propiedades de scamoles

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Experimental and simulated thermal properties and
process time for canned escamoles (Liometopum
apiculatum) under sterilization conditions
Miguel Angel Ruiz-Cabrera
a
, Alicia De Anda-Salazar
a
, Raúl González-García
a
, Miguel
Abud-Archila
b
& Alicia Grajales-Lagunes
a
a
Facultad de Ciencias Químicas, Universidad Autónoma de San Luis Potosí, Av. Dr.
Manuel Nava # 6, Zona Universitaria, C.P. 78210, San Luis Potosí, S.L.P., México
b
División de Estudios de Posgrado e Investigación, Instituto Tecnológico de Tuxtla
Gutiérrez Chiapas, Carretera Panamericana km 1080. C.P. 29050, Tuxtla Gutiérrez,
Chiapas, México
Published online: 24 Jul 2014.
To cite this article: Miguel Angel Ruiz-Cabrera, Alicia De Anda-Salazar, Raúl González-García, Miguel Abud-Archila &
Alicia Grajales-Lagunes (2014): Experimental and simulated thermal properties and process time for canned escamoles
(Liometopum apiculatum) under sterilization conditions, CyTA - Journal of Food, DOI: 10.1080/19476337.2014.936512
To link to this article: http://dx.doi.org/10.1080/19476337.2014.936512
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2. Experimental and simulated thermal properties and process time for canned escamoles
(Liometopum apiculatum) under sterilization conditions
Propiedades térmicas y tiempo de proceso experimental y simulado para escamoles enlatados
(Liometopum apiculatum) en condiciones de esterilización
Miguel Angel Ruiz-Cabreraa
, Alicia De Anda-Salazara
, Raúl González-Garcíaa
, Miguel Abud-Archilab
and
Alicia Grajales-Lagunesa
*
a
Facultad de Ciencias Químicas, Universidad Autónoma de San Luis Potosí, Av. Dr. Manuel Nava # 6, Zona Universitaria, C.P. 78210,
San Luis Potosí, S.L.P., México; b
División de Estudios de Posgrado e Investigación, Instituto Tecnológico de Tuxtla Gutiérrez Chiapas,
Carretera Panamericana km 1080. C.P. 29050, Tuxtla Gutiérrez, Chiapas, México
(Received 13 December 2013; final version received 16 June 2014)
Sterilization process of canned pickled escamoles and canned brined escamoles was studied in order to analyze the heat transfer mechanisms
as well as to calculate the thermal properties and process time. Sterilization process was performed using water immersion and saturated steam
at 115°C and 121°C. Transient temperature changes in the cold point inside of the can containing either pickled or brined escamoles were
determined experimentally and compared with simulation results. Additionally, the physicochemical, nutritional and sensory quality properties
of sterilized escamoles were also evaluated. Uniform and conductive heating profiles were observed in both products. The thermal
conductivity (k), specific heat (Cp) and density (ρ) were significantly affected (p < 0.05) by the temperature and by the heating medium.
Results also showed that maximum quality retention and the lowest process times were achieved for canned pickled escamoles.
Keywords: canned escamoles; heat transfer; process time; thermal and physicochemical properties
El proceso de esterilización para el enlatado de escamoles en escabeche y en salmuera fue estudiado para analizar los mecanismos de
transferencia de calor y para calcular las propiedades térmicas y el tiempo de proceso. El proceso de esterilización se realizó usando
inmersión en agua y vapor saturado a 115°C y 121°C. Los cambios de temperatura en el punto frío dentro de la lata la cual contenía
escamoles en escabeche o escamoles en salmuera fueron determinados experimentalmente y por simulación. Las propiedades
fisicoquímicas, nutricionales y sensoriales de los productos terminados también fueron evaluadas. Transferencia de calor por conducción
fue observada en ambos productos. La conductividad térmica (k), el calor específico (Cp), y la densidad (ρ) fueron afectados significa-
tivamente (p < 0,05) por la temperatura y por el medio de calentamiento. Los resultados también mostraron que los productos con mayor
calidad y menor tiempo de proceso fueron los escamoles en escabeche.
