Pectin
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.
They are synthesised in the plant's
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.
Pectin is composed of three main
polysaccharide types:
* Homogalacturonan, which is composed of repeated
D-galacturonic acid monosaccharide subunits, that are methyl-esterified to a varying degree.
* Rhamnogalacturonan I which is composed of alternating
L-rhamnose and
D-galacturonic acid subunits that contain α-(1-5)-L-arabinan and β-(1-4)-D-galactan side chains.
* 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 releases small amounts of
methane in a non-enzymatic reaction.
Pectin is used as an oral
demulcent to alleviate symptoms of
sore throat and mouth in some
throat lozenges. Among these is the popular Luden's Throat Drops brand.
Pectin is considered to be a possible means for concealing evidence of THC in a drug test. The successful results of such usage are unconfirmed..
Apples,
plums,
gooseberries 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.
Keppler, Frank et al. Methane emissions from terrestrial plants under aerobic conditions.
Nature 439, 187-190
