Several industrial fields use emulsifiers in their products, with the ones of natural
origin gaining increasing relevance. Identifying and using diversified sources for
their extraction is a pertinent topic regarding sustainability principles, biodiversity
preservation, or cost rationalization. This is the case of Quillaja bark saponin
(QS), for which saponin-rich extracts, for example, Tribulus terrestris (TT), are
being highlighted as viable alternatives, even though constraints like performance
are still on the table. In this context, an experimental design using binary
emulsifier mixtures of TT with pure QS was carried out by changing their composition
(50–90%wt. TT), content (1.5–4.5%wt.), and high-pressure homogenization
conditions (5–15 cycles). The emulsions were characterized by zeta
potential, morphology, droplet size, and stability (expressed as the number of
days without creaming formation). Moreover, the cream index for 30 days was
determined to indicate the destabilization extent. The zeta potential showed stable
emulsions (values below 41 mV); even still, creaming formed for samples
using a low emulsifier and high TT contents. The emulsions’ mean droplet diameter
(D [3, 2]) was between 78 and 921 nm, with smaller sizes agreeing with
higher stability. The statistical analysis indicated an optimum composition range
comprising an emulsifier content between 3.9 and 4.5%wt. and TT content
between 50 and 56%wt. to reach stable products. Overall, TT can provide an
effective solution when combined with QS, decreasing the dependence on
Quillaja bark.
The authors are grateful to the Foundation for Science
and Technology (FCT, Portugal) for financial support
through national funds FCT/MCTES (PIDDAC) to CIMO
(UIDB/00690/2020 and UIDP/00690/2020), SusTEC
(LA/P/0007/2021), LSRE-LCM (UIDB/50020/2020
and UIDP/00690/2020), and ALiCE (LA/P/0045/2020).
FCT for the PhD research grant of T.B. Schreiner
(2020.05564.BD). National funding by FCT, P.I.,
through the institutional scientific employment program
contract of A. Santamaria-Echart.
