Innovative Food Science and Emerging Technologies 7 (2006) 195 – 202
www.elsevier.com/locate/ifset
Vacuum pulse and brine composition effect on pickling kinetics
of whole jalapeño pepper
H. Mújica-Paz a,⁎, L.D. Argüelles-Piña a , L.C. Pérez-Velázquez a , A. Valdez-Fragoso a ,
J. Welti-Chanes b
a
Facultad de Ciencias Químicas, Universidad Autónoma de Chihuahua, Av. Universidad s/n, Ciudad Universitaria, Chihuahua, Chih. 31170, México
Departamento de Ingeniería Química y Alimentos, Universidad de las Américas-Puebla, Santa Catarina Mártir, Cholula, Puebla, 72820, México
b
Received 23 November 2004; accepted 13 February 2006
Abstract
The combined effect of pickling time and pickling solutes concentration was studied on pickling whole jalapeño pepper by applying a vacuum
pulse (VP) of 666 mbar for 5 min. Sodium chloride and acetic acid concentrations ranged from 10–15.1% to 2.3–3.2% (w/w), respectively, and
the pickling or processing time varied from 0.3 to 30 days. The response surface methodology was used to evaluate the influence of the process
variables on water loss (WL), solutes gain (SG) and weight reduction (WR) of jalapeño pepper. Processing time showed a linear effect on most of
the pickling rate parameters (p b 0.01). Sodium chloride concentration affected WL, SG and WR of pepper pickled with VP, but the interaction
between acetic acid and processing time affected WL (p b 0.10) and WR (p b 0.05). In general, the use of VP enhanced solutes and weight gain and
it also reduced pickling time by around 50%, in comparison to pickling conducted without VP.
© 2006 Elsevier Ltd. All rights reserved.
Keywords: Vacuum impregnation; Pickles; Jalapeño pepper; Mass transfer
Industrial relevance: Vacuum pulse application in conjunction with increasing pickling solutes concentration resulted in a significant reduction of pickling time of
whole jalapeño pepper, compared to industrial pickling. Thus, mass transfer rates of cold packing can be accelerated by vacuum pulse without heat treatment
application, which can lead to significant time and energy savings in the pickling industry.
1. Introduction
Whole jalapeño peppers are commercially pickled by
dipping fresh peppers in bulk tanks containing a solution of
acetic acid and sodium chloride at room temperature and
atmospheric pressure. At equilibrium, relatively high concentrations of pickling solutes in the pepper tissue are reached.
Such concentrations not only improve palatability of jalapeño
pepper but also contribute to prolong the shelf-life, due to the
preserving effect of low pH and depressed water activity
(aw) (Guerra-Vargas, Jaramillo-Flores, Dorantes-Alvarez, &
Hernández-Sánchez, 2001; Daeschel, Fleming, & Pharr, 1990).
The pickling process conducted at room temperature, known
as cold packing, is preferred by some manufacturers over the
pickling with pasteurization, because it reduces the amount of
⁎ Corresponding author. Tel./fax: +52 614 414 4492.
E-mail address: [email protected] (H. Mújica-Paz).
1466-8564/$ - see front matter © 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.ifset.2006.02.001
energy required and allows retention of firmness and color of
pickled product (Daeschel, et al., 1990). The main disadvantage
of the cold packing process is, however, the long processing
time to attain preserving concentrations in the tissue pepper, due
to the low mass transfer rates.
Vacuum pulse application on osmotic dehydration–impregnation by immersion in a hypertonic solution has been the focus
of many studies as an innovative technique that promotes
vacuum impregnation (VI) of external solutions into the pores
of the product by the coupling action of hydrodynamic and
diffusion mechanisms (Fito & Pastor, 1994).
VI has been applied in the fortification of fruits and
vegetables with minerals (Welti-Chanes et al., 2001; MújicaPaz, et al., 2002; Ortíz, Salvatori, & Alzamora, 2003) and in the
incorporation of protective agents into the tissue of apple slices
(Martínez-Monzó, Martínez-Navarrete, Chiralt, & Fito, 1998).
