TITLE:
Evaluation of the Antioxidant Activity of Ethanolic Extracts of Some Varieties of Onions
AUTHORS:
María del Carmen Gutierrez, Patricia Della Rocca, Elizabeth De Seta, Fernando Reina
KEYWORDS:
Onion; Antioxidant Activity; Polyphenolic; Ethanolic Extracts; Emulsified Oil
JOURNAL NAME:
Journal of Agricultural Chemistry and Environment,
Vol.3 No.2B,
May
2,
2014
ABSTRACT: The content of
polyphenolic substances in commercial onions has been determined. The antioxidant
activity of their ethanolic extracts, as well as their effects on the oxidation
of edible corn oil during accelerated ageing was studied. Maceration of
taxonomically identified commercial vegetable samples, previously peeled and
thinly sliced, was carried out at ambient temperature, out of direct light,
with occasional agitation and ultrasound, employing 95% ethyl alcohol as the
extraction solvent, allowing them to stand for 7 days. The total polyphenolic
contents were determined on the filtrated extracts using the Folin-Ciocalteau
method. The antioxidant activity was evaluated on emulsions of ethanolic
extracts of onion prepared in edible commercial corn oil, using sorbitan
monooleate as emulsifying agent. The peroxide values were analyzed using the
iodometric method; oxidation induction times were obtained from the peroxide
evolution graphs, using the tan- gent method. Oil samples emulsified with
ethanolic onion extracts showed an extension of the induction period. A 7-day
ageing study at 45?C was additionally performed to determine the conjugated
dienes on pure commercial corn oil and its emulsions by visible
spectrophotometry. The spectral analysis showed an increase of the measured
absorbancies in oil samples without additives and no change for the oils
emulsified with onion extract. An increasing of diene values was observed for
corn oil without additives during ageing; no changes in the value were observed
in oils emulsified with onion extracts.