ARTICLE IN PRESS. Whey protein concentrate/l-carrageenan systems: Effect of processing parameters on the dynamics of gelation and gel properties

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1 FOOD HYDROCOLLOIDS Food Hydrocolloids 22 (28) Whey protein concentrate/l-carrageenan systems: Effect of processing parameters on the dynamics of gelation and gel properties G. Spahn a, R. Baeza b, L.G. Santiago a,, A..R. Pilosof b a Instituto de Tecnología de Alimentos, Facultad de Ingeniería Química, Universidad Nacional del Litoral, Paraje El Pozo, 3 Santa Fe, Argentina b Departamento de Industrias, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, 1428 Núñez, Ciudad Autónoma de Buenos Aires, Argentina Received 18 December 26; accepted 12 October 27 Abstract The thermal characteristics, dynamics of gelation and gel properties of commercial whey protein concentrate (WPC), WPC/lcarrageenan (l-c) mixtures () and WPC/l-C spray-dried mixtures () have been characterized. In a second stage, the effect of the gelling variables (T, ph, total solid content) on gelation and textural properties of was evaluated through a Doehlert uniform shell design. The presence of l-c either in mixtures () or in promoted the WPC gelation at lower concentration (8%). showed higher rates of formation and better gel properties (higher hardness, adhesiveness, springiness and cohesiveness) than. Nevertheless, when the effects of ph (6. 7.), heating temperature (75 9 1C) and total solid content (12 2 wt%) on gelation dynamics and gel properties of 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). r 27 Elsevier Ltd. All rights reserved. Keywords: Whey protein; Carrageenan; Gelation dynamic; Textural properties 1. Introduction Both proteins and polysaccharides are capable of forming gels and therefore have an important effect on the structural and textural properties of foods. The thermodynamic incompatibility of proteins and polysaccharides is gaining an increasing attention because of the wide-range applications of phase-separated biopolymer systems (Tolstoguzov, 23). b-lactoglobulin, the main protein of whey protein concentrate (WPC), controls thermal and gelation properties of the total whey proteins. It forms two types of gels: white particulate gels between ph 4 and 6 and transparent fine-stranded gels above and below this region. The effect Corresponding author. Tel.: address: lsanti@fiqus.unl.edu.ar (L.G. Santiago). of ph on b-lactoglobulin gels has been previously studied using viscoelastic measurements (Stading & Hermansson, 199), large deformation properties (Stading & Hermansson, 1991) and microscopy (Langton & Hermansson, 1992). Texture depends on mechanical properties, which in turn depend largely on the structure of gel network. echanical properties can be divided into small deformation properties and large deformation properties. Small deformation properties are measured using non-destructive methods, whereas testing by large deformation includes fracture properties of the material. Large deformation properties are usually performed by compression or tension (Stading & Hermansson, 1991). Stading and Hermansson (199) found that it was possible to differentiate between fine-stranded and particulate b-lactoglobulin gels by using viscoelastic measurements, but not to differentiate within each type of gel. On 268-5X/$ - see front matter r 27 Elsevier Ltd. All rights reserved. doi:1.116/j.foodhyd

2 G. Spahn et al. / Food Hydrocolloids 22 (28) the other hand, large deformation measurements show differences in properties between the fine-stranded gels formed at low and high ph. At high ph a rubber-like behavior was found, whereas at low ph gels were brittle (Stading & Hermansson, 1991). Langton and Hermansson (1992) found that the microstructure of whey protein gels at different ph is similar to the microstructure of b-lactoglobulin gels at similar ph, although the region of particulate gels is expanded for whey proteins. In previous studies (Baeza, Gugliotta, & Pilosof, 23; Baeza and Pilosof, 21), an enhancement of the functional properties of b-lactoglobulin due to the presence of polysaccharides like l-carrageenan (l-c) was observed. It has been reported that, under conditions of limited thermodynamic incompatibility between b-lactoglobulin and polysaccharides, the critical concentration for protein gelation is greatly reduced and different gel products may be obtained according to the relative concentrations of biopolymers and ph (Baeza and Pilosof, 21). Novel gelled products can be obtained from ingredients that include WPC/polysaccharide mixtures in their formulation. In this sense, it would be appropriate to develop dried mixtures with the suitable protein/polysaccharide ratio and total concentration to obtain a gelled system by subjecting the re-hydrated mixture to a heat treatment. Therefore, a better understanding of the gelation and physical properties of the gels obtained from dried WPC/ polysaccharide mixtures is necessary. The aim of the present work was (1) to study the effect of the spray-drying process on the dynamics of gelation and gel properties of WPC/l-C mixtures (); and (2) to evaluate gelation variables (T, ph, total solid content) of WPC/l-C spray-dried mixtures () in order to improve their gelation and textural properties. 