Pectin is a structural heteropolysaccharide contained in the primary
cell wallThe cell wall is the tough, usually flexible but sometimes fairly rigid layer that surrounds some types of cells. It is located outside the cell membrane and provides these cells with structural support and protection, and also acts as a filtering mechanism. A major function of the cell wall is to...
s of
terrestrial plantA terrestrial plant is one that grows on land. Other types of plants are aquatic , epiphytic , lithophytes and aerial ....
s. It was first isolated and described in 1825 by
Henri BraconnotHenri Braconnot was a French chemist and pharmacist.He was born in Commercy, his father being a counsel at the local parliament...
. 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 fiberDietary fiber, dietary fibre, or sometimes roughage is the indigestible portion of plant foods having two main components:* soluble fiber that is readily fermented in the colon into gases and physiologically active byproducts, and* insoluble fiber that is metabolically inert, absorbing water as it...
.
Biology
In plant cells, pectin consists of a complex set of polysaccharides (see below) that are present in most primary cell walls and particularly abundant in the non-woody parts of terrestrial plants. Pectin is present not only throughout primary cell walls but also in the middle lamella between plant cells where it helps to bind cells together.
The amount, structure and chemical composition of pectin differs among plants, within a plant over time and in various parts of a plant. During
ripeningRipening is a process in fruits that causes them to become more palatable. In general, a fruit becomes sweeter, less green, and softer as it ripens. Even though the acidity of fruit increases as it ripens, the higher acidity level does not make the fruit seem tarter, which can lead to the...
, pectin is broken down by the
enzymeEnzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
s
pectinasePectinase is a general term for enzymes, such as pectolyase, pectozyme and polygalacturonase, commonly referred to in brewing as pectic enzymes. These break down pectin, a polysaccharide substrate that is found in the cell walls of plants. One of the most studied and widely used commercial...
and
pectinesterasePectinesterase is a ubiquitous cell-wall-associated enzyme that presents several isoforms that facilitate plant cell wall modification and subsequent breakdown. It is found in all higher plants as well as in some bacteria and fungi...
, in which process the fruit becomes softer as the middle lamellae break down and cells become separated from each other. A similar process of cell separation caused by the breakdown of pectin occurs in the abscission zone of the
petioleIn botany, the petiole is the stalk attaching the leaf blade to the stem. The petiole usually has the same internal structure as the stem. Outgrowths appearing on each side of the petiole are called stipules. Leaves lacking a petiole are called sessile, or clasping when they partly surround the...
s of
deciduousDeciduous means "falling off at maturity" or "tending to fall off", and is typically used in reference to trees or shrubs that lose their leaves seasonally, and to the shedding of other plant structures such as petals after flowering or fruit when ripe...
plants at leaf fall.
Pectin is a natural part of human diet, but does not contribute significantly to nutrition. The daily intake of pectin from fruits and vegetables can be estimated to be around 5 g (assuming consumption of approximately 500 g fruits and vegetables per day).
In human digestion, pectin goes through the small intestine more or less intact. Pectin is thus a soluble
dietary fiberDietary fiber, dietary fibre, or sometimes roughage is the indigestible portion of plant foods having two main components:* soluble fiber that is readily fermented in the colon into gases and physiologically active byproducts, and* insoluble fiber that is metabolically inert, absorbing water as it...
.
Consumption of pectin has been shown to reduce blood cholesterol levels. The mechanism appears to be an increase of viscosity in the intestinal tract, leading to a reduced absorption of cholesterol from bile or food. In the large intestine and colon, microorganisms degrade pectin and liberate short-chain fatty acids that have positive influence on health (prebiotic effect).
Chemistry
Homogalacturonans are linear chains of α-(1-4)-linked
D-galacturonic acidD-Galacturonic acid is a sugar acid, an oxidized form of D-galactose. It is the main component of pectin, in which it exists as the polymer polygalacturonic acid. It has an aldehyde group at C1 and a carboxylic acid group at C6. Other oxidized forms of D-galactose are D-galactonic acid and...
.
Substituted galacturonans are characterized by the presence of saccharide appendant residues (such as D-
xyloseXylose is a sugar first isolated from wood, and named for it. Xylose is classified as a monosaccharide of the aldopentose type, which means that it contains five carbon atoms and includes an aldehyde functional group. It is the precursor to hemicellulose, one of the main constituents of biomass...
or D-
apiose Apiose is a branched-chain sugar found as residues in galacturonans-type pectins; that occurs in parsley and many other plants.Apiose 1-reductase uses D-apiitol and NAD+ to produce D-apiose, NADH, and H+....
in the respective cases of xylogalacturonan and apiogalacturonan) branching from a backbone of D-galacturonic acid residues.
