Rheological properties of the mucilage gum (Opuntia ficus indica)L. Medina-Torresa, E. Brito-De La Fuentea,*, B. Torrestiana-Sanchezb, R. Katthainc

aFood Science and Biotechnology Department, Chemistry Faculty E, National Autonomous University of Mexico (UNAM), 04510 Mexico, D.F. MexicobChemical and Biochemical Department, Technological Institute of Veracruz, Calle 9 No. 50-2, Costa Verde, Boca del Rio, 94294 Veracruz, Mexico

cAditivos Internacionales, 03700 Van Dyck 42, Col. Mixcoac, D.F. Mexico

Received 22 January 1999; received in revised form 18 October 1999; accepted 14 January 2000

Abstract

The rheological properties of aqueous solutions of the mucilage isolated from Opuntia ficus indica have been examined. Steady-shearviscosities in a range of shear rate from 1 to 300 s21 were observed as a function of mucilage concentration, temperature, pH and ionicstrength. A non-Newtonian shear-thinning behavior was observed. A quite important increase in pseudoplasticity (or shear thinning) due toincrease in the mucilage concentration, in the range from 1 to 10% (w/w) was showed. In the range of shear rates examined, viscosity valuesof a mucilage solution at 10% are similar to those shown by a xanthan 3% aqueous solution, both at 258C. The Ostwaldde Waele or powerlaw model successfully correlated the viscosityshear rate data. The viscosity was dependent on ionic strength, as in the case of polyelec-trolytes, and decreased with ionic strength. This behavior was more pronounced when using divalent cations. A marked dependence ofviscosity on pH was also observed, as pH was increased from acidic to alkaline conditions, the viscosity increased.

Elastic steady-shear properties were evaluated as the primary normal stress difference. Mucilage aqueous solutions showed high elasticproperties, similar to high elastic synthetic polymers like polyisobutylene. At constant shear stress, the normal stresses decreased as themucilage concentration was increased.

The mechanical spectra in the linear viscoelasticity range were observed at a frequency range from 1 to 50 rad/s, in the temperature rangefrom 5 to 358C. At low mucilage concentration (,3%) the behavior was typical of a dilute solution. However, with increasing concentration,the solution tended toward a weak gel behavior. A cross-over point between G 0 and G 00 was observed at low frequencies (

rheological properties of some products (Pimienta-Barrios,1991).

Although several studies on the chemical structure andcomposition for some of these polysaccharides have beenreported (McGarvie & Parolis, 1979), practically no infor-mation on their functional properties is currently available.Studies on the composition of mucilage cells from Opuntiaficus indica (a member of the cactaceae family) revealedthat the mucilage is a high molecular weight polysaccharidethat behaves as a polyelectrolyte. The mucilage is a poly-saccharide that contains a molecular structure of up to30,000 different sugars (McGarvie & Parolis, 1981).

The polymer is a polysaccharide that contains residues ofarabinose, galactose, galacturonic acid, rhamnose andxylose (McGarvie & Parolis, 1979). While these studiestried to relate the molecular properties to the physiologicalfunction of the mucilage in the plant, no attempt to charac-terize the flow properties of the mucilage gum was carriedout.

The aim of the present study is to characterize the rheo-logical properties of mucilage gum (Opuntia ficus indica).These data are required in order to gain insight on the func-tional properties of this biopolymer. The principal topics tobe examined here are the effects of concentration, tempera-ture and ionic strength on the flow properties of mucilagesolutions.

The approach is to use steady-shear viscosity as well assmall strain oscillatory shear tests on solutions formulatedfrom mucilage gum isolated and purified in our laboratory.Elastic flow properties are also investigated through thenormal stress difference, a material function. The experi-mental data are analyzed considering the potential thatthis mucilage has to modify the functional properties ofthe systems formulated with it.

2. Materials and methods

2.1. Isolation and purification of the mucilage

The isolation and purification technique followed here isa modification of the extraction procedure reported in theliterature (McGarvie & Parolis, 1979). Stems from Opuntiaficus indica were selected from Milpa Alta (Mexico) andthey were from the same batch. A pulp was obtained afterthe clean stems were macerated. Then, the pulp was centri-fuged at 10 000 rpm, decanted, and precipitated in acetonefollowing a 1:2 mucilaginous pulp: acetone ratio. The preci-pitated was then collected, washed with isopropyl alcoholwith a 1:1 volume ratio and finally it was dried.

