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Pectins are important polysaccharide structure constituents of plant middle lamellae and primary cell walls ensuring their water retention performance and the pH stability [1, 11]. Due to the high gelling, stabilising and thickening properties they are widely used in the food and pharmaceutical industry [3, 9]. Commercial pectin substances are extracted from the waste material, especially citrus peels (from orange, grapefruit, lemon and lime fruit), apple pomace and sugar beet pulp. The high concentration of pectins is found also in other fruits and vegetables, mainly soy hull, mango peels and sunflower heads [3, 11, 12, 14]. The properties of pectins result mainly from their chemical structure. The pectin backbone is primarily composed of homogalacturonan (Fig. 1), which is a linear polymer consisting of α-1→4-linked d-galacturonic acid units, partially methylesterified or O-acetylated [3, 9]. Other structural elements of pectins are rhamnogalacturonan type I (Fig. 2) and type II (Fig. 3), xylogalacturonan (Fig. 5), arabinan (Fig. 6), arabinogalactan type I (Fig. 7) and type II (Fig. 8) [3, 5, 8]. The gelling property of pectins depends on the degree of methyl esterification of their carboxyl groups (DE). According to this parameter there are high ester pectins (DE > 50) and low ester pectins (DE < 50). The high ester pectins form gels in the presence of high sugar concentrations exceeding 55% and pH lower than 3.5, while in the case of low ester pectins the gelation process occurs even at low concentrations of sugar but the presence of divalent ions is required (e.g. calcium) [18, 21]. The aim of this study was a review of the available literature regarding the sources of pectins, their types, chemical structure and physicochemical properties.
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