129
the so-called egg box structure. In the latter, there is an ionic interaction between
calcium ions and oxygen group of the adjoining chains, which results in the cross
linking of the chains. There is a positive correlation between molecular weight and
gel strength (Whistler and Daniel 1993). This gelling property is employed in jams
and jellies while as the other properties allow pectin to be used as a stabilizer in fruit
juices and acidified milk drinks, protein rich fruit drinks, and fortified anti-oxidant
foods and as a fat replacer in emulsified meat products. Apart from these uses, it has
been seen as a target encapsulating agent for the drug delivery, wound healing ability and tissue engineering. Further its use in healthcare, pharmaceuticals and cosmetics is also growing owing to its, non toxicity, biocompatibility and
biodegradability. It has been reported to decrease blood fat, inhibit the lipase activity, and reduce the occurrence of heart diseases and growth and proliferation of
cancer cells. However the growing demand in the market sometimes requires alterations or modifications in the pectin macromolecule in order to tailor the needs.
Accordingly, the backbone of the pectin constituting the hydroxyl and the carboxyl
groups and the side chains constituting neutral sugars can be altered to prepare the
broad range of derivatives. As in case of acidic or alkaline demethoxylation or amidation, where the high methoxylated pectins can undergo structural modifications in
the galacturonic acid by changing ratio of the hydrophilic and hydrophobic groups
yielding low-methoxylated (LMP) or amidated (AP) pectins. These modifications
can also affect the pectin-water interactions.
Classification, Isolation and Purification
Classification
The pectins employed for industrial use are recognised on the basis of methyl–
esterification. The classification of pectin is done on the basis of methyl- esterification
of GalA units (also known as degree of methylation) or DM (Deuel 1943). DM can
be defined as the percentage of the molar ratio of methyl-esters to that of GalA units
(includes both free GalA and substituted GalA). This is the most crucial parameter
that affects various physicochemical properties of pectins like gelling, surface tension and emulsion formation (Müller-Maatsch et al. 2014). So accordingly, pectins
can be classified as high methoxyl (HM) and low methoxyl (LM) pectins depending
upon the degree of methyl esterification. Methyl groups can esterify the carboxyl
groups on the continuous poly-(GalA) chain of pectin in varying proportions resulting in certain degree of methyl esterification (DE or DM). If DE is greater than 50%,
it is known as high methoxyl (HM) pectin and if DE is lesser than 50%, it is known
as low methoxyl (LM) pectins. High methoxyl (HM) forms gel in high co-solute
concentration of 55–75% and acidic (pH 2.50–3.50) systems (Oakenfull and Scott
1984) whereas low methoxyl (LM) pectins can form gel in presence of cations over
a broad pH range (Hoefler 1991). Apart from this conventional classification,
Pectin
the so-called egg box structure. In the latter, there is an ionic interaction between
calcium ions and oxygen group of the adjoining chains, which results in the cross
linking of the chains. There is a positive correlation between molecular weight and
gel strength (Whistler and Daniel 1993). This gelling property is employed in jams
and jellies while as the other properties allow pectin to be used as a stabilizer in fruit
juices and acidified milk drinks, protein rich fruit drinks, and fortified anti-oxidant
foods and as a fat replacer in emulsified meat products. Apart from these uses, it has
been seen as a target encapsulating agent for the drug delivery, wound healing ability and tissue engineering. Further its use in healthcare, pharmaceuticals and cosmetics is also growing owing to its, non toxicity, biocompatibility and
biodegradability. It has been reported to decrease blood fat, inhibit the lipase activity, and reduce the occurrence of heart diseases and growth and proliferation of
cancer cells. However the growing demand in the market sometimes requires alterations or modifications in the pectin macromolecule in order to tailor the needs.
Accordingly, the backbone of the pectin constituting the hydroxyl and the carboxyl
groups and the side chains constituting neutral sugars can be altered to prepare the
broad range of derivatives. As in case of acidic or alkaline demethoxylation or amidation, where the high methoxylated pectins can undergo structural modifications in
the galacturonic acid by changing ratio of the hydrophilic and hydrophobic groups
yielding low-methoxylated (LMP) or amidated (AP) pectins. These modifications
can also affect the pectin-water interactions.
Classification, Isolation and Purification
Classification
The pectins employed for industrial use are recognised on the basis of methyl–
esterification. The classification of pectin is done on the basis of methyl- esterification
of GalA units (also known as degree of methylation) or DM (Deuel 1943). DM can
be defined as the percentage of the molar ratio of methyl-esters to that of GalA units
(includes both free GalA and substituted GalA). This is the most crucial parameter
that affects various physicochemical properties of pectins like gelling, surface tension and emulsion formation (Müller-Maatsch et al. 2014). So accordingly, pectins
can be classified as high methoxyl (HM) and low methoxyl (LM) pectins depending
upon the degree of methyl esterification. Methyl groups can esterify the carboxyl
groups on the continuous poly-(GalA) chain of pectin in varying proportions resulting in certain degree of methyl esterification (DE or DM). If DE is greater than 50%,
it is known as high methoxyl (HM) pectin and if DE is lesser than 50%, it is known
as low methoxyl (LM) pectins. High methoxyl (HM) forms gel in high co-solute
concentration of 55–75% and acidic (pH 2.50–3.50) systems (Oakenfull and Scott
1984) whereas low methoxyl (LM) pectins can form gel in presence of cations over
a broad pH range (Hoefler 1991). Apart from this conventional classification,
Pectin