2.2. Analytical determinations

2.2.1. Sugar compositionThe sugar composition of the mucilage was determined

by HPLC (Beckman Mod. 110B). A Waters 60 A column,4 mm in diameter, packed with aminopropylmethylsilyl-

bonded amorphous silica was used. The mobile phase wasacetonitrilewater at 258C. A refraction index detector (IR)(PerkinElmer, model LC-30) and an integrator (VarianModel 4400) were used with the HPLC. A sample of10 mg of dried mucilage powder was degraded by heatingat 808C for 24 h with 1 M sulfuric acid (2 ml), and cooled atroom temperature before the analysis. The results werecompared with the following standard samples: l-arabinose(commercial grade, Difco Laboratories, USA), l( 1 )-rham-nose monohydrate (commercial grade, Merck, USA), d-galactose (commercial grade, Pfanstiehl Laboratories Inc.,USA), d-xylose (commercial grade, Difco Laboratories,USA).

2.2.2. Molecular weightThe molecular weight of the mucilage was estimated by

HPLC (PerkinElmer Model 250), equipped with a G 2000SW (TSK-GEL) column, a refraction index detector, IR(PerkinElmer series 200) and an integrator (Spectra-Physics, model SP4270). A flow rate of 0.7 ml/min wasused. Dextrans (commercial grades, Sigma USA, Leuconos-toc mesenteroides, strain B-152 and Dextran T70 Producedby Pharmacia Biotechnology, Sweden) with molecularweight from 5000 to 87 000 were used as standards. Themucilage was dissolved in deionized water and then filteredbefore the analysis.

2.3. Rheological properties

2.3.1. Preparation of solutionsAqueous mucilage solutions at different concentrations

ranging from 1 to 10% (w/w) were prepared by dissolvingthe dry biopolymer with agitation. Several concentrations ofK1, Na1, Ca11, Mg11 (commercial grade, J.T. Baker,USA) were used in order to obtain the desired ionic strength(I). This ranged from 0 to 0.6 M. Additionally, aqueoussolutions of xanthan gum food grade (Kelco, Milles,USA) and carboxymethylcellulose (CMC) (Hercules,USA) were dispersed in deionized water solution andstudied for comparison purposes.

2.3.2. Rheological measurementsAll the rheological measurements were performed in a

rotational rheometer (Haake, Germany, Mod. CV20N)using a cone and plate geometry (PK20/4; coneangle 48; plate diameter 19.57 mm) and a temperaturecontrol bath (Haake, Germany, Mod. F3T). The solutionswere characterized regarding their steady-shear viscosityfunction, h (g ), using a unidirectional steady-shear flow,with shear rates ranging from 0.3 to 300 s21. The viscoelas-tic properties, storage modulus G 0 and loss modulus G 00were determined through small amplitude oscillatory shearflows at frequencies ranging from 1 to 50 rad/s. Prior to anydynamic experiments, a strain sweep test at a constantfrequency of 1.0 rad/s allowed to fix the upper limit of thelinear viscoelastic zone at a strain value of of 0.30. Thus,

L. Medina-Torres et al. / Food Hydrocolloids 14 (2000) 417424418

this strain level was used in all dynamic tests. It must benoted here that in most publications 15% strain is used.However, for several systems like carrageenan and xanthan,the upper limit of the linear behavior has been reported toextend up to strain value of 0.15 (Rodriguez-Hernandez &Tecante, 1999) or even higher like 0.50 strain for xanthan(Rochefort & Middleman, 1987).

The steady-shear primary normal stress difference (N1)which is a measure of the elastic flow properties was deter-mined using the cone and plate geometry PK20/4. For allrheological measurements, reported values are the mean ofat least two replicates.

3. Results and discussion

3.1. Analytical determinations

3.1.1. Sugar compositionThe experimental results on mucilage sugar composition

are summarized and compared with some reports fromliterature in Table 1. As it can be seen in this table, ourresults are quite similar. The main sugar component ofmucilage is arabinose followed by xylose.

3.1.2. Molecular weightFrom elution profiles, a molecular weight for the

mucilage of 2:3 104 was determined. It must bemention here that this MW is quite different from the4:3 106 value reported in the literature, obtained fromultra-centrifugation experiments (Trachtenberg & Mayer,1982). Differences in isolation techniques and contami-nation of the mucilage with other cell compounds, forexample, those originating in the cell walls, may explainthese results. In addition, differences in the varieties ofthe cactaceae studied may also explain the above MWdifferences (Trachtenberg & Mayer, 1982).

