To induce the electro-deposition of pectin onto surface of NaCas
nanoparticles, pH adjustment and thermal treatment are needed to
trigger the electrostatic interactions between negatively charged
carboxylate groups of pectin and positively charged amino acid
residues of NaCas.
Fig. 2 showed the characterizations of the formulations
at three different pHs
Both formulations followed thesimilar trend regarding the changes of particle size, PDI, and zeta
potential.
The particle size had no significant difference upon the
pH reduction for both formulations.
After thermal treatment,
however, the particle size was greatly increased.
The formulation 2
(Fig. 2B) exhibited a mild increase without statistical significance,
while the increase in particle size was significant upon heating
under all pH conditions in formulation 1 (Fig. 2A).
Compared to
particle size, the changes in PDI followed the opposite trend (Fig. 2C
and 2D).
PDI was greatly increased to 0.35e0.40 upon the initial pH
reduction, and then significantly decreased to about 0.20e0.25
upon thermal treatment.
This indicated that without heating,
pectin was only loosely attached or adsorbed onto the surface of
NaCas/peppermint oil nanoemulsion droplets which is perhaps the
cause of a high PDI
However, heating process greatly facilitated the
electrostatic interactions between pectin and NaCas, and promoted
the formation of compact and homogeneous particles, evidenced
by significant reduction in their PDI.
Similar phenomenon was also
reported in previous studies
In both formulations, the absolute value of zeta potential
was gradually and significantly decreased upon pH reduction,
however, the thermal treatment did affect the zeta potential
(Fig. 2E and 2F
As pH became more acidic, more positively charged
amino acid residues were exposed and available to interact with
pectin, resulting in the neutralization of the overall negative
charges of the nanocomplex particles.