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ORIGINAL ARTICLE
Year : 2014  |  Volume : 5  |  Issue : 2  |  Page : 70-77  

Novel extraction and application of okra gum as a film coating agent using theophylline as a model drug


1 Department of Pharmaceutics and Pharmaceutical Technology, Faculty of Pharmaceutical Sciences, University of Jos, PMB 2084 Jos 930001, Plateau State, Nigeria
2 Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland, 20 N Pine Street, Baltimore MD 21201, USA

Date of Web Publication30-May-2014

Correspondence Address:
Ikoni J. Ogaji
Department of Pharmaceutics and Pharmaceutical Technology, Faculty of Pharmaceutical Sciences, University of Jos, PMB 2084 Jos 930001, Plateau State, Nigeria.

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Source of Support: US Government through Fulbright (Junior Scholar Development ) Fellowship,, Conflict of Interest: None


DOI: 10.4103/2231-4040.133427

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  Abstract 

The purpose of this study was to investigate the effect of extraction and application of okra gum as an aqueous film coating agent. Powdered okra pods dispersed in demineralized water was heated at 80 ± 2 o C for 30 minutes in the presence of sodium chloride. The filtrate was successively centrifuged at 4000 rpm for 30, 60, or 120 minutes and freeze dried. The samples were used as film former at different concentrations in aqueous film coating operations. Near infrared (nIR) absorption spectra, photomicrographs, and some physicochemical properties of the coated tablets were evaluated. The okra gum samples had different nIR spectra and possessed good processing and application quality due to relatively low viscosity. A six-fold concentration of this gum from the novel extraction yielded glossy theophylline tablets within a short time. A t (18) = 2.895, P < 0.005, t critical = 1.734 were obtained for the independent analysis of the hardness of core and coated theophylline tablets. A 3.0% concentration of the okra samples at a flow rate of 3 ml/min for 100 minutes showed that F = 3.798, DF = 29, P < 0.035, F critical = 3.354 in tablet hardness among samples and F = 15.632, DF = 29, P < 0.0001, F critical = 2.152 were obtained on film thickness among tablet samples during the coating and drying operation. Novel extraction process enhanced the film coating potential of okra gum by delivering more solids on the substrate at a shorter time with improved operation efficiency.

Keywords: Application, film former, laboratory coater, okra gum, extraction method, viscosity


How to cite this article:
Ogaji IJ, Hoag SW. Novel extraction and application of okra gum as a film coating agent using theophylline as a model drug. J Adv Pharm Technol Res 2014;5:70-7

How to cite this URL:
Ogaji IJ, Hoag SW. Novel extraction and application of okra gum as a film coating agent using theophylline as a model drug. J Adv Pharm Technol Res [serial online] 2014 [cited 2020 Sep 24];5:70-7. Available from: http://www.japtr.org/text.asp?2014/5/2/70/133427


  Introduction Top


Film coating of pharmaceutical oral solid dosage forms has been widely used for functional and non-functional purposes, to coat tablets, capsules, granules, powders, and pellets. [1],[2] Today, it is more common to use aqueous solvent than organic solvents, because aqueous solvent is non-flammable, environmental-friendly, cheap, readily available, and safe. Film coating is preferred to sugar coating because it involves low weight increase of 2 to 3% and less rigid coats which reduce the cracking and other defects observed in sugar coating. [1] Among other benefits, [3],[4] polymer is the main ingredient in a film coating operation and could be a natural or synthetic polymer. [1],[2]

Okra gum is a natural polymer obtained from the pods of okra plant (Abelmoschus esculentus). It has been used as a binder, [5],[6] hydrophilic polymer matrix, [7] suspending, [8] and bioadhesive agents. [9] The potential of okra gum, obtained by traditional extraction, as a film coating agent was reported. [10] The use was limited to 0.62% w/v in a laboratory coating equipment due to high viscosity when the gum was extracted using the traditional method. [11] The present study was an attempt to improve on the flow and spray characteristics of okra gum for use as a film-coating agent in conventional laboratory coating equipment by modifying the viscosity through a novel extraction method. The samples obtained were used as aqueous film formers in the coating of theophylline tablets in a laboratory coating equipment.

