Novel Processing Technologies for Fruits - Tropical and Subtropical Fruits: Postharvest Physiology, Processing and Packaging - page 78

of total carotenoids dropped by 12.6% when the juice
was thermally pasteurized, whereas the decrease was only
6.7% when the juice was treated with PEF. Similar re-
sults were observed for vitamin A (15.62% and 7.52%
for HTST and PEF, respectively). The decrease in the
concentrations of total carotenoids and vitamin A during
storage in refrigeration was greater in the untreated orange
juice and the pasteurized juice than in the juice treated with
PEF. Pasteurized orange juice had greater yellow tendency
( b ∗ ) and less red tendency ( a ∗ ) than the untreated orange
juice, while PEF orange juice had a coloration more similar
to the untreated orange juice. Color difference values ( E )
during storage were greater in HTST orange juice than the
PEF-treated one. The orange juice with no thermal treat-
ment had less nonenzymatic browning than the pasteurized
one. There were no significant variations in the HMF con-
tent of the juices pasteurized or treated by PEF with respect
to the untreated orange juice; during refrigerated storage,
HMF was always below the maximum values established.
HIPEF was applied to watermelon juice using a re-
sponse surface methodology (Oms-Oliu et al., 2009). The
selected responses were lycopene, vitamin C, and antioxi-
dant capacity. The independent variables were electric field
strength (from 25 to 35 kV/cm), pulse frequency (from
50 to 250 Hz), pulse width (from 1 to 7 μ sec), treatment
time (from 50 to 2050 μ sec), and polarity mode (monopolar
or bipolar). Juices treated at 25 kV/cm for 50 μ sec at 50 Hz
using mono- or bipolar 1 μ sec pulses exhibited the high-
est vitamin C retention (96.4-99.9%). A significant loss of
vitamin C ( > 50%) was observed when HIPEF treatment
was set up at 35 kV/cm for 2050 μ sec at 250 Hz applying
mono- or bipolar 7 μ sec pulses. Pulse polarity, electric field
strength, pulse frequency, pulse width, and treatment time
affected vitamin C retention of fruit juices after HIPEF pro-
cessing. The lycopene content was slightly higher than that
of untreated samples when HIPEF treatments set up at 35
kV/cm with pulses of 250 Hz. However, the application of
35 kV/cm at low frequency led to a decrease in the lycopene
content of treated watermelon juice of up to 10-12% com-
pared to the fresh fruit juice. Maximal lycopene content
of 114% in watermelon juice was achieved with 7 μsec
bipolar pulses for 1,050 μsec at 35 kV/cm and frequencies
ranging from 200 to 250 Hz. Antioxidant capacity reten-
tion of HIPEF-treated watermelon juice ranged from 78%
to 106%.
Aguil o-Aguayo et al. (2010) studied the effects of HIPEF
processing (35 kV/cm for 1727 μ sec applying 4 μ sec pulses
at 188 Hz in bipolar mode) on color and viscosity in wa-
termelon juice during 56 days of storage in polypropylene
bottles and compared to thermal treatments (90 ◦ C for 30-

60 sec). HIPEF treated juice maintained brighter red color
than thermally treated juices along the storage time. In ad-
dition, the application of HIPEF as well as heat at 90 ◦ C
for 60 sec led to juices with higher viscosity than those
untreated for 56 days of storage.

Microbial inactivation
The PEF processing has a unique way to inactivate
certain types of micro-organisms. Since its effectiveness
on the micro-organisms widely varies, it is important to de-
termine the processing conditions and factors that affect the
microbial inactivation. Some of those factors can be catego-
rized under three main groups: (1) processing factors: treat-
ment time, temperature, electric field intensity, pulse width,
and pulse wave shapes; (2) microbial factors: type of micro-
organism, microbial load, and the age of micro-organisms;
and (3) environmental factors: pH, antimicrobials and ionic
compounds, conductivity, and medium ionic strength. The
effects of critical process factors on pathogens of concern
and kinetics of inactivation are not well defined and may
be considered as investment risk.
Inactivation of L. brevis (10 8 CFU/ml) on samples of
orange juice was compared in PEF and HTST continuous
flow systems (Elez-Martınez et al., 2005). PEF processing
of orange juice was more effective in inactivating L. brevis
than HTST. L. brevis destruction was higher when the elec-
tric field strength and the treatment time increased, and also
when the pulse frequency and the pulse width decreased. A
5.8 log reductions of L. brevis was observed when inocu-
lated orange juice was processed at 35 kV/cm for 1,000 μ sec
using 4 μ sec pulse width in bipolar mode and 200 Hz at
less than 32 ◦ C. Electron microscopy revealed mechanical
breakdown of cell walls of the sample processed by PEF.
Microbial inactivation in watermelon and melon juices
under PEF was reported by Mosqueda-Melgar et al. (2007).
Juices were inoculated with Salmonella enteritidis, Listeria
monocytogenes and Escherichia coli to give a final concen-
tration of 10 7 10 8 CFU/ml approximately of each one. The

application of PEF treatment to E. coli populations induced
maximum reductions up to 3.91 (at 1,250 μsec) and 4.01 (at
2,000 μsec) log10 units in melon and watermelon juices, re-
spectively, when 250 Hz was used. L. monocytogenes was
reduced by 4.27 (at 100 Hz) and 3.77 (at 250 Hz) log10
units in melon and watermelon juices, respectively, when
2,000 μ sec treatment time was used. Maximum reductions
of 3.75 (at 1,250 μ sec and 175 Hz) and 4.27 (at 2,000 μ sec
and 100 Hz) log10 units of S. enteritidis were achieved in
melon and watermelon juices, respectively. Among three
micro-organisms, L. monocytogenes was found to be more

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