Materials and methods
Gellan gum was received as a generous gift sample from CP Kelco (Mumbai, India). Dibasic calcium phosphate (DCP) IP, lactose
IP, polyvinyl pyrollidone (PVP), and talc IP were used as received. All other solvents and chemicals were of AR grade. Deionized
double distilled water was used throughout the study.
Modification of gellan gum by microwave. Accurately weighed pure gellan gum (PGG) and deionized water were heated until the gum was completely hydrated. Aqueous hot
solutions were poured in a lidless glass petri dish and cooled to room temperature. The entire mass was dried using a microwave
unit (model MS-1921HE, LG Electronics, India) at 700 W for various time intervals. Dried material (modified gellan gum, MGG)
was collected, passed through a #85 sieve, and preserved in a dessicator for further study. The experimental design was a
32 full-factorial design, and nine batches were prepared. The two independent variables were the amount of distilled water
1) and the time of exposure in microwave (X
2). The low (–1), medium (0), and high (+1) values of X
1 were 60, 70, and 80 mL; the low (–1), medium (0), and high (+1) values of X
2 were 8, 10, and 12 min, respectively. The swelling ratio in distilled water, HCl buffer (pH 1.2) and phosphate buffer (pH
6.8) were selected as dependent variables. The experimental design is shown in Table I.
Table I: Factorial design for modification of gellan gum by microwave treatment.(ALL FIGURES ARE COURTESY OF THE AUTHORS)
Swelling ratio. The experiment was carried out in a 100-mL stopper graduated cylinder. The initial bulk volume of 1 g of MGG was noted and
water was added in sufficient quantity to yield a 100-mL uniform dispersion. The sediment volume of the swollen mass was noted
after 24 h at room temp. The swelling ratio was calculated by taking the ratio of the swollen volume to the initial bulk volume
DSC thermograms were obtained (Model TA-60, Shimadzu, Japan). About 2 mg of sample were scanned in a hermetically sealed
standard aluminum pan and heated over a 50–300 °C temperature range at a rate of 10 °C/min under constant purging of nitrogen
at 40 mL/min. An empty sealed aluminum pan was used as a reference. The characteristic peaks and specific heat of the melting
endotherm were recorded.
About 2% (w/w) of PGG and MGG samples, with respect to the potassium bromide (KBr) disk, was mixed with dry KBr (FT-IR grade).
The mixture was ground into a fine powder before compressing into a disk. Each disk was scanned at a resolution of 4 cm–1 over a wave number region of 400–4000cm–1 using an FT-IR spectrometer (Spectrum GX FTIR system, Perkin Elmer, Waltham, MA). The characteristic peaks of IR transmission
spectra were recorded.
X-ray powder diffractometry. These studies were performed with samples of PGG and MGG. The samples were filled into an aluminum sample holder and exposed
to Cu K-α radiation (40 kV x 40 mA) in a wide-angle X-ray powder diffractometer (model X'Pert MPD, Philips Analytical, The
Netherlands). Each sample was scanned in a continuous mode with the diffraction angle, 2θ, increasing from 5 < 2θ <100.
Average particle size of PGG and MGG was measured with optical microscopy.
Angle of repose.
The authors used the fixed-funnel and free-standing method to measure the angle of repose. The measurement was made in triplicate
and the mean angle of repose was calculated.
Bulk and tapped density. Bulk and tapped densities of PGG and MGG were determined. The powder was placed inside the measuring cylinder of a tapped
density apparatus, and the bulk volume was recorded. The samples were subjected to 200 taps, and the tapped volume was recorded.
The bulk and tapped densities were computed.
Carr's index and Hausner ratio.
The Carr's index and Hausner ratio of PGG and MGG were calculated by the equations provided in Aulton 2002 (33).
Preparation of lactose and DCP tablet. Lactose was passed through a 60-mesh sieve and granulated using 10% w/v solution of PVP in alcohol. MGG was added intra-granularly.
The wet coherent mass was passed through a 20-mesh sieve. The wet granules were dried at 60 °C in a tray dryer. Fines were
removed by sifting the granules on a 60-mesh sieve. The powder blend was then lubricated with talc. Lubrication was performed
in a glass jar for 2 min (34). Granules of DCP were prepared similarly. Lactose (Batches A1 and A2) and DCP (Batches B1 and
B2) tablets were prepared with and without disintegrant, respectively. Tablets were prepared on a rotary tablet press using
flat-faced punches and dies (model Rimek-II, Karnavati Engg., Ahmedabad, India). The turret was rotated at a fixed speed of
30 rpm. Target weight of each tablet was 100 mg. The tablets were evaluated for disintegration time (DT), hardness and friability.
Formulations are shown in Table II.
Table II: Formulation of lactose and DCP tablets.
Disintegration time. The time required for disintegration of six tablets per batch was carried out in a USP disintegration test apparatus (model
ED2L, Electrolab, Mumbai, India) containing 900 mL distilled water at 37 ± 0.50 °C.
Hardness and friability test.
A hardness tester (Monsanto type) was used to measure tablet hardness (n = 5). Friability was evaluated as the percentage weight loss of 20 tablets tumbled in a friabilator (USP XXIII, model EF2,
Electrolab, Mumbai) for 4 min at 25 rpm. The tablets were dedusted, and the loss in weight caused by fracture or abrasion
was recorded as percentage friability.