142
Solution Behaviour
When pectin is homegenoulsy dispersed in water, the molecules of pectin which are
far apart from each other do not interact with each other, and the effect of this dispersion is seen only as a slight increase in viscosity. This increase of viscosity may
be attributed to the increased proportion of hydrated molecules which causes the
distortion in the velocity pattern of the liquid (Guimarães et al. 2009). As we
increase the concentration of pectin, the viscosity of the solution increases and this
pattern has been observed for pectin from citrus peel (Sousa et al. 2015), tamarillo
fruit pulp (do Nascimento et al. 2016), dragon fruit peel (Muhammad et al. 2014),
mango pulp (Iagher et al. 2002), apple pomace and cacao pod husks (Vriesmann
and Petkowicz 2013). An increase in the concentration results in the decrease of the
intermolecular distances between pectin molecules which provides a platform for
intermolecular interactions such as hydrogen bonding. When a graph is plotted
between shear stress and shear rate of the pectin solutions, it is observed that pectin
solutions demonstrate a Newtonian behaviour (Fig. 5), but only up to a certain concentration. At concentrations upto 3%, these dispersions exhibit characteristics of
Newtonian liquids and when the concentration of pectin is increased, these
Newtonian liquids may display shear thinning behaviour i.e. with the increase in
shear rate the viscosity of the solution decreases.
Here the most important factor is the molecular weight of pectin which determines the concentration of pectin at which the transformation from Newtonian to
shear thinning takes place. However many studies have reported an increase in
pseudoplasticity with an increase in pectin concentration (Muhammad et al. 2014;
do Nascimento et al. 2016; Sato et al. 2008; Sousa et al. 2015).
Gel Forming Ability of Pectin
Pectin gel consists of a three-dimensional (3D) network of polymer chains with
solvent and solutes trapped within. The formation of the gel is dependent upon the
molecular structure, the behaviour of junction zones which form the site of polymer
crosslinking, and the intermolecular forces which are responsible for holding the
network together (Axelos and Thibault 1991a). In case of high molecular weight
polysaccharides like pectins, complexity arises at the junction zones. As such a
number of individually weak interactions like hydrogen bonds and electrostatic
interactions between molecular structures come into play. The solution behaviour of
the pectin polysaccharides like HMP and LMP is different although the macromolecular properties like, composition, size and conformation have the same effect on
the characteristics of the gel.
N. Noor et al.
Solution Behaviour
When pectin is homegenoulsy dispersed in water, the molecules of pectin which are
far apart from each other do not interact with each other, and the effect of this dispersion is seen only as a slight increase in viscosity. This increase of viscosity may
be attributed to the increased proportion of hydrated molecules which causes the
distortion in the velocity pattern of the liquid (Guimarães et al. 2009). As we
increase the concentration of pectin, the viscosity of the solution increases and this
pattern has been observed for pectin from citrus peel (Sousa et al. 2015), tamarillo
fruit pulp (do Nascimento et al. 2016), dragon fruit peel (Muhammad et al. 2014),
mango pulp (Iagher et al. 2002), apple pomace and cacao pod husks (Vriesmann
and Petkowicz 2013). An increase in the concentration results in the decrease of the
intermolecular distances between pectin molecules which provides a platform for
intermolecular interactions such as hydrogen bonding. When a graph is plotted
between shear stress and shear rate of the pectin solutions, it is observed that pectin
solutions demonstrate a Newtonian behaviour (Fig. 5), but only up to a certain concentration. At concentrations upto 3%, these dispersions exhibit characteristics of
Newtonian liquids and when the concentration of pectin is increased, these
Newtonian liquids may display shear thinning behaviour i.e. with the increase in
shear rate the viscosity of the solution decreases.
Here the most important factor is the molecular weight of pectin which determines the concentration of pectin at which the transformation from Newtonian to
shear thinning takes place. However many studies have reported an increase in
pseudoplasticity with an increase in pectin concentration (Muhammad et al. 2014;
do Nascimento et al. 2016; Sato et al. 2008; Sousa et al. 2015).
Gel Forming Ability of Pectin
Pectin gel consists of a three-dimensional (3D) network of polymer chains with
solvent and solutes trapped within. The formation of the gel is dependent upon the
molecular structure, the behaviour of junction zones which form the site of polymer
crosslinking, and the intermolecular forces which are responsible for holding the
network together (Axelos and Thibault 1991a). In case of high molecular weight
polysaccharides like pectins, complexity arises at the junction zones. As such a
number of individually weak interactions like hydrogen bonds and electrostatic
interactions between molecular structures come into play. The solution behaviour of
the pectin polysaccharides like HMP and LMP is different although the macromolecular properties like, composition, size and conformation have the same effect on
the characteristics of the gel.
N. Noor et al.