dry matter) without and with pectin addition (target concentrations in final products: 0.2% w/w and 0.4% w/w, respectively). Dynamic oscillation rheometry with parallel plate geometry was used to evaluate the changes in viscoelastic properties of samples. All applied low-molecular cosolutes (1% w/w) decreased the firmness of processed cheese. The nature of cosolute was not significant, i.e. the firmness of final products was declined by various cosolutes to the similar level regardless of their (i) reducing or non-reducing ability; (ii) structure (mono- or disaccharide, aldose or ketose); or (iii) steric arrangement (comparison of two epimers – d-glucose and d-galactose). The reduction of sample rigidity due to cosolute addition was observed in both cases, i.e. in processed cheese without and also with pectin.     

Effect of controlled gelatinization in excess water on digestibility of waxy maize starch

An aqueous dispersion of waxy maize starch (5%, w/w) was controlled gelatinized by heating at various temperatures for 5 min. The treated samples were analysed using in vitro Englyst assay, light microscopy, differential scanning calorimetry, X-ray diffraction, and Fourier-transform infrared spectroscopy. When heated, SDS and RS levels were decreased inversely with RDS. A high SDS content (>40%) was kept prior to the visible morphological and structural changes (before 60 °C). Swelling factor began to increase slightly at 50–60 °C and continued to maximum value at 80 °C. A large decrease in ΔH, crystallinity, and ratio of 1047/1022 cm⁻¹ attributed to partially dissociation of crystalline clusters and double helices occurred at 65–80 °C. These changes showed that controlled gelatinized starch with slow digestion property occurred in the molecular rearrangement process before granule breakdown and SDS mainly consists of amorphous regions and a small portion of less perfect crystallites.     

Characterization of gelation time and texture of gelatin and gelatin–polysaccharide mixed gels

The effects of cooling rate, holding temperature, pH and polysaccharide concentration on gelation characteristics of gelatin and gelatin–polysaccharide mixtures were investigated using a mechanical rheometer which monitored the evolution of G′ and G″. At low holding temperatures of 0 and 4 °C, elastic gelatin gels were formed whereas a higher holding temperature of 10 °C produced less elastic gels. At slow cooling rates of 1 and 2 °C/min, gelling was observed during the cooling phase in which the temperature was decreased from room temperature to the holding temperature. On the other hand, at higher cooling rates of 4 and 8 °C/min, no gelation was observed during the cooling phase. Good gelling behavior similar to that of commercial Strawberry Jell-O^® Gelatin Dessert was observed for mixtures of 1.5 and 15 g sucrose in 100 ml 0.01 M citrate buffer containing 0.0029–0.0066 g low-acyl gellan. Also, these mixed gels were stronger than Strawberry Jell-O^® Gelatin Desserts as evidenced by higher G′ and gel strength values. At a very low gellan content of 0.0029 g, increasing pH from 4.2 to 4.4 led to a decrease in the temperature at the onset of gelation, G′ at the end of cooling, holding and melting as well as an increase in gel strength. The gelation time was found to decrease to about 40 min for gelatin/sucrose dispersions in the presence of 0.0029 g gellan at pH 4.2 whereas the corresponding time at pH 4.4 was higher (79 min). In general, the gelation time of gelatin/sucrose dispersions decreased by a factor of 2 to 3 in the presence of low-acyl gellan. The addition of low-acyl gellan resulted in an increase in the gelation rate constant from 157.4 to 291 Pa. There was an optimum low-acyl gellan content for minimum gelation time, this optimum being pH dependent. Addition of guar gum also led to a decrease in gelation time to 73 min with a corresponding increase in the gelation rate constant to 211 Pa/min though these values were not sensitive to guar gum content in the range of 0.008–0.05 g. The melting temperature of gelatin/sucrose/gellan as well as gelatin/sucrose/guar mixtures did not differ significantly from that of pure gelatin or Strawberry Jell-O^® Gelatin Desserts. At pH 4.2, the melting rate constant was highest at a low-acyl gellan content of 0.0029 g whereas the rate constant was insensitive to low-acyl gellan content at pH 4.4. Addition of guar did not seem to affect the melting temperature or the melting rate constant.     

