Pectin is found in most plants, but is most concentrated in citrus fruits (oranges, lemons, grapefruits) and apples. Pectin obtained from citrus peels is referred to as citrus pectin.
The extraction of pectins can lead to large variations in the chemical structure of the final material. Pectins are industrially extracted from citrus peels and apple pomace by hot acidified water. Extraction conditions of pH 1.5 to 3.0 and temperatures of 60-100 C for 0.5 to 6 hours are varied to give a material that has the desired gelling capacity and degree of methylation. The separation of the viscous material from the swollen and partially disintegrated plant material remains a problem. Grinding and washing with ethanol are used but this can lead to co-precipitation with intracellular proteins, starches and nucleic acids.
Another method by which this contamination may be avoided is by wet ball milling at low temperature. Enzymatic degradation of the pectin is avoided by addition of a surfactant like sodium dodecyl sulphate (SDS). Sodium deoxycholate (SDC) is used dilute to remove pigments and lipids and a treatment with 90% dimethyl sulphoxide (DMSO) will remove the bulk of the starch.
The advantage of alcohol treatment is that the resulting preparation is in a very suitable form for further modification to high methoxylated (HM) pectins using acid treatment or to low methoxy pectin (LM) by treatment with ammonia. The disadvantage of alcoholic treatment could be the possibility of reinforcing hydrogen bonding between cell wall constituents and effecting the extraction of the pectins. The extraction method may therefore be optimised for the type of pectin required, be it modified or native.
Pectins can also be extracted using enzymes. Scientific studies have all extracted pectins using galacturonase enzymes. This results in short but branched segments. In order to extract unaltered pectins arabinase and galactanase could be used to avoid degradation.
Additional information on pectin can be accessed using the arrows in the Further Reading box below.