Physico-Chemical Characterization and Evaluation of Two Local Cactus Mucilages (Opuntia Spp.) as Suspending Agents
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Date
2010-05
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Addis Ababa University
Abstract
Ethiopia is one of the countries where cactus grows naturally. Cactus pear (Opuntia spp.),
Cactaceae family, is a plant with an impressive genetic diversity of over 400 species. Cactaceae
are well adapted to arid and hot drylands, where the plants have a marked capacity to withstand
prolonged drought. The peculiar feature of the plant to adapt such areas is because of the
presence of mucilage in specialized cells of the cladodes. Mucilage is a complex carbohydrate
with a highly branched structure, which contains varying proportions of L-arabinose, Dgalactose,
L-rhamnose and D-xylose, as well as galacturonic acid in different proportions. It
swells in water and form viscous mass. Hence, recently an attention is being paid for its potential
use in industry: food, cosmetic and pharmaceutical sectors.
The objective of this study is to determine the physico-chemical properties of mucilages of
Opuntia ficus-indica and Opuntia stricta, the two most abundant cactus species in Ethiopia, and
evaluate their suspending ability in pharmaceutical suspensions.
The physico-chemical properties of the mucilages were compared between themselves. The
suspending abilities of the mucilages were compared with NaCMC. The dissolutions of the
suspensions were performed using the USP paddle method at 25 rpm.
The yield of mucilage from both Opuntia spp. was found to be comparable. The solubility and
SP of the mucilages were also studied. With increase in temperature the solubility increased and
was comparable in both mucilages. However, at all the treatment levels the SP were higher in
mucilage of OS than that of OFI the differences of which were statistically significant. At 100%
RH the moisture sorption property of OFI and OS were 95.4% and 76.9%, respectively. The pH
values of both mucilages were found to decrease upon increasing mucilage concentration which
at 12% (w/v) dispersions were 5.57 and 5.87 for OFI and OS, respectively. The results showed
that these pH values are to be classified within low acid group. The conductivity, at 12% (w/v),
of OFI was found to be 13.12 mS/cm while that of OS was 9.31 mS/cm. The apparent viscosities
at 12% (w/v) were 9,017 mPas and 10,060 mPas for OFI and OS, respectively. The apparent
x
viscosities of the dispersions decreased with increase in shear rates which rendered the
dispersions a pseudoplastic flow.
These physico-chemical properties of the mucilages can signal on their potential use in
pharmaceutical formulations especially suspensions. Hence, Paracetamol suspensions using the
mucilages and NaCMC as suspending agents were formulated. The apparent viscosities of the
suspensions in all the suspending agents concentration levels and applied shear rates were in the
order of NaCMC>OS>OFI with non-Newtonian flow and accordingly the flow rates of the
suspensions were in the order of OFI>OS>NaCMC. The sedimentation volumes (%) of the
suspensions in all the suspending agent concentration levels were higher for OS followed by OFI
and then NaCMC. The high sedimentation volumes (%) of suspensions, in turn, were
accompanied by ease of redispersibility of that order. The effect of electrolyte on sedimentation
volume (%) had dual effect. It was only the suspensions that had NaCMC that showed increase
in sedimentation volume (%) in all molar NaCl concentration. However, in suspensions that had
mucilages of OS and OFI, an initial increase in sediment volumes (%) were accompanied by
decrease after 1x10-3M and 1x10-2M of NaCl, respectively. Moreover, the effect of pH on
sedimentation volume (%) was addressed. Hence, the suspensions from NaCMC were stable in
acidic media while suspensions from OFI and OS were stable in basic media. Dissolution of the
suspensions which had mucilages attained the acceptable ranges (≥ 80% drug release in 30 min)
in 5 min. Similarly, except A6 formulations A2, A3, A4 and A5 have attained the limit but the
release was not as quick as the previous formulations.
Hence, it can be concluded that mucilages of Opuntia spp. (Opuntia ficus-indica and Opuntia
stricta) can be used as alternatives to NaCMC as suspending agent in suspension formulations.
Key words: Cactus, Mucilage, Opuntia spp., Sedimentation volume, Suspension, Suspending
agent
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Keywords
Cactus, Mucilage; Opuntia spp.; Sedimentation volume; Suspension; Suspending agent