Impact of pulsed light treatment on quality characteristics and oxidative stability of fresh-cut avocado

1. Impact of pulsed light treatments on quality characteristics and
oxidative stability of fresh-cut avocado
Ingrid Aguiló-Aguayo 1,2
, Gemma Oms-Oliu 2
, Olga Martín-Belloso 2
,
Robert Soliva-Fortuny*
Department of Food Technology, University of Lleida e Agrotecnio Center, Av. Alcalde Rovira Roure 191, 25198 Lleida, Spain
a r t i c l e i n f o
Article history:
Received 5 August 2013
Received in revised form
23 April 2014
Accepted 25 April 2014
Available online 4 May 2014
Keywords:
Pulsed light
Fresh-cut avocados
Microbiological stability
Chlorophylls
Lipid oxidation
a b s t r a c t
Fresh-cut avocado pieces were subjected to pulse light (PL) treatments on both sides (3.6, 6.0 and 14 J/
cm2
per side) with the purpose of evaluating their effect on the microbial burden, color, chlorophyll
stability and lipid oxidation for 15 days of storage at 4
C.
Exposure of fresh-cut avocado to the highest dose led to the highest reductions in aerobic mesophylic
microorganisms (1.20 log CFU/g) and inhibited the proliferation of yeasts and molds for 3 days, pro-
longing their microbiological shelf life up to 15 days. Hue values of fresh-cut avocados were better
maintained after applying PL treatments. This behavior was partially related with the high chlorophyll
retention observed in the same PL-treated samples. In fact, an increment up to around 1.3-fold of
chlorophyll a and b was observed after applying 6.0 J/cm2
to fresh-cut avocados. The lipidic fraction of
fresh-cut avocados subjected to PL treatments exhibited minimal peroxide formation and stable specific
extinction coefficients at 232 and 272 nm for 15 days. These results indicate that the treatments did not
result in an increase of rancidity processes, which remained at the induction stage.
Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction
Avocado (Persea americana Mill.) is a fruit with an outstanding
taste and creamy texture. Its lipidic content, which is predominantly
constituted by monounsaturated fatty acids, provides potential
health benefits in preventing cancer and cardiovascular diseases
(Awad Fink, 2000; Plaza, Sánchez-Moreno, De Pascual-Teresa, De
Ancos, Cano, 2009). Unfortunately, the shelf-life of avocado is
severely determined by both microbial spoilage and oxidative pro-
cesses (Elez-Martínez, Soliva-Fortuny, Gorinstein Martín-Belloso,
2005; Wong, 1989, pp. 229e245; Yahia Gonzalez-Aguilar, 1998).
Most of the quality changes observed throughout storage of avocado
pulp are the result of enzymatic browning, catalyzed by polyphenol
oxidase, and lipid oxidation, involving the production of peroxides
and other secondary products through an oxygen attack on the
unsaturated fatty acids (Gunstone Norris, 1982, pp. 95e139;
Soliva-Fortuny, Grigelmo-Miguel, Odriozola-Serrano, Gorinstein,
Martín-Belloso, 2001). This process results in rancidity and
subsequent production of undesirable flavors and quality losses. On
the other hand, pigments such as chlorophylls are also important
contributors to the appearance and health-promoting properties of
avocado (Ashton et al., 2006; Lassen, Bacon, Sutherland, 1944).
Nevertheless, the presence of naturally occurring chlorophyll pig-
ments promotes the photooxidation of avocado oil under lighted
conditions. Singlet oxygen is produced and reacts with unsaturated
fatty acid which forms hydroperoxides. The decomposition of these
hydroperoxides initiates a free-radical type of autooxidation
inducing color changing (Werman Neeman, 1986).
Minimal processing techniques, including the addition of pre-
servatives from synthesis sources have been proposed to extend
shelf life and marketability of fresh-cut avocados (Dorantes-Alvarez
et al.,1998; Elez-Martínez et al., 2005; Guzmán-Gerónimo, López,
Dorantes-Alvarez, 2008; Soliva-Fortuny et al., 2001). As an alter-
native strategy, emerging non-thermal technologies including
Pulsed light (PL) is under study for their great potential in
extending shelf life of fresh-cut products without compromising
their nutritional value (Aguiló-Aguayo, Charles, Renard, Page,
Carlin, 2013; Charles, Vidal, Olive, Filgueiras, Sallanon, 2013;
Gómez, García-Loredo, et al., 2012; Oms-Oliu, Aguiló-Aguayo,
Martín-Belloso, Soliva-Fortuny, 2010; Ramos-Villarroel, Aron-
Maftei, Martín-Belloso, Soliva-Fortuny, 2012; Ramos-Villarroel,
Aron-Maftei, Martín-Belloso, Soliva-Fortuny, 2014). PL involves
* Corresponding author. Tel.: þ34 973 702678; fax: þ34 973 702596.
E-mail address: rsoliva@tecal.udl.cat (R. Soliva-Fortuny).
1
Present address: IRTA, XaRTA-Postharvest, Edifici Fruitcentre, Parc Científic i
Tecnològic Agroalimentari de Lleida, Parc de Gardeny, 25003 Lleida, Spain.
2
Tel.: þ34 973 702593; fax: þ34 973 702596.
Contents lists available at ScienceDirect
LWT - Food Science and Technology
journal homepage: www.elsevier.com/locate/lwt
http://dx.doi.org/10.1016/j.lwt.2014.04.049
0023-6438/Ó 2014 Elsevier Ltd. All rights reserved.
LWT - Food Science and Technology 59 (2014) 320e326

2. the use of short-time high-peak pulses of bread-spectrum white
light on the surface of either foods or packaging materials. Ac-
cording to Woodling and Moraru (2005), it is the UV portion of the
spectrum that plays the main role in microbial inactivation.