2. aterials and methods 2.1. aterials Commercial WPC was kindly provided by ilkaut S.A. (Frank, Santa Fe province, Argentina). The composition of WPC was 5.6% moisture and 82.4% protein (dry basis). The l-c was provided by DEGUSSA (Buenos Aires, Argentina) Preparation of Solutions of WPC and l-c were obtained by dissolving the dry matter in distilled water at room temperature under agitation and storing overnight to complete hydration. ph was adjusted with.1 N NaOH or HCl. solutions were obtained by mixing (1:1 ratio) solutions of WPC and l-c of appropriate concentration in order to obtain an 8:1 ratio of WPC:l-C (ratio of biopolymers in the dry mixture) Preparation of The was obtained by spray drying in a pilot plant spray dryer (Niro Atomizer) the liquid mixture of WPC/l-C. The drying conditions were inlet air temperature 18 1C and outlet air temperature 85 1C. The final composition of the was protein 67.3% (w/w) (wet basis) and moisture 8.1% (w/w). The WPC:l-C ratio (8:1) and spray-drying conditions were chosen taking into account industrial operation conditions, previous experiments and the viscosity of the WPC/l-C liquid mixtures (Lizarraga, De Piante Vicin, Gonzalez, Rubiolo, & Santiago, 26) Preparation of WPC or solutions Solutions of WPC or were obtained by dissolving the dry matter (WPC or spray-dried mixture) in distilled water at room temperature under agitation and storing overnight to complete hydration. The ph was adjusted with.1 N NaOH or HCl ethods Thermal transition A ettler TA 4 DSC was used to obtain the thermal transition parameters of WPC and the mixed systems ( and ). Fifty milligrams of the solutions were heated in aluminium pans (4 ml volume) from 5 to 1 1C at 1 1C/min, with an empty pan as reference. The onset denaturation temperature (T onset ) was determined by the intersection of the extrapolated leading edge of the heating curve with the baseline. The peak temperature (T p ) indicating the apparent denaturation temperature was determined from the maximum heat flow. The total calorimetric apparent enthalpy change (DH T ) was calculated from the peak area using a straight baseline between the onset and final temperatures of the thermal transition. All calorimetric parameters reported are the average of two replicates Gel formation Tilting test. Hermetic sealed glass containers with 2 ml of solutions of, and WPC solutions were heated at 77 1C in a dry bath, and tilted at consecutive lengths of time. The gel time (t gel ) was reached when there was no deformation of the meniscus upon tilting. The gel time was evaluated for solutions of and containing between 8% and 1% (w/w) total solid concentration. For WPC the concentrations studied were 7.1%, 8.% and 8.9% (w/w), which correspond to the WPC content in the mixtures Small strain measurements. Dynamic oscillation measurements were performed using a Phar Physica controlled stress Rheometer (CR 3). Solutions of dried and non-dried systems ( and ) were placed on the bottom plate of a parallel plate measuring device with a gap setting of 1 mm. The heating temperature was controlled

3 156 ARTICLE IN PRESS G. Spahn et al. / Food Hydrocolloids 22 (28) with a Peltier system (Viscotherm VT2, Phar Physica) and liquid paraffin was applied to the exposed surfaces of the samples to prevent evaporation. During gelling experiments, frequency was kept constant at 1 Hz and strain was kept at.1%. The samples were heated from 2 1C to the desired temperature (74 9 1C) at two different heating rates: 5 and 25 1C/min. In the experimental design, the heating rate was 25 1C/min. The samples were maintained at constant temperature for 3 min, cooled to 5 1C and held at this temperature for 5 min. Temperatures at which the storage and loss modulus (G and G, respectively) crossed were taken as the gel point. Temperatures (T gel ) and time (t gel )at this point were evaluated Gel characterization Rheological parameters After the gel point, G, G and tan d changes were recorded for 3 min during the constant temperature heating step. After the heating step, the systems were cooled to 5 1C. The final G value obtained after the heating step was evaluated as G max, and the value after the cooling step was G C. The frequency dependence of G for the stable gels formed during heating and cooling steps was evaluated at a constant strain of 1% and at a frequency range of.1 