Rhamnogalacturonan I pectins (RG-I) contain a backbone of the repeating disaccharide: 4)-α-D-galacturonic acid-(1,2)-α-L-
rhamnoseRhamnose is a naturally occurring deoxy sugar. It can be classified as either a methyl-pentose or a 6-deoxy-hexose. Rhamnose occurs in nature in its L-form as L-rhamnose . This is unusual, since most of the naturally occurring sugars are in D-form...
-(1. From many of the rhamnose residues, sidechains of various neutral sugars branch off. The neutral sugars are mainly D-
galactoseGalactose , sometimes abbreviated Gal, is a type of sugar that is less sweet than glucose. It is a C-4 epimer of glucose....
, L-
arabinoseArabinose is an aldopentose – a monosaccharide containing five carbon atoms, and including an aldehyde functional group.For biosynthetic reasons, most saccharides are almost always more abundant in nature as the "D"-form, or structurally analogous to D-glyceraldehyde.For sugars, the D/L...
and D-xylose, the types and proportions of neutral sugars varying with the origin of pectin.
Another structural type of pectin is rhamnogalacturonan II (RG-II), which is a less frequent complex, highly branched polysaccharide. Rhamnogalacturonan II is classified by some authors within the group of substituted galacturonans since the rhamnogalacturonan II backbone is made exclusively of D-galacturonic acid units.
Isolated pectin has a molecular weight of typically 60–130,000 g/mol, varying with origin and extraction conditions.
In nature, around 80% of carboxyl groups of galacturonic acid are
esterifiedEsters are chemical compounds derived by reacting an oxoacid with a hydroxyl compound such as an alcohol or phenol. Esters are usually derived from an inorganic acid or organic acid in which at least one -OH group is replaced by an -O-alkyl group, and most commonly from carboxylic acids and...
with
methanolMethanol, also known as methyl alcohol, wood alcohol, wood naphtha or wood spirits, is a chemical with the formula CH3OH . It is the simplest alcohol, and is a light, volatile, colorless, flammable liquid with a distinctive odor very similar to, but slightly sweeter than, ethanol...
. 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 – or in short HM vs. LM-pectins, with more or less than half of all the galacturonic acid esterified.
The non-esterified galacturonic acid units can be either free acids (carboxyl groups) or salts with sodium, potassium or calcium. The salts of partially esterified pectins are called pectinates, if the degree of esterification is below 5% the salts are called pectates, the insoluble acid form, pectic acid.
Some plants such as
sugar beetSugar beet, a cultivated plant of Beta vulgaris, is a plant whose tuber contains a high concentration of sucrose. It is grown commercially for sugar production. Sugar beets and other B...
,
potatoThe potato is a starchy, tuberous crop from the perennial Solanum tuberosum of the Solanaceae family . The word potato may refer to the plant itself as well as the edible tuber. In the region of the Andes, there are some other closely related cultivated potato species...
es and
pearThe pear is any of several tree species of genus Pyrus and also the name of the pomaceous fruit of these trees. Several species of pear are valued by humans for their edible fruit, but the fruit of other species is small, hard, and astringent....
s contain pectins with acetylated galacturonic acid in addition to methyl esters. Acetylation prevents gel-formation but increases the stabilising and emulsifying effects of pectin.
Amidated pectin is a modified form of pectin. Here, some of the galacturonic acid is converted with
ammoniaAmmonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...
to
carboxylic acidCarboxylic acids are organic acids characterized by the presence of at least one carboxyl group. The general formula of a carboxylic acid is R-COOH, where R is some monovalent functional group...
amideIn chemistry, an amide is an organic compound that contains the functional group consisting of a carbonyl group linked to a nitrogen atom . The term refers both to a class of compounds and a functional group within those compounds. The term amide also refers to deprotonated form of ammonia or an...
. These pectins are more tolerant of varying calcium concentrations that occur in use.
To prepare a pectin-gel, the ingredients are heated, dissolving the pectin. Upon cooling below gelling temperature, a gel starts to form. If gel formation is too strong,
syneresisSyneresis , in chemistry, is the extraction or expulsion of a liquid from a gel, as when lymph drains from a contracting clot of blood. Another example of syneresis is the collection of whey on the surface of yogurt...
or a granular texture are the result, whilst weak gelling leads to excessively soft gels. 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.
Amidated pectins behave like low-ester pectins but need less calcium and are more tolerant of excess calcium. Also, gels from amidated pectin are thermo-reversible – they can be heated and after cooling solidify again, whereas conventional pectin-gels will afterwards remain liquid.
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.
Sources and production
Apples, guavas,
quinceThe quince , or Cydonia oblonga, is the sole member of the genus Cydonia and native to warm-temperate southwest Asia in the Caucasus region...
