All green land plants contain pectic substances which in combination with cellulose are responsible for the structural properties of fruits and vegetables. Commercial pectin is mostly derived from citrus fruit or apples. Pectin has only been produced industrially since early in the 20th century, but has been used traditionally for gelling jams.
Pectin production depends on the type of pectin desired.The first three steps are standard for every pectin extraction.
- Extraction from the plant material with hot acidified water.
- Purification of the liquid extract through filtrations and centrifugation.
- Isolation of pectin from the solution, and – if low ester (LM) pectin is the end product than the last step follows:
- De-esterification of the high ester (HM) pectin.
The end product is a white powder and is typically mixed with sugar to produce consistent properties to meet the desired product specifications.
Chemical Structure and Properties
Pectin is an essentially linear polysaccharide containing from a few hundred to about 1000 saccharide units in a chain-like configuration; this corresponds to average molecular weights from about 50,000 to 150,000. The saccharide units are galacturonic acid units These acid groups are partly esterified with methyl groups and the free acid groups may be partly or fully neutralized with sodium, potassium, calcium or ammonium ions.
Pectin is in general classified according to its Degree of Esterification (DE). The DE is the ratio of esterified acid groups (the galacturonic acid methyl esters) compared to the total acid groups. The most typical classification is high methyl (HM) and low methyl (LM) pectin.
In HM-pectin a relatively high portion of the carboxyl groups occur as methyl esters. When pectin contains less than 50% of the carboxyl acid units, the methyl ester is normally referred to as LM-pectin. In general, LM pectin is obtained from HM pectin by a treatment under mild acidic or alkaline conditions.
The degree of esterification (DE) influences the properties of pectin, especially the solubility and the gel forming characteristics. The highest DE that can be achieved by extraction of natural raw material is approximately 75%. If pectins are needed with a lower DE for example from 20-70%, a controlled de-esterification in the manufacturing process will take place.
The pectin can be further diversified by amidation which also creates different properties. Amidated pectin is obtained from high ester pectin when ammonia is used in the alkaline de-esterification process. In this type of pectin some of the remaining carboxylic acid groups have been transformed into the acid amide. The useful properties of amidated pectin may vary with the proportion of ester and amide units and with the degree of polymerization. Commercial pectin is normally blended with sugars for standardization purposes, and some types may also contain suitable food grade buffer salts to control of pH and create a desirable setting environment.
Another way pectin is classified is the speed of setting. The degree of esterification of HM-pectins affects their relative speed of gelation as reflected by the designations ‘slow set’ and ‘rapid set’ HM pectin. The higher the DE, the faster the setting rate, In the case of LM pectin, the degree of esterification of LM-pectins controls their calcium reactivity. Some types of LM-pectins also contain amide groups (LMA pectins), which strongly affects the calcium reactivity.
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