1 Hz Longitudinal compression measurements Two millilitres of WPC and WPC/l-C mixtures ( and ) were poured into cylindrical containers, heated at the design temperature for 3 min and then stored overnight at 5 1C. Texture profile analysis (TPA) was performed on the cylindrical gel specimens using a Stable icro System TA-XT21 Texture Analyser. The gels were compressed with a cylindrical probe (36 mm diameter) to 3% of their original height at.5 mm/s. The average of two replicates was reported Experimental design A Doehlert uniform shell design for three factors was selected and analysed using software Statgrafics 3.1. The effect of process variables (ph, total solid content (S) and heating temperature (T)) on gelling properties of was studied. Real and coded values are shown in Table 1. Three Table 1 Real and coded values of studied variables for Dohelert experimental design Variables Real and (coded) values T (1C) 75 ( 1); (.5); 82.5 (); (.5); 9 (1) S a (% w/w) 12 (.866); (.5774); (.2887); 16 (); (.2887); (.5774); 2 (.866) ph 6 (.8165); 6.5 (); 7 (.8165) a Total solid content. replicates of the central point allowed calculation of the pure error of the methods. A full quadratic model containing 1 coefficients was used to describe the following responses: gelation rate (1/t gel ), gelation temperature (T gel ), rate constant of gel structure development (k G ), storage modulus after cooling (G C), hardness, adhesiveness, springiness and cohesiveness. Each response was described by the following equation: Y ¼ b þ b 1 X 1 þ b 2 X 2 þ b 3 X 3 þ b 4 X 2 1 þ b 5X 2 2 þ b 6X 2 3 þ b 7 X 1 X 2 þ b 8 X 1 X 3 þ b 9 X 2 X 3, where b i are the regression coefficients given by the full quadratic model, Y is the response and X 1 3 the variables studied. Independent variables which were found significant (po.5, or po.1) in the full model were retained in the reduced model. 3. Results and discussion 3.1. Thermal transitions Table 2 shows the parameters (T onset, T p and DH) obtained from the denaturation endotherms for WPC, and. It can be observed that the onset denaturation temperature (T onset ) is lower for ; this phenomenon could be related to protein structure changes due to the thermal treatment during the drying process. A significant change was not observed either in peak temperatures (T p ) or in enthalpy of denaturation (DH) among the different systems Dynamics of gelation Gelation times (t gel ) for WPC, and solutions at different total solid contents obtained by a tilting test at 77 1C are shown in Fig. 1. It can be seen that WPC did not gel at concentrations below 9% (w/w). Nevertheless, the presence of l-c in liquid mixtures () promoted protein gelation at lower concentration and time than WPC alone. For, gelation was observed at 8% (w/w) of the total solid content, which corresponds to 7.1% protein in the mixture. This effect would be related to the existence of thermodynamic incompatibility between the protein and the polysaccharide at ph above the protein isoelectric point. Gelation times were higher for than, indicating that the spray-drying process decreased the rate of development of the gel structure. Table 2 Calorimetric parameters for WPC, spray-dried WPC/l-C mixture () and WPC/l-C mixture () obtained by DSC Sample T onset (1C) T p (1C) DH (J/g) WPC ð1þ

4 G. Spahn et al. / Food Hydrocolloids 22 (28) t gel (min) 1 5 T gel ( C) Total solid content (S%) Fig. 1. Gelation times obtained by a tilting test performed at 77 1C, for WPC solutions (&), WPC/l-C mixtures (K) and WPC/l-C spray-dried mixtures (n). The gelation temperatures of WPC, and, determined by dynamic oscillation measurements, are plotted in Fig. 2. Storage (G ) and loss modulus (G ) were recorded to show the structure development during heating at different temperatures. The gel point parameters (time, t gel and temperature, T gel ) were determined as the G and G crossover at different heating rates: 5 1C/min (Fig. 2a) and 25 1C/min (Fig. 2b). The sequence of events during the course of thermally induced protein gelation can be separated into those that occur in the fluid and solid phases (Foegeding, Bowland, & Hardin, 1995). The dividing line between fluid and solid phase reactions is the gel point (t gel ), where the liquid is transformed to solid. The primary gel structure as well as its further development (after t gel ) occur as a result of denaturation/aggregation reactions. The formation rate of the primary gel structure may be evaluated as 1/t gel. The time evolution of G after the gel point was fitted by the following equation (Baeza et al., 23): G ¼ G 1 ð1 expð k GtÞÞ, (2) where G 1 is the plateau value of G after a long time and k G refers to the rate constant of gel structure development. As can be seen in Fig. 2a, gelation temperature (T gel ) for both and increased with heating temperature; in