,
plumA plum or gage is a stone fruit tree in the genus Prunus, subgenus Prunus. The subgenus is distinguished from other subgenera in the shoots having a terminal bud and solitary side buds , the flowers in groups of one to five together on short stems, and the fruit having a groove running down one...
s, gooseberries,
orangesAn orange—specifically, the sweet orange—is the citrus Citrus × sinensis and its fruit. It is the most commonly grown tree fruit in the world....
and other
citrusCitrus is a common term and genus of flowering plants in the rue family, Rutaceae. Citrus is believed to have originated in the part of Southeast Asia bordered by Northeastern India, Myanmar and the Yunnan province of China...
fruits, contain large amounts of pectin, while soft fruits like
cherriesThe cherry is the fruit of many plants of the genus Prunus, and is a fleshy stone fruit. The cherry fruits of commerce are usually obtained from a limited number of species, including especially cultivars of the wild cherry, Prunus avium....
, grapes and
strawberriesFragaria is a genus of flowering plants in the rose family, Rosaceae, commonly known as strawberries for their edible fruits. Although it is commonly thought that strawberries get their name from straw being used as a mulch in cultivating the plants, the etymology of the word is uncertain. There...
contain small amounts of pectin.
Typical levels of pectin in plants are (fresh weight):
- apricot
The apricot, Prunus armeniaca, is a species of Prunus, classified with the plum in the subgenus Prunus. The native range is somewhat uncertain due to its extensive prehistoric cultivation.- Description :...
, 1%
- carrot
The carrot is a root vegetable, usually orange in colour, though purple, red, white, and yellow varieties exist. It has a crisp texture when fresh...
s approx. 1.4%
The main raw-materials for pectin production are dried citrus peel or apple
pomacePomace , or marc , is the solid remains of grapes, olives, or other fruit after pressing for juice or oil. It contains the skins, pulp, seeds, and stems of the fruit....
, both by-products of juice production. Pomace from sugar-beet is also used to a small extent.
From these materials, pectin is extracted by adding hot dilute acid at pH-values from 1.5 – 3.5. During several hours of extraction, the protopectin loses some of its branching and chain-length and goes into solution. After filtering, the extract is concentrated in vacuum and the pectin then
precipitatedEthanol precipitation is a method used to purify and/or concentrate RNA, DNA and polysaccharides such as pectin and xyloglucan from aqueous solutions.- Theory :DNA is polar due to its highly charged phosphate backbone...
by adding ethanol or isopropanol. An old technique of precipitating pectin with aluminium salts is no longer used (apart from alcohols and polyvalent cations; pectin also precipitates with proteins and detergents).
Alcohol-precipitated pectin is then separated, washed and dried. Treating the initial pectin with dilute acid leads to low-esterified pectins. When this process includes ammonium hydroxide, amidated pectins are obtained. After drying and milling, pectin is usually standardised with sugar and sometimes calcium-salts or organic acids to have optimum performance in a particular application.
Worldwide, approximately 40,000 metric tons of pectin are produced every year.
Uses
The main use for pectin (vegetable agglutinate) is as a gelling agent, thickening agent and stabilizer in food.
The classical application is giving the jelly-like consistency to jams or
marmaladeMarmalade is a fruit preserve made from the juice and peel of citrus fruits, boiled with sugar and water. The benchmark citrus fruit for marmalade production in Britain is the "Seville orange" from Spain, Citrus aurantium var...
s, which would otherwise be sweet juices. For household use, pectin is an ingredient in
gelling sugarGelling sugar or Jam sugar or Jelly sugar or sugar with pectin is a kind of sugar, which is used to produce preserves and which contains pectin as a gelling agent...
(also known as "jam sugar") where it is diluted to the right concentration with sugar and some citric acid to adjust pH.
In some countries, pectin is also available as a solution or an extract, or as a blended powder, for home jam making.
For conventional jams and marmalades that contain above 60% sugar and soluble fruit solids, high-ester pectins are used. With low-ester pectins and amidated pectins less sugar is needed, so that diet products can be made.
Pectin can also be used to stabilize acidic protein drinks, such as drinking yogurt, and as a fat substitute in baked goods. Typical levels of pectin used as a food additive are between 0.5 – 1.0% - this is about the same amount of pectin as in fresh fruit.
In medicine, pectin increases
viscosityViscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity...
and volume of
stoolFeces, faeces, or fæces is a waste product from an animal's digestive tract expelled through the anus or cloaca during defecation.-Etymology:...
so that it is used against
constipationConstipation refers to bowel movements that are infrequent or hard to pass. Constipation is a common cause of painful defecation...
and
diarrheaDiarrhea , also spelled diarrhoea, is the condition of having three or more loose or liquid bowel movements per day. It is a common cause of death in developing countries and the second most common cause of infant deaths worldwide. The loss of fluids through diarrhea can cause dehydration and...
. Until 2002, it was one of the main ingredients used in
KaopectateKaopectate, known medically as bismuth subsalicylate, is an orally taken medication from Chattem, Inc. for the treatment of mild diarrhea. It is also sometimes used to treat indigestion, nausea and stomach ulcers...