Several studies have shown that VI improves the color of cut
fruits by the impregnation of antibrowning agents (Sapers,
196
H. Mújica-Paz et al. / Innovative Food Science and Emerging Technologies 7 (2006) 195–202
Garzarella, & Pilizota, 1990), increases firmness of canned
peaches and apricots by incorporation of calcium (Javeri,
Toledo, & Wicker, 1991; French, Kader & Labavitc, 1989),
improves texture and palatability of fruits (Moreno, Bugueño,
Velasco, Petzold, & Tabilo-Munizaga. 2004), and reduces
microbial counts of chicken meat by infiltration of acid solution
into the pores of chicken skin (Deumier, 2004). It has also been
reported that VI increases the mass transfer rates in the salting of
cheese (González-Martínez, Cháfer, Fito, & Chiralt, 2002) and
cod fish (Andrés, Rodríguez-Barona, Barat, & Fito, 2002), in
the brining of poultry meat (Deumier, Bohuon, Trystram, Saber,
& Collignan, 2003), and in the osmotic dehydration of fruits
(Moreno et al., 2004; Mújica-Paz, Valdez-Fragoso, LópezMalo, Palou, & Welti-Chanes, 2003a; Rastogi & Raghavarao,
1996). In addition to higher mass transfer rates, VI predominantly leads to lower water loss, higher solutes uptake and a
uniform distribution of solutes, which are significant advantages over conventional osmotic dehydration treatments
(Rastogi & Raghavarao, 1996; Mújica-Paz, et al., 2003a;
Deumier, 2004; Deumier, Trystram, Collignan, Lahcène, &
Bohuon, 2003).
The sensitivity of food matrices to VI mainly depends on the
applied vacuum level and the impregnation properties of the
product (Mujica-Paz, Valdez-Fragoso, López-Malo, Palou, &
Welti-Chanes, 2003b). The impregnation properties, such as the
impregnated liquid fraction (X) and the effective porosity (εe),
indicate how much of an isotonic solution penetrates into the
internal pores. In a previous work effective porosity of jalapeño
pepper and the impregnated isotonic solution fraction were
found to be 11% and 0.12%, respectively (Mújica-Paz, et al.
2003c). These results indicated that jalapeño pepper has good
impregnation properties, and therefore, it would be feasible to
apply VI in pickling process of jalapeño pepper to incorporate
the solution with pickling solutes into its pores.
On the other hand, the amount of impregnated solution
depends on solution viscosity which is strongly related to the
solutes concentration (Barat, Chiralt, & Fito, 2001; Barat,
Rodríguez-Barona, Andrés, & Fito, 2002; Mújica-Paz, et al.,
2003b; Cháfer, González-Martínez, Chiralt, & Fito, 2003).
Solute concentration is considered an important variable of the
osmotic dehydration–impregnation by immersion in a hypertonic solution, such as pickling process, because it determines
the mass transfer rates (Torreggiani, 1995; Ozen, Dock,
Ozdemir, & Floros, 2002) and consequently the processing
time.
Therefore, the purpose of this study was to determine the
effect of vacuum application and pickling solute concentration
on mass transport parameters of pickling whole jalapeño
pepper.
2. Materials and methods
2.1. Raw material and solution preparation
A lot of fresh jalapeño peppers (Capsicum annum var.
“Mitla”) were obtained from local producers. Peppers, free from
physical damage, were sorted for homogeneous size and ma-
turity and then kept under refrigeration and used in pickling
trials within a period of six days. Pickling solutions were
prepared with predetermined quantities of sodium chloride,
acetic acid, calcium chloride and sodium bisulfite (purity N
95%).
2.2. Analytical methods
Analytical determinations were carried out on finely blended
samples of three fresh or processed peppers. Moisture content
and titratable acidity were determined following the official
methods of the AOAC (1984). Moisture content was determined by vacuum oven drying at 70 °C and 50 Torr for 6 h
(method 22.013) and titratable acidity (expressed as percentage
of acetic acid) was analyzed by titrating the sample with 0.1 N
NaOH to pH 8.2 (method 22.008). Sodium chloride concentration was measured with a salt meter accurate to ± 0.05% (Atago
Mod. ES-421, Japan). Determinations were performed by
triplicate.
2.3. Pickling experiments
Two sets of pickling experiments were conducted, with or
without vacuum pulse application. Pickling without vacuum
pulse represented the actual industrial pickling. Weighed whole
peppers were dipped in the acidified brine in a ratio pickling
brine to whole jalapeño peppers of five to one (w/w) (around
1225 to 225 g). Sodium chloride and acetic acid concentrations
were in the range 10–15.1% and 2.3–3.2% (w/w), respectively.