addition, T gel was higher for WPC/l-C spray dried mixtures. This result agrees with the higher gelation time obtained for by the tilting test. However, when samples were heated at 25 1C/min, no significant differences were observed between the spray-dried () and the mixed () systems. This phenomenon could be due to the high rate of heating as compared to the gelation rate. After the gel point, during the solid phase of gelation, aggregation could be diffusion limited because of the high viscosity of the gel matrix (Baeza et al., 23). It can be observed in Fig. 3 that the rate constant of gel structure development increased with heating temperature and was lower for the spray-dried mixture. The results obtained would indicate that a modification of the protein structure T gel ( C) Fig. 2. Gelation temperature obtained by dynamic oscillation measurements for 16% solutions of WPC/l-C mixtures (K) and WPC/l-C spraydried mixtures (n). Heating rates: 5 1C/min (a) and 25 1C/min (b). occurred during the drying process, hindering protein protein interactions during gel formation Gel properties Table 3 shows the elastic modulus obtained after 3 min of heating at constant temperature (G max). The elastic modulus (G c) and tan d at 1 Hz after cooling the gels at 5 1C were also included. It can be seen that when samples were heated at C, showed lower G max and G c values than, suggesting the formation of a less solid character structure. At 8 1C, on the contrary, above protein denaturation temperature (Table 2), an important increase in G max and G C parameters is observed, both systems showing similar values of these parameters. Low values of tan d indicated the formation of a viscoelastic structure both for and gels. According to the rubber elasticity theory, G c should be larger at higher

5 158 ARTICLE IN PRESS G. Spahn et al. / Food Hydrocolloids 22 (28) K G (min -1 ) Fig. 3. Rate constant of gel structure development (k G ) for 16% solutions obtained from elastic modulus (G ) development during heating (Eq. (2)). Table 3 Viscoelastic properties of WPC, spray-dried WPC/l-C mixture () and WPC/l-C mixture () at 16% (w/w) total solid concentration and different final heating temperatures (heating rate: 25 1C/min) Heating temperature (1C) G max (Pa) G c (Pa) (1 Hz) Tan d (1 Hz) temperature (Bowland, Foegeding, & Hamann, 1995; Boye, Alli, Ismail, Gibbs, & Konishi, 1995). This relationship has been exhibited by and gels. An increase in G during heating and after cooling is indicative of covalent and hydrophobic interactions contributing to matrix rigidity (Bowland et al., 1995). Textural characteristics of the gels formed at 74 and 8 1C are shown in Fig. 4. Gels produced with WPC, and exhibited different textural properties. It is important to remark that gels showed the highest hardness, springiness and cohesiveness at both temperatures and adhesiveness at 8 1C. On the other hand, the differences in textural properties between and were more important at 8 1C. The lower rate of formation of the primary gel structure and the further development of gels would be related to the lower values of textural properties. The effect of the drying process on WPC structure in the presence of l-c could affect gel characteristics (thickness of strands and pores in gel structure) and, consequently, the response to large deformation measurements. The results show that the drying process of the mixtures can modify the dynamics of gel formation and gel properties. However, gel properties of could be improved by modifying factors that affect gel formation, such as ph, heating temperature and total solid content. To this end, a Doehlert uniform shell design of three factors was performed. The effects of total solid content (S), heating temperature (T) and ph on the dynamics of gelation (1/t gel, T gel and k G by dynamic oscillation rheology), rheological parameters (tan d, G c, elastic modulus after cooling) and textural parameters (hardness, adhesiveness, springiness and cohesiveness) were studied. Fitting the full second-order model to the obtained responses showed that total solid content (S) was the most important factor influencing the rate of primary gel structure formation (1/t gel ), as indicated by the largest value of estimated coefficient (Table 4). The largest and positive values of linear and quadratic terms indicated that 1/t gel increased with increasing total solid content, and also suggested the existence of a minimum in 1/t gel when S increased (positive value of S 2 coefficient). The most important variables affecting T gel were S (po.5) and T (po.1). The negative values of the linear regression coefficients indicated that T gel was reduced by increasing S and T. The negative quadratic terms for both variables showed the existence of a maximum. As regards k G, the most important factors