Rheological Modeling and Characterization of Ficus platyphylla Gum Exudates

Ficus platyphylla gum exudates (FP gum) have been analyzed for their physicochemical parameters and found to be ionic, mildly acidic, odourless, and yellowish brown in colour.e gum is soluble in water, sparingly soluble in ethanol, and insoluble in acetone and chloroform.e nitrogen (0.39%) and protein (2.44%) contents of the gum are relatively low.e concentrations of the cations were found to increase according to the following trend, Mn>Fe>Zn>Pb>Cu>Mg>Cd>Ca. Analysis of the FTIR spectrum of the gum revealed vibrations similar to those found in polysaccharides while the scanning electron micrograph indicated that the gum has irregular molecular shapes, arranged randomly. e intrinsic viscosity of FP gum estimated by extrapolating to zero concentrations in Huggins, Kraemer, Schulz-Blaschke, and Martin plots has an average value of 7 dL/g. From the plots of viscosity versus shear rate/speed of rotation and also that of shear stress versus shear rate, FP gum can be classi�ed as a non-Newtonian gum with characteristics-plastic properties. Development of the Master_s curve for FP gum also indicated that the gum prefers to remain in a dilute domain (C < C), such that ηηspααC . e apparent activation energy of �ow for FP gum (calculated from Arrhenius-Frenkel-Eyring plot) was relatively low and indicated the presence of fewer interand intramolecular interactions.


Introduction
Plant gums are essential in the pharmaceutical and food industries for controlling drug release and in modifying the texture of food [1].Gums are also used in the food primarily as thickeners and gelling agent due to their ability to alter the rheological properties of the solvent in which they are dissolved [2].Some gums such as guar gum has a number of applications in the mining and mineral processing industry [3].In the froth �oatation of base metal and platinum group metal ores, guar gum is used as a depressant of naturally hydrophobic waste mineral such as tale.e role of the polysaccharide is to adsorbed on the talc surface, render it hydrophilic and prevent its �oatation.
Several researches have been carried out on gelling and rheological properties of gums and data obtained from such researches have assisted food manufacturer and other industrialist in selecting the required gum or gums for a given purpose [2][3][4][5][6][7][8][9][10][11][12].However, literature is scanty on characterization and rheological properties of FP gum.erefore, the aim of the present study is to characterize and model gum exudates taken from the Ficus platyphylla tree.Ficus platyphylla commonly called �ake rubber tree, red Kano rubber tree, and gutta-percha tree in English, "ogbagba" in Nupe, belongs to the family, Moraceae.Ficus platyphylla is a tall tree of about 18 meters in height and about 6 meter in diameter.e tree is initially epiphytic, with a widely spreading crown of open and wooded savanna and it is believed to have migrated from Senegal to Northern and Southern Nigeria.In view of its geographical location and the possibility of utilizing FP gum for industrial and other purposes, there is serious need to study the physiochemical and rheological behavior of FP gum.

Collection of Samples.
Crude FP gum was obtained as dried exudates from their parent trees grown in Falgore 2.2.Puri�cation of the �um.e procedure adapted for the puri�cation of the gum was that of Femi-�yewo et al. �13].e crude sample of the gum was dried in an oven at 40 ∘ C for 2 hrs and grounded using a blender.It was hydrated twice using chloroform water (in a ration of 70 : 30 for water : chloroform) for �ve days with intermittent stirring to ensure complete dissolution of the gum and then strained through a 75 m sieve to obtain particulate free slurry which was allowed to sediment.Chloroform is capable of interacting with water to form chloroform hydrate, which has an extensive hydration power.ereaer, the gum was precipitated from the slurry using absolute ethanol, �ltered and defatted with diethyl ether.e precipitate was redried at 40 ∘ C for 4� hours.e dried �akes were pulverized using a blender and stored in an air tight container.Figure 1 presents photographs of crude and puri�ed samples of FP gum.

Physiochemical Analysis.
In order to characterize the gums, it was subjected to the following physiochemical tests.

2.3.�. Determination of Percentage �ield of the Puri�ed �ums.
e dried, precipitated, and puri�ed gum(s) obtained from the crude dried exudates were weighed and the percentage yields were expressed in percentage using the weight of the crude gum(s), as the denominator.

