Food and Nutrition Sciences, 2013, 4, 321-334 Published Online March 2013 (
Effect of Instant Controlled Pressure Drop Process
Coupled to Drying and Freezing on Antioxidant Activity of
Green “Poblano” Pepper (Capsicum annuum L.)
Carmen Téllez-Pérez1,3, Anaberta Cardador-Martínez1, Sabah Mounir2,
José Gerardo Montejano-Gaitán1, Vaclav Sobolik3, Karim Allaf3*
1Tecnológico de Monterrey-Escuela en Ingeniería, Biotecnología y Agronomía, Querétaro, México; 2Department of Food Science,
Faculty of Agriculture, Zagazig University, Zagazig, Egypt; 3LaSIE FRE 3474 CNRS, Laboratory Engineering Science for Environ-
ment, University of La Rochelle, La Rochelle, France.
Email: *
Received January 23rd, 2013; revised February 23rd, 2013; accepted March 3rd, 2013
Different food operations have been intensified through assisting them by instant controlled pressure drop DIC treat-
ment. Such processes should be defined in order to preserve the main nutritional and sensorial contents of the raw mate-
rial. The present paper is dedicated to study the evolution of the main bioactive compounds (total phenolics and flavon-
oids) and functional properties such as the antioxidant activity of processed samples in the case of Green “Poblano”
Pepper (Capsicum annuum L.). Results issued from DIC-assisted hot air drying, and DIC-assisted freezing, allowed to
identifying the impact of DIC studied operating parameters, which were the saturated steam pressure and the processing
time, and the best DIC treatment correlated with the considered operation.
Keywords: Instant Controlled Pressure Drop; Capsicum; Phenols; Flavonoids; Antioxidant Activity; Drying; Freezing
1. Introduction
Pepper is derived from a Greek word originally used for
black and white pepper, but subsequently applied to gen-
era belonging to seven different families, all of which
have pungent fruits or seeds. “Chilli” comes from one of
the indigenous languages of Mexico, where Capsicum
has been consumed for more than 5000 years. The bell
peppers, paprikas and pimientos, together with most of
the Mexican chillies, are all included in C. annuum . This
is now the most widespread and economically important
cultivated species of all the Capsicum [1].
The pepper (Capsicum annuum, L.) is highly appreci-
ated for its flavor, color, pungency, taste, aroma, and for
its physiological and pharmaceutical uses [2]. Pepper is
an excellent source of phytochemicals and essential nu-
trients such as ascorbic acid, capsaicinoids, flavonoids,
phenolic compounds, carotenoids, etc. [3]. Recent re-
searches have shown that dietary capsaicin is effective in
reducing oxidant stress, rheumatism, arthritis, neuralgia,
lumbago, cancer and diabetes among other diseases [4-6].
Hence, it is very important to study food processing
techniques in terms of their ability to preserve the natural
bioactive molecules of pepper.
Thermal treatments of a food systematically induce
physical changes and chemical reactions, which in turn
affect its sensory characteristics and nutritional value,
either advantageously or adversely [7,8]. Antioxidants,
well-known for their health properties related to the pre-
vention of degenerative diseases are damaged by long
thermal treatments [9-12].
Drying is one of the oldest and most effective means
of preserving foods. However, some studies have shown
that long periods of heating cause losses of sensorial
(texture, taste, flavor, and color) and nutritional quality
[9,13], such as reduction of ascorbic acid content [14].
Comparatively during the freezing process ice crystals
can also cause physical, structural, chemical and nutri-
tional damage [15,16].
Dehydrofreezing is a new food processing of partial
dehydration prior to freezing. It has shown advantages on
texture properties and energy consumption, due to the
effect of diminishing the tissue damage by removing part
of water from vegetable tissue prior to freezing [15,16].
Instant Controlled Pressure Drop process, well known
by the French acronym “DIC” (Détente Instantanée Con-
trôlée), is based on the thermo-mechanical effects in-
duced by subjecting the raw material for a short period of
time to saturated steam (about 0.1 - 0.6 MPa according to
*Corresponding author.
Copyright © 2013 SciRes. FNS
Effect of Instant Controlled Pressure Drop Process Coupled to Drying and Freezing on
Antioxidant Activity of Green “Poblano” Pepper (Capsicum annuum L.)
the product), followed by an abrupt pressure drop to-
wards a vacuum (about 5 kPa). This abrupt pressure drop
(ΔP/Δt > 0.5 MPa/s) triggers simultaneously autovapori-
zation of volatile compounds, swelling, possibly ruptur-
ing some cell walls and instantaneously cooling the
products, which stops thermal degradation [17,18].
The aim of the present study was to evaluate and
compare the effects of traditional methods of drying and
freezing to the DIC process coupled to drying and freez-
ing, on the phytochemical content (phenols and flavonoids)
and the antioxidant activity of Green Poblano Pepper.
2. Materials and Methods
2.1. Materials
2.1.1. Chemicals
Folin-Ciocalteau reagent 2N, 2-Aminoethyl diphenyl bo-
rate 98%, 2,2-Diphenyl-1-picrylhydrazil (DPPH ), Gallic
acid, 2,2-azinobis (3-ethylbenzothiazolin) 6-sulfonic acid
(ABTS), (±)-6-Hydroxy-2,5,7,8-tetramethylchromane-2-
carboxylic acid (Trolox), Rutin hydrate 94% (HPLC)
powder, were obtained from sigma. All other reagents
and chemicals of analytical grade were procured from
local sources and milli-Q water was used.
2.1.2. Samples
Physiologically ripe Green Poblano Pepper was bought at
local market in Querétaro, Mexico on December 2010
and was transported to the laboratory.
2.2. Processing Methods
Before any treatments, good quality peppers (absence of
mold and insect contamination) were manually selected
and washed. From whole washed fruit the peduncles,
seeds, capsaicin glands, and placenta, were eliminated.
The pericarp was manually diced to an average thickness
of 8 mm.
The comparative study of traditional methods of dry-
ing and freezing with the DIC process, was carried out as
shown on Figure 1. Fresh diced Poblano Peppers were
divided into three parts, 1) Raw Material (RM); 2) Dry-
ing and 3) Traditional Freezing (TF). The RM was stored
for two days at 4˚C until analysis.