Theophylline was used as the model drug in this study. Theophylline is a drug that has been used for several decades in the treatment of asthma. [12] It is a readily available drug, widely used as a model drug in coating operations in drug product development involving many polymers. [13-18]


  Materials and methods Top


Materials

The materials used in this study were donated to the laboratory by the respective manufacturers as indicated. Theophylline and magnesium stearate (Spectrum Chemicals, Brunswick, New Jersey, USA), microcrystalline cellulose (Mendell Apenwest Company, NY, USA), silicon dioxide Aerosil 200 (Degussa Corporation, NJ, USA), pregelatinized starch (National Starch Food Innovation, NJ, USA), Glycerin (Parchem fine and Specialty chemicals, New Rochelle, New York, USA), and okra gum (from matured okra pods, harvested in July, 2010 in Jos, Plateau State of Nigeria) and processed in our laboratory. All other reagents were of analytical grade.

Methods

Extraction of okra gum

The method of ogaji and Hoag [19] was adopted in the extraction of okra gum samples. Briefly, a 100 g powdered sun-dried okra pods was dispersed in about two liters of demineralized water with continuous stirring on a magnetic stirrer. The dispersion was heated at 80 ± 2 o C for 30 minutes in the presence of 0.017 moles of sodium chloride, allowed to cool to room temperature at 25 ± 1.0 o C, and screened through muslin to remove debris and sediments. The filtrate was centrifuged at 4000 rpm for 30, 60, or 120 minutes to obtain K2, K3, or K4 samples, respectively. The gum was washed severally with distilled water and freeze dried. A 50 g sample was dispersed in a liter of demineralized water, allowed to stand for 24 hours and extracted with ethanol 96% after clarification, to obtain sample K1. [11] The gum was dried at 50 ± 2 o C for 24 hour.

Determination of viscosity

The viscosities of samples of the okra mucilage were determined on Brookfield rheometer (DV-III + model, Brookfield Engineering, USA) using CPE 40 according to the method described by Ogaji. [20]

pH determination

The determination of the pH of 1% w/v mucilage of okra gum samples was carried out using the Orion pH/ISE meter (Model 720 A, Thermo Electron Corporation, MA, USA) at 25 o C.

Production of theophylline core tablets

The tablet formulation consisted of theophylline, pregelatinized starch, microcrystalline cellulose, silicon dioxide, maize starch, and magnesium stearate. Theophylline tablets were prepared by direct compression method to contain theophylline 50 mg per tablet. The tablets were compressed on a B2 instrumented rotary press (KEY Industries Pharmaingdale Inc. NJ, USA) to a target weight of 270.0 ± 27.0 mg.

Weight uniformity of theophylline tablets

The test was carried out according to the United States Pharmacopoeia and National Formulary (USP/NF) test method [21] using a Mettler Toledo analytical balance (Model AB 104-S, Switzerland).

Friability of Theophylline Tablets

The USP/NF test method [21] was used and the result was average of three replicates.

Hardness of theophylline tablets

The test was carried out on a KEY hardness tester (Model HT-300, KEY International Industries, USA) according to the USP/NF test method. [21]

Disintegration time of tablets

Disintegration time of Theophylline tablets in water was investigated using the disintegration apparatus maintained at 37 ± 1 o C in a water bath (Haake water bath, USA) according to USP/NF test method. [21]

Dimensions of tablets

Ten tablets were randomly selected from each batch and their thicknesses and diameters were evaluated using an ASTM venier caliper (Model EC 06, Tresna Instruments, USA).

Near infrared spectra of theophylline tablets

Scanning and data acquisition on the two flat surfaces of the randomly selected twenty tablets were carried out on Vision software of the Near Infrared spectroscopy (Model 6500, Rapid Content Analyzer FOSS NIRSystem, USA) as described by Ogaji. [20]

Dissolution profile of the tablets

The dissolution rate profile was evaluated in a SR8-Plus automated dissolution apparatus (Hanson Research Corporation, USA) interfaced with spectroscopic software version 3.0 on UV 160 U- UV- visible recording spectrometer (Shimadzu Scientific Instruments, Japan). The dissolution medium was Millipore water, maintained at 37 ± 2 o C. The paddle was rotated at 50 rpm and the absorbance of dissolved theophylline was measured at 272 nm every 5 minutes. Kinetic data acquired was transferred to Microsoft Excel for further processing. [20]

