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Pectine

Sources and Extraction

Pectin is widely found in plant tissues where it serves, in combination with cellulose, as intercellular structural substance (membranes, middle lamellae). Peelings of citric fruits contain about 20% of pectin, apple skins about 15%, sunflower seed about 25% and sugar beet pulp about 20%.. The key resources are citrus albedo and pomace. The main production countries are USA, Israel and European countries. To extract pectin, the raw material is treated with acidified water (pH value 1.5-3.0) at temperatures between 60° and 100° C. Thereby, insoluble proto pectin is decomposed to soluble pectin. The raw extract is filtrated and starch, if present, is encymatically removed. The pure extract is concentrated and spray dried or roll dried, or the pectin is precipitated with alcohols.

Agar Agar .
The precipitation gives purer products and today is the favoured treatment. By adequate modifications in the processing and controlled partial de-esterification, pectins with different grades of esterification and polymerisation can be extracted. The annual production is estimated at about 12 000 tons, which are almost exclusively used in the food industry.

Properties

Appearance

Pectine is a white to yellowish or slightly brownish powder.

Composition

Pectin is a polyuronide composed of a main chain of α-(1-4) linked galacturon acid units. The carboxyl groups are partially esterified with methanol. Depending on the provenance of the pectin, the secondary hydroxyl groups may be partially esterified with acetate. The macromolecule can contain covalent bonded side chains of neutral sugars (xylose, β-(1-4)-D-galactane, α-(1-5)-L-arabane). Rhamnose units bonded in position 1 and 2 with the galacturon acid units are integrated in the main chain. The rather stretched pectin molecule thus has a kink. Depending on the quantity of carboxyl groups esterified with methanol, pectins are devided into high esterified pectins (methoxyl content > 7 %, degree of esterification > 50 %) and low esterified pectins (methoxyl content < 7 %, degree of esterification < 50 %). The high esterified pectins are devided into fast-gelling pectins (degree of esterification > 72 %), medium-fast (degree of esterification 66 bis 72 %) and slow-gelling pectins (degree of esterification < 66 %). High esterified pectins require sugar and acid to gel, low esterified pectins need calcium ions for gelification. The molar weight of the current products ranges between 30 000 – 300 000 dalton.

Pectin is being transformed by a number of enzymes: pectin esterase (pectin methyl esterase: E.C. 3.1.1.11) saponifies the methyl ester, which produces low esterified bonds; exo-polygalacturonase (pectinase, poly-[1,4-α-galacturonid]-galacturonase E.C. 3.2.1.67), endo-polygalacturonae (poly-[1,4-α-D-galacturonid]-glycanohydrolase E.G. 3.2.1.15) splits the external ether bridges of the pectin chains, thus generating depolymerisations; pectinlyasen, pectatlyasen (E.C. 4.2.2.10, E.C. 4.2.2.2) split the pectin chains by trans-elimination reactions.

Solubility

High as well as low esterified pectins with water produce a colloidal, opalizing solution. The solubility increases with decreasing degree of polymerisation and increasing degree of esterification. Further, pectin is soluble in dimethylformamide, dimethylsulfoxic and warm glycerin. The viscosity of aqueous pectin solutions is depending on the molecular weight and the degree of esterification and increased with these. Concentration, pH value, temperature and other parts in the solvent influence the viscosity. The optimal stability of the viscosity is reached at pH values between 4 and 5. Higher and lower pH values lead to depolymerisation and therefore to loss of viscosity and gel strength.. Alkali pectates are water soluble, bivalent and trivalent metal ions respectively give either precipitation or gelation.

The outstanding property of pectin is its gelation capacity. The acid of the sugar/acid gels inhibits the inter-molecular charge-rejection effects, the sugar competes with the pectin for the available water. Both effects lead to chain associativity and thus to gelation. Low esterified pectins produce gels by forming bridges between the Ca-ions and the carboxyl and hydroxyl groups of the galacturon acids. Gels of high esterified pectins are not heat reversible, those between low esterified pectins and Ca-ions however are fusible.

Application properties

Pectins are mainly used as gelling agent, e.g. with jams, jelly sweets, baking resistent marmalades (high esterified pectins) and low sugar jams or jellied milk products (low esterified pectins). On a smaller scale, they are used as stabilisers (mayonnaises, salad dressings, ice creams) and for medical application (e.g. intestinal diseases). Traded compounds often contain sugar (for adjusting the gelation degree) and puffer salts (for adjusting the gelation time).

Toxicologic Evaluation

Pectin is a natural ingredient of the human nutrition. For this reason and considering the existing toxicologic data, a limitation of the allowed daily intake (ADI) is not regarded as necessary for people’s health.