Such ranges encompass solute concentration levels used in
pickling industry. All pickling solutions contained constant
concentration of calcium chloride (0.2% w/w) and sodium
bisulfite (0.16% w/w) as a firmness and antimicrobial agent,
respectively. At the beginning of the VI process, the systems
pepper-pickling brine was subjected to a vacuum pulse of
666 mbar (Felisa pump, Mod. 1600 L, México) for 5 min (ti,
impregnation time). These vacuum pressure and application
time values were chosen because they have been reported as the
conditions leading to the highest impregnation of isotonic
solution in the pepper tissue (Mújica-Paz, et al., 2003c). After
the vacuum pulse, the pickling systems were held at
atmospheric pressure for a predetermined relaxation time (tr)
that varied between 0.3 and 30 days.
After the processing time (tp), peppers were taken out of the
pickling solution, sliced in half longitudinally, and drained in a
colander for 5 min (td) for removing solutions that adhered to
the surface of the pepper. The drained peppers were then
weighed and a sample was blended for analytical determinations. The pickling process at atmospheric pressure (without
vacuum pulse) was conducted at the same combination of solute
concentration and processing time (tp), the later being
equivalent to ti + tr .
Experiments were performed at around 23 ± 2.4 °C, and three
replicates were run simultaneously, under each combination of
variables. For each experimental condition, initial and final
weight of the peppers, and the water, sodium chloride and
acidity contents were measured.
H. Mújica-Paz et al. / Innovative Food Science and Emerging Technologies 7 (2006) 195–202
197
Table 1
Independent variable levels of the central composite design and responses a for the pickling of jalapeño pepper
Run
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Actual variable levels b
Responses c
X1
X2
X3
Without vacuum pulse
With vacuum pulse
WL
SG
WR
WL
SG
WR
15.1
0.3
24
15.1
15.1
15.1
15.1
15.1
6.3
24
6.3
15.1
30
6.3
15.1
6.3
15.1
24
6.3
15.1
12.6
12.6
14.1
12.6
15.0
12.6
12.6
10
11.0
11.0
14.1
12.6
12.6
11.0
12.6
11.0
12.6
14.1
14.1
12.6
2.7
2.7
2.5
2.7
2.7
2.7
3.2
2.7
2.5
2.5
2.5
2.7
2.7
3.0
2.3
3.0
2.7
3.0
3.0
2.7
21.96
1.89
25.26
22.75
35.47
21.92
18.49
16.53
11.71
18.83
16.27
21.86
16.82
10.10
21.10
16.22
22.00
22.30
17.22
23.07
4.89
0.23
6.1
4.97
4.26
4.71
4.59
4.71
1.55
5.15
2.49
4.85
6.61
2.19
4.67
6.10
4.94
6.32
2.69
4.93
17.07
1.66
19.16
17.78
31.21
17.21
13.90
11.82
10.16
13.68
13.78
17.01
10.21
7.91
16.43
10.12
17.06
15.98
14.53
18.14
5.44
0.04
7.49
5.92
10.94
5.30
5.13
0.72
0.43
6.32
7.68
5.02
2.38
3.81
9.28
5.36
5.33
− 2.34
9.50
5.23
7.32
0.39
7.78
7.46
8.49
7.54
7.95
7.01
2.86
7.79
4.62
7.48
9.8
4.04
6.51
7.42
7.59
8.81
3.54
7.26
− 1.88
− 0.35
− 0.29
− 1.54
2.45
− 2.24
− 2.82
− 6.29
− 2.43
− 1.47
3.06
− 2.46
− 7.42
− 0.23
2.77
− 2.06
− 2.26
− 11.15
5.96
− 2.03
a
Average value of three replicates.