The most crucial challenge of PL processing is to optimize the
processing conditions to extend shelf-life of fresh-cut products,
while assuring appropriate quality. Hence, the present research
examines the impact of PL treatments in aspects related to the
shelf-life of fresh-cut avocados including microbial growth, quality
attributes and oxidative stability of the lipid fraction.
2. Material and methods
2.1. Fresh-cut avocado preparation
Avocados (var. Hass) were purchased unripe at a local market and
maintained under controlled conditions at 10 C until they reached
the desired level of ripeness, as defined by Soliva-Fortuny, Elez,
Sebastián, and Martín (2000) (Table 1). The whole fruits were
rinsed with chlorinated tap water. As well, any surface and tool in
contact with the fruit (working area, cutting blades and gloves) were
washed and disinfected with a solution of sodium hypochlorite con-
taining 200 ppm of free chlorine (pH 7). Avocados were peeled, the pit
was removed and the flesh was cut into pieces of
3.0 cm  1.5 cm  1.5 cm. CIELAB values of the fruit flesh were
determined with a colorimeter (Konica Minolta Sensing, Inc., Chroma
Meter Model CR-400, Osaka, Japan). The firmness was determined
using a TA-XT2 texturometer (Stable Micro Systems Ltd., Surrey, En-
gland, UK) by measuring the force required for a 4-mm-diameter
probe to penetrate to a depth of 10 mm into an avocado piece.
Determination of pH (Crison Instruments S.A., Crison 2001 pH-meter,
Alella, Barcelona, Spain) and soluble solids content (Atago Company
Ltd, Atago RX-1000 refractometer, Atago, Japan) were also carried out.
2.2. PL treatments and packaging
PL treatments were carried out with an automatic laboratory
flash lamp system which comprises two xenon lamps individually
and symmetrically located above and below the chamber (Ster-
iBeam Systems GmbH, SteriBeam XeMaticA-2L, Kehl, Germany). Six
pieces of avocado (approximately 25 g) were placed on a poly-
propylene trays of 500 m3
(MCP Performance Plastic Ltd., Kibbutz,
Hamaapil, Israel) that allows full transmission of the light spec-
trum. One tray was treated at a time. The tray was placed in a
sample holder at a distance of 5 cm between the flash lamps. The
emitted spectrum ranged from 200 to 1100 nm with 15% to 20% of
the light in the UV region. The duration of one pulse emitted by
each lamp was 0.3 ms with a fluence of 0.4 J/cm2
. The total light
energy reaching the sample was calculated according to photo-
diode readings at the sample holder. Measurements were cali-
brated with a standard light source and the overall fluence per
pulse was estimated following manufacturer’s directions. Both av-
ocado sides were simultaneously treated with 9, 15 and 35 pulses,
corresponding to fluences of 3.6, 6.0 and 14 J/cm2
emitted per lamp
to each sample side.
Once treated, trays were sealed with a 64 mm-thick poly-
propylene film with an oxygen permeability of
110 cm3
mÀ2
dayÀ1
barÀ1
at 23 C and 0% RH (Tecknopack SRL,
Mortara, Italy) using a vacuum compensated packing machine
(ILPRA Systems España, S.L., ILPRA Food Pack Basic V/6, Mataró,
Spain). The packages were stored for 15 days at 4 Æ 1 C in darkness
up to random withdrawal for analysis.
2.3. Microbiological analyses
Total aerobic mesophilic and yeast and mold populations on
fresh-cut avocados were evaluated during refrigerated storage. At
each sampling time, two replicate packages were withdrawn and
their content was homogenized. Portions of 10 g of avocado were
crushed in sterile conditions for 2 min with 90 ml of peptone water
(0.1 g/100 ml) (Scharlau Chemie, S.A., Barcelona, Spain) with a
Stomacher Lab Blender 400 (Seward Medical, London, England).
Two trays were taken at each sampling time throughout 15 days of
storage and two replicate analyses were performed from each one.
Serial dilutions of the obtained homogenates were poured in plate
count agar and chloramphenicol glucose agar (Biokar Diagnostics,
Beauvais, France) and incubated at 30 Æ 1 C for 72 h and at
25 Æ 1 C for 5 days for mesophilic aerobic bacteria counts (ISO
4833, 1991) and for yeast and mold counts (ISO 7954, 1987),
respectively.
2.4. Color evaluation
Color was measured with a colorimeter (Minolta Sensing Inc,
Minolta Chroma Meter Model CR-400, Osaka, Japan). The equip-
ment was set up for a D65 illuminant and 10 observer angle. Two
trays were taken at each sampling time throughout 15 days of
storage and triplicate analysis was carried out from each one. CIE L*
(lightness), a* (red-green) and b* (yellow-blue) parameters were
measured through reflectance values. These values were used to
calculate the hue angle (h) (Eq. (1)).
h ¼ arctan
b*
a*
(1)
2.5. Chlorophylls extraction and measurement
Chlorophyll extraction was carried out using a modification of
the method described by Lancaster, Lister, Reay, and Triggs (1997).
Chlorophylls were extracted from a sample of 0.5 g avocado with
5 ml of cold acetone containing 1 g/100 ml of calcium carbonate to
prevent degradation. The mixture was homogenized with an Ultra
Turrax T25 (IKAÒ
WERKE, Germany) for 30 s at maximum speed
and the homogenate was centrifuged at 15,000 Â g for 10 min at
4 C (Beckman Instruments Inc., Centrifuge AVANTIÔ J-25, Full-
erton, CA, USA). The total volume of the extract was measured and
its absorbance was recorded spectrophotometrically at 663 and
645 nm, using a 1 cm path cuvette (Cecil Instruments Ltd., Cecil CE
1010, Cambridge, UK). The concentrations of chlorophylls a and b
were calculated from equations (2) and (3), respectively
(Maclachlan Zalik, 1963).