Palabras claves: escamoles enlatados; transferencia de calor; tiempo de proceso; propiedades térmicas y fisicoquímicas
Introduction
The consumption of insects as food or “entomophagy” has sig-
nificantly increased worldwide, either for pleasure or to satisfy
the food needs in developing countries. Insects can be consid-
ered as an important source of protein and other nutrients such as
fat, vitamins and minerals (Ramos-Elorduy, Pino-Moreno, &
Conconi, 2006). Especially in developed countries such as
Angola, Brazil, Colombia, China, Ecuador, Peru, Thailand,
Zaire, Mexico, Nigeria, Republic of Congo and Zambia, humans
have selected around 2000 species of edible insects. For
instance, several species of grasshoppers (Sphenarium histrio
mexicanum), maguey worms (Comadia redtembacheri) and
escamoles (Liometopum apiculatum) are part of the diet of
some ethnic groups in Mexico (Ramos-Elorduy, Costa, Pino-
Moreno, Cuevas, & García, 2007). Escamoles are the larvae of
ants of the genus Liometopum, consisting of a mixture of imma-
ture states known as pupa, with an average length of 7–10 mm,
3–5 mm in diameter and a yellow-pearl color as shown in
Figure 1 (color online only). They are known as “Mexican
caviar” because of its delicious taste and high cost. The most
important escamoles production zones in Mexico are located in
the states of Mexico, Hidalgo, Tlaxcala, Zacatecas and San Luis
Potosi, all of them with short collection periods from February to
April. Escamoles have a chemistry composition consisting of
approximately 73% water, 10% protein, 10% carbohydrates
and 6% lipid (Ramirez-Garcia, Ruiz-Cabrera, & Grajales-
Lagunes, 2013). Nevertheless, due to its high proteolytic
enzymes content, escamoles have a very poor shelf life, and
only a very small proportion of the yearly harvest reaches the
national market, mainly due to the lack of a good method of
preservation that facilitates transportation and storage.
Escamoles cannot be stored for more than 8 days at 4°C because
decay will take place after that span. On the other hand, a
puncture of the walls and loss of its natural juices during thawing
has been observed in frozen escamoles (results not published).
Canning and thermal sterilization as preservation methods may
be an alternative for a better utilization of escamoles and could
be suitable for creating new variety of products at a large scale.
Thermal sterilization process has been widely used as a method
of preservation for some products such as tuna fish, vegetables
*Corresponding author. Email: grajales@uaslp.mx
CyTA - Journal of Food, 2014
http://dx.doi.org/10.1080/19476337.2014.936512
© 2014 Taylor & Francis
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3. and pates (Garrote, Silva, Roa, & Bertone, 2006; Kızıltas,
Erdogdu, & Palazoglu, 2010; Plazl, Lakner, & Koloini, 2006)
because the high heat destroys microorganisms and inactivates
enzymes to preserve the safety and quality of the food. The heat
transfer during thermal processing of a food has been directly
related to the type of food and sterilization method. Therefore,
heat transfer analysis has been recommended in literature to
improve its design and operation as well as to save energy in
canned products (Desrosier, 2006). For instance, Chen and
Ramasswamy (2007) pointed out that heat transfer modes in a
canned food is conduction for solid foods, natural convection for
low-viscosity liquid foods, convection plus conduction for liquid
foods with solid particles and convection followed by conduc-
tion for liquid foods containing starch or high-viscosity modi-
fiers. However, in the literature, no information is available
regarding the analysis of heat transfer, thermal properties and
determination of required processing time for canned escamoles.
Therefore, the aim of this study was to characterize the steriliza-
tion process through temperature measurements in the cold point
of the can in order to estimate and elucidate the thermal proper-
ties, heat transfer mechanisms and processing time for canned
escamoles. Additionally, the physicochemical, nutritional and
sensorial characteristics were evaluated in the product after ster-
ilization process.
