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Pectins (also known by the singular pectin) are a diverse family of biopolymers with a complex range of structures. Their common feature is a polysaccharide backbone of 1,4-linked α-d-galacturonic acids. Pectins are derived from dicotyledonous and some monocotyledonous plants and make up one third of the cell wall materials. Pectin has been widely used as a gelling and stabilizing agent in food, as an incipient ingredient in pharmaceuticals, in personal care products and in other polymer products. It is recognized as safe (GRAS) by the United States Food and Drug Administration (FDA). Commercial pectin is extracted using acids from by-products of the food industry such as citrus peel, apple pomace and sugar beet pulp. There are two types of pectin: high methoxyl (HM) pectin with a degree of methylation (DM) > 50% and low methoxyl (LM) pectin. LM pectins are usually manufactured from HM pectins by de-esterification. HM pectins gel by cross-linking homogalacturonan residues through hydrogen bonds and hydrophobic forces between the methoxyl groups, assisted by a high sugar concentration and low pH. In contrast, LM pectins gel by forming ionic linkages via calcium bridges between two carboxyl groups from two different chains in close proximity, known as the ‘egg-box’ model. The viscoelastic behavior of both gels depends on intrinsic and extrinsic factors. Chemical modifications of pectin such as alkylation, amidation and thiolation have been used to manipulate hydrophilicity, hydrophobicity and adhesion.

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