X1 — processing time (treatment without vacuum pulse) or relaxation time (treatment with vacuum pulse) (days), X2 — sodium chloride concentration (%, w/w),
X3 — acetic acid concentration (% w/w).
c
WL — water loss (%, w/w), SG — solids gain (%, w/w), and WR — weight reduction (%, w/w).
b
of whole jalapeño pepper, as well as fitting a second-order
equation of the form
2.4. Experimental design
Fifteen pickling conditions were run according to a central
composite rotatable design (Table 1), with five additional
replications of the center point, for both set of pickling
experiments (Cornell, 1990). Each independent variable was
at five levels (Table 1). The selected experimental design allows
studying the effect of processing time, sodium chloride and
acetic acid concentration (Xi) on the pickling rate parameters (Y)
Y ¼ b0 þ
3
X
bi X i þ
1
3
X
bii X12 þ
1
3
X
ð1Þ
bij Xi Xj
1
where b0, bi, bii and bij are constant, linear, quadratic and cross
product regression coefficients of the polynomial model.
Table 2
Results of analysis of variance for the fitted models
F value*
Variable
Model
X1
X2
X3
X 21
X 22
X 23
X1X2
X1X3
X2X3
Lack of fit
Coefficient R2
Without vacuum pulse
With vacuum pulse
WL
SG
WR
WL
SG
WR
29.23***
65.01***
74.29***
2.67
105.24***
5.96**
5.25**
0.028
0.98
0.20
22.21ns
0.963
56.69***
462.38***
2.45
2.51
39.35***
3.29*
1.46
0.089
0.13
1.66
22.32ns
0.981
16.94***
13.73***
55.44***
2.95
66.35***
6.14**
3.44*
0.039
0.89
0.37
34.01ns
0.938
6.89***
0.010
13.58***
3.84*
10.16***
0.15
2.11
15.79***
10.66***
4.53*
64.3ns
0.861
18.22***
133.94***
3.32*
1.28
24.66***
0.082
1.45
0.003
0.068
0.16
70.33ns
0.942
7.14***
22.15***
6.83**
4.98**
0.84
0.22
3.23
13.14***
9.41**
3.15
67.12ns
0.865
Significance level ***p b 0.01, **p b 0.05, and *p b 0.10; nsnon-significant.
X — relaxation time (vacuum treatment) or processing time (atmospheric treatment) (days), X2 — NaCl concentration (% w/w), X3 — acetic acid concentration
(% w/w).
WL — water loss (%), SG — solids gain (%), and WR — weight reduction (%, w/w).
198
H. Mújica-Paz et al. / Innovative Food Science and Emerging Technologies 7 (2006) 195–202
Table 3
Regression models with significant variables for the prediction of pickling rate parameters
Treatment
Equations
R2
Without vacuum pulse
WL = − 59.339 + 2.282X1 − 9.571X2 + 78.704X3 − 0.0609X 21 + 0.488X 22 − 14.838X 23
SG = − 10.799 + 0.413X1 + 1.641X2 − 0.007X 21 − 0.062X 22
WR = − 35.805 + 1.866X1 − 11.327X2 + 70.434X3 − 0.054X 21 + 0.555X 22 − 13.428X 23
WL = − 183.587 + 5.193X1 + 12.686X2 + 49.612X3 − 0.020X 21 − 0.181X1X2 − 0.847X1X3 − 3.202X2X3
SG = − 2.798 + 0.647X1 + 0.247X2 − 0.012X 21
0.959
0.969
0.930
0.8311
0.9254
0.7311
With vacuum pulse
WR = − 67.926 + 4.422X1 + 3.646X2 + 8.970X3 − 0.182X1X2 − 0.877X1X3
WL (water loss), SG (solids gain), and WR (weight reduction) are the pickling parameters (Y) given by Eq. (1) and expressed as % (w/w).
X1 — relaxation time (vacuum treatment) or processing time (atmospheric treatment) (days), X2 — NaCl concentration (% w/w), X3 — acetic acid concentration
(% w/w).
The pickling rate parameters water loss (WL), solutes gain
(SG), and weight reduction (WR) were the studied response
variables. WL is defined as the g of water lost per 100 g initial
weight, SG as the g of solutes gained (acetic acid + sodium
chloride) per 100 g initial weight, and WR as the g of weight
reduction per 100 g of initial weight. These parameters were
calculated as described in the literature (Lerici, Pinnavaia, Dalla
Rosa, & Bartolucci, 1985; Mújica-Paz, et al., 2003a).