Materials and methods
Sample preparation and sterilization tests
Escamoles were collected at Ejido de Pocitos, at the Municipality
of Charcas San Luis Potosi, México and immediately they were
carefully washed with sodium hypochlorite at 150 ppm and were
frozen at −80°C until its use. Pickled and brined escamoles were
prepared according to the Official Mexican Norm (NOM-002-
SCFI, 1993) as shown in Table 1. Cylindrical cans of 250 mL
volume with a diameter of 66 mm and height of 75 mm were used
in all experiments. The filling of the cans were performed at 80°C
considering a headspace of 10 mm as indicated in Figure 2 and
hermetically sealed using a sealing machine (DIXIE Double
Seamer model 25D-600, Athens, GA, USA). The thermal
exhausting was carried out with saturated steam at 80°C.
Sterilization process was performed using saturated steam and
water immersion at 115°C and 121°C, both in a stationary vertical
autoclave. Saturated steam at pressures of 1.1 and 1.5 kg/cm2
and
boiling water with over-pressure of 2.2 kg/cm2
with compressed
air were used, respectively, as heating mediums. A factorial
experimental design completely randomized with three factors at
two levels each and one replicate for each experimental condition
was used. A total of 16 runs were conducted (Table 2).
Cold point measurement
The cold point temperature inside the cans filled with escamoles
products was determined by placing T-type thermocouples in the
geometric center (at r = 0) at three different heights along the axis
(L/2, 5L/12, L/3) of the cans as shown in Figure 2. The tempera-
ture as a function of sterilization time was recorded with a data
Table 1. Formulation of brined and pickled escamoles.
Tabla 1. Formulación de los escamoles en salmuera y escabeche.
Pickled escamoles Brined escamoles
75 g of escamoles (40.54%) 90 g of escamoles (48.64%)
90 mL of vinegar at 2% of acetic
acid (48.64%)
95 mL water solution with 2% salt
(51.35%)
20 g of pickled
Note: Pickled composition: carrot 45.5%, onion 41.03%, oil 11.68% and spices 1.72%.
Nota: Composición del escabeche: zanahoria 45,5%, cebolla 41,03%, aceite
11,68% y especias 1,72%.
Figure 1. Picture of escamoles ant (Liometopum apiculatum).
Figura 1. Escamoles de hormiga (Liometopum apiculatum).
Headspace
r = 0
L
L/2 5L/12 L/3
r = R
Figure 2. Experimental setup and illustration of the location of thermocouple to measure cold point temperature in the geometric center (r = 0) at three
different heights along the axis of the cans.
Figura 2. Ilustración experimental de la ubicación de los termopares para determinar la temperatura del punto frio en el centro geométrico (r = 0) a tres
diferentes alturas a lo largo del eje de la lata.
2 M.A. Ruiz-Cabrera et al.
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4. acquisition system (CALplex) with an accuracy of ±0.5°C and
read by a personal computer through the data acquisition program.
Calculation and validation of the process time
The process time was calculated using Equation (1)
F0 ¼
Z t
0
10
T tð ÞÀTref
z dt (1)
where F0 is the lethality/sterilization value, T is the cold point
temperature, Tref is the reference temperature (121.1°C) and z
value is a temperature sensitivity indicator, which represents the
temperature range between which the D value (decimal reduction
time) curve passes through one logarithmic cycle z = 10°C for
Clostridium botulinum (Ramaswamy & Marcotte, 2006;
Simpson, Abakarov, Almonacid, & Teixeira, 2008). Equation
(1) was solved by numerical integration of the temperature-
time profile measured during the sterilization process. The cal-
culated processing time was validated taking into account the
Official Mexican Norm (NOM-130-SSA1, 1995). For this, the
cans were incubated for 14 days at 35°C in a Thermolyne Type
41900 incubator. After this incubation time, the samples were
subjected to microbiological examinations in which mesophilic,
thermophilic, aerobic and anaerobic were determined for pro-
ducts with pH values higher than 4.6 while mesophilic, anaero-
bic, aerobic, mushrooms and yeast were determined for products
with pH values lowest than 4.6.
Chemical composition, physicochemical parameters and
sensory evaluation of the final product
Chemical composition of final product was determined by the
method of Association of Official Analytical Chemists (AOAC,
1990). The pH of drained product was determined with a glass
electrode attached to a Thermo-Orion pH-meter (model
410Aplus) and water activity (Aw) with water activity meter
(Aqualab Series 3 TE), both at room temperature. The sensory
evaluation was performed with 52 untrained judges using a 7-
point hedonic scale: 1 = “dislike very much”, in the middle
“neither like nor dislike” and 7 = “like very much”.