Dehydration involved two different methods, hot air
drying and freeze drying (FD).
Hot air drying of Peppers was applied at 60˚C, 265 Pa
as partial pressure of vapor and 1.2 m·s1 of air flux.
Drying was carried out until 5% d.b (dry basis) and sam-
ples were identified as Total Hot Air Drying (THAD).
Freeze drying (FD) stated by 3-min liquid nitrogen
freezing, followed by a sublimation stage at 20˚C, 0.66
Pa for 12 h and a desorption stage at 25˚C, 0.66 Pa for 12
h; both stages were carried out in a standard freeze drier
Tradi onal
Tradi onal
Figure 1. Schematic diagram of processing of green poblano
pepper by dehydration and free zing methods.
(Virtis FM 6.6ES 374330, USA).
2.2.1. I n s tant Cont rolled Pressure Drop DIC
The DIC equipment LABIC0.1 (ABCAR-DIC Process;
La Rochelle; France) consisted of three major compo-
nents; first a double jacket processing vessel 1) where
samples were setting and treating, different conditions of
saturated steam pressure and a vacuum were provided;
second, a vacuum system, which consisted mainly of a
vacuum tank 2) and a water ring vacuum pump 3) and
third the decompression system through an instant but-
terfly valve connecting/separating the processing and the
vacuum tank 2). Saturated steam (F1) was supplied into
the processing vessel, through the valve (V1). The dou-
ble jacket was heated by saturated steam (F2). The reac-
tor was equipped by a vent (V3). The vacuum tank was
cooled by tap water (F3) circulating in the double jacket.
Manometers and pressure sensors showed the vessel and
tank pressures. Condensates were removed from the res-
ervoir through the trap 4) with a system of valves (V4,
V5 and V6) [19]. Figure 2 shows the schematic diagram
of DIC equipment reactor LABIC0.1.
For the DIC treatment of peppers, samples were en-
closed in a perforated stainless steel container and set in
the reactor 1) at the atmospheric pressure and then this
was closed. By opening the valve (V2) an initial vacuum
was performed. After closing (V2), saturated steam was
injected into the reactor by the valve (V1); injection was
upheld manually during the given treatment time, and it
was afterward closed. The abrupt pressure drop towards a
vacuum was carried out by an abrupt opening (<0.5 s) of
the valve (V2). This abrupt pressure drop triggered an
adiabatic auto-vaporization of superheated liquid con-
tained in the material, instantaneously cooling the struc-
ture, and swelling and even rupturing the cell walls as
Copyright © 2013 SciRes. FNS
Effect of Instant Controlled Pressure Drop Process Coupled to Drying and Freezing on
Antioxidant Activity of Green “Poblano” Pepper (Capsicum annuum L.) 323
F1 V1
Tp Pp
Figure 2. Schematic diagram of DIC Equipment LABIC0.1
(ABCAR-DIC Process; La Rochelle; France): (1) DIC Re-
actor; (2) Vacuum tank; (3) Vacuum pump; (4) Trap, V1-
V7-valves, F1 and F2-saturated steam injection, F3-cooling
water, P-Pressure gauge and T-thermocouples.
well. Finally, atmospheric pressure was restored in the
autoclave by the vent (V3) and the material was recov-
ered. The pressure in the vacuum tank 2) was almost
constant and equal to 5 kPa.
Instant Controlled Pressure Drop process (DIC) in-
cluded two main steps (Figure 3) of heating and pressure
1) Pre-dried peppers (22% d.b) were introduced on the
DIC processing reactor LABIC0.1 (ABCAR-DIC Proc-
ess; La Rochelle, France). Afterward a vacuum of 3 kPa
was established (Figure 3A). The initial vacuum was
carried out to facilitate and mediate the close exchange
between the incoming steam and the product surface.
Saturated steam was injected into the reactor at a fixed
pressure level (P) ranged from 0.15 and 0.45 MPa (Fig-
ure 3B). Once tested pressure was reached, this was
maintained for a given thermal treatment time “t” ranged
between 20 and 60 s (Figure 3C). Operating parameters
of “P” and “t” were selected as shown in experimental
design section.
2) Once treatment time finished, samples were sub-
jected to an Instant controlled pressure drop (ΔP/Δt > 0.5
MPa·s1) towards vacuum of 5 kPa (Figure 3D).
After a vacuum stage period time, pressure was re-
leased toward the atmospheric pressure (Figure 3E) and
samples were removed from the reactor. Obtained sam-
ples just after DIC treatment were called DIC-Swelling
DIC-S samples were divided in two preserving meth-
ods. One part consisted to a second drying stage at the
same conditions of THAD to obtain DIC-Dried products
Figure 3. Schematic time-pressure profiles of a DIC proc-
essing cycle. A: establishment of the vacuum; B: injection of
steam; C: maintain of treatment pressure during selected
time; D: instant controlled pressure drop towards vacuum
and E: establishment of the atmospheric pressure.
(DIC-D) and the other part consisted to a freezing (20˚C)
to obtain DIC-Frozen products (DIC-F). To compare the
impact of DIC treatment of both preserving methods, one
part of DIC-S samples was also studied (stored at 4˚C).
2.2.2. Freezing Methods
Traditional Freezing (TF) was applied on fresh pepper
under 20˚C. Experiments were carried out in a chest
freezer (Frigidaire Gallery, GLFC1326FW, USA).
2.3. Assessment Methods
2.3.1. Proximal Analysi s
The water content (method 925.10), the crude protein
content (Kjeldahl method 981.10, conversion factor of
6.25) and the amount of ashes (method 923.03) were
evaluated through AOAC Official method [20]; the lipid
content by the Goldfish method [21], the crude fiber by
the Crude Fiber Analysis in Feeds by Filter Bag Tech-
nique (AOCS method). The carbohydrates were calcu-
lated by difference on 100 g of fresh sample as basis.