Chlorophyl a ¼
ð12:3$A663 À 0:86$A645Þ$V
1000$d$w
(2)
Chlorophyl b ¼
ð19:3$A645 À 3:6$A663Þ$V
1000$d$w
(3)
Table 1
Physico-chemical characteristics of fresh Hass avocados before processing.
pH 6.72 Æ 0.02
Total acidity (g citric acid/100 g fruit pulp) 0.13 Æ 0.01
Soluble solids content (
Brix) 8.56 Æ 0.50
Pulp maximum penetration force (N) 0.453 Æ 0.012
Skin maximum penetration force (N) 9.0 Æ 0.1
Pulp color
L* 46.07 Æ 0.16
a* À19.70 Æ 0.38
b* 30.29 Æ 0.44
Results are the mean Æ SD of three measurements.
I. Aguiló-Aguayo et al. / LWT - Food Science and Technology 59 (2014) 320e326 321

3. where the contents of chlorophylls a and b are expressed in mg/g, V
is the volume of extract in ml, d is the length of light path in cm and
w is the fruit sample weight. Two trays were taken at each sampling
time throughout 15 days of storage and two replicate analyses were
performed from each one.
2.6. Oil analysis
2.6.1. Oil extraction
Avocado pulp was heated up to 60 C for 30 min and periodically
stirred to improve mechanical and enzymatic degradation of oil
cells (Elez-Martínez, Soliva-Fortuny, Martín-Belloso, 2007). Next,
avocado paste was centrifuged at 22,100 Â g for 30 min at 4 C
(Beckman Instruments Inc., Centrifuge AVANTIÔ J-25, Fullerton,
CA). The supernatant oil phase was separated from the aqueous
phase and filtered to remove impurities.
2.6.2. Lipid oxidation measurements
Peroxide values and specific extinction coefficient at 232 nm
(k232) nm and 270 nm (k270) were selected as markers for oxidative
deterioration of lipids during storage of PL-treated fresh-cut
avocados.
Peroxides were determined according to a modification of the
method proposed by García, Seller, and Pérez-Camino (1996) for
olive oil. A sample of 2 g avocado oil was placed in a 250 ml
Erlenmeyer flask, previously purged with nitrogen. The sample was
shaken and dissolved in 25 ml of a mix of acetic acid (60 ml/100 ml)
and chloroform (40 ml/100 ml) solution. Next, 1 ml of saturated
potassium iodide solution was added and the flask was placed in
darkness for 5 min. After that period, 75 ml of distilled water were
added and the mixture was titrated with 0.005 mol equi/L sodium
thiosulphate with a starch indicator solution (1 g/100 ml). Results
were expressed in milliequivalents of oxygen per kg of oil.
For the measurement of k232 and k270, an oil sample of 100 mg
was diluted to 10 ml in a graduated flask with cyclohexane (spec-
trophotometry grade). The sample was homogenized and absor-
bances at 232 nm and 270 nm were determined
spectrophotometrically (Cecil Instruments Ltd., model CE 1010,
Cambridge, U.K.) with a 1-cm-path quartz cuvette using pure
cyclohexane as a blank. Two trays were withdrawn at each sam-
pling time throughout 15 days of storage and two replicate analyses
were carried out from each one.
2.7. Data analysis
Statistical analysis was performed using Statgraphics plus v.5.1
software (Manugistics, Inc., Rockville, MA, USA). Data were
analyzed by multifactor analysis of variance and a Duncan multiple
range test was applied to determine differences among means with
a significance level of 5%.
3. Results and discussion
3.1. Effect of PL on microbial stability
PL treatments caused a reduction in the overall aerobic counts
on fresh-cut avocado (Table 2). The most significant reduction
(1.20 log CFU/g) was observed after exposing both sides of fresh-cut
avocados to total amount fluences of 14 J/cm2
. In contrast, 1.05 and
0.85 log reductions were achieved when applying doses of 3.6 and
6.0 J/cm2
, respectively. The microbiocidal effects of PL have been
demonstrated in different food products. One log reduction on the
microflora present in both skin and peduncle scar parts of tomato
fruit was obtained with a fluence of 4 J/cm2
(Aguiló-Aguayo et al.,
2013). These authors also observed that fluences of 2.2 J/cm2
allowed a 2.3 log reductions of Saccharomyces cerevisiae inoculated
onto the tomato surface. Recently, Ramos-Villarroel et al. (2012)
reported that PL treatments of 12 J/cm2
caused 3 and 2 log re-
ductions in the counts of Escherichia coli and Listeria innocua,
respectively, inoculated on fresh-cut mushrooms. According to
Oms-Oliu et al. (2010), PL treatments of 12 J/cm2
provided initial
inactivations of mesophylic aerobic microorganisms and fungi of
0.7 and 1.3 log cycles, respectively, in fresh-cut mushrooms. An
important microbial inhibition with log reductions from 0.21 to
2.04 was achieved after treating fresh-cut vegetables such as
spinach, celery, green paprika, soybean sprouts, radicchio, carrot,
iceberg lettuce, and white cabbage by delivering pulses for 45 s and
180 s with intensities of 7 J (Gómez-López, Devlieghere, Bonduelle,
Debevere, 2005). The mechanism of microbial inactivation by PL
has been explained through the photochemical effect inducing
structural changes in DNA of bacteria, viruses, and other pathogens,
thus preventing the cell from replicating (Takeshita et al., 2003).
Ramos-Villarroel, Martín-Belloso, and Soliva-Fortuny (2011a)
demonstrated that the antimicrobial action of PL against microor-
ganisms also involved the agglutination of the cytoplasmatic con-
tent, leading to a disruption of cell membranes.