Heat transfer simulation
The simulations were performed by computational fluid dynamics
using the software Comsol Multiphysics version 3.5. During heat
transfer simulation, the headspace was not considered due to the
small variability in the effective heat transfer coefficients for head-
space between 5 and 10 mm (Ibrahim, 2007). In addition, it was
also assumed that pickled escamoles and brined escamoles were
completely homogeneous; then an analysis of transient energy
transport by conduction was performed. Two-dimensional geome-
tries in cylindrical coordinates, considering only the radial and
axial directions when the angle θ is equal to zero (Figure 3), were
used. The boundary conditions were considered as convective
energy flow. Thermophysical properties of food such as thermal
conductivity (k), specific heat (Cp), density (ρ) and the heat
transfer convection coefficient (h) were determined as described
in the following and supplied to the software. The governing
equation for heat transfer inside the cans can be written as
@T
@t
¼
k
ρCp
1
r
@
@r
r
@T
@r
þ
@2
T
@Z2
!
(2)
subjected to the following boundary and initial conditions:
T ¼ T0 when t ¼ 0 for all 0 r
R and À L=2 Z L=2
(3)
@T=@r ¼ 0 when r ¼ 0 for all t ! 0
and À L=2 Z L=2
(4)
k@T=@r ¼ h T À T1ð Þ when r ¼ R for all t ! 0
and À L=2 Z L=2
(5)
k@T=@Z ¼ h T À T1ð Þ when Z ¼ Æ L=2
for all t ! 0 and 0 r R
(6)
where R and L are, respectively, the radius and height of the can.
Thermophysical properties determination
In this study, two different procedures were used for estimation of
thermophysical properties. In a first attempt, the resistance of
convective heat transfer was considered negligible fixing a high
value of h = 1 × 1010
W/m2/°C while k, Cp and ρ were assumed
to be a function of temperature and product composition; then, the
Equations (7)–(10) proposed by Choi and Okos (1986) were used:
k ¼
X
kiXi
v
ð Þ (7)
Cp ¼
X
CpiXi
m
ð Þ (8)
ρ ¼ 1=
X
ðXi
m
=ρiÞ (9)
where Cpi, Xi
m
, ρi, ki and Xi
v
are, respectively, the specific heat,
mass fraction, density, thermal conductivity and volume fraction
of constituent i. The latter was defined as follows:
Table 2. Experimental sterilization conditions for canned escamoles.
Tabla 2. Condiciones experimentales del proceso de esterilización para
el enlatado de escamoles.
Experiment
number Run order
Canned
product
Heating
medium
Sterilization
temperature (°C)
1 12 Pickled Steam 115
2 15 Brined Steam 115
3 8 Pickled Immersion 115
4 16 Brined Immersion 115
5 4 Pickled Steam 121
6 5 Brined Steam 121
7 9 Pickled Immersion 121
8 7 Brined Immersion 121
9 11 Pickled Steam 115
10 2 Brined Steam 115
11 6 Pickled Immersion 115
12 1 Brined Immersion 115
13 14 Pickled Steam 121
14 10 Brined Steam 121
15 13 Pickled Immersion 121
16 3 Brined Immersion 121
CyTA – Journal of Food 3
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5. Xi
v
¼ ðXi
m
=ρiÞ=
X
ðXi
m
=ρiÞ (10)
According to the Choi and Okos equations, an ideal mixing was
supposed, thereby, the thermophysical properties used in this
study are a weighted average of the property of each component
in the mixture. In a second attempt, a nonlinear regression (nlr)
procedure with COMSOL 3.5 software was used to adjust the
experimental cold point temperature data where h and k were
identified simultaneously. It is important to notice that Cp and ρ
values calculated with Equations (8) and (9) were also utilized in
this step. On the other hand, the goodness of fit between the
experimental and predicted temperature data was determined
using the sum of squared errors (SSE) according to Equation (11):
SSE ¼
XN
i¼1
Ti
À Ti
simulated
À Á2
(11)
where N is the number of temperature measurements, T and
Tsimulated are, respectively, the experimental temperature and
simulated temperature at the cold point. Selected data were
sent to MATLAB files to draw required plots where process
time was estimated.
