Pectin
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Pectin is a heterosaccharide derived from the cell wall of plants. Pectins are variable in their chain lengths; complexity; and the order of each of the monosaccharide units.
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Biosynthesis
They are synthesised in the plant Golgi apparatus and form a matrix in which the hemicellulose polysacharides of the plant cell are embedded. An important part of fruit walls, pectin is broken down to pectinic acid and finally pectic acid. During this chemical breakdown process, the fruit gets softer as the cell walls degenerate. Pectin is used as an edible thickening agent in processed foods.
Chemical composition
Pectin is composed of three main polysaccharide types:
- polygalacturonan, which is composed of repeated galacturonic acid monosaccharide subunits
- rhamnogalacturonan I which is composed of alternating rhamnose and galacturonic acid subunits)
- rhamnogalacturonan II which is a a complex, highly branched polysaccharide
Sources
Apples, plums and oranges contain much pectin, and pectin is sometimes found in yogurt, while soft fruits like cherries and strawberries contain little pectin. For commercial utilisation, pectin is extracted from shredded fruit peel or pulp by adding hot water. The pectin dissolves into the hot water, and may then be precipitated as a gel by adding ethanol.
Uses
Pectin is commonly used as the active ingredient in cough drops because it coats the upper trachea and prevents the spasms which precede coughing. Under acidic conditions, pectin forms a gel. This effect is used for making jams and jellies.