Food grade pectin is a high-molecular-weight polysaccharide, which is made of two parts: more than 65% galacturonic acid, and 35% of other polysaccharides and some little monosaccharides.
D-galacturonic acid
The basic structure of pectin is primarily composed of D-galacturonic acid units, which are polymerized by α-1,4 glycosidic linkages and partially of the carboxyl groups on the galacturonic acid residues occur as methyl esters (methylated).
The rest carboxyl groups on galacturonic acid exist as free acid or in the salt of potassium, sodium, ammonium, calcium and so on.
The percentage of total galacturonic acid reflects the purity of pectin, the content of which should not be less than 65% for its food grade.
Other polysaccharides
Other types of neutral saccharides are connected to the basic structure as side chains. Such saccharides mainly refer to galactose, rhamnose, arabinose, fucose, xylose, mannose and etc.
Degree of esterification or degree of methoxylation
Galacturonic acid is usually estered with methoxy group, amide group and the like. Degree of esterification (DE) is the sum of methylation, acetylation and amidation of polygalacturonic acid on the main chain of pectin.
DM refers to the degree of methylation of polygalacturonic acid on the long chain of pectin. DE has almost the same meaning as DM in pectin.
DE is the main item to distinguish the type of pectin, and it is also an important factor that reflects the physical and chemical properties of pectin, such as solubility, gel properties, and emulsion stability.
DE usually differs due to various raw materials origins and the manufacturing process. It generally ranges from 30% (e.g. sunflower pectin) to 70% (e.g. citrus, apple pectin).
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