Determination of Water Sorption and Swelling Property.
In order to determine the water sorption capacity of the gum, dried evaporating dishes were weighed and 2.0 g of each of the gum samples was weighed into the different dishes.e �nal weight of the dishes was noted and placed over water in desiccators.Aer 5 days, the dish was transferred to another desiccator over activated silica gel (desiccant) for another 5 days.e percentage sorption was calculated by difference in weight.
In order to study the swelling property of the gum, the sample (1.0 g) was placed in a 15 mL plastic centrifuge tube and the volume occupied was noted.Distilled water (10 mL) was added from a 100 mL measuring cylinder and stopper.e contents were shaken thoroughly for 2 minutes and further allowed to stand for 10 mins.Each sample was centrifuged at 1000 rpm for 10 minutes on a bench centrifuge.e supernatant was then decanted and the volume of sediment obtained was measured.e swelling index of the gum was calculated by dividing the volume occupy by the gum aer hydration by the volume before hydration.

Determination of Solubility
. e solubility of the gum was determined in cold and hot distilled water, acetone, chloroform, and ethanol.1.0 g sample of the gum was added to 50 mL of each of the above mentioned solvents and le overnight.25 mL of the clear supernatants were taken in small preweighted evaporating dishes and heated to dryness over a digital thermostatic water bath.e weights of the residue with reference to the volume of the solutions were determined using a digital top loading balance (Model.XP-3000) and expressed as the percentage solubility of the gums in the solvents.

Determination of Concentration of Metals.
Concentrations of Mg, Ca, Mg, Mn, Fe, Cu, Cd, and Pb were determined using Perkin Elmer atomic absorption spectrophotometer.Calibration curve for each metal was prepared and the concentration of the metal was in the analyte was estimated by extrapolation.

Determination of Nitrogen and Protein
Content.e nitrogen content of the gum was determined using the Kjedahl method and the protein content was estimated by multiplying the nitrogen content by a conversion factor of 6.25.2.5.Scanning Electron Microscopy.e morphological features of the gums were studied with a JSM-5600 LV scanning electron microscope (SEM) of JEOL, Tokyo, Japan.e dried sample was mounted on a metal stub and sputtered with gold in order to make the sample conductive, and the images were taken at an accelerating voltage of 10 kV.

Results and Discussions
3.1.Physiochemical Properties.Table 1 presents the physiochemical properties of FP gum.e analyzed parameters included physical properties (colour, taste, odour, pH, and solubility ion water and other solvents) and chemical properties (nitrogen content and protein content).e results for cationic composition of the gum are presented in Table 2. e colour of the gum was found to be yellowish brown.e gum is odourless but has a sweet taste which may be ascribed to its polysaccharide content.From the measured pH, it can be deduced that FP gum is mild acidic.e solubility of FP gum in water was found to increase with increasing temperature.e sparing solubility of the gum in ethanol and the nonsolubility in acetone and chloroform indicate that the gum is ionic.As a rule, ionic compounds are soluble in water and other solvent that have high-dielectric constant.e dielectric constant of ethanol is higher than that of chloroform and acetone, hence the preferential solubility of the gum in ethanol and not acetone or chloroform.
e puri�cation yield for FP gum was 52.0%.According to Cunha et al. [14], puri�cation yield of a given gum depends on the method of processing.is is because processing has the tendency of withdrawing some constituents of the gum.Literature is scanty on the nitrogen and protein contents of FP gum; however, values obtained from the present study are comparable to those reported for most food gums.
From Table 2, it can be seen that FP gums display a decreasing trend in concentrations of elements as follows.Mn > Fe > Zn > Pb > Cu > Mg > Cd > Ca.It is signi�cant to note that elements such as Mn, Ca, Zn, Cu, Fe, and Mg are useful for the biochemical functions of living organism.However, Pb and Cd are toxic at certain concentration.However, concentrations of Pb and Cd obtained from this work are below the tolerance limit [15].Figure 2 shows plot for the variation of water absorption properties.e �gure reveals that the water absorption capacity increased progressively up to the ��h day of immersion (i.e., 100% RH over water) and dropped sharply within 24 hours when subjected to action of desiccant.�y the ��h day in desiccant environment, water content of the gums had reduced considerably to between 1-4%.From the results obtained, it is indicative that if the gums are stored in a damp environment, the gums will quickly be hydrated and also have the tendency to rapidly loose such water molecules in the presence of desiccants (within �ve days).e observed results are consistent with the �ndings of Abdulsamad et al. [16] for cashew and acacia gums Generally, susceptibility to microbial and physicochemical deterioration as a result of high-moisture content may be some of the factors that can be associated with the water sorption potentials of the studied gums.erefore, FP gum can better be preserved in an air-tight container.

