Pectin classification
What is pectin?
A natural ingredient for every application needs
Chemically, pectin consists of the partial methyl esters of polygalacturonic acid and their salts (sodium, potassium, calcium, and ammonia), with a molecular weight of up to 150,000 Daltons.
Pectin is obtained by aqueous extraction of the appropriate edible plant materials, mainly from citrus peel and apple pomace, followed by a selective precipitation using alcohol or salts. The raw materials used contain a large amount of pectin with superior quality and are available in sufficient quantities to make the manufacturing process more cost effective.
Pectin is usually classified according to the degree of methoxylation (DM). The degree of methoxylation is expressed as a percentage of esterified galacturonic acid units to total galacturonic acid units in the molecule of pectin. It influences the properties of pectin, especially the solubility and the gel forming characteristics.
HM pectins
Pectin produced by the normal extraction process contains more than 50% of methoxyl groups and is classified as high methoxyl (HM) pectin. They are capable of forming gels in aqueous systems with high contents of soluble solids and low pH values.
HM pectin
LM pectins
Modification of the extraction process, or continued acid treatment, will yield conventional low methoxyl (LMC) pectin with less than 50% methoxyl groups.
LMC pectin
LMA pectin
LM pectins are characterized by their ability to form gels in the presence of bivalent salts, normally Ca++ ions, in systems with low solids content and a wide pH range.
The maximum yield using citrus peels
All vegetables and fruits contain pectin, but the amount varies between each type of fruit. The maximum yield occurs prior to ripening and varies from year to year due to different environmental conditions. The type and quality of fruits used, the harvest time and the enzymatic degradation are some factors influencing the chemical and physical properties of the final pectin.
The following classification is based on the average pectin content in different fresh fruits:
- High pectin content: lime, lemon, orange, and apple
- Average pectin content: apricot and blackberry
- Low pectin content: cherry, peach, and pineapple
In the citrus fruits (orange, lemon, and lime), pectin is mainly located in the albedo, the inner white layer of the peel that surrounds the juicy vesicles, and the lamellae. When the juice is extracted from the fruit, the peel and the albedo can be used to make the pectin.
Lemon peel: a source with a high content of pectin.
Pectin shows gel forming, thickening and stabilizing properties if it is properly dissolved in water and if it is stored in a cool and dry place. The general characteristics of pectin are shown below:
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Solubility
Pectin must be completely dissolved to ensure full utilization and to avoid heterogeneous gel formation. Any lumps formed during the preparation of the solution leads to loss of gel strength because the pectin lumps are not active. To produce a good pectin solution it is recommended that the pectin is pre-blended with sugar in the minimum ratio of 1:3 and dissolved preferably in hot water (85 - 90°C), at a soluble solids content below 20% using a suitable high-speed stirrer. Pectin will not dissolve in media where gelling conditions exist.
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Storage stability
Pectin should be stored in a cool dry environment. At increased temperatures, above ambient, the degradation of pectin will occur due to the reduction of molecular weight. The optimal pH for pectin is between 2.8 and 4.7.
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Viscosity
Pectin solutions show lower viscosity compared to other thickening agents. Polyvalent salts (such as Ca++ and Mg++) increase the viscosity of LM pectin solutions. In calcium-free solutions the viscosity drops when the acidity is increased.
Different types of pectin, different behavior of gelation
The optimal conditions for gelation of the different types of pectin are shown in the table below.
| Parameters | HM pectin | LM pectin |
|---|---|---|
| Degree of methoxylation (DM) | > 50% | < 50% |
| Soluble solid content (%) | ≥ 65% | 10 - 70% |
| pH | 2.0 - 3.8 | 2.6 - 7.0 |
| Bivalent ions, Ca++ (mg/g) | - | ≥ 15 |
HM pectin
HM pectin will only gel if the soluble solids content is higher than 65% and the pH is 2.0 - 3.8.
The gel is formed by cross-linking the polymer at junction zones in which mainly hydrogen bonds and the repulsion of methyl groups create areas where sugar and water can be trapped in the pectin network. The low pH value reduces the negative charges along the pectin chain, originated by the carboxylic group disassociation. Thus an electrostatic repulsion occurs which is responsible for gel formation and the pectin - pectin bond formation is avoided.
- The lower the DM level, the longer the setting time and the lower the set temperature.
- The higher the soluble solids content, the lower the numbers of hydrogen bonds. These bonds are stronger and thus the strongest gels are formed.
LM pectin
LM pectin forms gels in the presence of polyvalent cations, typically calcium (minimum quantity 15 mg Ca++ / g pectin). LM pectin forms gel over a wide range of pH, from 2.6 to 7.0, and with a soluble solid content between 10 - 70%.
The binding of Ca++ to pectin is not a simple ionic interaction, but involves intermolecular chelate binding of the cation, leading to the formation of macromolecular aggregates (“egg-box” cavity).
- The higher the solids level and the lower the pH, the pectin is more reactive.
- The higher the calcium content and lower the pH, the higher the setting temperature.
Mechanism of gelation
Natural product with positive effects on consumer’s health
Pectin is a food hydrocolloid that benefits from a high level of acceptance among consumers, a natural perception and is used in food globally.
The Joint Expert Committee on Food Additives (JECFA) of the Food and Agriculture Organisation (FAO) and the World Health Organisation (WHO) have approved the pectin as a safe additive for use in food and it has allocated an Acceptable Daily Intake (ADI) of “not specified”. This term is used when the toxicological, clinical and biochemical data support the conclusion that the total intake of that substance has no risk to the health, due to its natural presence and / or its use in accordance with the requirements of Good Manufacturing Practices (GMP) at best level necessary to achieve the desired technological effect.
In the US, pectin is Generally Recognised as Safe (GRAS). In most foods, it can be used according to good manufacturing practices in the levels needed for its application, “Quantum Satis”.
In Europe, pectins are differentiated into E440(i) for high methoxyl pectin and conventional low methoxyl pectins and E440(ii) for amidated low methoxyl pectin.
