**2. Pharmaceutical uses of pectin**

### **2.1 Drug delivery systems**

The polymer pectin has been put to several uses since its discovery over 200 years ago. Though its major application has been in the food industry where it has been used as a gelling agent, emulsifier, stabilizer, thickener, and more recently as a food packaging material, where they as used as edible films on fruits and vegetables etc. The most important use of pectin is based on its ability to form gels, hence its potential as an excipient; pectin has been used as a binding agent [32, 33] in tablets, carrier for drug delivery to the gastrointestinal tract from matrix tablets, and as a controlled-release matrix in tablet formulations [34–36]. It has also been used as a sustained release drug delivery system in gel beads prepared by the ionotropic gelation method [19, 37, 38], colon-specific drug delivery vehicle [39], and film-coated dosage forms. Gel formation is caused by hydrogen bonding between free carboxyl groups on the pectin molecules and between the hydroxyl groups of neighboring molecules [40]. Most of the unesterified carboxyl groups in pectin occur as partially ionized salts in a neutral or very slightly acid dispersion of pectin molecules. [41]. Those that are ionized produce a negative charge on the molecule, which together with the hydroxyl groups causes it to attract layers of water [38]. Because of their negative charge, the repulsive forces between these groups can be strong enough to preclude the creation of a pectin network. When acid is added, the carboxyl ions are converted to mostly unionized carboxylic acid groups [38]. The attraction between pectin and water molecules is lowered by a reduction in the number of negative charges, which also lowers the forces of repulsion between pectin molecules. Sugar further decreases the hydration of the pectin by competing for water [41]. These conditions decrease the ability of pectin to stay dispersed. When cooled, the unstable dispersion of less hydrated pectin forms a gel, a continuous network of pectin holding the aqueous solution. High methoxyl pectin produces gels with sugar and acid. Unlike Low methoxyl pectin, high methoxyl pectin does not contain sufficient acid groups to gel or precipitate with calcium ions, although other ions such as aluminum or copper cause precipitation under certain conditions [25]. The degree of esterification (DE) affects the rate at which gel formation takes place [38]. A higher DE causes a more rapid setting. Slow-set pectins (with DE 58–65%) gel at lower soluble solids and greater levels than rapid-set pectins (DE > 72 per cent). Low methoxyl pectins require the presence of divalent cations (usually calcium) for proper gel formation [38].

#### **2.2 Bioadhesive systems**

The ability of pectin to absorb water, swell and form bioadhesive bonds with biological tissue has found application in the preparation of mucoadhesive formulations such as patches [42]. Pectin has also been found useful as a demulcent in


#### **Table 1.**

*Some commercial drug products containing pectin.*

throat lozenges where it gives temporary relief for minor discomfort and protects irritated areas in sore mouth and sore throat [43]. The antihemorrhagic effect of pectin has also been utilized in wound healing as medical adhesives [44].