Rheological Study. e viscosity of FP gum was found
to increase with increasing pH (Figure 3) indicating that the emulsifying properties of the gum is pH dependent and that the gum is ionic [17].Also the increase in viscosity of FP gum with increasing concentration (plot not shown) can be explained as follows.Viscosity of a liquid depends on the strength of attractive forces between molecules, which depend on their composition, size, and shape and also on the kinetic energy of the molecules, which depend on the temperature.erefore, any factor that can affects composition, molecular shape and kinetic behavior will certainly affect viscosity.Increasing concentration implies increase in composition hence increase in viscosity.(ii) degradation of polymer; (iii) conformational (ordereddisordered) transition.For similar reasons, the viscosity of FP gum exhibited an inverse proportionality relationship with temperature.No degradation was observed since the viscosity measured upon heating and cooling were the same [18].e most appropriate model that best explains the dependence of viscosity of macromolecules on temperature is the Arrhenius-Frenkel-Eyring equation which can be written as follows [19]:

Effect of
where  (Pas) is a constant, which is related to the degree of orderliness or disorderliness of the system,  is the temperature, and  is the gas constant.From the logarithm of ( 1), ( 2) was obtained as follows: From application of Arrhenius-Frenkel-Eyring equation, a linear dependence of log( with 1/T was observed for FP gum concentrations of 2 and 5 g/L indicating that there is no order-disorder transition [20].From slopes of the plots (Figure 4), calculated values of   were 26.96 and 181.94 J/mol for 2 and 5 g/L, respectively (Table 3).e results indicate that the apparent activation energy of �ow tend to increase with increasing concentration, hence the strength of intra-and intermolecular interactions involving hydrogen bonding and FP gum is expected to increase with increasing concentration.It has been established that   is affected by factors that determine the �exibility and interaction of macromolecules.e activation energy of �ow is also dependent on the solute concentration [20].

Intrinsic Viscosity
Intrinsic viscosity is a measure of the hydrodynamic volume occupied by a macromolecule, which is closely related to the size and conformation of the macromolecular chain in a particular solvent [21].[ can be obtained using a linear regression graphic double-extrapolation procedure (GDEP) which involves extrapolating the course of speci�c viscosity to in�nite dilution.e intrinsic viscosity of a polymer, which can be determined experimentally, is a power series in concentration and can be written as follows, where  1 ,  2 ,  3 , … are dimensionless constants.Since  sp / is a reduced viscosity, which at    becomes the intrinsic viscosity, the above power series is oen truncated to a linear approximation known as the Huggins equation [22], where  1 is the Huggins constant, which is a dimensionless constant.Figure 5 shows Huggin plot for FP gum.Values of Huggins parameters deduced from the plot are presented in Table 4. e results revealed a high degree of linearity for the plot and calculated  � value was 0.84.According to Higiro et al. [23],  1 value larger than unity indicates polymerpolymer aggregation hence there is an absence of polymerpolymer aggregation in FP gum.e intrinsic viscosity can also be obtained from the Kraemer equation which can be expressed as follow [23], where  2 is also a dimensionless constant called Kraemer constant.Kraemer plot and parameters for FP gum are also presented in Figure 5 and (ii) both lines must extrapolate to the same intercept at zero concentration.
From the results of our study, the sum of the constant ( 1 +  1 = 845 + 11 = 955) is less than the critical value.Also Kraemer and Huggins plots (Figure 5) did not extrapolate to the same intercept at zero concentration.is suggests the interference of other effects (such as ionic strength, molecular aggregation, etc.) in the viscosity behavior of FP gum.In order to support and compare the results obtained from Huggins and Kraemer plots, values of intrinsic viscosity were also compared with those obtained from Schulz-Blaschke equation ( 9), Martin equation ( 10), where  SB and  M are Schulz-Blaschke and Martin dimensionless constants.In Figure 5, we also present Schulz-Blaschke and Martin plots for FP gum while values of intrinsic viscosity and other parameters deduced from the plots are also presented in Table 4. From the results obtained, it can be seen that calculated values of [ are comparable to each other and are also comparable to those obtained from Huggins and Kraemer plots.High degree of linearity was obtained for all the plots.erefore, the average value of [ for FP gum is 7.0.