Despite the reductions observed after processing, PL treatments
did not substantially extend the microbiological shelf-life of fresh-
cut avocados beyond two weeks (Table 2). In general, the prolifer-
ation of aerobic mesophilic microorganisms on PL-treated samples
was lower than on untreated samples. Microbial obtained for av-
ocado pieces subjected to different treatments sometimes overlap,
which could be partially explained by the shading effects caused by
irregularities in the product surface and overall geometry
(Woodling Moraru, 2005; Zacarías, Vaccari, Alfano, Irazoqui,
Imoberdorf, 2010).
On the other hand, yeast and mold growth was undetectable in
either untreated or treated samples just next to processing
(Table 2). Results seem to indicate that sanitizing treatments
greatly affected mold and yeast counts. Nevertheless, molds and
yeasts progressively became predominant on the fresh-cut product
surface during the week following processing. After those first days
of storage bacteria grew faster than fungi, probably as a result of the
modification of the in-package gas composition. Hence, yeast and
molds counts on both untreated and PL-treated avocados were kept
below 5 log (CFU/g) through 15 days of storage. According to
Table 2
Growth of aerobic mesophilic, yeast and molds (expressed as log CFU gÀ1
) on PL-
treated fresh-cut avocadoes stored for 15 days at 4 C.
Days Untreated 3.6 J/cm2
6.0 J/cm2
14 J/cm2
Aerobic mesophilic microorganisms
0 1.20 Æ 0.4aD
0.15 Æ 0.12aB
0.35 Æ 0.5aC
ndaA
3 2.25 Æ 0.15bD
2.22 Æ 0.7bC
1.84 Æ 0.3bB
1.39 Æ 0.12bA
5 3.70 Æ 0.8cC
2.50 Æ 0.3bA
3.86 Æ 0.16cD
3.60 Æ 0.14cB
7 6.40 Æ 1.12dD
3.00 Æ 0.3bA
4.20 Æ 0.8dC
3.50 Æ 0.10cB
11 7.15 Æ 0.13eC
4.03 Æ 0.12cA
4.40 Æ 0.13eB
4.40 Æ 0.10dB
15 8.17 Æ 0.3fC
7.47 Æ 0.21dB
7.39 Æ 0.4fB
6.50 Æ 0.7eA
Yeasts and molds
0 nda
nda
nda
nda
3 2.47 Æ 0.16bB
2.30 Æ 0.8cB
2.39 Æ 0.20bB
ndaA
5 3.30 Æ 0.25cBC
2.00 Æ 0.22bA
3.45 Æ 0.10cC
2.84 Æ 0.3bB
7 3.60 Æ 0.5dA
3.17 Æ 0.3cA
3.57 Æ 0.12cA
3.54 Æ 0.5cA
11 3.62 Æ 0.5dA
3.69 Æ 0.3eA
4.15 Æ 0.23dB
3.66 Æ 0.17cA
15 4.54 Æ 0.15eA
4.25 Æ 0.18eA
4.31 Æ 0.11dA
4.47 Æ 0.10dA
Data shown are the mean of two replicate measurements obtained from two
replicate packages Æ standard deviation.
Nd: Not detectable.
Values within a column followed by the same lowercase letter are not significantly
different by Duncan’s multiple-range test (P 0.05).
Values within the same line followed by the same uppercase letter are not signifi-
cantly different by Duncan’s multiple-range test (P 0.05).
I. Aguiló-Aguayo et al. / LWT - Food Science and Technology 59 (2014) 320e326322

4. Jacxsens, Devlieghere, Falcato, and Debevere (1999), spoilage of
fresh-cut fruits and vegetables is usually detected by consumers
when yeast counts reach levels above 5 log (CFU/g). PL doses of 14 J/
cm2
inhibited the proliferation of yeasts and molds in fresh-cut
avocado for 3 days, although differences among treatments dur-
ing storage were very slight (Table 2).
Our results contrast with those reported in PL-treated mush-
rooms, where the application of high doses of 28 J/cm2
extended
the shelf-life of samples up to 15 days (Oms-Oliu et al., 2010). Re-
sults reported by Izquier and Gómez-López (2011) are more in line
with our results. They observed that the application of fluences up
to 6.3 J/cm2
led to the minimal counts of naturally-occurring mi-
croorganisms on iceberg lettuce, white cabbage and Julienne-style
cut carrots. They reported no advantage of prolonging PL treat-
ments beyond the indicated fluence because no additional inacti-
vation is achieved, and there is a risk that samples get deteriorated
by the treatment. On the other hand, Ramos-Villarroel et al. (2014)
studied the bacterial inactivation in fresh-cut avocado as affected
by PL of specific spectra. They observed that PL treatments without
UV-C light (305e1100 nm) and an overall fluence of 10.68 J/cm2
caused reductions of 2.47 and 1.35 log CFU/g in the initial counts of
inoculated E. coli and L. innocua, respectively, in comparison with
those treated using only VIS-NIR light. These results suggest that
the bactericidal effects of PL may greatly depend upon several
factors such as the product to be treated, the amount of energy,
wavelength and type of microorganism.
PL treatments have good prospects for becoming an alternative
to traditional methods for decontamination of food surfaces.
However, more efforts for studying specific conditions for treat-
ment and storage of fresh-cut commodities should be explored in
order to enhance the shelf-life and quality attributes of the product.
3.2. Effect of PL on color and chlorophylls
Color parameters of fresh-cut avocados as affected by different
PL treatment conditions are shown in Fig. 1. Lightness (L*) is the
most indicative parameter associated with avocado enzymatic
browning (Gómez-López, 2002). Initial L* values of untreated fresh-
cut avocado was 49.68 Æ 0.54. Relative changes in lightness showed
a significant decrease in L* values in both untreated and PL-treated
samples for 15 days, thus indicating that oxidative browning was
evident during storage regardless the applied treatment (Fig. 1A).