, along with
kaoliniteKaolinite is a clay mineral, part of the group of industrial minerals, with the chemical composition Al2Si2O54. It is a layered silicate mineral, with one tetrahedral sheet linked through oxygen atoms to one octahedral sheet of alumina octahedra...
. Pectin is also used in throat lozenges as a
demulcentA demulcent is an agent that forms a soothing film over a mucous membrane, relieving minor pain and inflammation of the membrane. Demulcents are sometimes referred to as mucoprotective agents. Demulcents such as pectin, glycerin, honey, and syrup are common ingredients in cough mixtures...
. In cosmetic products, pectin acts as stabilizer. Pectin is also used in wound healing preparations and specialty medical adhesives, such as
colostomyA colostomy is a surgical procedure in which a stoma is formed by drawing the healthy end of the large intestine or colon through an incision in the anterior abdominal wall and suturing it into place. This opening, in conjunction with the attached stoma appliance, provides an alternative channel...
devices. Also, it is considered a natural remedy for nausea. Pectin rich foods are proven to help nausea.
Yablokov
et al., writing about the aftermath of the
ChernobylChernobyl or Chornobyl is an abandoned city in northern Ukraine, in Kiev Oblast, near the border with Belarus. The city had been the administrative centre of the Chernobyl Raion since 1932....
nuclear disaster, quote research conducted by the Ukrainian Center of Radiation Medicine and the Belarussian Institute of Radiation Medicine and Endocrinology with the conclusion that "adding pectin preparations to the food of inhabitants of the Chernobyl-contaminated regions promotes an effective excretion of incorporated radionuclides". The authors report on the positive results of using pectin food additive preparations in a number of clinical studies conducted on children in severely polluted areas, with up to 50% improvement over control groups.
In
ruminantA ruminant is a mammal of the order Artiodactyla that digests plant-based food by initially softening it within the animal's first compartment of the stomach, principally through bacterial actions, then regurgitating the semi-digested mass, now known as cud, and chewing it again...
nutrition, depending on the extent of lignification of the cell wall, pectin is up to 90% digestible by bacterial enzymes. Ruminant nutritionists recommend that the digestibility and energy concentration in forages can be improved by increasing pectin concentration in the forage.
In the
cigarA cigar is a tightly-rolled bundle of dried and fermented tobacco that is ignited so that its smoke may be drawn into the mouth. Cigar tobacco is grown in significant quantities in Brazil, Cameroon, Cuba, the Dominican Republic, Honduras, Indonesia, Mexico, Nicaragua, Philippines, and the Eastern...
industry, pectin is considered an excellent substitute for vegetable glue and many cigar smokers and collectors will use pectin for repairing damaged tobacco wrapper leaves on their cigars.
Pectin is also used in jellybeans.
Legal status
At the FAO/WHO joint Expert Committee on Food Additives and in the EU, no numerical acceptable daily intake (ADI) has been set, as pectin is considered safe.
In the US, pectin is GRAS –
generally recognized as safeGenerally recognized as safe is an American Food and Drug Administration designation that a chemical or substance added to food is considered safe by experts, and so is exempted from the usual Federal Food, Drug, and Cosmetic Act food additive tolerance requirements.-History:On January 1, 1958,...
. In most foods it can be used according to good manufacturing practices in the levels needed for its application, "quantum satis".
In the International Numbering System (INS), pectin has the number 440. In Europe, pectins are differentiated into the
E numberE numbers are number codes for food additives that have been assessed for use within the European Union . They are commonly found on food labels throughout the European Union. Safety assessment and approval are the responsibility of the European Food Safety Authority...
s E440(i) for non-amidated pectins and E440 (ii) for amidated pectins. There are specifications in all national and international legislation defining its quality and regulating its use.
History
Pectin was first isolated and described in 1825 by
Henri BraconnotHenri Braconnot was a French chemist and pharmacist.He was born in Commercy, his father being a counsel at the local parliament...
, though the action of pectin to make jams and marmalades was known long before. To obtain well set jams from fruits that had little or only poor quality pectin, pectin-rich fruits or their extracts were mixed into the recipe.
During the industrialization, the makers of fruit preserves soon turned to producers of apple juice to obtain dried apple
pomacePomace , or marc , is the solid remains of grapes, olives, or other fruit after pressing for juice or oil. It contains the skins, pulp, seeds, and stems of the fruit....
that was cooked to extract pectin.
Later, in the 1920s and 1930s, factories were built that commercially extracted pectin from dried apple pomace and later citrus-peel in regions that produced apple juice in both the USA and in Europe.
At first, pectin was sold as a liquid extract, but nowadays pectin is often used as dried powder that is easier to store and handle than a liquid.
External links