Film coating of tablets with okra gum samples

The film coating formula is shown in [Table 1]. Three graded coating suspensions of K1, K2, K3, or K4 sample of okra gum at 0.62, 1.2, and 3.0% w/v (represented by S1, S2, and S3, respectively) were formulated to assess the ease of flow and spray in a conventional laboratory coater. Approximately 750 g dedusted, uncoated theophylline tablets was coated in a Hi-Coater (Model HCT-30, Freund Engineering, Japan) at the following conditions: Coating pan speed, 10 rpm; inlet air temperature, 56-60 o C; outlet air temperature, 28-30 o C; and atomizing air pressure, 0.5 bars. Uniform distribution of the solids in the coating suspension was maintained throughout the process with the aid of a magnetic stirrer. The flow rate of the coating suspension was initially 1.5 ml/min for 30 minutes which was maintained at 3.0 ml/min thereafter. In-process evaluations of the coating were carried out at 30 minutes interval and at 50, 75, 100, 125, or 150 ml utilization of coating suspension.
Table 1: Formula of film coating suspension for coating theophylline core tablets

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Determination of some physicochemical properties of coated theophylline tablets

Weight uniformity, dimensions, friability, disintegration time, hardness, and dissolution time of the coated theophylline tablets were evaluated as described under uncoated theophylline tablets above. The hardness of theophylline-coated tablet samples were statistically analyzed with the aid of Data Analysis software (Window 10, Microsoft Excel, Microsoft Corporation, USA).

Determination of film thickness on coated theophylline tablets

Ten coated tablets were randomly selected at 30 minutes interval and film thickness was evaluated by weight and microscopy (Nikon, Japan) fitted with camera. [20] Photomicrographs of the cross section of the tablets were obtained and the film thickness was determined at different points on the filmstrip with the aid of Post Basic software (Linkam Scientific Instrument, UK). The film thickness among samples of theophylline-coated tablets at the end of the coating process was statistically evaluated using one factor analysis of variance (ANOVA).

Effect of curing on some physicochemical properties of coated tablets

At the end of the coating process, the tablets were subjected to curing at inlet temperature of 60 o C. Samples were taken at intervals for evaluation of the effect of curing on some physicochemical properties of the coated tablets. The effect of coating and curing on the film thickness on theophylline tablets drawn from different batches was analyzed with the aid of Data Analysis software (Window 10, Microsoft Excel, Microsoft Corporation, USA).

Effect of storage conditions on the integrity of coated tablets

Coated theophylline tablets were exposed to relative humidity conditions between 11 and 85% RH in a desiccator and the effect of storage on the integrity of the coated tablets was investigated over a six-month period.


  Results Top


The rheological properties and NIR absorption spectra of samples of Okra gum

Off white powdered okra gum samples with loss on drying of 1.4-2.5% were obtained. The pH of a 2% w/v aqueous dispersion of K1, K2, K3, and K4 samples were 6.59 ± 0.003, 6.27 ± 0.003, 6.23 ± 0.000, and 6.23 ± 0.003, respectively. [Figure 1] shows the nIR raw absorption spectra and its second derivative for the samples of okra gum. The absorption of K1, K2, and K3 samples at 1400 nm was respectively 0.265, 0.34087, and -0.021 while that of K4 was -0.085. The absorption increased with increase in wavelength. At 2300 nm, the nIR absorption spectrum was 0.696, 0.282, 0.240, and 0.125, respectively, for K1, K2, K3, and K4. The viscosities of a 2% w/v of okra samples at different shear rates are shown in [Table 2]. Sample K1 exhibited higher value of viscosity, torque, and shear stress than the others and the viscosity was generally of the order: K1 >K2 >K3 >K4 at a given spindle speed.
Figure 1: (a) Raw nIR spectra of samples of okra gum raw spectra (b) Second derivative nIR spectra of samples of okra gum at about 1400 nm (c) Second derivative nIR of samples of okra gum around 2300 nm

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Table 2: Rheological properties of 2% w/w samples of okra gum used in the film coating operation