Impact of cosolvents on formation and properties of biopolymer nanoparticles formed by heat treatment of β-lactoglobulin–Pectin complexes

The purpose of this study was to determine the influence of neutral cosolvents on the formation and properties of biopolymer nanoparticles formed by thermal treatment of protein–polysaccharide electrostatic complexes. Biopolymer particles were formed by heating (85 °C, 20 min) an aqueous solution containing a globular protein (β-lactoglobulin) and an anionic polysaccharide (beet pectin) above the thermal denaturation temperature (T_m) of the protein under pH conditions where the biopolymers formed electrostatic complexes (pH 5). The impact of two neutral cosolvents (glycerol and sorbitol) on the self-association of β-lactoglobulin and on the formation of β-lactoglobulin–pectin complexes was examined as a function of solution pH (3–7) and temperature (30–95 °C). Glycerol had little impact on the pH-induced self-association or aggregation of the biopolymers, but it did increase the thermal aggregation temperature (T_a) of the protein–polysaccharide complexes, which was attributed to its ability to increase aqueous phase viscosity. Sorbitol decreased the pH where insoluble protein–polysaccharide complexes were formed, and greatly increased their T_a, which was attributed to its ability to increase T_m, alter biopolymer–biopolymer interactions, and increase aqueous phase viscosity. This study shows that neutral cosolvents can be used to modulate the properties of biopolymer nanoparticles prepared by thermal treatment of protein–polysaccharide electrostatic complexes.     

Properties of enzyme modified corn, rice and tapioca starches

Corn, rice and tapioca starches were partially hydrolyzed by treating the starch dispersions with heat stable α-amylase. Dextrose equivalent (DE) of 8–12 was achieved by hydrolyzing the starch samples (10–20% w/v) for 30 min at 90 ± 2 °C. Scanning electron micrographs showed that starch granules had broken down to smaller particles. High performance liquid chromatography with refractive index detection indicated that oligosaccharides with broad molecular weight distributions are present in the reaction products. Hydrolyzed starch dispersions were analyzed for their rheological properties. The storage modulus values (G′) for 20% solid containing slurries were 7373 and 1470 Pa for untreated and enzyme treated samples, respectively, indicating a marked decrease in solid properties due to enzyme action. The complex viscosities (η^*) for native corn starch and hydrolyzed corn starch were 8243 and 1637 Pas, respectively, which indicate that the enzyme treatment decreases the overall resistance of the sample to flow such that the product can spread easily. Further 13C CP/MAS NMR and FTIR studies revealed the loss of ordered structures in the enzyme modified starches. Free flowing fat substitute in the form of fine powder was prepared by spray drying the hydrolyzed starch slurry.     

Microstructural characterization of β-lactoglobulin–konjac glucomannan systems: Effect of NaCl concentration and heating conditions

In the initial part of this study, the high temperature (85 °C) microscopic phase behaviour of β-lactoglobulin (0.4–6%, w/w)–konjac (0.05–0.75%, w/w) mixtures containing 50 mM NaCl was established using confocal laser scanning microscopy (CLSM). Also, the effects of heating time (heating temperature: 78 °C) and NaCl concentration (0–75 mM) on protein denaturation kinetics and the phase behaviour in 2%, w/w, β-lactoglobulin–0.4%, w/w, konjac mixtures were investigated using turbidimetry, protein denaturation measurement, CLSM and image analysis techniques. Segregative phase separation occurred in heat-treated β-lactoglobulin–konjac mixtures containing biopolymer and NaCl concentrations exceeding certain critical levels, due to heat and NaCl induced β-lactoglobulin denaturation/aggregation. The microstructural properties of selected heated (to 85 °C for 30 min) and cooled (to 25 °C) β-lactoglobulin–konjac mixtures containing different NaCl levels were studied using CLSM and rheological measurements and the results showed that the microstructure can be distinguished as miscible, phase separated or phase separated containing stable protein inclusions dependent on NaCl concentration. Response surface methodology was used to determine the minimum NaCl concentrations required for phase separation and for formation of phase separated systems containing stable inclusions in a wide concentration range of heated and cooled β-lactoglobulin (0.8–2%, w/w)–konjac (0.2–0.75%, w/w) mixtures. The results show that the microstructural and rheological properties of β-lactoglobulin–konjac mixtures can be controlled by selecting appropriate mixture biopolymer and NaCl concentrations and heating conditions.     

On the stability of oil-in-water emulsions to freezing

Oil in water emulsions (40 wt%) were prepared from a homologous series of n-alkanes (C10–C18). The samples were temperature cycled in a differential scanning calorimeter (two cycles of 40 °C to −50 °C to 40 °C at 5 °C min⁻¹) and in bulk (to −20 °C). The emulsions destabilized and phase-separated after freeze–thaw if the droplets were solid at the same time as the continuous phase and were more unstable if a small molecule (SDS or polyoxyethylene sorbitan monolaurate) rather than a protein (whey protein isolate or sodium caseinate) emulsifier was used. The unstable emulsions formed a self-supporting cryo-gel that persisted between the melting of the water and the melting of the hydrocarbon phase. Microscopy provides further evidence of a hydrocarbon continuous network formed during freezing by a mechanism related to partial coalescence which collapses during lipid melting to allow phase separation.     

