摘要：The content of polyphenolic 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 tangent method. Oil
samples emulsified with ethanolic onion extracts showed an extension of the
induction period. A 7 day ageing study at 45℃ 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
absorbances 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.