3. Results and discussion
Table 1 shows the average values of the calculated mass
transfer parameters water loss (WL), solutes gain (SG) and
weight reduction (WR) of pickled jalapeño pepper. Important
differences are observed in the mass transfer parameters
between the two pickling treatments. WL values are lower for
the pepper pickled with VP (4.95 ± 3.37%) than the pepper
pickled without VP (19.08 ± 6.67%), while slightly higher SG
values are observed in peppers pickled with VP (6.58 ± 2.30)
than the pepper non-vacuum-treated (4.34 ± 1.67%). Application of VP resulted in weight gain of pepper, shown by the
negative values of WR (− 1.63 ± 3.77%), contrary to a clear
weight reduction of the pepper pickled without initial VP
(14.74 ± 5.75%).
(a)
3.1. Statistical analysis
Response surface regression and analysis of variance
(ANOVA) of obtained results were performed using the Design
Expert software (2002, V.6.0.6). This analysis allowed to fit the
second-order polynomial and to determine the significance of
the independent variables on pickling rate parameters, which
was assessed by the F-test (Table 2).
According to the F-test all regression models for the
response variables were significant (p b 0.01) (Table 2). A
high proportion of the variability was explained for the response
models for the pickling of jalapeño pepper without vacuum
pulse (VP) (R2 N 0.938). In the case of pickling with VP, fairly
lower values of the coefficient of determination were found for
the WL (R2 = 0.861) and WR (R2 = 0.865) models, which can be
attributed to the inherent variability of the VP treatment. The six
models had no significant lack of fit at 1% significant level.
Therefore, the polynomial equations developed for both set of
responses were suitable for representing the relationship
between independent and dependent variables. The regression
coefficients of significant variables and its interactions are
presented in Table 3.
Analysis of variance (Table 2) shows linear and quadratic
effect of processing (or relaxation) time on the pickling rate
(b)
WL (% w/w)
15.1
WL (% w/w)
15.1
-10
8
[NaCl]sol (% w/w)
[NaCl]sol (% w/w)
25
13.8
20
11
12.6
2
17
13.8
12.6
5
11
11.3
-2
6
3
5
11.3
3
10.0
10.0
0.3
7.7
15.2
22.6
processing time (days)
30.0
0.3
7.7
15.2
22.6
30.0
processing time (days)
Fig. 1. Water loss (WL) of jalapeño pepper pickled without (a) and with initial vacuum pulse (b), as a function of processing time and NaCl concentration.
[CH3COOH]sol = 3.2% (w/w).
H. Mújica-Paz et al. / Innovative Food Science and Emerging Technologies 7 (2006) 195–202
parameters, except in the case of water loss (WL) and weight
reduction (WR) of pepper pickled with VP, where no linear
and no quadratic effects were observed, respectively. WL and
WR obtained with VP were, however, significantly influenced
by the interaction processing time–sodium chloride concentration (X1X2) (p b 0.01) and processing time–acetic acid
concentration (X1X3), at p b 0.01 (WL) and p b 0.05 (WR). The
interaction sodium chloride–acetic acid concentrations (X2X3)
influenced WL (p b 0.1) of pepper pickled with VP. Sodium
chloride concentration in the pickling solution (X2) was a
significant factor for all the pickling rate parameters,
excepting the solutes gain (SG) of pepper pickled without
VP. Acetic acid concentration (X3) only showed a significant
effect on WL (p b 0.10) and WR (p b 0.05) of pepper pickled
with VP.
3.2. Pickling rate parameters
The six fitted polynomial equations containing significant
factors or its interactions terms (Table 3) were used to display
contour plots (Fig. 1 to Fig. 4). Contour plots of Fig. 1 to Fig. 3
were generated by setting an acetic acid concentration in the
solution of 3.2%, because, among the three studied pickling
factors, acetic acid concentration was the factor that least
influenced rate parameters (Table 2).
3.2.1. Water loss (WL)
The quadratic effect exerted by processing time on WL
(Table 2) is shown in Fig. 1, for both treatments, with and
without VP. In general, higher WL values were obtained in
pepper pickled without VP than in the pepper treated with VP.