2.3.2. An tioxidant Extraction
Before extraction, 10 g of each various pepper samples;
RM, FD, TF, THAD, DIC-S, DIC-D and DIC-F were
milled and homogenized in a high-speed blender (40 s)
and moisture content was measured (AOAC method)
[20]. Samples (0.5 g) were extracted with 10 mL of
MeOH:HCl (99:1,%v/v), 2 h in the dark, using an orbital
shaker operated at 200 rpm at room temperature, and
centrifuged at 6000 rpm for 20 min. The extraction solu-
tions were filtered through Whatman No. 4 filter paper
and stored in the dark at 20˚C until analysis [22]. For
each sample duplicate extraction and analysis were car-
ried out.
Copyright © 2013 SciRes. FNS
Effect of Instant Controlled Pressure Drop Process Coupled to Drying and Freezing on
Antioxidant Activity of Green “Poblano” Pepper (Capsicum annuum L.)
2.3.3. Total Phenolic Content
Total phenols content was estimated by usingFolin-Cio-
calteau colorimetric method [23]. Briefly, 20 µL of the
extracts were diluted with 1.5 mL of Milli-Q water and
oxidized with 0.1 mL of 0.5 N Folin-Ciocalteaureagent,
after five minutes the reaction was neutralized with 0.3
mL sodium carbonate solution (20%). The absorbance
values were obtained by the resulting blue color meas-
ured at 760 nm with a spectrophotometer (UV-Vis Dou-
ble Beam UVD-3500, Labomed, Inc. USA), after 2-h,
25˚C incubation on darkness. Quantification was done on
the basis of a standard curve of Gallic acid, concentration
ranging from 0 to 500 μg·mL1 (r2 = 0.99). Results were
expressed as mg of Gallic acid equivalent per grams of
dry matter (mg Gallic acid eq/g d.b).
2.3.4. Flavo no i ds Con tent
The spectrophotometric assay for the quantitative deter-
mination of flavonoid content adapted for its use with
microplates, was used [24]. Briefly, the method consisted
of mixing 50 μL of the methanolic extract with 150 μL of
distilled water and 50 μL of a solution of 10 g·L1
2-aminoethyldiphenylborate in a 96-well microtitration
flat-bottom plate. The absorbance of the solution was
monitored at 404 nm after 15 min with a spectropho-
tometer (XMarkMicroplate Spectrophotometer Bio-Rad
Laboratories, Japan). Extract absorption was compared
with that of a rutin standard at concentrations ranging
from 0 to 200 μg·mL1 (r2 = 0.99). Flavonoid content was
expressed as mg rutin equivalent per gram of dry matter
(mg rutin eq/g d.b).
2.3.5. DPPH Scaven ging Capa ci ty
2,2-Diphenyl-1-picrylhydrazil (DPPH) is a free radical
used for assessing antioxidant activity. Reduction of
DPPH by an antioxidant or by a radical species results in
a loss of absorbance at 520 nm. Determination of anti-
oxidant capacity adapted for microplates was used [22].
Briefly, according to the results obtained of total phenol
content, standards (Trolox) and samples were prepared at
500 µM in methanol; then 20 µL of extract or standard
were mixed with 200 µL of DPPH solution (125 µM in
80% methanol) on 96-well flat-bottom visible light plate,
samples were prepared in triplicate. The plate was then
covered and left in the dark at room temperature (20˚C),
after 90 min, absorbance at 520 nm was measured in the
microplate spectrophotometer. Data were expressed as a
percentage of DPPH discoloration.
2.3.6. Trolo x E qui val ent Antioxid ant Capacity by
The Trolox equivalent antioxidant capacity (TEAC) method
is based on the ability of an antioxidant to scavenge the
preformed radical cation ABTS relative to that of the
standard antioxidant Trolox. The total antioxidant capac-
ity of extracts was realized according to the improved
ABTS method described by Re et al. [25], and adapted
for its use in microplates. Briefly, ABTS radical cation
was produced by reacting 7 mM of 2,2’-azinobis (3-
ethylbenzothiazo line-6-sulfonic acid), diammonium salt
(ABTS) and 2.45 mM potassium persulfate after incuba-
tion at room temperature in dark for 16 h. The stock so-
lution of ABTS was diluted with ethanol just before use
to an absorbance of 0.80 ± 0.1 at 734 nm. Standards and
samples prepared at 500 µM in methanol were used. The
200 µL of ABTS solution and the 20 µL standard (Trolox)
or sample solutions were added to the well on the visible
light 96-microwell plate and mixed thoroughly. The ab-
sorbance readings were taken at 734 nm just 6 min after
using a visible-UV microplate reader. Trolox standard
concentrations range from 0 to 500 µM. TEAC of the
sample was calculated as µM of Trolox needed to give
the same degree of discoloration than the samples at 500
2.4. Experimental Design and Statistical Analysis
for DIC Treatment
A five-level central composite rotatable design was em-
ployed to evaluate the effect of the DIC operating pa-
rameters. After preliminary trials, the saturated steam
pressure “P” (MPa) and the processing heating time “t”
(s), were used as independent variables (n = 2), ranged
between 0.15 - 0.45 MPa and 20 - 60 s, respectively. The
antioxidant activity and the total phenolic and flavonoid
contents [26,27], were the considered responses (de-
pendent variables). Thus, the studied design included
224 11;11;11and11
 as factorial
2n22 40;0;0and0
 
 
as star trials; and the central point (0,0) was triplicated.
The total trials were 11. The value of α (axial distance)
depending on the number (n) of operating parameters
was calculated as 4n
 . The operative DIC
parameters applied are shown on Tables 1 and 2. Stat-
graphics Plus software (version XVI) was used for statis-
tical analysis.
3. Results
3.1. Physico-Chemicals Properties
Proximate analysis of pepper (on 100 g of fresh weight)
Table 1. Coded and real levels of independent variables
used in the experimental design. Axial distance α = 1.4142.
Coded level
Factor α 1 0 1 +α
Processing Pressure (MPa) 0.15 0.19 0.30 0.410.45
Processing Time (s) 20 26 40 5460
Copyright © 2013 SciRes. FNS
Effect of Instant Controlled Pressure Drop Process Coupled to Drying and Freezing on
Antioxidant Activity of Green “Poblano” Pepper (Capsicum annuum L.)
Copyright © 2013 SciRes. FNS
Table 2. Run experimental values.