Fruit flesh darkening is triggered by a decompartmentalization
process allowing substrates, phenolic compounds, to come into
contact with tyrosinase (Jolivet, Arpin, Wichers, Pellon, 1998).
Light microscopy observations in PL-treated apples confirmed that
color modifications were ascribed to the breakage of cellular
membranes, which would cause a loss of functional cell compart-
mentalization, increasing enzyme-substrate contact with the
consequent increase in tissue browning (Gómez, Salvatori, García-
Loredo, Alzamora, 2012). The modification on color generally
reported in PL-treated products, has led to recommend the appli-
cation of antibrowning agents before PL flashing (Gómez, García-
Loredo, et al., 2012). Ramos-Villaroel et al. (2014) reported that
treatments with greater contamination effect also caused a steeper
increase in the respiratory activity of cut avocado, speeding up
processes associated with quality decay. The application of com-
pounds to stabilize color of PL-treated fresh-cut avocado could
substantially help to extend the shelf-life of the fresh-cut product.
Namely, the use of L-cysteine has been recommended as a good
alternative to prevent color changes during the commercial shelf
life of PL-treated fresh-cut avocados (Ramos-Villarroel, Martín-
Belloso, Soliva-Fortuny, 2011b).
Untreated fresh-cut avocado exhibited a hue angle (h) value of
122.5 Æ 3.0. Although enzymatic browning in fresh-cut avocados did
not seem to be avoided through the application of PL treatments,
results showed that PL-treated samples better maintained hue angle
(h) values over time than untreated avocado pieces. Namely, fresh-
cut avocados subjected to a fluence of 14 J/cm2
exhibited the highest
relative hue values (0.95 Æ 0.03) after 7 days of storage (Fig. 1B).
Fig. 2 shows that chlorophyll content was better maintained by
PL processing. Analysis revealed that chlorophyll a was predomi-
nant in fresh-cut avocado samples (Fig. 2A and B). In fact, differ-
ences among PL treatments revealed at least no loss in the
concentrations of chlorophyll a and b of fresh-cut avocados when
applying total amounted fluences of 6.0 J/cm2
. Hence, cholorophyll
a and b concentrations after PL processing were up to 1.3-fold
higher than those in unprocessed samples. PL treatments could
have helped to preserve chlorophyll from destabilization by
delaying biochemical pathways of chlorophyll metabolism. Never-
theless, a relationship between color changes and chlorophyll
values was not found, indicating that chlorophyll changes were not
enough to have an impact in color. Activity reduction of enzymes
such as peroxidase and chlorophyll oxidase caused by PL processing
may be a plausible explanation for a decrease of the degradation
rate of chlorophylls (Hendry, 1987).
On the other hand, extensive breakage of membranes has been
demonstrated by microscopic observations on fresh-cut apples
Fig. 1. Effect of pulsed-light treatments on the relative lightness (A) and hue angle (B)
values of fresh-cut avocado for 15 days at 4 Æ 1 C (mean of three replicates Æ standard
deviation). Values of untreated samples (,). Values for 3.6 (B), 6.0 (D), and 14 (Â) J/
cm2
corresponded to total amounted fluences emitted by flash lamps situated above
and below the product samples. Relative changes of luminosity and hue angle were
calculated respect lightness ðLÃ
0Þ and hue angle ðh
0Þ of untreated fresh-cut avocados.
LÃ
t and h
t are the lightness and hue angle values of each pulsed-light treated fresh-cut
avocado. Data shown are the mean of two replicate measurements obtained from two
replicate packages Æ standard deviation.
I. Aguiló-Aguayo et al. / LWT - Food Science and Technology 59 (2014) 320e326 323

5. treated at high fluences of 71.6 J/cm2
, favoring the accessibility of
deleterious enzymes (Gómez, García-Loredo, et al., 2012; Gómez,
Salvatori, et al., 2012). The decay of chlorophyll observed in fresh-
cut avocados treated at total amounted fluences of 14 J/cm2
could
be a response of a possible breakdown of intracellular membranes,
allowing chlorophylls to come into contact with the remaining
active chlorophyllase. On the other hand, chlorophylls are known to
be easily degraded by conditions such as heat and light (Tonucci,
1992). Photooxidative stress during high light intensities may also
play a major role in the observed chlorophyll loss (Artés, Mínquez,
Hornerno, 2002).
3.3. Effect of PL on the oxidative stability of fresh-cut avocado lipid
fraction
Peroxide value is an indicator of the initial stages of oxidative
change since the formation of hydroperoxides as primary oxidation
products is measured (Kamal-Eldin, Mäkinen, Lampi, 2003). In
general, peroxide values of oil obtained from untreated and PL-
treated fresh-cut avocados slightly increased during the first 7
days of storage, reaching a maximum and slightly decreasing up to
day 11. The highest peroxide index (3.12 meq O2/kg oil) was ach-
ieved in the lipidic phase of fresh-cut avocado processed at 14 J/cm2
after a week of storage (Table 3). The observed increase may be due
to the action of lipidic enzymes such as lipoxygenases released
from the fruit cells and favored by the intensity of the PL treatment.
In addition, the availability of oxygen in the package headspace
may also help to promote the oxidation of the product during
storage (Elez-Martínez et al., 2005). Nevertheless, the highest
peroxide value reached was below the limits of the Codex Ali-
mentarius, which establishes that an oil sample is within specifi-
cations when the peroxide index is below 10 meq/kg.
To provide a complete view of the oxidative changes, k232 and
k270 were also determined in PL-treated fresh-cut avocados lipid
fraction (Table 3). UV specific extinction determination is a good
indicator of the secondary phase of oxidation in unsaturated oils
(Gutierrez, Perdiguero, Garcia, Castellano, 1992). The k232
parameter mainly measures the presence of hydroperoxides,
whereas k270 is an index of the content in a-b diketones, a-unsat-
urated ketones and other oxygenized groups that show the
extension of the oxidation (García et al.,1996; Malheiro et al. 2009).
