2.2. Selection of gelators and emulsifier
Monolaurin and MAG/DAG mixture were selected as gelators through initial
screening tests against other plausible gelators. Typically, a
combination of gelators with different HLB values is ideal due to the
improved physical properties seen in developed gels (Co & Marangoni,
2012). However, combining different gelators such as sucrose stearates,
DAG and TAG combinations, and select phytosterols all exhibited a
lowered ability to adequately form gels with algal oil and oil-in-water
(O/W) emulsions. Other gelators including monolaurin and the MAG/DAG
mixture were tested at a higher concentration than those used for the
purpose of this study, at 15% w/w. This cursory test acted as a
screening to find the best gelator for algal oil and O/W emulsion.
Monolaurin and the MAG/DAG mixture not only developed a stable gel at
15%, w/w, concentration but also formed promising oleogels and emulgels
at decreased concentrations as well.
The selection of emulsifier and emulsifier concentration for O/W
emulsions followed parameters set forth elsewhere (Hyatt, Zhang, &
Akoh, 2021). First, the interfacial and surface tension of four selected
emulsifiers at three concentrations, 0.1, 0.5, and 1.0% were determined
via a CSC-DuNouy Interfacial Tensiometer Model 70545 (CSC Scientific
Company, Fairfax, VA) following parameters discussed in a previous study
(Akoh, 1992). Interfacial and surface tensions were measured in order to
determine potential stability of different emulsifiers at varying
concentrations for developed emulsions (Bourrel, Graciaa, Schechter, &
Wade, 1979). Additionally, particle size analysis was performed on
sample emulsions following parameters mentioned elsewhere (Kowalska &
Żbikowska, 2016). Particle size analyses were carried out using a
Malvern Panalytical Mastersizer S (Malvern Panalytical Ltd, Malvern, UK)
with a small volume sample dispersion unit. Data analysis was completed
using the Mastersizer software (Malvern Panalytical Ltd, Malvern, UK).
Overall, the best performing emulsifier and concentration was S1170 at a
concentration of 0.5% (w/w/w) with 5% algal oil and 94.5% deionized
water. Emulsions developed using S1170 at 0.5% concentration had the
smallest initial particle size with an average of 0.481 µm, and the
lowest interfacial and surface tensions with averages of 7.9 and 46.6
dynes/cm, respectively. These values were significantly different from
the results of other combinations of emulsifier and concentration.