DIC Treatment
Factor 1 2 3 4 5 6 7 8 9 10 11
Processing Pressure (MPa) 0.45 0.30 0.30 0.41 0.41 0.30 0.19 0.19 0.15 0.30 0.30
Processing Time (s) 40 60 40 54 26 40 26 54 40 20 40
Table 3. Total phenolic and flavonoids content of dried and
frozen poblano pepper (values represent the mean of tripli-
cates measures ± the standard error).
presented an initial moisture content of 91.13 ± 0.74 g;
crude protein (nitrogen × 6.25) of 1.33 ± 0.12 g; total
lipids of 0.11 ± 0.001 g; crude fiber of 1.07 ± 0.02; crude
ash of 0.45 ± 0.11 g; available carbohydrates (by differ-
ence) of 5.91 ± 0.99 g. Obtained results were in accor-
dance with those of green bell peppers [28], only small
differences can be pointed out on the values obtained for
green Poblano peppers, which showed slightly higher
contents of protein, total carbohydrates, minerals and
fiber, and lower amounts of moisture content and lipids,
which can be attributed to differences in the varieties.
Process TPC
(mg Gallic acid eq/g d.b)
(mg rutin eq/g d.b)
RM 24.55 ± 0.57 11.86 ± 0.37 48.30 ± 1.50
FD 23.39 ± 1.83 14.27 ± 0.52 61.02 ± 2.20
THAD24.67 ± 0.80 11.00 ± 0.33 44.58 ± 1.33
TF 17.17 ± 1.45 14.92 ± 0.56 86.89 ± 3.28
TPC2.0053 36.49P0.925t
124.91P1.164Pt 0.0127t
 
3.2. Total Phenolic and Flavonoids Content of
Dried and Frozen Poblano Pepper
Most of the studies that evaluate the total phenol content
of pepper focus on the differences among the varieties
[29-32], the changes at different ripening stages fruit [33,
34] and on the impact of agricultural cultivation practices
[32,35]; nevertheless little information exist about the
impact of drying or frozen treatment conditions on the
content of this bioactive molecules. Thus, this study fo-
cused on the impact of these preserving methods on the
phytochemical content of Poblano Pepper. Tables 3 and
4 summarize these results.
For DIC-S and DIC-F, under the selected range of DIC
treatment conditions any of the factors, “P” and “t”, pre-
sented significant effects on the TPC. Even so, these
treatments showed higher values of TPC under P: 0.41
MPa and t: 54 s, being these 29.72 and 33.62 mg of Gal-
lic acid equivalents/g d.b for DIC-S and DIC-F respec-
tively. In fact, under these operating conditions the DIC-
F presented the best performance to preserve phenolic
compounds, being 1.95 times better than TF and 1.36
times better than RM.
From Figure 5, it can be observed the impact of the
THAD and the DIC-D treatments on the structure of
dried Poblano peppers. THAD samples presented a col-
lapsed structure, contrary the DIC-D samples presented a
high porous structure.
Obtained results showed that Total Phenol Content
(TPC) varied widely according to different drying and
freezing conditions. In the case of FD samples, it was
observed that compared to RM (24.55 mg Gallic acid
equivalents/g d.b), it reduced the TPC on 5%. Respect to
Freezing, the traditional method (TF) showed the highest
loss of TPC (30%) respect to RM. On the other hand, an
interesting good impact of DIC-assisted drying and
freezing, on the total phenol content of peppers is shown
(Table 4). In fact, DIC-S (Point 1), DIC-D (Point 3) and
DIC-F (Point 4) increased the TPC of pepper compared
to RM, being observed that under high values of the
saturated steam pressure “P” and the holding time “t” of
DIC treatment conditions, the TPC was increased. Spe-
cifically for DIC-D, as observed on Figure 4, the thermal
holding time and the quadratic effect of this factor had a
significant effect on increasing the TPC, meaning that the
higher the holding time, the higher the TPC of dried sam-
Obtained results were quite relevant because contrary
to most of the studies of thermal processapplied on pep-
pers as drying [14], microwave heating, stir frying and
boiling water [10] that shows important reductions of
TPC respect to RM, the DIC process as a high tempera-
ture and short time treatment allowed to optimize the
TPC, showing that degradation of polyphenols are re-
lated not only to applied temperature, but also to proc-
essing time.
Regarding the Total Flavonoids Content (TFC) of Po-
blano Pepper some studies have shown that it contains
important quantities of flavonoids [33,34,36-38], how-
ever it has been showed that they are quite affected by
food preparation and processing, decreasing their content
by 50% in some cases [39].
Equation (1) is the adequate empirical regression model
(R2 = 90.73%) of the TPCDIC D: At this respect, this study showed that both of studied
Effect of Instant Controlled Pressure Drop Process Coupled to Drying and Freezing on
Antioxidant Activity of Green “Poblano” Pepper (Capsicum annuum L.)
Table 4. Total phenol and flavonoids content of dried and frozen poblano pepper couple to DIC; Values represent the mean
of triplicates ± the standard error.
