3.3 Emulsion microstructure
All emulsions formed water droplets dispersed in the continuous oil
phase as a free and aggregated network. The control CO emulsions without
any additive (S0) showed a few larger droplets with some aggregation as
most droplets were destabilized phase-separated (Figure 3A). The
incorporation of S0.125 showed the initial appearance of extensive water
droplet network formation (dark irregular-shape matter in the image)
(Figure 3B). Such droplet aggregation also appeared with AA or CA
addition into the aqueous phase (Figure 3C, D and G, H). When S0.125%
was incorporated with AA (Figure 3E, F) and CA (Figure 3I, J), a more
extensive water droplet network structure was identified, where free
droplets were hard to locate in the continuous phase. It can be said
that the water droplet network’s extension was responsible for their
higher emulsion height (Figure 1 and 2). Similar water droplet
aggregation was also observed for W/O emulsions stabilized with Span 80
and lecithin emulsifiers (Ushikubo & Cunha, 2014).
MO-emulsions without any aqueous phase additive (S0) showed water
droplets well distributed in the continuous phase (Figure 4A). Similar
to CO emulsion, the microstructure of MO-emulsions with S0.125 (Figure
4B), AA (Figure 4C, D) or CA (Figure 4G, H) also demonstrated a water
droplet network formation. The addition of S0.125% with AA or CA in
MO-emulsions developed an extensive water droplets network structure
similar to CO-emulsions.
The microstructure of emulsions formed with LMP and Ca are presented in
Figure 5. CO-emulsions without Ca (S0, Figure 5 I-A) and with Ca (Figure
5 I-B) showed dispersed water droplets with some degree of droplet
coalescence. The incorporation of LMP formed an extensive water droplets
network throughout the emulsion, making it challenging to capture the
emulsion’s clear images (Figure 5 I-C, I-D). However, the mixture of LMP
and Ca illustrated a different structure related to gel-formation due to
the interaction between calcium ions and the carboxyl groups in the
pectin molecules (Yuliarti & Othman, 2018). The structure formed by
LMP-Ca in the aqueous phase can coexist with the water droplet network
(Figure 5 I-E, I-F). All MO-emulsions, in the presence of LMP (with or
without Ca) (Figure 5 II-B, II-A), also formed an extensive water
droplets network compared to the emulsions without LMP (Figure 5 II-C,
II-D). Comparing the CO and MO-emulsions with LMP, it can be said that
the presence of MO led to a finer droplet network that was better able
to provide emulsion stability against phase separation. Overall, CO and
MO-emulsions with LMP (Figure 5) showed a more expanded water droplets
network of smaller water droplets than the emulsions with S, AA, CA, or
their mixture (Figures 3 and 4). Such droplet networks could be
responsible for increasing emulsion stability against phase separation
reported in Figures 1 and 2.