L. Medina-Torres et al. / Food Hydrocolloids 14 (2000) 417424 419

Table 1Sugar composition of the mucilage gum (Opuntia ficus indica)

Composition This work(wt%)

This work(mol%)

McGarvie andParolis (1981)(mol%)

Arabinose 44.04 46.68 42.4Galactose 20.43 17.92 18.4Xylose 22.13 23.45 24.5Rhamnose 7.02 6.76 6.4Galacturonic acid 6.38 5.19 8.4

Fig. 1. Effect of mucilage concentration on the steady-shear viscosity at 258C. Data at pH 4.8 and I 0:1025 M:

3.2. Steady-shear flow measurements3.2.1. Concentration effect

Typical viscosity curves, as a function of mucilageconcentration, are shown in Fig. 1. In general, the mucilagesolutions behave as shear thinning fluids which means thattheir viscosity decreases as the rate of deformationincreases. For this case, the shear thinning behavior canbe fitted to well within experimental error by theOstwaldde Waele or power law model (Brito-De LaFuente, Choplin & Tanguy, 1997) given by:

h k _gn21 1where k is the consistency index (Pa sn) and n the fluidbehavior index. The parameters n and k are obtained bylinear regression analysis.

The fits of the experimental results given in Fig. 1 to Eq.(1) are illustrated by the continuous lines and they representquite well the experimental data. The values of the para-meters n and k are also given in Fig. 1.

Steady-shear viscosity data of polysaccharide solutions ina wide range of deformation rates, including a Newtonianzone at low shear rates, are usually well represented by theCross model (Morris, Cutler, Ross-Murphy, Rees & Price,1981) given by:

h h01 1

_g

l

p 2where h is the steady-shear viscosity (Pa s), l a structuralrelaxation time, p an exponent related to the shear-thinning

behavior and h 0 the limiting Newtonian viscosity at lowshear rates.

It must be noted that, in order to use the Cross model,experimental data in the low shear range are required. Thevalue of h 0 is normally obtained by using low shear visco-metry. Furthermore, using the latter technique, the hydro-dynamic volume of isolated polysaccharide coils alsoknown as intrinsic viscosity (h ) can be determined.This index gives valuable information regarding the confor-mation of polysaccharide molecules in solution. However,in many engineering applications, process shear rates aremainly in the shear-thinning region but outside the lowshear Newtonian zone.

Eq. (2) has been found to represent macromolecular solu-tions of polysaccharides in random coil configuration, forexample, galactomannans as well as other non-gelling poly-saccharides like dextrans, l-carrageenans, cellulose deriva-tives, among others (Morris et al., 1981). It must be notedthat Eq. (2) also represents the linear region of the function-ality h g ((typically described by the well-known power-law model or Eq. (1). A comparison of the Cross modelwith the Ostwaldde Waele model shows that the parametern is equal to 1 2 p: Then, using the fluid behavior index nreported in Fig. 1, the parameter p is found to change from0.44 to 0.77 as the mucilage gum concentration increasesfrom 1 to 10% (w/w) thus describing important changes inpseudoplasticity levels.

Morris et al. (1981) found empirically a value of p equalto 0.76 as the terminal slope of the function log h vs. log gat high shear rates for random coil polysaccharides solu-tions of high polydispersity. The estimated p value for muci-lage 10% found in this work is very close to the terminalslope reported before suggesting again a random coilconfiguration for mucilage aqueous solutions. Additionally,in this study k varies from 0.15 to 25.47 (Pa sn) as mucilageincreases from 1 to 10%.

It must be noted that steady-shear viscous flow propertiesof commercially important biopolymers like xanthan gumand CMC are similar to those shown in Fig. 1 for our muci-lage. As the results of Fig. 1 suggest, viscosity values of amucilage solution at 10% are comparable with a xanthansolution at 3%. This result is quite interesting consideringthe economical and technical importance of the xanthangum.