Total phenolic content TPC
(mg Gallic acid eq/g d.b)
Total Flavonoids content TFC
(mg rutin eq/g d.b)
Ratio between the Flavonoids and
Phenolic compounds RFP (%)
DIC-Swelling DIC-DriedDIC-Frozen DIC-Swelling DIC-DriedDIC-Frozen DIC-Swelling DIC-Dried DIC-Frozen
1 29.72 ± 1.54 27.15 ± 0.2927.79 ± 1.36 15.19 ± 0.2610.42 ± 0.3911.79 ± 0.8851.09 ±0.89 38.38 ± 1.44 42.42 ± 3.16
2 21.94 ± 0.82 28.98 ± 2.1229.50 ± 2.05 11.82 ± 0.299.90 ± 1.3615.57 ± 0.4053.85 ± 1.33 34.18 ± 4.69 52.79 ± 1.36
3 22.05 ± 1.04 30.39 ± 1.4727.61 ± 0.55 13.87 ± 0.569.90 ± 0.6111.86 ± 0.4262.92 ± 2.53 32.59 ± 2.02 42.94 ± 1.54
4 23.12 ± 2.14 29.61 ± 0.6933.62 ± 0.14 13.24 ± 0.989.90 ± 0.5515.10 ± 0.7757.25 ± 4.23 33.43 ± 1.86 44.92 ± 2.30
5 20.67 ± 1.85 20.19 ± 0.4330.62 ± 1.53 12.94 ± 0.347.78 ± 0.6614.96 ± 0.8262.61 ± 1.66 38.56 ± 3.29 48.84 ± 2.69
6 23.83 ± 3.35 28.20 ± 0.2628.08 ± 2.00 12.33 ± 0.459.31 ± 0.2614.69 ± 0.5151.73 ± 1.90 33.01 ± 0.92 52.31 ± 1.82
7 20.04 ± 0.31 23.34 ± 0.6627.43 ± 1.49 11.01 ± 0.149.24 ± 0.1013.65 ± 0.4954.97 ± 0.71 39.57 ± 0.44 49.76 ± 1.78
8 22.87 ± 1.45 25.60 ± 0.4327.79 ± 1.38 12.20 ± 0.508.91 ± 0.1714.45 ± 1.0353.35 ± 2.20 34.82 ± 0.66 51.98 ± 3.71
9 20.68 ± 0.86 22.70 ± 0.3930.03 ± 1.21 12.07 ± 0.278.84 ± 0.3314.52 ± 1.5658.35 ± 1.29 38.92 ± 1.46 48.36 ± 5.21
10 19.71 ± 0.50 16.94 ± 0.9830.00 ± 2.02 10.51 ± 0.096.54 ± 0.0815.97 ± 0.6153.31 ± 0.48 38.64 ± 0.47 53.24 ± 2.02
11 26.20 ± 0.15 26.37 ± 0.3128.91 ± 0.50 12.42 ± 0.299.88 ± 0.1813.49 ± 0.3247.42 ± 1.09 37.47 ± 0.69 46.65 ± 1.09
Standardized Effect
P:Saturated steam pressure(MPa)
t:Thermalprocessing time(s)
0.20 0.4
Saturated steampressure
TPC(mgGallicacid eq/gd.b)
Figure 4. Effects of steam pressure (MPa) and holding time (s) of DIC-drying on the TPC of green poblano peppers. A:
pareto chart and B: surface response plot.
Figure 5. Poblano pepper dried by THAD (left) and DIC-D
(right). DIC treatment conditions: P = 0.30 MPa and t = 60 s.
drying process, THAD and DIC-D (P: 0.45 MPa, t: 40 s),
decreased the TFC respect to RM (11.86 mg rutin
equivalents/g d.b) by 7% and 12% respectively.
Therefore, it was observed that the flavonoid content
of DIC-D largely changed according to DIC treatment
conditions, with the thermal holding time “t” as the most
responsible of this changes (Figure 6A); the higher the
time, the higher the TFC. Else, as observed on Figure 6B,
while pressure impact is negligible for low values of “t”,
the interaction of factors showed that high values of
treatment time imply a positive impact of steam pressure
on the TFC. The empirical regression model (R2 =
82.33%), Equation (2), allowed to determine the optimal
operating conditions (P: 0.45 MPa, t: 56 s) to maximize
the response (10.92 mg rutin equivalents/g d.b).
TFC5.3546 12.4569P0.2372t
2.2801P0.39587Pt 0.0037t
 
 
On the other side, FD and DIC-S (P: 0.45MPa, t: 40 s)
increased the TFC respect to RM, 1.20 times and 1.28
times respectively. Else, for DIC-S it was observed that
both operating parameters: saturated steam pressure “P”
Copyright © 2013 SciRes. FNS
Effect of Instant Controlled Pressure Drop Process Coupled to Drying and Freezing on
Antioxidant Activity of Green “Poblano” Pepper (Capsicum annuum L.) 327
Standardized effect
P:Saturated steam pressure(MPa)
t:Thermalprocessing time(s)
Standardized effec
P:Saturated steam pressure(MPa)
t:Thermalprocessing time
Figure 6. Effects of steam pressure (MPa) and holding time (s) of DIC treatment on the total flavonoids content of poblano
peppers. A and B: DIC-dried (left—pareto chart and right—surface response plot); C and D: DIC-swelling (left—pareto
chart and right—surface response).
and the thermal processing time “t”, had significant ef-
fects on the TFC (Figure 6C). The higher the saturated
steam pressure, the higher the TFC (Figure 6D). Statis-
tical analysis of the experimental design allowed to obtain
the prediction model (R2 = 89.39%) for the TFC Equa-
tion (3) and the optimal operating conditions to maxi-
mize the response (P: 0.45 MPa, t: 40.3 s) at 14.91 mg.
rutin equivalents/g d.b.
TFC3.0600 3.9208P0.4276t
30.1726P0.14509Pt 0.0044t
 
On the other hand, freezing conditions (TF and DIC-F)
enhanced the preservation of TFC, being the DIC-F the
best process, by increasing 1.34 times (P: 0.30 MPa, t: 20
s) the TFC respect to RM.
Furthermore, some research works had shown that the
relation between total flavonoids and phenol content of
peppers changed depending on variety and ripening
stages [33,36]; however there is not much information
about changes during processing. Regarding this aspect,
to better understand the impact of the different studied
drying and freezing treatments, the relation between the
flavonoids and phenols was calculated by Equation (4):
(Total Flavonoids content of sample)
RFP% (Total Phenol content sample)
Hence, this study showed that fresh Poblano Pepper
had a RFP of around 48%, suggesting that flavonoids were
the most important group of phenolic compounds of fresh
fruit. Else, important changes on the RFP where found on
the different preservation process (Tables 3 and 4).
For drying, two behaviors were founded. In the case of
FD an increase on the RFP of 1.26 times respect to RM
was founded. On the other hand, in the case of DIC-D
and THAD, a decrease on the RFP compared to RM was
founded, being this of 18.07% (P: 0.19 MPa, t: 26 s) and
7.70%, respectively. This behavior showed that these
drying processes preserved other kind of phenolics better
than flavonoids.