affecting this response were heating temperature (T) (po.5) and total solid content (S) (po.1). While the positive values of the linear regression coefficient for T indicated that the gel structure development rate increased with increasing temperature, the negative quadratic term for the same variable showed the existence of a maximum. Total solid content (S) showed negative linear and quadratic terms, indicating a non-linear k G decrease with S. Neither ph nor the interactions among the different variables were significant for any of the three measured responses (1/t gel, T gel and k G ). Tan d has not been included in Table 4 since it was not significantly affected (p4.5) by the three factors studied. Nevertheless, it must be noted that tan d is considered to represent the relative viscoelasticity within the network (Aguilera, Xiong, & Kinsella, 1993), and the values of this response in our experience (.188 and. 28) were typical of viscoelastic gels. All terms, except the quadratic one for ph and the interaction term for TxpH, were statistically significant for G c (Table 4). The most important factors were total solid content (S) and heating temperature (T), while ph was the least important variable. The positive values of linear coefficients for the three variables indicated that when S, T and ph increased, gel solid character increased. The positive values of quadratic terms for S and T suggested the existence of a minimum, while the positive values of interaction coefficients, SxT and SxpH, suggested a synergic interaction between these variables, contributing to an increase in the gel solid character.

6 G. Spahn et al. / Food Hydrocolloids 22 (28) Hardness (g) WPC Springiness WPC Adhesiveness (g.s) WPC Cohesiveness WPC Fig. 4. Textural properties of gels formed from 16% (w/w) total solid content solutions at 74 and 8 1C: (a) hardness, (b) springiness, (c) adhesiveness, (d) cohesiveness. Table 4 Estimated coefficients for the multiple linear regressions Coefficients 1/t gel T gel k G G c Hardness Cohesiveness Constant Linear T S ph Quadratic T S ph Interaction T S T ph S ph R po.1. po.5.

7 151 G. Spahn et al. / Food Hydrocolloids 22 (28) Adhesiveness and springiness were not included in Table 4 since they did not fit the model (Eq. (1)). Nevertheless, springiness values were high ( ) and similar to those reported for propylene glycol alginate (PGA)+b-lactoglobulin gels heated between 8 and 88 1C (Baeza et al., 23), thus suggesting the formation of more flexible structures. Variables that had the most important effect on hardness and cohesiveness were mainly T and S and their interactions. The ph and its interactions had a minor effect on both responses. Hardness and cohesiveness of gels increased with T and S, which coincided with the increase in gel solid character (G c). Hardness showed a minimum, as indicated by the positive quadratic terms for T and S. The high and negative values of the interaction terms, TxpH and TxS, suggested antagonic effects regarding both hardness and cohesiveness. Conversely, SxpH showed a synergic interaction for hardness, indicating that the higher ph and S, the harder the gels. 4. Contour plots Contour plots were generated for each response as a function of total solid content and T. The ph had little influence and was fixed at 6.5. The contour plot for the primary structure formation rate (1/t gel ) as a function of T and S is plotted in Fig. 5a. Independently of T, the rate of primary structure formation increased with S; suggesting that the aggregation rate was driven by total solid content. This result is in agreement with the fact that a higher total solid content promotes a higher aggregation rate. Besides, all samples gelled on the heating ramp, so it could be supposed that 1/t gel is not dependent on the final heating temperature. Since t gel and T gel are related at the gel point, the most important variable affecting T gel was also S, and when S increased T gel decreased (Fig. 5b). At high values of total solid content (S), T gel was not affected by heating temperature (T), since a high total solid concentration promotes aggregation reactions. For low S values heating treatment was more important, and thus when heating temperature (T) increased gelation temperature (T gel ) decreased. This result suggests that higher driving force (heating temperature) had a strong influence on both the system viscosity properties and the system diffusion rate, and so it could be more probable for aggregation reactions to take place and develop larger aggregates, forming the gel matrix at a lower gelation temperature (T gel ). Gelation temperature (T gel ) shows a wide range of values ( C), Fig. 5. Contour plots for (a) 1/t gel ; (b) T gel ; (c) k G ; and (d) G c as a function of total solid content (S) and temperature (T) at ph 6.5.