In general, initial k232 and k270 values were well maintained
throughout storage time in all the samples with no significant
changes caused by PL treatments (Table 3). In addition, concen-
trations did not exceed the limits reported in the EEC regulation
1989/2003 (2.5 and 0.22 for k232 and k270, respectively).
These results indicate that PL seemed not to dramatically affect
the stability of the lipidic fraction during storage of processed
samples, which could be related with the presence of natural
occurring antioxidants (e.g. tocopherols, poliphenols), not yet
degraded by the treatments. The stability of both k232 and k270
values suggests that rancidity processes in PL-processed samples
were still in the induction stage. Thus, the quality of the lipid
fraction in the PL-treated fresh-cut avocados remained acceptable
for 15 days. Resistance to oxidation of oil contained in complex
matrices such as fruit comes from a delicate equilibrium among
pro-oxidant substances, antioxidants and process conditions,
which could favor or delay the lipid oxidation (Nicoli, Anese,
Parpinel, 1999; Wagner, Derkits, Herr, Schuch, Elmadfa, 2002).
No studies have evaluated the impact of PL treatments on the
oxidative rancidity in vegetables. The induction of oxidative
Fig. 2. Changes in the concentration of chlorophyll a and b in fresh-cut avocado pre-
served by pulsed-light treatments and stored for 15 days at 4 C (mean of three
replicates Æ standard deviation). Legend: untreated samples (-). Values for 3.6 ( ), 6.0
( ) and 14 ( ) J/cm2
corresponded to overall amounted fluences emitted by flash
lamps situated above and below the product samples. Data shown are the mean of two
replicate measurements obtained from two replicate packages Æ standard deviation.
Table 3
Changes in the peroxide value and in the UV spectrophotometric absorbance k232
and k270 of oil from PL-treated fresh-cut avocados stored for 15 days at 4 C.
Days Untreated 3.6 J/cm2
6.0 J/cm2
14 J/cm2
Peroxide index (meq O2/kg oil)
0 2.27 Æ 0.15bC
2.02 Æ 0.20cB
1.60 Æ 0.10aA
1.78 Æ 0.05aAB
3 2.15 Æ 0.30bA
1.72 Æ 0.20cA
2.13 Æ 0.02dA
1.89 Æ 0.10aA
7 2.71 Æ 0.14bB
2.65 Æ 0.01dB
2.66 Æ 0.10cA
3.12 Æ 0.01bC
11 1.52 Æ 0.22aBC
0.61 Æ 0.11aA
1.90 Æ 0.10bC
1.18 Æ 0.14aB
15 1.52 Æ 0.23aA
1.23 Æ 0.10bA
2.01 Æ 0.10eC
1.38 Æ 0.60aA
k232
0 1.17 Æ 0.03cA
1.18 Æ 0.06cA
1.28 Æ 0.05aA
1.15 Æ 0.02aA
3 0.97 Æ 0.03aA
0.98 Æ 0.04aA
1.32 Æ 0.10aB
1.28 Æ 0.11aB
7 1.10 Æ 0.01bA
1.10 Æ 0.06bcA
1.18 Æ 0.23aA
1.11 Æ 0.15aA
11 1.07 Æ 0.04bA
1.06 Æ 0.05bcA
1.21 Æ 0.06aA
1.03 Æ 0.10aA
15 1.13 Æ 0.02bCA
1.11 Æ 0.02cA
1.28 Æ 0.10aA
1.20 Æ 0.07aA
k270
0 0.110 Æ 0.002cA
0.091 Æ 0.010bA
0.083 Æ 0.003aA
0.094 Æ 0.003abA
3 0.082 Æ 0.015bcA
0.087 Æ 0.010bA
0.105 Æ 0.003aA
0.089 Æ 0.021abA
7 0.089 Æ 0.020bcA
0.109 Æ 0.003bA
0.100 Æ 0.030aA
0.110 Æ 0.010cA
11 0.088 Æ 0.015bcA
0.087 Æ 0.015bA
0.071 Æ 0.003aA
0.073 Æ 0.002aA
15 0.061 Æ 0.004aA
0.060 Æ 0.002aA
0.071 Æ 0.003aA
0.072 Æ 0.005aA
Data shown are the mean of two replicate measurements obtained from two
replicate packages Æ standard deviation.
Values within a column followed by the same lowercase letter are not significantly
different by Duncan’s multiple-range test (P 0.05).
Values within the same line followed by the same uppercase letter are not signifi-
cantly different by Duncan’s multiple-range test (P 0.05).
I. Aguiló-Aguayo et al. / LWT - Food Science and Technology 59 (2014) 320e326324

6. processes by PL processing is still one of the drawbacks in some
high fat content food products like meats. As reported Wambura
and Verghese (2011), oxidation processed more rapidly during
storage in sliced ham treated with PL.
4. Conclusion
PL processing exerted a positive influence on the surface
decontamination of fresh-cut avocados. Despite maximum doses of
14 J/cm2
led to the higher microbial inactivation after processing
fresh-cut avocados, fluences of 3.6 J/cm2
led to the lowest counts
from day 5 to 11 of storage. PL processed showed a marked influ-
ence in reducing the microbial spoilage of PL-treated samples but
only could extend their shelf-life up to 15 days.
Color changes in PL-treated fresh-cut avocados were distin-
guished by a better maintenance of h values during storage but the
application of compounds to stabilize color would be required. The
results suggest that pulse light treatments could help to preserve
chlorophylls in fresh-cut avocados since higher chlorophyll stability
during storage was observed in PL-treated samples than in un-
treated avocados. Focusing on the evaluation of avocado oil
oxidation, PL treatments did not affect the stability of the lipidic
fraction of processed samples, and thus allowed keeping the oil
acceptability for at least 15 days of storage.