Particularly for DIC-D, it was founded that the thermal
holding time was the most influencing parameter com-
pared to the saturated steam pressure (Figure 7A). The
lower the holding time, the higher the RFP. Else, under
high values of steam saturated pressure, the RFP was
increased (Figure 7B). Statistical analysis of the experi-
mental design allowed to obtain the prediction model
Equation (5) for the RFP (R2 = 75.04%).
To maximize the RFP, the optimum conditions were P:
0.14 MPa and t: 20 s. Optimal value: 42.99%.
%RFP61.15 95.8897P0.44895t
157.959P0.0622Pt 0.0040382t
 (5)
Copyright © 2013 SciRes. FNS
Effect of Instant Controlled Pressure Drop Process Coupled to Drying and Freezing on
Antioxidant Activity of Green “Poblano” Pepper (Capsicum annuum L.)
0 0.5 1 1.5 2 2.5 3
Standardized effec
P:Saturated steam pressure(MPa)
t:Thermalprocessing time(s)
Saturated steam pressure
0.4 0.20
Figure 7. Effects of steam pressure (MPa) and holding time (s) of DIC-dried treatment on the RFP of green poblano peppers.
A: pareto chart and B: surface response plot.
On the other hand, although under the selected range
of DIC treatment conditions, any of the factors, “P” and
“t” presented significant effects on the RFP of DIC-F and
DIC-S, the DIC treatment exhibited an interesting be-
havior on DIC-F (P: 0.30 MPa, t: 20 s) and DIC-S (P:
0.30 MPa, t: 40 s) compared to RM, by raising it on 1.1
and 1.3 times respectively.
Finally, it has been found that frozen process pre-
served advantageously the RFP; being the TF the process
that preserves better the RFP (86.89%). Lower tempera-
tures resulted in significantly better retention of flavon-
3.3. Antiradical Activity by DPPH of Dried and
Frozen Poblano Pepper
In recent years the free radical scavenging activity (DPPH
method) has been widely applied to estimate the antioxi-
dant activity of different varieties of fresh pepper [29,31,
34,37,40], nevertheless few information exist about its
changes by processing. In this study, to evaluate the im-
pact of the different preserving process, the antiradical
activity (ARA) was studied at 500 micromolar Gallic
acid equivalents concentration of pepper extracts.
At this respect, results showed that fresh Poblano
Pepper (RM) had an interesting antiradical activity, being
this of 38.55% of DPPH discoloration (Table 5). This
result could be related to the presence of high amounts of
phenolic and flavonoid compounds on the extracts, and
also to another compounds as capsaicinoids, carotenoids,
ascorbic acid, etc. [31,40].
First of all, we highlight the absence of any correlation
between ARA and TEAC, although both should reveal
the antioxidant activity. This observation was done simi-
larly by Celiktas et al., 2007 in their work concerning the
Rosmarinus officinalis extracts [41], and by Ramdane
and Mohan, 2004 [42] with their review on the correla-
tion among different antioxidant assays.
Else, among the studied preserving process (Tables 5
Table 5. Antiradical activity by DPPH (ARA) and by
trolox equivalent antioxidant capacity (TEAC) of dried
and frozen poblano pepper (For both ARA and TEAC
in terms of antioxidant activity, higher is better).
Treatment ARA (% of DPPH
Discoloration) TEAC
RM 38.55 ± 2.31 143.42 ± 4.58
FD 43.91 ± 6.10 232.82 ± 10.48
THAD 27.70 ± 2.88 195.55 ± 2.41
TF 48.69 ± 1.28 101.61 ± 7.57
Raw Material (RM), Freeze Drying (FD), Traditional Hot Air Drying
(THAD), Traditional Freezing (TF) and Pre-drying (Pre-D) of Green Po-
blano Pepper. Values represent the mean of triplicates measures ± the stan-
dard error.
and 6) the DIC-S (P: 0.41 MPa, t: 26 s), THAD and DIC-
F (P: 0.41, t: 54 s), reduced the ARA500 of peppers on
31.86%, 28.15% and 3.94% respectively compared to
RM. In the case of DIC-S it was founded that the quad-
ratic effect of steam pressure and the interaction between
the pressure and time had a significant impact on the
ARA (Figure 8A). In fact, higher values of holding time
and steam pressure increased the ARA (Figure 8B). Sta-
tistical analysis of the experimental design allowed to
obtain the prediction model Equation (6) for the ARA
(R2 = 85.16%). The optimum conditions to obtain 31.98%
of ARA were calculated at P: 0.45 MPa and t: 20.2 s.
500DIC S
ARA23.0455 31.207P0.01237t
168.313P1.5224Pt 0.00487t
For the DIC-F process, any of the studied DIC factors
(P and t) presented a significant effect on the ARA. The
highest value achieved in this range was obtained under
P: 0.41 MPa and Time: 54 s (37.03% of DPPH discolora-
tion), and the average of all treatments was of 31.70%.
On the other hand, respect to RM, the DIC-D (P: 0.45
MPa, t: 40 s), FD and TF increased the ARA on 1.05,
1.13 and 1.26 times respectively. Under the selected
Copyright © 2013 SciRes. FNS
Effect of Instant Controlled Pressure Drop Process Coupled to Drying and Freezing on
Antioxidant Activity of Green “Poblano” Pepper (Capsicum annuum L.) 329
Table 6. Antiradical activity by DPPH (ARA) and TEAC of dried and frozen poblano pepper couple to DIC.