Flow Behavior of FP Gum.
Base on the relationship between viscosity and shear rate or shear stress, gums can be classi�ed as Newtonian or non-Newtonian.e behaviour of Newtonian colloids can be highlighted as follows [25]: (i) the only stress generated in simple shear �ow is the shear stress , the two normal stress differences are zero; (ii) the shear viscosity does not vary with shear rate; (iii) the viscosity is constant with respect to the time of shearing and the stress in liquid falls to zero immediately the shearing is stopped; (iv) the viscosities measured in different types of deformation are always in simple proportion to one another.
Non-Newtonian �uids are those that show deviation from the above listed features.e velocity gradient, dv/dx, is a measure of the speed at which the intermediate layers move with respect to each other.It describes the shearing the liquid experiences and is called shear rate (Υ).Shear stress is the force per unit area required to produce the shearing action.erefore, viscosity can be de�ned as the ratio of shear stress to shear rate.In order to characterize FP gum as Newtonian or non-Newtonian �uid, several tests were employed.�ne of the methods for analyzing non-Newtonian �ow involves the construction of a plot of viscosity versus spindle speed using same spindle.If such plots are linear, then the �uid is said to be non-Newtonian [25].Figure 6(a) shows the variation of viscosity of FP gum with the speed of rotation ( 2 > 0.8).e plot indicated that FP gum is a non-Newtonian �uid.Also from the plots, the yield stress (i.e., the amount of force needed to be applied to the gum before it can �ow) was estimated by extrapolating to zero rpm (Table 5).e results indicated that the yield stress (12.64 and 8.292 for 2 and 5% FP gum) for FP gum is concentration dependent.e power law index (  ()) was also calculated through the angle the plot made with the -axis ().It has been found that if  is less than 45 degrees, the �uid is pseudoplastic but if greater than 45 degrees then it is dilatant.From the calculated values of  for 2 and 5% concentrations, it is indicative that FP gum is a pseudoplastic �uid.e �uid behavior of FP gum was also analyzed using the relationship between shear stress () and shear rate (Υ), which can be expressed as follows, where  is the consistency coefficient and  is the �ow behavior index.Taking the logarithm of both sides of (11) yields (12) log ()  log    log Υ.
From ( 12), a plot of log() versus log Υ should be linear with slope and intercept equal to  and log .were also developed.From the plots, it can be seen that FP gum display plastic behaviour.e power law equation relating speci�c viscosity and concentration can be expressed as follows [23], Taking logarithm and rearranging ( 13), ( 14) is obtained ln  sp  = log () +  log .
From ( 14), a plot of ln( sp ) versus log  should give a straight line with slope and intercept equal to "b" and "a", respectively.Figure 7 shows the power-law plots for FP gum.From the plot, it can be seen that the "b" value is 1.168According to Lai et al. [27]; b value is an index that can be used to predict the conformation of a polymer.It has been found that b value greater than unity is associated with random coil conformation or entanglement, whereas b value less than unity is associated with rod like conformation [21].erefore, FP gum is more random coil like than rod like.

Coil Overlaps Parameter of FP Gum.
In dilute solution, polymer coils are separated from each other and relatively free to move independently [28].However, with increasing concentration, the coil may overlap and interpenetrate each other.e transition from dilute solutions to concentrated solutions is usually accompanied by a pronounced change in the concentration dependence of solution viscosity and the corresponding viscosity is called critical or coil overlap concentration (  ).Morris et al. [29], found that for a random coil like, the slope of double logarithm plots of  sp versus   [ was close to 1.4 in a dilute solution but increased to 3.3 in concentrated regime.ese changes were characterized with a   transition at   [   and  sp  1. Figure 8 shows a plot of log( sp ) versus the coil overlap parameter (  [) for FP gum (the master's curve).From the plot, it is evident that there was no change in slope of the double logarithm plot indicating that no molecular entanglements were obtained.e slope value (1.163, which approximate the value of 1.168 obtained for "b" value from the power law equation) is lower than the threshold value stated by Morris et al. [29], indicating that FP gum is in the dilute domain (    ), hence the relationship between speci�c viscosity and concentration of FP gum is  sp   12 .Our results compares favourable with those obtained for some food gums [29].

