4. Conclusion
In this project we investigated the use of phenolic compounds
obtained from grape seed and apple as emulsion and antioxidant
stabilizers. This first study showed that oxidized grape seed
tannins can be used to stabilize oil in water emulsion. Tannin
structure plays an important part on emulsion properties: best
candidates are relatively high molecular weight tannins, which
underwent oxidation reactions (i.e. their chemical structure, and
thus their solution properties are different from initial molecules).
Emulsions stabilized with tannins were compared with emulsions
obtained in the same conditions using model emulsifiers as PVA
and with Eumulgin . In certain physicochemical conditions, the
oxidized tannins allowed to obtain a stability equivalent to that
of the PVA. The oil in water formed emulsions were up to 50% of
methyloleate, with drop mean sizes in the micrometer range.
Emulsion stabilization appeared to be due to electrostatic repulsions
at high pH’s ( pKa), and emulsion breaking was mainly
due to droplet flocculation, as observed by laser granulometry
experiments. At pHpKa, emulsion stabilization would be due
to steric repulsions and/or stabilization by tannin aggregates. It
was demonstrated for the first time, that depending on their origin,
concentration, and oxidation degree, tannins presented good antioxidant
activity in oil in water emulsions, and thus they protect oil
against oxygen damages. Grape seed tannins presented a higher
antioxidant activity than the apple ones (G15ox > A6 > A15ox)
measured by the CAT test. This research shows the potential use
of the winery and distillery by-products and wastes for the production
of high added value extracts rich in oxidized tannins that
could be used as antioxidants emulsifiers.