Biomedical Engineering Reference
In-Depth Information
Classification of the pectic substances is an area that grabbed much attention of the
polymer biochemistry. Pectic polysaccharides are in fact, recognized in several forms
and accordingly, they have been classified into distinct groups. The American Chemi-
cal Society classified pectic substances into four main groups as follows (Kertesz,
1951).
1. Protopectin : the term protopectin is applied to the water insoluble parent pectic
substances, which occurs in plants and which upon restricted hydrolysis, yields
pectinic acids
2. Pectinic acid : the term pectinic acid is used for colloidal polygalacturonic acid
containing more than a negligible proportion of methyl ester groups
3. Pectin : the term pectin designates those water-soluble pectinic acids of varying
methyl ester content and degree of neutralization which are capable of forming
gels with sugar and acids under suitable condition
4. Pectic acid : the term pectic acid is applied to pectic substances, mostly com-
posed of colloidal polygalacturonic acids and essentially free from methyl es-
ter groups. Normal or acid salts of pectic acids are called pectates.
However, it needs mentioning in this context that classification and nomenclature
of pectic substances in consideration to their chemical solubility in different solvents
has also been emphasized. In this context, pectic substances are classified broadly into
the following groups (Barnier and Thibault, 1982).
1. Water-soluble pectic substances (WSP)--are those pectic substances which
are soluble in water and include pectin and colloidal pectinic acids of high
methyl ester content.
2. Oxalate-soluble pectic substances (OXP)--include pectic acids and the col-
loidal pectinic acids of low methyl ester content
3. Acid-soluble (HP) and Alkali-soluble pectic substances (OHP)—are the groups
includes protopectin of having methyl ester content.
FraCtioNal ChaNGes oF PeCtiC PolysaCCharides iN deVeloPiNG
Fruits
Pectic substances are the major components of cell wall and middle lamella of plant
tissues which undergo structural changes during development and ripening of the
fruits and thereby contributing significantly to textural softening of ripening fleshy
fruits (Proctor and Peng, 1989). Solubilization of pectic polysaccharides which oc-
curs to different extent among fruits and fruit tissues, are involved with enzymic and
physical mechanism (Gross, 1990), such as hydrolysis of polygalacturonate backbone,
modification of side chains and disruption of ionic or hydrogen bonds (Liyama et al.,
1994). The participation of cell wall modifying enzymes that is pectin methyl esterase
and polygalacturonase in pectic metabolism during fruit ripening (Majumder and Ma-
zumdar, 2002) causes molecular mass downshift, decreased methyl esterification, and
glycosylation (Malis-Arad et al., 1983), which in turn alters the physical properties
of the cell wall (Klein et al., 1995). The change-over of pectic substances from cell
wall bound to soluble form has been well documented in a number of fruits, although
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