Pectin is a structural heteropolysaccharide contained in the primary cell walls of terrestrial plants. It is produced commercially as a white to light brown powder, mainly extracted from citrus fruits, and is used in food as a gelling agent, particularly in jams and jellies. It is also used in fillings, medicines, sweets, as a stabilizer in fruit juices and milk drinks, and as a source of dietary fiber.
Pectins, also known as pectic polysaccharides, are rich in galacturonic acid.
Isolated pectin has a molecular weight of typically 60–130,000 g/mol, varying with origin and extraction conditions.
In nature, around 80 percent of carboxyl groups of galacturonic acid are esterified with methanol. This proportion is decreased to a varying degree during pectin extraction. The ratio of esterified to non-esterified galacturonic acid determines the behavior of pectin in food applications. This is why pectins are classified as high- vs. low-ester pectins (short HM vs. LM-pectins), with more or less than half of all the galacturonic acid esterified.
In high-ester pectins at soluble solids content above 60% and a pH-value between 2.8 and 3.6, hydrogen bonds and hydrophobic interactions bind the individual pectin chains together. These bonds form as water is bound by sugar and forces pectin strands to stick together. These form a 3-dimensional molecular net that creates the macromolecular gel. The gelling-mechanism is called a low-water-activity gel or sugar-acid-pectin gel.
In low-ester pectins, ionic bridges are formed between calcium ions and the ionised carboxyl groups of the galacturonic acid. This is idealised in the so-called “egg box-model”. Low-ester pectins need calcium to form a gel, but can do so at lower soluble solids and higher pH-values than high-ester pectins. Normally low-ester pectins form gels with a range of pH from 2.6 to 7.0 and with a soluble solids content between 10 and 70%.
High-ester pectins set at higher temperatures than low-ester pectins. However, gelling reactions with calcium increase as the degree of esterification falls. Similarly, lower pH-values or higher soluble solids (normally sugars) increase gelling speed. Suitable pectins can therefore be selected for jams and for jellies, or for higher sugar confectionery jellies.
pectin is traditionally used as a gelling agent in a wide range of fruit-based products, such as jams, marmalades, jellies, fruit preparations for yoghurts and desserts and fruit filling for bakery products.
Pectin can be used to improve the mouth-feel and the pulp stability in juice based drinks and as a stabiliser in acidic protein beverages.
Pectin also reduces syneresis in jams and marmalades and increases the gel strength of low calorie jams.
Pectin is used in confectionery jellies to give a good gel structure and a clean bite.
The typical dosage of pectin in food applications is between 0.5 - 1.0%.
Besides its use in the food industry, pectin is also used in pharmaceutical and cosmetic products.
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