5 Depends on their methoxyl content, pectin is commonly categorized as high methoxyl pectin HMP
or low methoxyl pectin LMP, with methoxyl content is 7 and 7, respectively. HMP can form a gel under acidic conditions in the presence of high sugar concentration Evangliou et al. 2000. On the other
hand, LMP forms gel by interaction with divalent cations, particularly Ca
2+
, according to the “egg box” model Durand et al. 1990. Figure 5 and 6 below show molecular structure of high methoxyl and low
methoxyl pectin.
Figure 5 Chemical structure of high methoxyl pectin HMP Taranathan 2003
Figure 6. Chemical structure of low methoxyl pectin LMP Taranathan 2003 Pectin consists of galacturonic acid monomers that form a long-chain molecule. The main chain is
interrupted by a rhamnose group with branched chain assembling neutral sugars arabinose, galactose. Carboxyl groups acid groups of galacturonic acid can be esterified or amidated IPPA 2002. In addition
to D-galacturonic acid as the main component, pectin also has D-galactose, L-arabinose, and L-rhamnose in various amounts. The chemical composition of pectin varies greatly depends on the source and the
conditions that is used in insulation Willats et al. 2006.
3. Pectin characteristic
Committee on Food Chemical Codex 1996, states that the pectin is mostly composed of methyl esters of polygalacturonic acid and sodium, potassium, calcium or ammonium salts. Pectin is a coarse to
fine powder which is white, yellow, grey or brown and abundant in mature fruits and vegetables. Glicksman 1969 stated that dry pectin that has been purified will forms white crystals with solubility
varies according to its methoxyl content. The physical properties of pectin depend on its chemical characteristics Guichard et al. 1991. Factors affecting the rate of gel formation, plasticity and gel
strength are pH, pectin concentration, temperature, calcium ion, and sugar Chang and Miyamoto 1992. Viscosity of pectin solution has a fairly wide range depends on the concentration of pectin, salt, and size
of polygalacturonic acid chains Rouse 1977. Pectin with methoxyl levels lower than 7 can form a gel with presence of bivalent metal ions.
Bivalent metal ions can react with carboxyl groups of the two molecules and form pectic acid bridge. In the formation of this gel, sugar is unnecessary and gel texture formed is less strong Guichard et al. 1991.
Gel formation of pectin with a high degree of methylation also influenced by the concentration of pectin, sugar percentage, and pH. The larger concentration of pectin, the stronger the gel is formed. Concentration
of 1 has produced a pretty good gel strength. Sugar added should not be more than 65 so that the formation of crystals on the surface of the gel is preventable Guichard et al. 1991. Gel formation of high
methoxyl pectin occurs through hydrogen bonds between free carboxyl group and between hydroxyl groups. At low methoxyl pectin, ability to form a gel with sugars and acids is lost. Instead of that, this
kind of pectin is capable to form a gel in the presence of calcium ions Gliksman 1969.
6 According to May 1990, pectin is a negatively charged polygalacturonic acid. Pectin reacts to
positively charged macromolecule. Gel formation can occur rapidly at low pH, but this reaction can be inhibited by the addition of salt. According to Rouse 1977, pectin degradation and decomposition can be
caused by the oxidation reaction. Rate of degradation depends on temperature, pH, and concentration of oxidizing agent.
4. Production of pectin
