146
mechanism involved, the first step comprising of dimerization of two macromolecules and the second step involving the aggregation of these dimmers (Axelos and
Thibault 1991b).The unbranched, non esterfied blocks of galacturonan are held
together by calcium ions. The important parameters that modify the intra and intermolecular interactions include the distribution of non-methyl-esterified carboxyl
groups and the charge density. Following the changes in conformation, the interchain hydrogen bonding takes place by placement of the carboxyl group outward
from the polymer backbone (Gilsenan et al. 2000; Mansel et al. 2015). The major
forces responsible for the stabilization of the egg-box structure are stabilization of
the egg-boxes formed between the two neighbouring chains are electrostatic interactions, hydrogen bonding and to a lesser extent by van der Waals interactions.
Overall the stabilization of the egg-boxes is brought by the forces in the order
electrostatic interactions ˃hydrogen bonding ˃Van der Waals interactions. The stability of the egg-boxes is dependent upon six consecutive carboxyl groups that is
present on the interior of each interacting chain (Powell et al. 1982). The formation
of the gel is hindered by the presence of methyl ester groups in the primary backbone. The transformation of LMP-calcium mixtures from a state of liquid to gel
with increasing G’ takes place as the DM decreases henceforth increasing the gel
strength. The probability of the formation of egg box structure is increased as the
DM increases which increases the length of the residues of non-mehtylated
GaIA. The stronger gel is formed with the formation of greater amount of “eggboxes”. Also the impact of calcium ions on the gel strength was studies and it was
reported by Dobies et al. (2004) that as the concentration of the calcium ions
increased, the value of G’ increased which in turn increased the strength of the
LMP-calcium gel. This mechanism of action lies in the fact that higher concentration of the calcium ions permits the formation of additional cross-links of nonmethylated GalA, which in turn create a more elastic and denser gel network
(Basak and Bandyopadhyay 2014). The addition of calcium or iron ions cab be
used as an alternative to thickening agents in fluids as these increase the pseudoplasticity. On the contrary addition of the magnesium ions can result in the formation of weak pectin gels as a consequence of decreasing G’. The dispersion of
LMP in aqueous calcium solution is carried out at 70 °C. This is followed by cooling the mixture slowly. At an elevated temperature, hydrophobic interactions
favour the egg-box structure via calcium bridging. Upon cooling there is an
increased interdimer associations that support the gel formation. The gel formation
is further encouraged by the electrostatic interactions of the single dissociated
carboxyl groups of pectin chains with calcium. Also just like in HMP gelation,
addition of sugar increases the inter-chain reactions in LMP gels. But with the
increase in the concentration of sugar, hydrogen bonding may be promoted as a
result of dehydrating effect of sugars which will in turn decrease the cross-linking
by calcium ions. This will overall have an adverse effect on LMP gels (Fu and
Rao 2001).
N. Noor et al.
mechanism involved, the first step comprising of dimerization of two macromolecules and the second step involving the aggregation of these dimmers (Axelos and
Thibault 1991b).The unbranched, non esterfied blocks of galacturonan are held
together by calcium ions. The important parameters that modify the intra and intermolecular interactions include the distribution of non-methyl-esterified carboxyl
groups and the charge density. Following the changes in conformation, the interchain hydrogen bonding takes place by placement of the carboxyl group outward
from the polymer backbone (Gilsenan et al. 2000; Mansel et al. 2015). The major
forces responsible for the stabilization of the egg-box structure are stabilization of
the egg-boxes formed between the two neighbouring chains are electrostatic interactions, hydrogen bonding and to a lesser extent by van der Waals interactions.
Overall the stabilization of the egg-boxes is brought by the forces in the order
electrostatic interactions ˃hydrogen bonding ˃Van der Waals interactions. The stability of the egg-boxes is dependent upon six consecutive carboxyl groups that is
present on the interior of each interacting chain (Powell et al. 1982). The formation
of the gel is hindered by the presence of methyl ester groups in the primary backbone. The transformation of LMP-calcium mixtures from a state of liquid to gel
with increasing G’ takes place as the DM decreases henceforth increasing the gel
strength. The probability of the formation of egg box structure is increased as the
DM increases which increases the length of the residues of non-mehtylated
GaIA. The stronger gel is formed with the formation of greater amount of “eggboxes”. Also the impact of calcium ions on the gel strength was studies and it was
reported by Dobies et al. (2004) that as the concentration of the calcium ions
increased, the value of G’ increased which in turn increased the strength of the
LMP-calcium gel. This mechanism of action lies in the fact that higher concentration of the calcium ions permits the formation of additional cross-links of nonmethylated GalA, which in turn create a more elastic and denser gel network
(Basak and Bandyopadhyay 2014). The addition of calcium or iron ions cab be
used as an alternative to thickening agents in fluids as these increase the pseudoplasticity. On the contrary addition of the magnesium ions can result in the formation of weak pectin gels as a consequence of decreasing G’. The dispersion of
LMP in aqueous calcium solution is carried out at 70 °C. This is followed by cooling the mixture slowly. At an elevated temperature, hydrophobic interactions
favour the egg-box structure via calcium bridging. Upon cooling there is an
increased interdimer associations that support the gel formation. The gel formation
is further encouraged by the electrostatic interactions of the single dissociated
carboxyl groups of pectin chains with calcium. Also just like in HMP gelation,
addition of sugar increases the inter-chain reactions in LMP gels. But with the
increase in the concentration of sugar, hydrogen bonding may be promoted as a
result of dehydrating effect of sugars which will in turn decrease the cross-linking
by calcium ions. This will overall have an adverse effect on LMP gels (Fu and
Rao 2001).
N. Noor et al.