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Some physicochemical properties of batches of coated theophylline tablets

Some physical properties of coated theophylline tablets

The viscosity of a 0.62%w/v (S1) coating suspension was 33.04 ± 0.001-75.48 ± 0.003cP at 100 rpm. The coating suspension passed through the spray nozzles easily. The tubing and nozzles of the coating equipment were not blocked during the entire coating operation, irrespective of the okra gum sample used. Good coated theophylline tablets were obtained from the formulations due to the free flow of the coating suspension that led to the deposition of coating suspension droplets and the subsequent film formation on the substrate. The viscosity of coating suspension containing K1 at 1.2%w/v (S2) was 158.27 ± 0.008 cP and was too viscous to be pumped or sprayed through the nozzles of the spray gun to coat the tablets. The viscosity of the coating suspension (formulation S3) at 100 rpm was 83.6 ± 0.23, 80.8 ± 0.15, and 77.6 ± 0.22 cP, respectively, for samples K2, K3, and K4, and their pH was 7.30 ± 0.003. The coated tablets were glossy with firm and intact film that did not peel off when rubbed against a white paper background. [Figure 2] shows the photomicrograph of a typical film deposit on theophylline tablet while some physicochemical properties of the coated theophylline tablets at this concentration are also shown in [Table 3]. The average weight of the coated tablets was between 270.6 ± 0.37 and 271.0 ± 0.33 mg for all the formulations. The hardness of the coated tablets was 6.54 ± 0.222, 6.24 ± 0.188, and 5.88 ± 0.036 kgf, respectively, for formulations K2, K3, and K4 while that of the core tablets was 5.72 ± 0.175 kgf. The disintegration time of the coated tablets was within 2 minutes, irrespective of the sample. [Table 4]a shows the statistical data on the hardness of the uncoated and coated theophylline tablets as well as those with the film thickness of samples of theophylline coated with the okra gum samples. At (18) = 2.895, P < 0.005 was obtained for the independent analysis of the hardness of core and coated theophylline tablets. [Table 4]b shows that F = 3.798, DF = 29, P < 0.035 in the analysis of variance (ANOVA) of hardness of theophylline tablets coated with samples of okra gum. ANOVA on the film thickness during the coating and drying process of a batch of the coated theophylline tablets is presented in [Table 4]c while [Table 4]d shows that F = 0.039, DF = 29, P < 0.96 in the evaluation of the film thickness among batches of theophylline tablets after coating with novel samples of okra gum (3.0%w/v) at 3.0 ml/min for 100 minutes . [Table 5] shows the effect of curing the coated tablets over a 60-minute period on some characteristics of the tablets. A value of t (18) = 0.617, P < 0.272 was obtained on the hardness of the coated tablets cured for 1 hour at 60 o C while the t (18) =1.599, P < 0.06 with respect to the dimensions of the cured tablets in the one tail test with a t critical of 1.73 when the diameters of samples from curing at 30 minutes and 1 hour were compared. The average diameter of the coated tablets decreased from 10.42 mm (SD = 0.009) to 10.389 mm (SD = 0.015) after 1 hour of curing at 60 o C. Similarly, the thickness of the tablets decreased from 3.665 mm (SD = 0.036) to 3.638 mm (SD = 0.025). The dissolution studies showed that a 100% release of theophylline was attained within 15 minutes, irrespective of the sample. The coated tablets stored at 11, 40, 50, and 75% RH absorbed and desorbed moisture from the environment within the first 24-48 hours but equilibrated thereafter for the next 6 months, absorbing about 0.02% w/w moisture. The moisture sorption during this period was double (0.04% w/w) at 85% RH.
Figure 2: Photomicrograph of a typical film deposit on theophylline tablets

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Table 3: Some physicochemical properties of coated batches of theophylline tablets

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Table 4:

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Table 5: Effect of curing on some physical properties of theophylline coated tablets

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NIR spectroscopy to demonstrate film coating with okra gum on theophylline tablets

