General Data

Pectins are cell wall polysaccharides which have a structural role in plants. They are predominantly linear polymers based on a 1,4-linked alpha-D- galacturonate backbone, interrupted randomly by 1,2-linked L-rhamnose. Polygalacturonic acid as the principal constituent is partly esterified with methyl groups, and the free acid groups may be partly or fully neutralized with monovalent ions (Na⁺, K⁺, NH4⁺). The degree of methylation (DM) has an essential influence on the properties of pectin, especially on its solubility and its requirements for gelation which are directly derived from the solubility. The DM of 50 percent divides commercial pectins into high methoxyl (HM) pectins and low methoxyl (LM) pectins. These two groups of pectin are gelled by different mechanisms:

HM pectins require a minimum amount of soluble solids (SS, e.g. glucose) and a pH within a moderate range around 3.0 in order to form gels. LM pectins require the presence of a controlled amount of calcium ions for gelation, and need neither sugar nor acid. LM pectin gelation resembles the behaviour of alginate. D-Galacturonic acid blocks in pectins are almost mirror images of the L-guluronic acid blocks of alginates:

No universally accepted terminology for pectins has been agreed upon. However, the following terminology is generally accepted:

Pectins. Substances that originate from plants, contain pectinic acid as a major component, are water soluble, and are able to form gels under suitable conditions. Based on viscometry, the average molecular weight falls within the range 50.000 - 200.000. Light scattering is particularly sensitive to the presence of aggregates and apparent molecular weight in the range 1.000.000 or more may be obtained;

Pectinic acids. Polygalacturonic acids partly esterified with methanol. Salts are called pectinates;

Pectic acids. Polygalacturonic acids with no or only negligible methyl ester content. Salts are called pectates.

Economy

Sources of pectins:

There exist two major sources for pectins. They are either extracted from citrus peel (mostly lemon and lime) or from apple peels. Apple pectin has a slightly darker, brownish colour compared to citrus pectin that is a light, almost white powder. The two pectin types do not show essentially differences regarding their properties.

Some suppliers for pectins:

Apple pectin:

Herbstreith & Fox KG
Phone Number: +49-(0)7082-7913-0
Fax Number: +49-(0)7082-20281
Street Address: Turnstraße 37,
D-75305 Neuenbürg, Germany
E-Mail: info@herbstreith-fox.de

Citrus pectin:

Hercules Aqualon
Phone: +49-(0)211-7491-0
Fax: +49-(0)211-7491-200
Street Address: Paul-Thomas Straße 56/58
D-40599 Düsseldorf, Germany
E-Mail: Europe, USA, Asia and Pacific

Sources of pectates in laboratory scale:

Dr. Peter Gemeiner,
Institute of Chemistry, Slovak Academy of Sciences, Dúbravská cesta 9,
SK-842 38 Bratislava, Slovak Republic
Phone:+421 7 59410211
Fax: +421 7 59410222
E-mail: chempege@savba.sk
http://nic.savba.sk/sav/inst/chem/intro.html

Mechanical Properties

They vary to a large extent with the macromolecular characteristics (molecular weight, galacturonate content, rhamnosyl "kinks" content and esterification). Mechanical properties of calcium alginate gel (CAG) and CPG particles are quite similar. It should be, however, pointed out that alginates usually are prepared technologically in a 2-3 % (w/v) concentration and CPG in a 5-10% (w/v) concentration due to their viscosity differences. As a result, the alginate particles reveal much smaller mechanical parameters when comparing the particles prepared of like viscous solutions (2 % alginate and 5 % pectate).

Figure shows mechanical properties of polyuronate gel beads. Alg10_1: 1% (w/v) Protanal LF 10/60; Alg20_1: 1% (w/v) Protanal LF 20/60 Pronova, Drammen, Norway; FAL101_5: 5% pectinate type 1, Federal Agricultural Research Centre, Braunschweig, Germany; SAS4_5: 5% pectate type 4, Slovak Academy of Sciences, Bratislava, Slovak Republic. Deformation power F(N): the power needed for 50% deformation of size.

The calcium pectate gels as an immobilization matrix are much less sensitive to chelating compounds such as phosphate, lactate and citrate and anti-gelling cations (Na⁺ or Mg²⁺) which destroy alginate gels.
Pectates like alginates may form strong complexes with polycations such as chitosan or polypeptides, or synthetic polymers such as polyethylenimine they may be used to stabilize the gel. The gels have been found stable in a range of organic solvents and are therefore, in contrast to other hydrogels, potentially useful in applications involving entrapment of enzymes in non-aqueous systems.

Encapsulation Mechanism

There exist two different mechanisms for making calcium polyuronate gels (CPG, CAG): external and internal gelation. The easiest and most often used method for encapsulation is external gelation, where polysaccharide solution containing "biomaterials" is dripped into a hardening bath of calcium chloride and the drops are gelled by diffusion of calcium from outside. The internal gelation can be achieved by slow calcium ion liberation within the ionic polyuronate via spontaneous breakdown of D(+)-gluconic acid delta-lactone, resulting in acidification of pectate solution containing a insoluble calcium salt (citrate complex).

Encapsulation Procedure

In most applications involving encapsulation of living cells or other biological materials the bead size needs to be small (< 1 mm) mostly because diffusion limitations. From this reason and for a low productivity rate is popular dripping procedure with a syringe improved by some ways:

Jet Breakup Technique:
Bead formation is achieved by...
... coaxial air stream that pull droplets from a needle tip into a gelling bath - Coaxial Bead Generator, Pronova Biomedical a.s, tel: +47 22 95 86 50, fax: +47 22 69 64 70
... an electrostatic force that pull droplets from a needle tip into a gelling bath - Electrostatic Bead Generator, Pronova Biomedical a.s, tel: +47 22 95 86 50, fax: +47 22 69 64 70
... magnetically driven vibrator which transmittes vibrations to the polyuronate solution in the pulsation chamber and causes a disturbance in the jet as it passes the nozle which results in the break-up - Nisco Engineering AG, http://www.nisco.ch
... combination of electrostatic and magnetic pulsation - Inotech AG, http://www.inotechintl

Jet Cutting Method:
Bead formation is achieved by means of a rotating cutting tool which cuts jet into uniform cylindrical segments. These segments form spherical beads while falling down into a gelling bath - geniaLab BioTechnologie GmbH, http://www.geniaLab.com

Spinning Disk Atomization
Bead formation is achieved by specially designed spinning disk atomizer from Global Powder AB (Täby, Sweden)

Emulsification / Internal Gelation Methodology
Small diameter CAG and CPG beads are formed via internal gelation of polyuronate solution emulsified within vegetable oil. Gelation is initiated by addition of an oil-soluble acid thereby reducing the pH of the polyuronate solution and releasing soluble Ca²⁺ from the citrate complex.

Biocompatibility

The pectin is a natural product with long record of safety that favors the use of pectin in human applications particularly in food.

Shape

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Modifications

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Applications

Pectins are used mainly as gelling agents in acidic foods. Jams, jellies, and marmelades still absorb the major part of the world's production. New uses are being developed for pectin as a gelling agent, a thickener and a protective colloid in foods. Calcium pectates could be a better alternative to calcium alginates in multiple application of bioencapsulation technologies e.g.: as a carrier for drug delivery to patiens for various therapeutic purposes, for cell immobilization (insulin regulation in diabetes; interferon production; treatment of hemophilia B, kidney and liver failure; industrial biotransformation processes) and for enzyme immobilization (biosensors).

Examples of cell immobilizations in CPG (calcium pectate gels):