8 G. Spahn et al. / Food Hydrocolloids 22 (28) and the fact that the gel structure can be formed at low T gel might be due to the polysaccharide (l-c)-induced aggregation process. These results are in agreement with those obtained by other researchers for polysaccharide b-lactoglobulin systems. Baeza et al. (23), Baeza and Pilosof (21), Zasypkin, Dumay, and Cheftel (1996) found that xanthan, PGA and l-c promoted the formation of larger aggregates of b-lactoglobulin that continued growing with time. Capron, Nikolai, and Durand (1999) found that k-carrageenan accelerated the aggregation of small b-lactoglobulin particles to larger fractal constituents. The dependence of the rate constant of the gel structure development (k G ) on heating temperature (T) and total solid content (S) is shown in Fig. 5c. WhenT was low (75 1C) and S was high, k G was lower than.5, but when heating temperature (T) increased, k G increased, independently of the total solid content (S) values. The fact that heating temperature, T, was the most important variable would be related to its effect on the diffusion coefficient in the solid matrix. After the gel point, when entering the solid phase of gelation, aggregation would be diffusion limited because of the high viscosity of the gel matrix. When T is increased, the driving force would increase and so would the diffusion and gelling rates (Baeza et al., 23). It must be noted that the highest values for k G were obtained between C and % of total solid content. The contour plot for G c response is shown in Fig. 5d. As can be observed, gel solid character increased synergistically with heating temperature (T) and total solid content (S). Baeza et al. (23) suggested that the formation of particles at high temperature should mainly involve exchange reactions between thiol groups exposed upon protein unfolding. Besides, when ph increased the solid character of gels also increased (results not shown), suggesting that at ph 7. chemical aggregation takes place, while at ph 6. physical aggregation with weaker bonds predominates (Stading et al., 199, 1991). Fig. 6a and b illustrate the hardness and cohesiveness dependence of T and S. The maximum values for hardness and cohesiveness were obtained under conditions of both high total solid content (S4.3) and low heating temperature (To.2) or low S (So.3) and high T (T4.2). Cohesiveness values were similar to those obtained by Baeza et al. (23) for PGA+b-lactoglobulin gels heated during 12 min between 72 and 88 1C. Nevertheless, hardness values were higher than those reported by the same researchers. The high cohesiveness and hardness values obtained at T48 1C suggested a high level of denaturation of WPC protein in (T p ¼ C) involved in the gel structure. Similar results were indicated by Baeza et al. (23) for b-lactoglobulin and PGA+ b-lactoglobulin gels heated at temperatures higher than b-lactoglobulin denaturation temperature (T476 1C). The high temperature would contribute to covalent aggregate formation. The information provided by these results suggests that selecting gelling conditions for, i.e., values of S4.3 and.6oto.2, gels at lower gelation temperature with good rate of primary structure formation and with intermediate values for the rate constant of the gel structure development can be formed. Besides, these gels would have good solid character, high hardness and cohesiveness. 5. Conclusion The results revealed a significant effect of the spraydrying process of WPC/l-C mixture, both on the dynamics of formation and gel properties of the biopolymer mixture. The presence of l-c promotes the gelation of WPC at lower concentrations and temperatures. The mixture of WPC/l-C (without spray drying) showed higher formation rates and better gel properties than. These effects would be related to thermal modification of WPC structure or complexation between l-c and WPC protein, which also Fig. 6. Contour plots for (a) hardness and (b) cohesiveness as a function of total solid content (S) and temperature (T) at ph 6.5.