Acknowledgments
This work was supported by the Ministerio de Economía y
Competitividad through the Projects AGL2006-04775 and
AGL2010-21572. I. Aguiló-Aguayo thanks the Ministerio de Educa-
ción y Ciencia (Spain) for awarded PhD grant. ICREA Academia
Award is also acknowledged by O. Martín-Belloso.
References
Aguiló-Aguayo, I., Charles, F., Renard, C. M. G. C., Page, D., Carlin, F. (2013). Pulsed
light effects on surface decontamination, physical qualities and nutritional
composition of tomato fruit. Postharvest Biology and Technology, 86, 29e36.
Artés, F., Mínquez, M. I., Hornerno, D. (2002). Analysing changes in fruit pigments.
In D. B. MacDougall (Ed.), Colour in food: Improving quality (pp. 248e282).
Cambridge: Woodhead Publishing Limited.
Ashton, O. B. O., Wong, M., McGhie, T. K., Vather, R., Wang, Y., Requejo-Jackman, C.,
et al. (2006). Pigments in avocado tissue and oil. Journal of Agricultural and Food
Chemistry, 54(26), 10151e10158.
Awad, A. B., Fink, C. S. (2000). Phytosterols as anticancer dietary components:
evidence and mechanism of action. Journal of Nutrition, 130(9), 2127e2130.
Charles, F., Vidal, V., Olive, F., Filgueiras, H., Sallanon, H. (2013). Pulsed light
treatment as new method to maintain physical and nutritional quality of fresh-
cut mangoes. Innovative Food Science and Emerging Technologies, 18, 190e195.
Dorantes-Alvarez, L., Parada-Dorantes, L., Ortiz-Moreno, A., Santiago-Pineda, T.,
Chiralt-Boix, A., Barbosa-Cánovas, G. (1998). Effect of anti-browning com-
pounds on the quality of minimally processed avocados. Food Science and
Technology International, 4(2), 107e113.
Elez-Martínez, P., Soliva-Fortuny, R. C., Gorinstein, S., Martín-Belloso, O. (2005).
Natural antioxidants preserve the lipid oxidative stability of minimally pro-
cessed avocado puree. Journal of Food Science, 70(5), S325eS329.
Elez-Martínez, P., Soliva-Fortuny, R., Martín-Belloso, O. (2007). Oxidative rancidity
in avocado puree as affected by a-tocopherol, sorbic acid and storage atmo-
sphere. European Food Research and Technology, 226(1e2), 295e300.
García, J. M., Seller, S., Pérez-Camino, M. C. (1996). Influence of fruit ripening on
olive oil quality. Journal of Agricultural and Food Chemistry, 44(11), 3516e3520.
Gómez, P. L., García-Loredo, A., Nieto, A., Salvatori, D. M., Guerrero, S.,
Alzamora, S. M. (2012). Effect of pulsed light combined with an antibrowning
pretreatment on quality of fresh cut apple. Innovative Food Science and Emerging
Technologies, 16, 102e112.
Gómez, P. L., Salvatori, D. M., García-Loredo, A., Alzamora, S. (2012). Pulsed light
treatment of cut apple: dose effect on color, structure, and microbiological
stability. Food and Bioprocess Technology, 5(6), 2311e2322.
Gómez-López, V. M. (2002). Some biochemical properties of polyphenol oxidase
from two varieties of avocado. Food Chemistry, 77(2), 163e169.
Gómez-López, V. M., Devlieghere, F., Bonduelle, V., Debevere, J. (2005). Factors
affecting the inactivation of micro-organisms by intense light pulses. Journal of
Applied Microbiology, 99(3), 460e470.
Gunstone, F. D., Norris, F. A. (1982). Lipids in foods; Chemistry, biochemistry and
technology. Publ. Robert Maxwell.
Gutierrez, F., Perdiguero, S., Garcia, J. M., Castellano, J. M. (1992). Quality of oils
from olives stored under controlled atmosphere. Journal of the American Oil
Chemists’ Society, 69, 1215e1218.
Guzmán-Gerónimo, R. I., López, M. G., Dorantes-Alvarez, L. (2008). Microwave
processing of avocado: volatile flavor profiling and olfactometry. Innovative
Food Science and Emerging Technologies, 9(4), 501e506.
Hendry, G. A. F., Houghton, J. D., Brown, S. B. (1987). The degradation of chloro-
phyll e a biological enigma. New Phytology, 107, 255e302.
INTERNATIONAL ORGANIZATION FOR STANDARDIZATION (ISO) 7954:1987. (1987).
Microbiology e General guidance for the enumeration of yeast and mold-colony-
count technique at 25 degrees C. Genève, Switzerland.
INTERNATIONAL ORGANIZATION FOR STANDARDIZATION (ISO) 4833:1991. (1991).
Microbiology e General guidance for the enumeration of microorganisms-colony-
count technique at 30 degrees C. Genève, Switzerland.
Izquier, A., Gómez-López, V. M. (2011). Modeling the pulsed light inactivation of
microorganisms naturally occurring on vegetable substrates. Food Microbiology,
28(6), 1170e1174.
Jacxsens, L., Devlieghere, F., Falcato, P., Debevere, J. (1999). Behavior of Listeria
monocytogenes and Aeromonas spp. on fresh-cut produce packaged under
equilibrium-modified atmosphere. Journal of Food Protection, 62(10), 1128e
1135.
Jolivet, S., Arpin, N., Wichers, H. J., Pellon, G. (1998). Agaricus bisporus browning: a
review. Mycological Research, 102(12), 1459e1483.