3.2.2. Temperature effectRegarding the influence of temperature on the mucilage

viscous properties, for concentrations ranging from 3 to10%, data shown in Fig. 2 suggest that these solutions areslightly temperature dependent, in a range from 5 to 708C.This means, as the temperature increases, viscositydecreases. In the range of concentration studied here, thisbehavior is independent of the mucilage concentration.Viscositytemperature dependence can be represented byan Arrhenius type equation as shown in Fig. 2 by the lines

L. Medina-Torres et al. / Food Hydrocolloids 14 (2000) 417424420

Fig. 2. Effect of the temperature on the steady-shear viscosity of mucilageaqueous solutions. Data at shear rate 100 s21, pH 4.8 and I 0:1025 M:

(Lewis, 1987) given by:

h A exp EaR

1T

3

where Ea is an energy of activation, R represents the univer-sal gas constant, A is a fitting constant and T the absolutetemperature. A higher Ea value means a more rapid changein viscosity with temperature. Mucilage 10% showed thehigher value of Ea according to the data shown in Fig. 2.It is interesting to note here that several biopolymers likexanthan have shown quite stable viscous properties withregard to temperature (Kang & Pettitt, 1983; Rajinder,1995) like the mucilage of this work.

3.2.3. Effect of ionic strengthThe effect of ion concentration on viscosity is important

not only to determine whether the mucilage behaves aspolyelectrolyte but also to estimate functional rheologicalproperties. Charged molecules show a strong viscositydependence on ionic strength. Smidsrod and Haug (1971)have represented this functionality by:

h h1 1 SI21=2 4where h1 is the extrapolation of h at infinite ionic strength.The latter value is a function of the molecular weight. S isthe slope of the function h vs. I21/2 according to Eq. (4) andit is a function of the polymer chain stiffness.

The experimental results regarding the effect of ionicstrength on the mucilage viscous properties are shown inFig. 3 for a mucilage concentration of 5%. The predictionsfrom Eq. (4) are also shown in the same figure. It is clear thatan increase in salt concentration results in a decrease in h ,as expected for polyelectrolytes.

Typical values of S for samples of xanthan are in therange of 0.550.66 (Lillford & Norton, 1991). By compar-ing the results shown in Fig. 3 where S changes from 0.20 to0.57 with data for xanthan, it is clear that S is a parameterthat also depends on the ionic strength.

A similar tendency as the one shown in Fig. 3 is observedindependently of the value of shear rate used to evaluate thesteady-shear viscosity function. According to data shown inFig. 3, it is clear that viscosity reduction is more dependenton the Ca11 and Mg11 ion concentration than on Na1 orK1. These results suggest that mucilage is a negativelycharged polyelectrolyte molecule. At zero ionic strengthor without a counter ion, a negative charge produces strongintermolecular repulsion and thus a more expanded mole-cule. This may explain the high viscosity of mucilage indeionized water. On the other hand, the addition of positiveions reduces repulsion and molecule expansion producing asignificant reduction in viscosity. These results are agree-ment with intrinsic viscosity results reported by Trachten-berg and Mayer (1982) for mucilage.

3.2.4. Effect of pHThe effect of pH on the steady-shear viscosity is shown in

Fig. 4. From this figure is clear that increasing the pH causesan increase in the viscosity values. In the alkaline region,viscosity values show a tendency to a constant value. On theother hand, they decrease sharply between pH 7.0 and 2.0.The ionization of the mucilage carboxyl groups above pH7.0 may explain the increase in the viscosity. A similarargument was given by Trachtenberg and Mayer (1982) toexplain the increase in the intrinsic viscosity of mucilagewith the pH.

From the above results, it is clear that both pH and ionicstrength affect the hydrodynamic and thus the flow proper-ties of the mucilage molecules. These properties arepresumably a result of the conformational changes in the

L. Medina-Torres et al. / Food Hydrocolloids 14 (2000) 417424 421

Fig. 3. Influence of ionic strength on the steady-shear viscosity of a 5% (w/w) mucilage solution, at 258C. Data at shear rate 100 s21, pH 4.8 andI 0:1025 M:

Fig. 4. pH dependence of the steady-shear viscosity for mucilage 5% (w/w)and 258C. Data at shear rate 100 s21 and I 0:1025 M:

molecule and should be taken into account in order to deter-mine the functional properties of the mucilage.

3.2.5. Elastic propertiesThe primary normal stress difference in steady-shear

flows (N1) is a material function that allows the evaluationof elastic properties. This material function is defined by:

N1 t11 2 t22 C1 _g 2 5

where t11 2 t22 is the primary normal stress difference andC 1 the first coefficient of normal stresses.

Elastic flow properties may be quite important for manyindustrial applications like coating, texture, etc. Severalempirical applications of cactus extracts (containing muci-lage) like paints, shampoos, syrups, etc. are based on theelastic properties of this biopolymer (Ramirez, 1972). Then,in this work it was considered important to estimate theelastic response of mucilage solutions in steady-shear flows.

