2.2.2.2 Pectin Pectin, in general, is a group of polysaccharides found in nature in the primary cell walls of all seed bearing plants and are invariably located in the middle lamella. It has been observed that these specific polysaccharides actually function in combination with both cellulose and hamicellulose as an intercellular cementing substance. One of the richest sources of pectin is lemon or orange rind which contains about 30% of this polysaccharide.
Pectin is naturally found in a number of plants namely: lemon peel, orange peel, apple pomace, carrots, sunflower-heads, guava, mangoes and papaya. The European countries, Switzerland and USA largely produce pectin either from apple pomace or peels of citrus fruits. Evaluation and standardization of pectin is based on its ‘Gelly-Grade’ that is, its setting capacity by the addition of sugar. Usually, pectin having ‘gelly grade’ of 100, 150 and 200 are recommended for medicinal and food usuages.
Biological Sources Pectin is the purified admixture of polysaccharides, obtained by carrying out the hydrolysis in an acidic medium of the inner part of the rind of citrus peels, for instance: Citrus limon (or Lemon) and Citrus aurantium belonging to the family Rutaceae, or from apple pomace Malus sylvestris Mill (Syn: Pyrus malus Linn, family: Rosaceae).
Geographical Source Lemon and oranges are mostly grown in India, Africa and other tropical countries. Apple is grown in the Himalayas, California, many European countries and the countries located in the Mediterranean climatic zone.
Preparation The specific method of preparation of pectin is solely guided by the source of raw material i.e., lemon/orange rind or apple pomace; besides the attempt to prepare either low methoxy group or high methoxy group pectins.
In general, the preserved or freshly obtained lemon peels are gently boiled with approximately 20 times its weight of fresh water maintained duly at 90ºC for a duration of 30 minutes. The effective pH (3.5 to 4.0) must be maintained with food grade lactic acid/citric acid/tartaric acid to achieve maximum extraction. Once the boiling is completed the peels are mildly squeezed to obtain the liquid portion which is then subjected to centrifugation to result into a clear solution. From this resulting solution both proteins and starch contents are suitably removed by enzymatic hydrolysis. The remaining solution is warmed to deactivate the added enzymes. The slightly coloured solution is effectively decolourized with activated carbon or bone charcoal. Finally, the pectin in its purest form is obtained by precipitation with water-miscible organic solvents (e.g., methanol, ethanol, acetone), washed with small quantities of solvent and dried in a vaccum oven and stored in air-tight containers or polybags.
Note: As Pectin is fairly incompatible with Ca2+, hence due precautions must be taken to avoid the contact of any metallic salts in the course of its preparation.
Description
Appearance : Coarse or fine- powder
Colour : Yellowish white
Odour : Practically odourless
Taste : Mucilaginous taste
Solubility : 1. Completely soluble in 20 parts of water forming a solution containing negatively charged and very much hydrated particles. 2. Dissolves more swiftly in water, if previously moistened with sugar syrup, alcohol, glycerol or if first mixed with 3 or more parts of sucrose.
Chemical Constituents Pectin occurs naturally as the partial methyl ester of a (1→4) linked (+) – polygalacturonate sequences interrupted with (1–2) – (–) – rhamnose residues. The neutral sugars
that essentially form the side chains on the pectin molecules are namely: (+) – galactose, (–) –arabinose, (+) – xylose, and (–) – fructose. Schneider and Bock (1938) put forward the following probable structure for pectin galacturonan:
Chemical Tests
1. A 10% (w/v) solution gives rise to a solid gel on cooling.
2. A transparent gel or semigel results by the interaction of 5 ml of 1% solution of pectin with 1 ml of 2% solution of KOH and subsequently setting aside the mixture at an ambient temperature for 15 minutes. The resulting gel on acidification with dilute HCl and brisk shaking yields a voluminous and gelatinous colourless precipitate which on warming turns into white and flocculent.
Uses
1. It is employed mostly as an intestinal demulscent. It is believed that the unchanged molecules of polygalacturonic acids may exert an adsorbent action in the internal layers of the intestine, thereby producing a protective action along with Kaolin to prevent and control diarrhoea.
2. As a pharmaceutical aid pectin is used frequently as an emulsifying agent and also as a gelling agent preferably in an acidic medium.
3. It is employed extensively in the preparation of jellies and similar food products e.g., jams, sauces, ketchups.
4. Poectin in the form of pastes exerts a bacteriostatic activity and hence, is used frequently in the treatment of indolent ulcers and deep wounds.
5. A combination of pectin and gelatin find its application as an encapsulating agent in various pharmaceutical formulations to afford sustained-release characteristics.