9 1512 ARTICLE IN PRESS G. Spahn et al. / Food Hydrocolloids 22 (28) affects the ability of the protein to aggregate and gel structural characteristics. Nevertheless, the study of the effect of ph, heating temperature and total solids on gelation dynamics and gel properties of the spray-dried mixture revealed gels with a wide range of textural properties. Although ph did not affect the gelation dynamics, it had some effect on rheological and textural properties in the range studied. The primary structure formation rate increased with total solids, independently of heating temperature, which indicated that this gelation stage was governed by aggregation of particles promoted by the polysaccharide. The further development of the gel depended mainly on temperature due to the increasing particles diffusion rate on the solid phase and the promotion to higher aggregation rate. The results also proved that the response surface methodology is an excellent tool for determining the best conditions of total solid, ph and heating temperature to obtain gels with the desired properties. Acknowledgements This research was supported by CYTED through project XI.17 and project 15AC274. The authors also acknowledge the support of the Universidad de Buenos Aires, Universidad Nacional del Litoral (CAI+D 12H/429), Agencia Nacional de Promocio n Científica y Tecnolo gica and Consejo Nacional de Investigaciones Cientı ficas y Te cnicas de la Repu blica Argentina. References Aguilera, J.., Xiong, Y. L., & Kinsella, J. E. (1993). Viscoelastic properties of mixed dairy gels. Food Research International, 26, Baeza, R., Gugliotta, L., & Pilosof, A.. (23). Gelation of b-lactoglobulin in the presence of propylene glycol alginate: Kinetics and gel properties. Colloids and Surfaces B: Biointerfaces, 31, Baeza, R., & Pilosof, A.. R. (21). ixed biopolymer gels systems of b-lactoglobulin and non-gelling gums. In E. Dickinson, & R. iller (Eds.), Food colloids fundamentals of formulation (pp ). Cambridge: The Royal Society of Chemistry. Bowland, E. L., Foegeding, E. A., & Hamann, D. D. (1995). Rheological analysis of anion-induced matrix transformations in thermally induced whey protein isolate gels. Food Hydrocolloids, 9, Boye, J. I., Alli, I., Ismail, A. A., Gibbs, B. F., & Konishi, Y. (1995). Factors affecting molecular characteristics of whey protein gelation. International Dairy Journal, 5, Capron, I., Nikolai, T., & Durand, D. (1999). Heat induced aggregation of b-lactoglobulin in the presence of iota-carrageenan. Food Hydrocolloids, 13, 1 5. Foegeding, E., Bowland, E., & Hardin, C. (1995). Factors that determine the fracture properties and microstructure of globular protein gels. Food Hydrocolloids, 9, Langton,., & Hermansson, A.. (1992). Fine stranded and particulate gels of b-lactoglobulin and whey protein at varying ph. Food Hydrocolloids, 5(6), Lizarraga,. S., De Piante Vicin, D., Gonzalez, R., Rubiolo, A., & Santiago, L. (26). Rheological behaviour of whey protein concentrate and lambdacarrageenan aqueous mixtures. Food Hydrocolloids, 2(5), Stading,., & Hermansson, A.. (199). Viscoelastic behavior of b-lactoglobulin gel structures. Food Hydrocolloids, 4(2), Stading,., & Hermansson, A.. (1991). Large deformation properties of b-lactoglobulin gel structures. Food Hydrocolloids, 5(4), Tolstoguzov, V. (23). Some thermodynamic considerations in food formulation. Food Hydrocolloids, 17(1), Zasypkin, D. V., Dumay, E., & Cheftel, J. C. (1996). Pressure and heatinduced gelation of mixed beta-lactoglobulin/xanthan solutions. Food Hydrocolloids, 1,