Fig. 1a shows that high WL values (around 25%) were
obtained over a pickling time range of 15–20 days and a sodium
chloride concentration range of 14–15%. Jalapeño pepper
pickled with VP showed negative WL values (up to − 10%), at
high sodium chloride concentration in the pickling solution
(N12.6%) and beyond 20 days of processing (Fig. 1b). These
(a)
results indicate that during the traditional pickling process
pepper dehydration predominates, while water gain of jalapeño
pepper can occur on certain conditions of pickling with initial
VP. External solution uptake, and consequently water gain, has
also been observed in the osmotic dehydration of apple (MújicaPaz, et al., 2003a) and papaya (Moreno et al., 2004) with
vacuum pulse application, as well as in the brining of meats and
impregnation of acid solutions into the follicles of poultry skin
(Deumier, Bohuon, et al., 2003; Deumier, 2004). The uptake of
external solution has been attributed to the pressure changes to
which the solid–liquid system is exposed. At the beginning of
the pickling process a VP is applied for a short time and then the
process continues at atmospheric pressure for longer times. So,
initial pressure changes allow the exchange of internal gas
occluded in pores or capillaries of the solid product by the
external solution through hydrodynamic mechanism (Fito &
Chiralt, 1997).
3.2.2. Solutes gain (SG)
The contour plots of Fig. 2 show the SG of pepper pickled
with and without VP as a function of processing time and
brine sodium chloride concentration, at an acetic acid concentration of 3.2%. Although acetic acid concentration had no
significant effect on SG (Table 2), it was kept at this level, for
the analysis under similar conditions of the other parameters.
SG is expressed as the g of solutes (acetic acid + sodium
chloride) gained per 100 g initial weight. Sodium chloride
concentration in the pickling solution had no significant effect
on SG of pepper pickled without VP (Table 2, Fig. 2a), but
SG was linearly dependent on concentration of sodium chloride in the treatments with VP (Fig. 2b). In the early stage of
this process, for a given value of SG, processing time decreased linearly with an increase in concentration of sodium
chloride.
The linear and quadratic effect of processing time on SG of
pickled pepper is clearly shown by the shape of the contour
plots (Fig. 2). SG increased with the processing time at levels
(b)
SG (% w/w)
6
12.6
SG (% w/w)
15.1
1
2
4
5
6
11.3
[NaCl]sol (% w/w)
[NaCl]sol (% w/w)
15.1
13.8
199
9
13.8
2
12.6
4
6
7
8
11.3
10.0
10.0
0.3
7.7
15.2
22.6
processing time (days)
30.0
0.3
7.7
15.2
22.6
30.0
processing time (days)
Fig. 2. Solutes gain (SG) of jalapeño pepper pickled without (a) and with initial vacuum pulse (b), as a function of processing time and NaCl concentration.
[CH3COOH]sol = 3.2% (w/w).
200
H. Mújica-Paz et al. / Innovative Food Science and Emerging Technologies 7 (2006) 195–202
(a)
(b)
WR (% w/w)
15.1
WR(% w/w)
15.1
-15
-15
19
19
13.8
[NaCl]sol (% w/w)
[NaCl]sol (% w/w)
12
15
15
10
10
12.6
11
10
10
11.3
13.8
55
-0
-0
12.6
-10
-10
-7
-4
-4
11.3
10.0
10.0
7.7
0.3
15.2
22.6
30.0
processing time (days)
0.3
7.7
15.2
22.6
30.0
processing time (days)
Fig. 3. Weight reduction (WR) of jalapeño pepper pickled without (a) and with initial vacuum pulse (b), as a function of processing time and NaCl concentration.
[CH3COOH]sol = 3.2% (w/w).
lower than 6.5% in the treatment conducted at atmospheric
conditions, whereas SG increased up to 9% in the process with
initial VP application. A SG of 8% was achieved in the pickling
with VP and relatively low sodium chloride concentration
(11.5%) and around 25-day treatment, which was not possible
on pickling without VP, at any combination variables within the
studied ranges. In addition, the application of VP accelerated the
SG rate and as it is seen in Fig. 2b, at a sodium chloride
concentration between 11.3% and 13.8%, the processing time to
attain a SG value of 6% in the tissue of jalapeño was roughly
50% lower than that required by the treatment in which VP was
not applied (Fig. 2a).