Fig. 5 shows N1 as a function of the steady-shear stresst 12. From these results, it is clear that mucilage aqueoussolutions show quite important elastic flow properties insteady-shear flows. As shown in Fig. 5, these propertiesare comparable, in a given t range, with those shown by aclassical elastic polymer like polyisobutylene. Our resultsshow that as t 12 increases, N1 increases. On the other hand, itcan be observed that at constant shear stress, N1 decreases asthe polymer concentration increases.

Elastic experimental results are represented by thefollowing equation as suggested by Broadbent and Lodge(1971):N1 m 0t12 n

0; 6where m 0 is a characteristic consistency index and n 0 a flowbehavior index (which may vary between 0 and 2 for shearthinning liquids). For all mucilage concentrations studiedhere, N1 was reasonably well predicted by Eq. (6). Thesolid lines in Fig. 5 represent N1 predictions from Eq. (6).The values of the parameters m 0 and n 0 are also reported inthe same figure. As the results of Fig. 5 suggest, as tincreases, N1 increases and the representation of experimen-tal data by Eq. (6) is quite acceptable. In this case, for 3 and10% (w/w) mucilage concentration, m 0 varies from 5.64 to0.065 (Pa s12n 0), and n 0 ranges from 1.92 to 2.02, respec-tively. A similar tendency was observed in the literature fora wide selection of synthetic polymers (Ait-Kadi, Choplin &Carreau, 1989).

3.3. Steady oscillatory flow measurements3.3.1. Concentration effect

Typical oscillatory flow curves as a function of mucilageconcentration in deionized water and 258C are shown in Fig.6. As can be observed, both the dynamic storage modulusG 0, and the viscous modulus G 00 show a dependency on thefrequency. The mechanical spectrum shown in this figure istypical of random coil polysaccharides solutions (Morris etal., 1981). In the experimental range of frequency examinedin Fig. 6, mucilage solutions show typical viscoelastic prop-erties rather than physical gel characteristics (Clark & Ross-Murphy, 1987). This behavior is clearly dependent on muci-lage concentration. At low mucilage concentration (,3%),G 00 is always superior to G 0. This means that, in a givenapplication and at these low mucilage concentrations, muci-lage solutions will show mainly viscous properties insteadof a clear tendency to form a gel.

L. Medina-Torres et al. / Food Hydrocolloids 14 (2000) 417424422

Fig. 5. Primary normal stress difference as a function of shear stress andmucilage concentration. Data at 258C, pH 4.8 and I 0:1025 M:

Fig. 6. Frequency dependence of the storage modulus G 0 and loss modulusG 00 for different concentrations of mucilage and xanthan gum solutions, indeionized water at 258C. Blank symbols, G 0. Filled symbols, G 00. Data atpH 4.8 and it . I 0:1025 M:

On the other hand, increasing mucilage concentration, G 0becomes greater than G 00 indicating a clear tendency to formmacromolecular networks with important elastic properties.The latter behavior has been observed for xanthan gum atconcentrations greater than 1% (Rajinder, 1995). It is impor-tant to mention here that this is the explanation of the greatsolid suspension capacity shown by xanthan solutions, animportant physical property widely used for commercialpurposes in many applications. In Fig. 6, data for xanthan1 and 2% are presented for comparison purposes. As theresults suggest, a mucilage solution at 10% exhibits superiorsuspension capabilities as compared with xanthan 2%.

The effect of temperature on the viscoelastic properties isanalyzed in Fig. 7 for a 5% (w/w) mucilage concentration indeionized water. The dependence of both dynamic modulusG 0 and G 00 on frequency is again observed regardless of thetemperature. A similar tendency has been reported byMorris et al. (1981) as typical of random coil polysacchar-ides solutions. It is important to note here that at 358C across-over point between G 0 and G 00 occurs at low frequen-cies suggesting a conformational change of mucilage. Asfrequency increases, G 0 crosses G 00 and the material behavessolid-like. This behavior has been reported for galactoman-nans and it has been explained as due to changes fromentanglements to random coil conformation. However, thenature of this phenomena still controversial and not at allclear.

Additionally, the elastic and viscous response ofmucilage concentration in oscillatory flows are alsodependent on both pH and ionic strength (data notshown here) as it was observed in steady-shear flows.This again suggests that the final mucilage rheologicalproperties are quite dependent on the molecular confor-mation of mucilage in solution.

