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Pectin, a natural polysaccharide commonly used as a gelling agent, thickener, emulsifier, and stabilizer in food with the European food additive number E440. This ingredient is mainly made from citrus peel and apple pomace, and commonly used to gel jams and jellies.
Pectin occurs naturally in plants and can be found in the cell walls and in the middle layer of the cell of most vegetables and fruits. The sources for commercial production of pectin mainly come from apple pomace and citrus peel. Both derived pectin are high methoxyl pectin.
1. Apple pomace
Apple pomace is the main by-product of apple juice manufacturing. Apples are first processed into juice, and the remaining pomace is used to make pectin. Dry pomace contains around 10% to 20% pectin.
Apple pectin can be used as a thickener in dairy products, a gelling agent for jams and jellies, a blending agent in fruit drinks and a stabilizer in various food processing.
2. Citrus peel
Citrus peel is the most common raw material used to produce pectin than apple pomace as high in pectin. Citrus pectin refers to pectin extracted from the peels of citrus fruits such as lime, lemon, orange and grapefruit.
Citrus peel is the main by-product of citrus fruit processing. Its pectin content accounts for about 20-30% of the dry weight. Compared with other types of pectin, it has strong gelation, high esterification degree, and large molecular weight.
3. Other sources
Pectin content varies according to the types, origin, maturity, storage period and manufacturing processing of plants. The following fruits also contain pectin but with lower content compared with the above two main sources:
What is pectin made of?
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.
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 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).
Three types of pectin
There are three types pectin if classified by the degree of esterification (DE):
- High methoxyl pectin (HMP): DE>50% (typically 55–75%)
- Low methoxyl pectin (LMP): DE