Survival kinetics of Ephestia kuehniella eggs during 46–75 °C heat treatment

The effect of heat treatment on the survival of Ephestia kuehniella eggs was examined. Samples of 60 eggs were immersed in hot water at constant temperature in the 46–75 °C range for 5–1200 s. Following heat treatment and cooling, the eggs were stored at 24 ± 1 °C in a growth chamber for 7 days before survival evaluation. Statistical analysis of the data demonstrated that the thermal survival kinetics were best represented by a first-order reaction. The rate constant had an Arrhenius-type dependence over the 54–75 °C temperature range. Kinetic parameters were estimated by non-linear regression. The activation energy (E_a) and rate constant (k_ref) at the reference temperature (T_ref = 64.8 °C), were determined as 102.2 ± 6.2 kJ mol⁻¹ and 0.061 ± 0.003 s⁻¹, respectively, over the 54–75 °C temperature range. A 0.01% survival rate was obtained after 50 s at 75 °C. The data at temperatures below 50 °C were not in accordance with those at higher temperatures. Above this temperature, mortality was likely due to physiological disorders, as noted on a DSC thermogram.     

Use of meat fluorescence emission as a marker of oxidation promoted by cooking

Accumulation of fluorescent pigments in cooked bovine meat (M. Longissimus thoracis) was studied in relationship with the heating parameters (time and temperature). Muscles were aged at 4 °C for 11 days under vacuum before cooking. Meat cooking was performed by applying jets of steam. Three different heating treatments were tested: two with constant surface temperatures of 65 and 96 °C for 300 s, and one with a continuously increasing surface temperature up to 207 °C. After extraction in water/dichloromethane/ethanol, fluorescence pigments were distributed between the apolar phase (emission 420–440 nm after excitation at 360 nm) and the polar phase, where two emission peaks were seen (emission 410–430 and 515 nm after excitation at 360 nm). Fluorescence in the two phases was little affected by heating at the two constant temperatures while it increased exponentially after 1 min of treatment, as the varying temperature reached 141 °C. The maximum fluorescence increases, measured in the extreme conditions of cooking (207 °C/300 s), were of 5000% in the apolar phase and 1700% in the polar phase. Thiobarbituric acid reactive substances (TBARS) and protein carbonyls were measured in parallel. The correlations between these two parameters and the fluorescence emission demonstrated that the interaction between proteins and aldehyde products of lipid peroxidation was mainly involved in the production of fluorescent pigments in cooked meat.     

Characterizing asymptotic D-values for Salmonella spp. subjected to different heating rates in sous-vide cooked beef

Inactivation rates of a cocktail of Salmonella spp. in sous vide cooked beef exposed to varied ‘come-up’ heating times of zero (control), and 1–3 h from 10 °C to the processing temperature of 58 °C were examined. The observed survival curves, determined for 58 °C, displayed a slight ‘shoulder’ followed by a non-zero asymptotic D-values. Comparisons of the survival curves confirm that the rate of heating can substantially influence the heat resistance of Salmonella spp. While there was no significant difference between the estimated asymptotic D-values for the control and 1-h come-up heating time survival curves, the estimated D-values were significantly larger for the 2- and 3-h come-up heating times curves. The estimated averages of the asymptotic D-values for the control and 1-h come-up time survival curves are approximately 5.7 min; for the 2-h come-up time curves, 7 min; and for the 3-h come-up time curves, 8 min. These findings could have substantial practical importance to food processors in sous vide cooked beef that are processed by slow heating rate/long come-up times and low heating temperatures.     

On solid-like rheological behaviors of globular protein solutions

Dynamic viscoelastic and steady flow properties of β-lactoglobulin, bovine serum albumin, ovalbumin, and α-lactalbumin aqueous solutions were investigated at 20°C. When a sinusoidal strain in the linear viscoelastic region was applied, the solutions of the globular proteins except for α-lactalbumin showed typical solid-like rheological behavior: the storage modulus G′ was always larger than the loss modulus G″ in the entire frequency range examined (0.1–100 rad/s). Under a steady shear flow, strong shear thinning behavior was observed with increasing shear rate from 0.001 to 800 s⁻¹, for the globular proteins except for α-lactalbumin. The values of the steady shear viscosity η were lower than those of the dynamic shear viscosity η* at a comparable time scale of observation, violating the Cox–Merz rule, and thus suggesting that a solid-like structure in a globular protein solution was susceptible to a steady shear strain. During isothermal gelation of the protein colloids at 70°C, no crossover between G′ and G″ was observed so that the gelation point was judged by an abrupt increase in the modulus or a sudden decrease in tanδ.