[Figure 3] shows both the raw and the second derivative nIR spectroscopy of talcum powder, titanium dioxide, core, and coated theophylline tablets. NIR prominent absorption of talcum powder occurs at 1396 and 2310 nm and the value is respectively -0.138 and 0.0126. [Figure 4] shows both the raw and the second derivative nIR spectroscopy to demonstrate the deposition of film coating materials. The prominent absorptions of the coated tablets, corresponding to that of talcum powder, are 1400 and 2300 nm and are directly proportional to the film thickness.
Figure 3: nIR spectra of coating materials used in the film coating (a) raw spectra (b) second derivative

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Figure 4: nIR spectra of coated theophylline tablets (a) raw spectra (b) second derivative showing levels of coating on substrate

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Effect of concentration of coating suspension on the coating process

Coating operation was successful with K2, K3, and K4, but not with K1 samples when prepared based on S 1 formulation.


  Discussion Top


The different nIR absorption and pH profiles of okra gum samples are due to the influence of the extraction processes. Changes in viscosity of the gum were due to the elevated temperature in the presence of electrolyte and the centrifugation that weakened inter-particle bond and increased particles size distribution. It appears that longer treatment was required for a marked difference between K3 and K2.

The coated theophylline tablets have minimal weight variation (SE of 0.33 to 0.40) due to well-controlled coating processes. The movement of tablets within the moving bed, the regularity and scattering of tablet presences in the spray region, and the projected surface area of tablet that receive the spray can impact and control the amount of coat a tablet receives during a typical coating operation. The moderate pan speed and the presence of baffles helped in ensuring uniform opportunities and appearance of tablets at the spray zone. [22],[23],[24] The resemblance of the disintegration time profile of the coated to those of the core tablets was probably due to the hydrophilic nature of the polymer and could be of advantage in taste or odor masking and for similar reasons. The increases in the dimensions of coated tablets were due to film deposition. The t value obtained at P = 0.05 showed a significant difference between the hardness of the core and those of the coated theophylline tablets. The significant difference in the hardness of the samples at P = 0.05 suggests that the samples were not drawn from the same lot, providing further evidence to claim that the application of film coating on the core theophylline tablets with okra gum influenced the outcome. The ANOVA on the theophylline tablets suggested a statistical difference at P = 0.05 in the hardness but not with film thickness among samples of the tablets coated with K2, K3, or K4. The study also shows that the hardness of the coated tablets was not influenced by curing.

Tablets increased in their diameters and thicknesses as a function of the duration of coating operation. The adhesion of coating materials to the tablet was due to the presence of the film former, which provided the binding force necessary for adhesion. The results of the curing study indicated that there were changes in the thickness and diameter of the coated tablets depending on the curing duration. Further heat treatment facilitated the removal of moisture and the coalescence of the gum leading to a good coat on the tablet.

In-process assessment of the film deposit on the theophylline tablets and hence coating efficiency was possible with the nIR spectroscopy because talcum powder exhibited pronounced absorptions in the near infrared region. Second derivatives are mathematical treatment of the raw data to rule out differences that may arise from packing, noise, and sample particle size differences. Near infrared spectroscopy has great potential for improving the monitoring and control of industrial processes.

A low viscosity polymer provides a platform for more solids and a firm film within a short period of time compared to a highly viscous polymer in a film coating operation. Low viscosity okra gum samples obtained from the novel extraction method were used at high concentration as film formers requiring less coating time than would have been possible with those from the traditional extraction process. All the okra samples provided a platform for film coating using the laboratory equipment without difficulties. There was no significant difference in the thickness of the film deposited on theophylline tablets with any of the three okra samples because at the polymer concentration of 3%w/v was within the viscosity range that can easily be handled by the laboratory coating equipment. Sample K4 might provide more solids than either K3 or K2 sample due to low viscosity and thereby reduce the coating duration. Although film coating is treated as a straightforward operation, the complexity of this unit operation may arise from the fact that multiple variables such as heat and mass transfer characteristics, the coating curing, the spray configuration, the nature of the coating material, the geometry of the system, the nature of the core, and the rate and extent of coating accumulation may influence the quality and degree of coating.


  Conclusion Top


Samples of okra gum with low viscosity were obtained from the novel extraction process compared to those obtained from the traditional extraction method. These samples are useful film coating agents, delivering more solids at reduced coating time than is possible with products from the traditional method.

 
  References Top

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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5]


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