Pectin
From Free net encyclopedia
Pectin is a heterosaccharide derived from the cell wall of plants. Pectins vary in their chain lengths, complexity and the order of each of the monosaccharide units.
Under acidic conditions, pectin forms a gel, and it can be used as an edible thickening agent in processed foods. This effect is used for making jams and jellies.
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Biosynthesis
They are synthesised in the plant Golgi apparatus and form a matrix in which the hemicellulose polysaccharides of the plant cell are embedded. An important part of fruit walls, pectin is broken down by the enzyme, pectinase to pectinic acid and finally pectic acid. During this chemical breakdown process, the fruit gets softer as the cell walls degenerate.
Chemistry
Pectin is composed of three main polysaccharide types:
- Polygalacturonan, which is composed of repeated D-galacturonic acid monosaccharide subunits
- Rhamnogalacturonan I which is composed of alternating L-rhamnose and D-galacturonic acid subunits
- Rhamnogalacturonan II which is a complex, highly branched polysaccharide
- The gelling characteristics of different pectins are influenced greatly by the degree of esterification of the molecule.
Pectin has recently been found to oxidize in air with release of methane.
Medical uses
Pectin is used as an oral demulcent to alleviate symptoms of sore throat and mouth in some throat lozenges.
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.
References
Keppler, Frank et al. Methane emissions from terrestrial plants under aerobic conditions. Nature 439, 187-190
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