Differences between SG levels of pepper pickled with and
without VP can be partially attributed to the initial pressure
gradient, which induced a bulk penetration of pickling solution
into the pores of pepper tissue caused by the action of hydrodynamic mechanisms (Chiralt et al., 2001) and facilitated by the
WR (% w/w)
3.2
[CH3COOH]sol (% w/w)
4
-10
11
3.0
-6
-6
-3
-3
2.8
-1
-1
-.6
-.6
-0.6
-0.6
2.5
-1
1
2.3
0.3
7.7
15.2
22.6
30.0
processing time (days)
Fig. 4. Interaction effect CH3COOH–processing time on WR of whole jalapeño
pepper pickled with initial vacuum pulse. [NaCl]sol = 12.5% (w/w).
effective porosity of jalapeño pepper (11.6%) (Mújica-Paz, et
al., 2003c). Once the pickling solution has almost filled the
intercellular pores, solute transport through cell walls occurs by
diffusion mechanisms driven by a concentration gradient. In
addition, the application of vacuum pulse induced quicker infiltration of the pickling solution to the inner void of whole
jalapeño pepper, leading to the establishing of a concentration
gradient in the external and internal sides of the pepper tissue,
which would contribute to the solute impregnation of the
pepper matrix (Mújica-Paz, Martínez-Monteagudo, SalaisFierro, Welti-Chanes, & Valdez-Fragoso, 2004). Therefore,
the combined effect of the impregnation–infiltration phenomena resulted in an increased interfacial and superficial area
and consequently in considerably greater pickling solute
incorporation.
According to these results, the application of VP allowed to
achieve, in less time, higher levels of preserving agents in the
tissue pepper (6–9% of acetic acid + NaCl). These concentrations are sufficiently high to prevent spoilage of the pepper, if
the pickling process is conducted without thermal treatment
(Guerra-Vargas et al., 2001). Heat processing is commonly used
to preserve pickled items at relatively low concentrations of
acetic acid (0.6%) and sodium chloride (0.6%) (Guerra-Vargas
et al., 2001; Fleming, Thompson, & McFeeters, 1993).
3.2.3. Weight reduction (WR)
The influence of sodium chloride concentration and processing time on WR of pepper pickled with and without VP is
shown in contour plots of Fig. 3, at a 3.2% of acetic acid
concentration. WR includes the overall effect of dehydration
and solute impregnation phenomena (WR = WL − SG). A significant interaction between sodium chloride concentration and
processing time (Table 3) can be seen in Fig. 3b. When
processing time is 0.3 days, as sodium chloride concentration
increased WR increased, but at 30-day processing as sodium
chloride concentration increased, the response WR decreased.
The interaction effect acetic acid concentration–processing time
H. Mújica-Paz et al. / Innovative Food Science and Emerging Technologies 7 (2006) 195–202
on WR (Table 3), is shown in Fig. 4, at a 12.5% sodium chloride
concentration.
It can be noted in Fig. 3b that negative WR values were
obtained in a wide range of operation variables during the
pickling of jalapeño pepper with initial VP, but only positive WR
values resulted from the treatment without vacuum application
(Fig. 3a). Negative WR values indicated an increase of whole
jalapeño pepper weight, which resulted from high SG levels
(Fig. 2b) and negative values of WL (Fig. 1b) (WR = WL − SG).
Such outcomes occur predominantly at high sodium chloride
concentration and large pickling times (Fig. 1b, Fig. 2b, and Fig.
3b). This result is similar to those reported in the acidification of
chicken meat using pulsed vacuum immersion (Deumier, 2004)
and in the osmotic dehydration of apple (Mújica-Paz, et al.,
2003a) and orange peel (Cháfer, González-Martínez, Ortola, &
Chiralt, 2001) with initial vacuum pulse application. This
general pattern may be associated with the relatively high
porosity of the products or with the vacuum pulse levels.
4. Conclusions
In general, higher solutes gain and lower water loss were
observed in the pickled pepper vacuum pulse treated, leading to
significant weight gain. In both treatments, an increase in
sodium chloride concentration increased water loss of pepper.
Interaction effects acetic acid concentration–processing time
and acetic acid concentration–sodium chloride concentration
influenced water loss and weight reduction of pepper pickled
with vacuum pulse. The application of vacuum pulse accelerated
pickling whole jalapeño pepper and reduced pickling time from
around 30 to 15 days compared to the industrial processing at
atmospheric pressure.
Acknowledgements
The authors would like to acknowledge the PROMEP-SEP
(México) for the financial support, Project No. UACHIH-PTC01-01.
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