|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. Pectin is the methylated ester of polygalacturonic acid. It is commercially extracted from citrus peels, apple pomace and sugar beet pulp. A typical pectin molecule comprises 200 to 1000 galacturonic acid units
connected in a linear chain. Pectins are heterogeneous materials, with a polysaccharide backbone that is uniform as .alpha.-1,4-linked polygalacturonic acid. Various neutral sugars have been identified in pectins such as xylose, galactose, rhamnose, arabinose.
Pectin occurs as a coarse or fine powder, yellowish-white in color, practically odorless, and with a mucilaginous taste. It is almost completely soluble in 20 parts water, forming a viscous solution containing negatively charged, very much hydrated particles. It is acid to litmus and insoluble in alcohol or in diluted alcohol, and in other organic solvents. It dissolves more readily in water, if first moistened with alcohol, glycerol or sugar syrup, or if first mixed with 3 or more parts of sucrose. It is stable under mildly acidic conditions; more strongly acidic or basic conditions cause depolymerization. A critical property of pectins, which is known to affect their gelation properties, is the extent to which the galacturonic acid units are esterified. The degree of esterification (DE) of pectins found naturally can vary considerably (from 60 to 90%).
Pectin is divided into two main categories: high methoxylated pectin HM pectin), which are characterized by a degree of methoxylation above 50% and low methoxylated pectin (LM pectin) having a degree of methoxylation below 50%. Degree of methoxylation (also referred to as DE or degree of esterification) is intended to mean the extent to which free carboxylic acid groups contained in the polygalacturonic acid chain have been esterified (e.g. by methylation). The LM pectins are further subdivided into two groups: low methoxylated amidated, and low methoxylated conventional. Low DE pectins are usually prepared by the de-esterification of extracted pectins, normally on a bench scale, by way of an enzymatic process, or, on an industrial scale, by the treatment with acid or ammonia in an alcoholic heterogeneous medium. For pectins with a low degree of methoxylation the gelation properties are known to depend on the DM and the molecular weight of the pectin.
Pectin is an important ingredient in making jams and jellies. Pectin is a general intestinal regulator that is used in many medicinal preparations, especially as an antidiarrhea agent. Modified citrus pectin (MCP) is citrus pectin that has been broken down to less complex molecules by modifying the pH. MCP is dissolves easily in water and absorbed much easily in the body. Modified citrus pectin is rich in galactoside residues, giving it an affinity for certain types of cancer cells. Galactose-rich, modified citrus pectin has a binding affinity for galectins on the surface of cancer cells, resulting in an inhibition, or blocking, of cancer cell aggregation, adhesion, and metastasis. Metastasis is one of the most life-threatening aspects of cancer and the lack of effective anti-metastatic therapies has prompted research on MCP's effectiveness in blocking metastasis of certain types of cancers, including melanomas, prostate, and breast cancers. Pectin is resistant to human digestion, but is almost completely degraded into short-chain fatty acids in the colon by bacteria. Pectin has a reduced tendency to have a laxative effect and stimulates bacterial growth in the colon.
Pectin can be extracted from many different plant sources. Fruits rich in pectin are the peach, apple, currant, and plum. Pectins are also found in root crops such as carrots and beetroot, as well as in tubers, such as potatoes.