Pectin

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. 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 usages.

Biological Source

Pectin is a purified polysaccharide substance obtained from the various plant sources such as inner peel of citrus fruits, apple, raw papaya, etc. Numbers of plants sources of pectin are mentioned below:

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, that is, 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 90°C for duration of 30 min. The effective pH (3.5–4.0) 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 hydro-lysis. 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, etc.), washed with small quantities of solvent and dried in a vacuum oven and stored in air-tight containers or poly bags. 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.

Morphology

Chemical Constituents

Pectin is a polysaccharide with a variable molecular weight ranging from 20,000 to 400,000 depending on the number of carbohydrate linkages. The core of the molecule is formed by linked D-polygalacturonate and L-rhamnose resi-dues. The neutral sugars D-galactose, L-arabinose, D-xylose and L-fructose form the side chains on the pectin molecule. Once extracted, pectin occurs as a coarse or fine yellowish powder that is highly water soluble and forms thick colloidal solutions. The parent compound, protopectin, is insoluble, but is readily converted by hydrolysis into pectinic acids (also known generically as pectins).

Chemical Tests

·A 10% (w/v) solution gives rise to a solid gel on cooling.

·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 min. The resulting gel on acidification with dilute HC1 and brisk shaking yields a voluminous and gelatinous colourless precipitate which on warming turns into white and flocculent.

Uses

Pectin is used as an emulsifier, gelling agent and also as a thickening agent. It is a major component of antidiarrhoeal formulation. Pectin is a protective colloid which assists absorption of toxin in the gastro-intestinal tract. It is used as haemostatic in cases of haemorrhage. As a thickener it is largely used in the preparation of sauces, jams and ketchups in food industry.

One of the best characterized effects of pectin supplementation is its ability to lower human blood lipoprotein levels. Pectin supplements appear to act as ‘enteroabsorbents’, protecting against the accumulation of ingested radioactivity.

Toxicology

Pectin is a fermentable fibre that results in the production of short-chain fatty acids and methane. Concomitant administration of pectin with beta-carotene containing foods or supplements can reduce levels of beta-carotene by more than one-half. There is some indication that concomitant ingestion of pectin with high energy diets may reduce the availability of these diets, as demonstrated in a controlled trial of undernourished children; urea production was also shown to be lower in children who ingested pectin with their caloric supplement.