Effect of cinnamaldehyde concentration on physicochemical properties of O/A nanoemulsions

Nanoemulsions are defined as colloidal systems, with average sizes on the nanometer
scale between 20 and 200 nm. In the food area, nanoemulsions have been used as
delivery systems for bioactive compounds, such as cinnamaldehyde. Cinnamaldehyde
is the major chemical compound in cinnamon essential oil. This compound has
recognized biological activity, especially antioxidant and antimicrobial activity.
However, cinnamaldehyde presents relative chemical instability to environmental and
processing conditions, allied to its high volatility, and reduced water-solubility, which
negatively impact the technical-functional properties presented by it. In this context,
the incorporation of cinnamaldehyde in nanoemulsions presents itself as an alternative
to maximize the physicochemical and biological stability, bioaccessibility and
bioavailability of this natural compound. Therefore, the objective of this study was to
evaluate the effect of cinnamaldehyde concentration on the physicochemical
properties of O/W nanoemulsions. The nanoemulsions were composed of a fixed mass
percentage of the surfactant tween 80 (1% m/m), deionized water and cinnamaldehyde
(0.5 to 6.0 % m/m). The nanoemulsified systems were produced by the high-energy
method with the aid of an ultrasonic cell disrupter at 90% amplitude and 4 cycles of 10
min. At the end of the process, the hydrodynamic diameter (HD), polydispersity index
(PDI), and zeta potential (PZ) were evaluated. The study was conducted in an entirely
randomized design, with two repetitions, in triplicate. The mean DH of the
nanoemulsions ranged from 61.89 to 213.54 nm. The nanoemulsions showed an
increase in DH with increasing cinnamaldehyde concentration. The substantial
increase in DH with the increase in concentration of the lipophilic component that
constitutes the dispersed phase in colloidal systems that present fixed values of the surfactant agent, promotes the formation of droplets without interfacial coverage of the
surfactant, which tend to regroup, Given its thermodynamic instability, coupled with
this, the high intensity turbulence generated by the sonochemical energy of ultrasound,
leads these droplets to collide with each other, regrouping and leading to the increase
of DH with the increasing concentration of the lipophilic component. The average PDI
of the cinnamaldehyde nanoemulsions ranged from 0.185 to 0.282. In general,
regardless of the concentration of cinnamaldehyde evaluated, the systems were
monodisperse, but it was possible to observe that the increase in concentration of
cinnamaldehyde promoted a slight positive effect on the PDI values. This behavior
corroborated what was expected and was directly related to the DH described
previously. The average PZ presented by the nanoemulsions ranged from -8.88 to -
18.05 mV. Progressive increases in cinnamaldehyde concentration, up to values close
to 4% (w/w) produced kinetically more stable nanoemulsions, given the progressive
and substantial increase in the distribution of surface charges at the interface of the
dispersed phase. However, above 4% cinnamaldehyde, the opposite behavior occurs.
Given the above, it was possible to evaluate the effect of cinnamaldehyde
concentration on DH, PDI and PZ in the colloidal systems obtained, with a positive
effect for DH and PDI with increasing cinnamaldehyde concentration and for PZ with
increments up to 4% (m/m).