Mucilage: A Rich Source of Excipients Present in Plant Parts with Gold Status

Large numbers of pharmaceutical excipients of natural origin are available nowadays. Plant materials like mucilages with a variety of pharmaceutical applications are most common. They are being used due to their abundance, safety, compatibility, cost-effectiveness and eco-friendly nature as compared to synthetic one and have various advantages over synthetic polymers. To compete with and replace arti(cid:977)icial excipients mucilages can be modi(cid:977)ied in many ways to obtain the required form of a drug delivery system. Currently, there are a vast amount of natural pharmaceutical excipients are there, and due to its increasing demand, it has become essential to identify or explore more plant mucilage sources to ful(cid:977)il the industrial need. Mucilages are polymeric mono-saccharides or mixed mono-saccharides combined with uronic acids. On hydrolysis, they yield a mixture of sugars and uronic acids, and the mucilages that are obtained from plant sources have translucent and amor-phous nature. Due to presence of hydrophilic moieties in mucilages, they can easily combine with water to form a gel or a thick viscous solution, and these extracted mucilages from the plant can be processed to a certain extent and incorporated in dosage forms to achieve the speci(cid:977)ic performance of the for-mulation. In this review, we describe isolation, characterization, pharmaceutical application and methods of modi(cid:977)ication to develop drug delivery systems.


INTRODUCTION
Use of Mucilage in drug delivery systems and dosage forms helps in modifying the release of drug from its dosage forms, enhancement of solubility, bioavailability, patient acceptability and also ensures ease of manufacture (Raymond et al., 2006;Patel et al., 2007). These materials of natural origin like mucilages are cheap, safe, readily available, ecofriendly, degradable, stable & compatible due to its natural source and capable of modi ication, they are seeking a lot of attention and importance in the ield of delivery of drugs (Malviya et al., 2011). These excipients of natural origin have replaced the synthetic excipients, and recently there is increased use of natural and non-toxic products. Currently, huge amounts of pharmaceutical excipients of natural origin are available and like other products of natural origin and due to its increasing demand it has become essential to identify or explore more plant mucilage sources to ful il the industrial need.
These mucilages obtained from plant sources are the hydrocolloids of Polysaccharides having sugar molecules & uronic acids that are liked with each other.
They are polymeric mono-saccharides or mixed mono-saccharides combined with uronic acids and on their hydrolysis produce a mixture of sugars and uronic acids. The mucilages that are obtained from plant sources are translucent and amorphous.
Due to the presence of hydrophilic moieties in mucilages, they can easily combine with water to form a gel or a thick viscous solution. Mucilages form large molecular aggregates in solution, and these mucilages are made up of complexes of polysaccharides having arabinose, galactose, rhamnose and galactouronic acid (Jani et al., 2009).
Mucilages and gums have many similar properties, but the only thing in which they differ is that mucilages are metabolic products which are formed within the cell and can be produced without making injury/incision to the plant. Mucilages and their polymeric derivatives from distinct sources are extensively used in pharmaceutical dosage forms (Galati et al., 2002). In this context; we have deliberated various aspects of mucilages starting from their Isolation, characterization, application and Modi ications of existing mucilages.

ISOLATION OF MUCILAGE
Various methods of isolation of mucilages depending on the presence of mucilage in a particular plant part such as stem, leaves, fruit, seeds, tubers etc. The techniques used for isolation from leaves, i.e. the drying process was not performed whereas, for extraction of mucilage from other plant parts, the stem drying process is essential. In the case of the method used for isolation from the fruit of a plant, they are made to be directly crushed in a mixer without drying.
Although there are differences in the methods followed in which chemicals are utilized for isolation. The standard chemicals used for isolation are Petroleum ether, acetone, ethanol etc. (Sumanta and Rahaman, 2018) In the low chart (Figure 1), the general isolation method for mucilage was described. But now a day's using some advanced techniques yield of mucilage was increased. In 2011 Biren Shah, et al. used a microwave-assisted extraction technique used for isolation of okra mucilage. Microwaveassisted extraction performed at the intensity of 160W for 40 minutes duration of heating increased 11.55% yield of mucilage when compared to the conventional heating method for 1 hour (Shah and Seth, 2011). Hence, mucilage can be extracted from various plants using the method mentioned in Figure 1.

Characterization of Mucilage
Preliminary con irmatory test for Mucilage is given in Table 1. (Khandelwal, 2008)

Structural Characterization
Mucilages contain sugar (Polysaccharides), so by using various chromatographic methods like TLC, HLPC & HPTLC presence of sugars can be con irmed and FTIR, Mass and NMR Spectroscopic can be used for structural elucidation.

Physicochemical Properties
Various physicochemical properties can be determined by using parameters such as hygroscopic nature, shape, texture, touch, colour, odour, taste, pH, solubility, swelling index, LOD, percentage yield, total ash, Acid insoluble ash, melting point, Moisture content, true density, bulk density, angle of repose and surface tension and presence of various microbes and pathogens can be determined by various microbial assays. Mucilages are vicious & produce thick gel-like mass in solution and to decide its commercial use and industrial application rheological properties of excipients are evaluated.

Impurity determination
To determine or detect the impurities present various analytical techniques can be used.

Pharmaceutical Applications of mucilages
Application of some plant mucilages are summarized given in Table 2.

Modi ication of existing mucilage
Mucilages are the biodegradable materials used in drug delivery systems, and they have some disadvantages like thickening, decrease in viscosity on prolonged storage, uncontrolled hydration rate & microbial growth, to overcome these disadvantages and problems it requires some modi ication. (Singh and Sharma, 2008).  These modi ications methods involve:

Carboxymethylation/carbomoyethylaion
Modi ication can be done by replacing some free hydroxylgroupswhich enhances the water/aqueous solubility of mucilage and clarity of the solution. (Rana et al., 2011)

Cross linking or grafting
Cross linking or grafting of vinyl monomers on polysaccharides using Physical & chemical Methods producing a promising material which can be used in drug delivery systems.

Physical methods:
Modi ication by physical means can be done by exposing mucilages/polymerstomicrowave, Ultra Violet, gamma radiations, dry heat and saturated steam. (Khan et al., 2006;Desai and Park, 2006) 2. Chemical Methods: Modi ication by chemical means include treating/heating mucilage/polymer with compounds like aldehydes, epichlorhydrin, borax or glutaraldehyde. (Micard et al., 2000) CONCLUSION There are large numbers of mucilage's available, having various applications in pharmaceutical preparations are reviewed and discussed. Natural excipients are preferable as not only they are fulilling their role but also providing health bene its by overcoming the risks associated with synthetic excipients. More research efforts should be provided on natural excipients to innovate non-toxic, biocompatible, cost-effective, eco-friendly suitable for the development of dosage forms.