ARA (% of DPPH discoloration) TEAC
DIC # DIC-Swelling DIC-Dried DIC-Frozen DIC-Swelling DIC-Dried DIC-Frozen
1 24.57 ± 2.81 40.69 ± 1.08 25.38 ± 2.32 98.58 ± 7.06 176.45 ± 32.51 265.85 ± 6.70
2 21.31 ± 0.54 12.43 ± 1.02 23.28 ± 2.20 223.42 ± 4.10 171.61 ± 11.44 238.88 ± 7.84
3 19.97 ± 2.26 16.58 ± 1.78 30.87 ± 1.42 116.45 ± 3.96 172.82 ± 17.56 291.61 ± 41.16
4 18.59 ± 0.31 18.10 ± 2.48 37.03 ± 1.86 247.67 ± 20.33 241.91 ± 28.39 209.79 ± 13.31
5 26.27 ± 4.16 16.58 ± 4.76 38.10 ± 1.52 233.42 ± 7.62 130.70 ± 33.73 314.33 ± 16.87
6 17.83 ± 5.03 14.66 ± 2.32 25.15 ± 1.55 205.55 ± 28.65 155.85 ± 9.64 298.88 ± 33.41
7 19.12 ± 3.10 27.79 ± 3.61 33.91 ± 2.28 243.12 ± 23.99 193.42 ± 8.59 365.24 ± 13.89
8 20.82 ± 1.07 17.83 ± 1.34 29.44 ± 3.12 252.52 ± 13.49 141.00 ± 5.68 331.00 ± 15.53
9 22.52 ± 0.15 17.65 ± 2.48 34.93 ± 2.10 242.52 ± 5.33 157.97 ± 3.44 414.64 ± 25.50
10 21.45 ± 1.70 26.31 ± 1.23 35.11 ± 2.69 254.03 ± 16.07 234.03 ± 26.60 244.64 ± 5.96
11 18.72 ± 1.12 13.54 ± 1.21 35.56 ± 4.65 145.55 ± 12.82 163.73 ± 11.82 352.52 ± 33.64
Values represent the mean of triplicates ± the standard error.
Standardized effec
P:Saturated steam pressure(MPa)
t:Therm alprocessing time(s)
Saturated steam pressure
0.4 0.20
Figure 8. Effects of steam pressure (MPa) and holding time (s) of DIC treatment on the ARA of green poblano peppers ex-
tracts at 500 µM equivalents of gallic acid. A and B: DIC-swelling (left—pareto chart and right—surface response plot).
range of DIC-D treatment conditions (P and t) an insig-
nificant effect on the ARA was presented; nonetheless
higher values were reached in two cases: at low values of
pressure and time and at high levels of pressure and time.
The highest value achieved in this range was obtained
under 0.45 MPa and 40 s as time, with 40.69% of discol-
oration. The ARA average of all treatments was 20.19%.
Finally, by analyzing the Pareto Chart of DIC-S and
the results of the DIC-D and DIC-F, it is clearly noted
that according to selected parameters of the DIC treat-
ment and the second assisted process, the ARA of sam-
ples can be optimized.
3.4. Trolox Equivalent Antioxidant Capacity by
ABTS of Dried and Frozen Poblano Pepper
To further understand the effect of the different studied
preserving process on the antioxidant activity of dried
and frozen peppers, the Trolox Equivalent Antioxidant
Capacity (TEAC) assay was also evaluated; samples with
high TEAC values have been considered a good antioxi-
dant activity.Hence, as showed on Table 5, for the RM
the TEAC was 143.42, meaning that even if the antioxi-
dant capacity of fresh pepper extract was good, the anti-
oxidant capacity was only 28.68% of that of Trolox solu-
tion at the same concentration. Concerning the impact of
preserving process on TEAC, results showed an increas-
ing on the antioxidant activity respect to RM for THAD
(1.36 times), FD (1.62 times), DIC-D (1.69 times, P: 0.41
MPa, t: 54 s), DIC-S (1.77 times, P: 0.30 MPa, t: 20 s)
and DIC-F (2.89 times, P: 0.15 MPa, t: 40 s).
Particularly for DIC-D the steam pressure (P) had
negative impact for the lowest holding time (t) value; and
positive effect for the highest holding time (t) value
(Figure 9A). High values of TEAC could be reached at
the highest values of both steam pressure and holding
time (Figure 9B). Statistical analysis of the experimental
design allowed to getting a prediction model Equation (7)
for the TEAC (R2 = 75.39%) and calculating the optimal
conditions of treatment as P = 0.45 MPa and t = 59.79 s;
with an optimal value of 285.62 TEAC.
Copyright © 2013 SciRes. FNS
Effect of Instant Controlled Pressure Drop Process Coupled to Drying and Freezing on
Antioxidant Activity of Green “Poblano” Pepper (Capsicum annuum L.)
Standardized effect
P:Saturated steam pressure(MPa)
t:Thermalprocessing time(s)
0.19 0.23 0.27
Saturated steam pressure
0.4 0.20
Standardized effect
P:Saturatedsteam pressure(MPa)
t:Thermalprocessing time(s)
Saturated steam pressure
0.4 0.20
Figure 9. Effects of steam pressure (MPa) and holding time (s) of DIC treatment on the TEAC of green poblano peppers ex-
tracts at 500 µM equivalents of gallic acid. A and B: DIC-Dried (Left—Pareto Chart and Right—Surface Response Plot); C
and D: DIC-Frozen (Left—Pareto Chart and Right—Surface Response Plot).
TEAC608.664963.495P 15.2853t
43.3062P26.5643Pt 0.08816t
 
In the case of DIC-F, the steam pressure showed a sig-
nificant impact on the TEAC (Figure 9C). The lower the
steam pressure, the higher the TEAC (Figure 9D). Sta-
tistical analysis of the experimental design led to obtain
an empirical prediction model Equation (8) for the TEAC
(R2 = 86.83%) and allowed to calculating the optimal
operation conditions at P = 0.14 MPa and t = 41 s; with
an optimal value of 415.23 TEAC. It was the best proc-
ess to increase the TEAC, having almost the same anti-
oxidant activity as Trolox.
1361.77P11.4128Pt 0.1672t
 
On the other side, for DIC-S at selected range of DIC
treatment, factors “P” and “t” presented a negligible ef-
fect on TEAC. The highest value of 254.03% was ob-
tained under P: 0.30 MPa and t: 20 s. Opposite results
were founded for TF, which reduced on 29% the TEAC
respect to RM. Overall, among the studied treatments,
results showed that by selecting the optimum parameters
conditions of DIC treatment, the antioxidant capacity
could be substantially improved.
4. Discussion
The impact of the different preserving methods on the
phytochemical content and antioxidant activity of Po-
blano Pepper could be linked to many reasons.