4. Conclusions

We have examined the rheological behavior of aqueousmucilage solutions from Opuntia ficus indica. Steady-shearviscosity measurements showed a non-Newtonian shear-thinning behavior, which could be correlated to the shearrate by the power law model. By comparing our results withdata from literature for other biopolymers, a random coilconfiguration for the mucilage is suggested.

Mucilage viscous solutions were found slightly tempera-ture dependent and this behavior is almost independent ofmucilage concentration. On the other hand, the steady-shearviscosity was dependent on ionic strength, in the same wayas typical polyelectolytes. As ionic strength increases, vis-cosity decreases. This latter behavior is more pronouncedwhen using divalent ions. A dependence of viscosity withpH was also observed. From acid to alkaline regions, vis-cosity increases sharply.

Elastic steady-shear properties were also examinedthrough measurements of the primary normal stress differ-ence N1. The normal stresses at constant shear stress areshown to decrease as the mucilage concentration increases.By comparing our data with high elastic synthetic polymers,it is evidenced that mucilage solutions have important elas-tic flow properties, which could be used in many practicalindustrial applications. Detailed discussion of such applica-tions is outside the scope of the present paper.

Finally, the mechanical spectra (or dynamic flow proper-ties) in the linear viscoelastic region, as a function of muci-lage concentration and temperature were studied. Bothfluid-like (G 00) and solid-like (G 0) behaviors were observedto be dependent on concentration and frequency. A cross-over point between G 0 and G 00 at 358C at low frequencieswas also noted suggesting a rearrangement of the assumedinitial entanglements to a random coil configuration.

References

Ait-Kadi, A., Choplin, L., & Carreau, P. J. (1989). Polymer Engineeringand Science, 9, 2651272.

Brito-De La Fuente, E., Choplin, L., & Tanguy, P. A. (1997). Transactionsof the Institution of Chemical Engineers A, 75, 52.

Broadbent, J. M., & Lodge, A. S. (1971). Rheologica Acta, 10, 557558.Clark, A. H., & Ross-Murphy, S. B. (1987). In K. Dusek, Advances in

polymer science (pp. 57192). vol. 83. Berlin: Springer.Kang, K. S., & Pettitt, D. J. (1983). In R. L. Whistler & J. N. BeMiller,

Industrial gums (pp. 119). London: Academic Press.Lewis, M. J. (1987). Physical properties of food and food processing

systems, . London: Ellis Horwood Ltd (pp. 465468).Lillford, P. J., & Norton, I. T. (1991). In G. O. Phillips, P. A. Williams &

D. J. Wedlock, Gums and stabilizers for the food industry (pp. 315).vol. 3. Oxford, London: IRL Press.

McGarvie, D., & Parolis, H. (1979). Carbohydrate Research, 69, 171179.McGarvie, D., & Parolis, H. (1981). Carbohydrate Research, 88, 305314.Morris, E. R., Cutler, A. N., Ross-Murphy, S. B., Rees, D. A., & Price, J.

(1981). Carbohydrate Polymers, 1, 521.Pimienta-Barrios, E. (1991). El nopal tunero. (Primera Edicion). Mexico:

Universidad de Guadalajara.

L. Medina-Torres et al. / Food Hydrocolloids 14 (2000) 417424 423

Fig. 7. Effect of temperature on the mechanical spectrum of mucilage 5%w/w solution in deionized water. Data at pH 4.8 and I 0:1025 M:

Rajinder, P. (1995). AIChE Journal, 41, 783794.Ramirez, M.E. (1972). Ed. I.P.N. COFFA-SEDICT Mundo cientifico

Revista especializada en divulgacion tecnica y cientfica, No. 4,Mexico, D.F.

Rinaudo, M. (1994). Food Hydrocolloids, 2, 2131.Rochefort, W. E., & Middleman, S. (1987). Journal of Rheology, 31 (4),

337369.

Rodriguez-Hernandez, A. I., & Tecante, A. (1999). Food Hydrocolloids,13, 5964.

Smidsrod, O., & Haug, A. (1971). Biopolymers, 19, 12131227.Trachtenberg, S., & Mayer, A. M. (1982). Phytochemistry, 21, 28352843.Whistler, R. L. (1993). In R. L. Whistler & J. N. BeMiller, Industrial gums,

polysaccharides and their derivatives (pp. 119). vol. 1. New York:Academic Press.

L. Medina-Torres et al. / Food Hydrocolloids 14 (2000) 417424424