Conclusions
Onion total phenols, flavonol content, and antioxidant activity
were affected by pressure and temperature variables of the 10 highpressure
processing treatments selected in our study.
Our results showed that processing onion (Allium cepa L. var.
cepa, ‘Grano de Oro’) with treatments that combine low temperature
(5 C) with pressures of 100 and 400 MPa at a constant time
(5 min) significantly increased the extractability of quercetin-40-
glucoside, total quercetin, and quercetin-3,40-diglucoside, yielding
an increase in their contents of 33, 26, and 17%, respectively,
compared with untreated onion. Low temperature (5 C) and high
pressure (400 MPa) treatments increased the extractability of total
phenol from onion. Moreover, processing onion at low (5 C) and
medium (27.5 C) temperatures combined with a high pressure of
400 MPa maintained the antioxidant activity of untreated onion. It
was shown a clear trend towards an increase in antioxidant activity
in pressurised onion from 100 to 400 MPa.
Concluding, in our study it was shown that processing onion at
400 MPa/5 C could represent a good high-pressure treatment that
would increase total phenol and flavonol extractability compared
with untreated onion. Processing onion at 400 MPa/5 C would
maintain the antioxidant capacity of the untreated onion. Thus,
400 MPa/5 C-processed onion would improve nutritional functionality
of fresh onion and would retain fresh onion antioxidant
activity.
Further studies would have to be done in order to establish the
optima range of pressures and temperatures that maintain onion
antioxidant activity and achieve higher bioactive compound
extractability compared with untreated onion. Bioavailability of
onion bioactive compounds that might be extracted during highpressure
processing would have to be studied in depth.