In the case of freeze dried samples, the reduction of
the TPC should be related to the large surface area ex-
posed during processing, which more prone the phyto-
chemicals degradation [43], and to the incapacity of the
process to inactivate the enzymes that causes degradation
of the phenolics compounds. On the other hand, the in-
crease of the TFC should be related to the structure al-
teration of the tissue, which made easier the flavonoids
extraction, particularly of those more non-polar [44]. The
increase of the RFP, reaffirmed that this process favored
the preservation of the pepper flavonoids respect to the
rest of phenolic compounds; similar results were founded
on freeze dried onion [44]. Regarding the antiradical ac-
tivity of FD samples, the increase of the ARA and TEAC
should be related to the increase of their total flavonoids
Copyright © 2013 SciRes. FNS
Effect of Instant Controlled Pressure Drop Process Coupled to Drying and Freezing on
Antioxidant Activity of Green “Poblano” Pepper (Capsicum annuum L.) 331
content. Shofian et al., 2011, showed a good preservation
of heat-sensitive antioxidant components by the FD
process [45].
For the THAD samples, the minimal increase of TPC
should be related to the intensification of drying condi-
tions (low temperature, high air flux and low relative
humidity of the air). Respect to the TFC, the decrease
could be related to the destruction by oxidation of some
flavonoids during the long-time of drying [46]. The de-
crease of the RFP showed that the THAD process pre-
served better other kind of phenolics than flavonoids.
Regarding the antiradical activity, the decrease of ARA
possibly should be related to a reduction on its TFC. The
ARA of total dried Korean peppers was also affected by
air drying conditions [3]. For TEAC, the increase could
be related to the nature of the assay and to the preserva-
tion of the total phenolic content of the extracts.
For traditional freezing samples, the loss of TPC could
be linked to oxidative enzyme reactions during the stor-
age [47]. Else, the preservation of the TFC should be
related to the tolerance of these molecules to freezing
temperatures. The TFC of Brussels sprouts were also
well preserved under freezing conditions [48]. Further-
more, the increase of the RFP showed that this process
favored the preservation of the pepper flavonoids respect
to other phenolic compounds. Moreover, among all the
studied preserving methods, the TF was the best method
to increase the ARA; this should be due to flavonoids
were the main responsible of antiradical activity of pep-
per and this process preserved quite well these bioactive
compounds. The reduction of the TEAC would be linked
to the reduction on the TPC of the samples.
In the case of the impact of the DIC treatment, the im-
provement of the TPC (DIC-S, DIC-D and DIC-F), the
TFC (DIC-S and DIC-F), the ARA (DIC-D) and the
TEAC (DIC-S, DIC-D and DIC-F) could be attributed to
the new generated food matrix structure, which was ex-
panded during DIC thermal-mechanical treatment, al-
lowing bioactive compounds to be more available, fa-
voring their extraction. The increasing of micro-alveola-
tion in the food matrix possibly favors the internal diffu-
sion of bioactive molecules. Therefore, in the specific
case of phenolic compounds, it could be possible that the
inactivation of the polyphenol oxidase enzyme that oc-
curs during heating in the cooking process would also
occur during the DIC process, avoiding the degradation
of polyphenols [49,50]. Additionally, high temperatures
(i.e. >90˚C) would cause the formation of phenolic com-
pounds because of the availability of precursors of phe-
nolic molecules by non-enzymatic inter-conversion be-
tween phenolic molecules [51].
Else, for the DIC-F the improvement of the TPC and
TFC would be also attributed to the reduction of moisture
content before freezing, which reduces the cell wall
damage, caused by traditional freezing. The study of
Mounir et al., 2011 [52], also showed more available
flavonoids after the DIC treatment of apples.
The decrease of the TFC and the RFP of the DIC-D
should be due to the fact that some flavonoids were de-
stroyed by oxidation during the second drying [53].
Furthermore, the increase of the RPF of the DIC-S and
the DIC-F would be related to the stabilization of pepper
flavonoid compounds during the DIC treatment. At this
respect, the study of Adamczak, 2009 [54], indicates that
drying temperatures in the order of 120˚C - 150˚C, stabi-
lizes better flavonoid compounds than a temperature of
40˚C - 60˚C.
Moreover, in the case of ARA, its increase on DIC-D
samples should be also related to the synthesis of new
molecules with antioxidant activity during the DIC treat-
ment; asMaillard derived melanoidins which have been
shown a varying degree of antioxidant activity [51]. Else,
other studies on peppers showed that boiling, steaming
[50,55,56] and drying at high temperatures (i.e. >90˚C)
[14,57] also increased the ARA. Opposite, the reduction
of ARA on the DIC-F and DIC-S samples, would be re-
lated to the changes of composition of their bioactive
molecules during storage.
According to the different obtained results from DIC
samples it has been highlighted the importance of ulterior
conditions of processing after DIC treatment to preserve
the bioactive compounds and to enhance the antioxidant
Therefore, even that ARA and TEAC assays were
based on similar redox reactions, the differences among
the obtained results would be related to their particular
limits of applications [58]. In this study, the use of
methanol solvent possibly restricted the cellular com-
pounds responsible for scavenge the DPPH radical, then
only methanolic soluble molecules, would have been
involved in this scavenging process [59].
5. Conclusion
The present work allowed us to study different food op-
erations assisted by instant controlled pressure drop DIC
treatment. The use of DIC as intensifying process had a
direct impact on active molecules and functional activity
in the case of Green “Poblano” Pepper (Capsicum annuum
L.). Results issued from DIC-assisted hot air drying, and
DIC-assisted freezing allowed identifying the most im-
portant factor in terms of DIC operating parameters.
Hence, the saturated steam pressure and the processing
time could normally be recognized to obtain the best DIC
treatment depending of the considered food operation.
6. Acknowledgements
The authors acknowledge the ConsejoNacional de Ciencia
Copyright © 2013 SciRes. FNS
Effect of Instant Controlled Pressure Drop Process Coupled to Drying and Freezing on
Antioxidant Activity of Green “Poblano” Pepper (Capsicum annuum L.)
y Tecnología (CONACyT-Mexico) and the Programme
de Coopération Post-Gradué Franco-Mexicain (PCP) for
the financial support given to this research. Also we wish
to thank ABCAR-DIC PROCESS SAS (La Rochelle,
France) for providing drier equipment and pilot-scale
DIC reactor.
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