FTIR Absorption
Bands in FP Gum. Figure 9 shows the FTIR spectrum of FP gum.e common features in the FTIR spectrum of the studied gum is the appearance of bands and peaks that are typical of polysaccharides.e 2800-3000 cm −1 wave number range is associated with the stretching modes of C-H bonds of methyl groups (−CH 3 ).e broad bands around 3400 cm −1 are consequence of the presence of -OH groups.However, in FP gum, this band is shied to 3422.80 cm −1 .e shis may be due to dissociating carboxylic acid.e 900-1200 cm −1 range represents various vibrations of C-O-C glycosidic and C-O-H bonds.
3.4.Surface Morphology of FP Gum. Figure 10 shows scanning electron micrograph of FP gum.e SEM was taken at �00 x magni�cation and �0 m scale.SEM is a strong analytical instrument that can be used to study the morphology of polymers such as gums and from the Figures, it is evident that the moleculea FP gums are irregular, tiny granules and slightly elongated with rugged appearance.e micrograph is indicative of an amorphous material.e shape and structure or surface topography of the polysaccharide gums may be affected by the method of extraction and puri�cation or preparation of the products.

Conclusions
From the results and �ndings of our study, the following conclusions are made (i) FP gum is a mild acidic and ionic gum that may be useful in the food, pharmaceutical industries; (ii) the viscosity of the gum increases with increase in concentration and with increasing pH but decreases with increasing temperature.Calculated value of the gum's intrinsic viscosity is 7.0 dL/g; (iii) surface morphology of FP gum consists of irregular and amorphous shaped molecules.e gum is more of random coillike and there is an absence of molecular entanglement within the gum; (iv) FP gum is in the dilute domain indicating that    * , and  sp   1.2 ; (v) FTIR spectrum of FP gum is closely related to those of polysaccharides; (vi) FP gum is a non-Newtonian �uid with plastic behavior.Calculated apparent �ow activation energy of FP gum is relatively low at low concentration and re�ects fewer intra-and intermolecular interaction.However, these properties tend to increase with increasing concentration.
In view of the above, it can be stated that FP gum possesses properties that are closely related to gums whose industrial utilization has been ascertained.erefore, FP gum has industrial potentials.

F 2 :F 3 :
Variation of water sorption capacity of FP gum with time.Variation of viscosity with pH for Ficus platyphlla (FP) gum.

Figure 6 (F 6 :
b) show the variation of log() with log Υ for 2 and 5 g/L concentrations of FP gum.Values of  (2.86 and 1.81) and  (0.255 ≈ 0.3 & 0.328 ≈ 0.3) deduced from the plots indicated that FP gum is a non Newtonian �uid.According to Chin et al.[26], for Variation of (a) viscosity with speed of rotation (b) log(shear stress), with log(shear rate), (c) viscosity with shear rate and (d) shear stress with shear rate for FP gum. a non-�ewtonian �uid, the apparent �ow behavior index () is not equal to unity.Also plots of shear stress versus shear rate (Figure6(d)) and viscosity versus shear rate (Figure6(c))

F 7 :F 8 :
Variation of log( sp ) with log(concentration) for FP gum (the power law plot).Double log plot for the variation of log( sp ) with log([  ) for FP gum (e master's curve).
T 1: Physicochemical and rheological properties of FP gum.
Measurements.With regard to solution and solvent viscosities of a macromolecules such as gum, the following relationships are signi�cant,

Table 4
[24]spectively.Interestingly, the [ calculated from Huggins and Kraemer plots were approximately the same (i.e,[  ) indicating agreement between the two models.However, calculated value of  2 was lower than that of  1 .Two conditions are essential in considering the signi�cant of Kraemer and Huggins constants, namely[24];