We found that thermal stability of oil samples enriched with
unencapsulated olive leaf extract was higher than those samples
with nano-encapsulated olive leaf extract. These phenomena could
be explained by the fact that in oil samples containing encapsulated
antioxidants, some layer forming biopolymers (pectin and
WPC in our case) around dispersed emulsion droplets are covering
the antioxidants within them and prevent their anti-oxidant activity
in oil samples. In particular, a complex formation between pectin
and WPC at high temperatures results in a strong barrier which
does not allow permeation of phenolic compounds into oil medium
around dispersed droplets. This was verified by observing the lowest thermal stability for the oil samples containing
nano-encapsulated olive leaf extract with pectin–WPC (Fig. 2).
Armando, Maythe, and Beatriz (1998) indicated that a higher oil
oxidation at high temperatures could be due to an increases rate
of complex formation between biopolymers; while at low temperatures,
the effect of blocking does not exist or is negligible.