Kamal-Eldin, A., Mäkinen, M., Lampi, A. M. (2003). The challenging contribution
of hydroperoxides to the lipid oxidation mechanism. In A. Kamal-Eldin (Ed.),
Lipids oxidation pathways (pp. 1e36). AOCS Press.
Lancaster, J. E., Lister, C. E., Reay, P. F., Triggs, C. M. (1997). Influence of pigment
composition on skin color in a wide range of fruit and vegetables. Journal of the
American Society for Horticultural Science, 122(4), 594e598.
Lassen, S., Bacon, K., Sutherland, J. (1944). The isolation and determination of
chlorophylls A and B in the California avocado. Oil Soap, 21(5), 139e141.
Maclachlan, S., Zalik, S. (1963). Plastid structure, chlorophyll concentration and
free amino acid composition of a chlorophyll mutant of barley. Canadian Journal
of Botany, 41, 95e99.
Malheiro, R., Oliveira, I., Vilas-Boas, M., Falcão, S., Bento, A., Pereira, J. A. (2009).
Effect of microwave heating with different exposure times on physical and
chemical parameters of olive oil. Food and Chemical Toxicology, 47, 92e97.
Nicoli, M. C., Anese, M., Parpinel, M. (1999). Influence of processing on the
antioxidant properties of fruit and vegetables. Trends in Food Science and
Technology, 10, 94e100.
Oms-Oliu, G., Aguiló-Aguayo, I., Martín-Belloso, O., Soliva-Fortuny, R. (2010). Ef-
fects of pulsed light treatments on quality and antioxidant properties of fresh-
cut mushrooms (Agaricus bisporus). Postharvest Biology and Technology, 56(3),
216e222.
Plaza, L., Sánchez-Moreno, C., De Pascual-Teresa, S., De Ancos, B., Cano, M. P.
(2009). Fatty acids, sterols, and antioxidant activity in minimally processed
avocados during refrigerated storage. Journal of Agricultural and Food Chemistry,
57(8), 3204e3209.
Ramos-Villarroel, A. Y., Aron-Maftei, N., Martín-Belloso, O., Soliva-Fortuny, R.
(2012). The role of pulsed light spectral distribution in the inactivation of
Escherichia coli and Listeria innocua on fresh-cut mushrooms. Food Control,
24(1e2), 206e213.
Ramos-Villarroel, A. Y., Aron-Maftei, N., Martín-Belloso, O., Soliva-Fortuny, R.
(2014). Bacterial inactivation and quality changes of fresh-cut avocados as
affected by intense light pulses of specific spectra. International Journal of Food
Science and Technology, 49(1), 128e136.
Ramos-Villarroel, A. Y., Martín-Belloso, O., Soliva-Fortuny, R. (2011a). Bacterial
inactivation and quality changes in fresh-cut avocado treated with intense light
pulses. European Food Research and Technology, 233(3), 395e402.
Ramos-Villarroel, A. Y., Martín-Belloso, O., Soliva-Fortuny, R. (2011b). Using
antibrowning agents to enhance quality and safety of fresh-cut avocado treated
with intense light pulses. Journal of Food Science, 76(9), S528eS534.
Soliva-Fortuny, R. C., Elez, P., Sebastián, M., Martín, O. (2000). Evaluation of
browning effect on avocado purée preserved by combined methods. Innovative
Food Science and Emerging Technologies, 1(4), 261e268.
Soliva-Fortuny, R. C., Grigelmo-Miguel, N., Odriozola-Serrano, I., Gorinstein, S.,
Martín-Belloso, O. (2001). Browning evaluation of ready-to-eat apples as
affected by modified atmosphere packaging. Journal of Agricultural and Food
Chemistry, 49(8), 3685e3690.
Takeshita, K., Shibato, J., Sameshima, T., Fukunaga, S., Isobe, S., Arihara, K., et al.
(2003). Damage of yeast cells induced by pulsed light irradiation. International
Journal of Food Microbiology, 85(1e2), 151e158.
Tonucci, L. H. (1992). Kinetics of the formation of zinc complexes of chlorophyll
derivatives. Journal of Agricultural and Food Chemistry, 40(12), 2341e2344.
Wagner, K. H., Derkits, S., Herr, M., Schuch, S., Elmadfa, I. (2002). Antioxidative
potential of melanoidins isolated from a roasted glucoseeglycine model. Food
Chemistry, 78(3), 375e382.
Wambura, P., Verghese, M. (2011). Effect of pulsed ultraviolet light on quality of
sliced ham. Food Science and Technology, 44, 2173e2179.
Werman, M. J., Neeman, I. (1986). Effectiveness of antioxidants in refined,
bleached avocado oil. JAOCS, Journal of the American Oil Chemists’ Society, 63(3),
352e355.
Wong, D. W. S. (1989). Fruit development and ripening physiology. Avocado.
I. Aguiló-Aguayo et al. / LWT - Food Science and Technology 59 (2014) 320e326 325

7. Woodling, S. E., Moraru, C. I. (2005). Influence of surface topography on the
effectiveness of pulsed light treatment for the inactivation of Listeria innocua on
stainless-steel surfaces. Journal of Food Science, 70(7), M345eM351.
Yahia, E. M., Gonzalez-Aguilar, G. (1998). Use of passive and semi-active atmo-
spheres to prolong the postharvest life of avocado fruit. LWT e Food Science and
Technology, 31(7e8), 602e606.
Zacarías, S. M., Vaccari, M. C., Alfano, O. M., Irazoqui, H. A., Imoberdorf, G. E.
(2010). Effect of the radiation flux on the photocatalytic inactivation of spores of
Bacillus subtilis. Journal of Photochemistry and Photobiology A: Chemistry, 214(2e
3), 171e180.
I. Aguiló-Aguayo et al. / LWT - Food Science and Technology 59 (2014) 320e326326