Statistical analysis
A linear model with binary interactions (Equation (12)) was used
to analyze the effect of the canned product (A), heating medium
(B) and sterilization temperature (T) on each of the response
variables (k, h, Cp, ρ, Aw, pH and process time):
Y ¼ b0 þ b1A þ b2B þ b3T þ b4A Â B
þ b5A Â T þ b6B Â T þ e
(12)
where b0–b6 are the regression coefficients of the model and e is
the experimental error (Montgomery, 2004). The analysis of
variance (ANOVA) was performed with a confidence interval
of 95% with Modde 7.0 software (Umetrics, Kinnelon, NJ,
USA). For the sensory evaluation, the ANOVA (p 0.05) was
performed using the software MINITAB 15 in which the mini-
mum significant difference was realized by Tukey test.
Results and discussions
Evolution of experimental and simulated temperature
It was noticed that the cold point temperature for sterilized
brined escamoles using water immersion was located at L/2,
whereas for brined escamoles treated with saturated steam, this
was located between L/2 and L/3. However, for sterilized pickled
escamoles using either water immersion or saturated steam, the
cold point was located at L/2. Based on the fact that temperature
evolution was similar for all experiments, as an example,
Figure 4 (a)–(b) and (c)–(d) shows the experimental and simu-
lated cold point temperature evolution when brined and pickled
escamoles were heated with water immersion and saturated
steam at 121°C, respectively. In Figure 4(a)–(b), it is seen that
both simulation procedures, Choi and Okos and nlr, satisfactorily
predicted the variation of the cold point temperature for brined
escamoles. However, the predicted values using the nlr proce-
dure are in better agreement with experimental values than those
predicted using the Choi and Okos equations when pickled
escamoles were used (Figure 4(c)–(d)). An ideal mixture
assumes that volumetric and energetic properties of a mixture
are just the linear combination of those of their pure constituents.
Probably, the discrepancy observed between simulated and
experimental data in pickled escamoles using Choi and Okos
equation may be attributed to deviation from the simple ideal
mixture model. Based on the latter assumption, brined escamoles
can be considered as a thermodynamically ideal mixture under
any conditions that were used in this study. As an example,
simulated temperature contours for the case of brined escamoles
treated with saturated steam at 121°C is given in Figure 5 at
different heating times. From Figure 5, it is evident that the
product adjacent to the walls of the can receive a rapid heating,
while the center where the temperature change was measured
was the slowest heating point in the can. On the other hand, it
may be inferred from Figure 5 that the heat transfer was mainly
by conduction with uniform kernels of temperature zone. It is
also important to indicate that similar trends were perceived in
the experiments performed with pickled escamoles.
Thermophysical properties
The thermophysical properties values estimated by Choi and Okos
and by nlr for each experimental condition are given in Table 3.
According to ANOVA (p 0.05) shown in Table 4, it can be
observed that thermal conductivity (k), specific heat (Cp) and
density (ρ) were influenced by the studied factors. With respect to
heat transfer convection coefficient, significant effect of the sterili-
zation variables was not observed. An increase of h with tempera-
ture, headspace and rotary speed has been reported in the literature
when a rotary retort was used (Garrote et al., 2006). However, in
this study, a stationary autoclave was used for the sterilization
θ
Z
r
0.066 m
0.075 m
Figure 3. Tri-dimensional schematic representation of the vertical can
used in this study.
Figura 3. Representación esquemática tridimensional de la lata en
posición vertical usada en este estudio.
4 M.A. Ruiz-Cabrera et al.
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6. processes. From Table 4, it can be noticed that k and Cp values were
directly proportional to the sterilization temperature, whereas the
opposite effect was found for ρ, which decreased with sterilization
temperature. On the other hand, similar values of thermal conduc-
tivity (k) were estimated using Choi and Okos equation and nlr
procedure in brined escamoles but different k values in pickled
escamoles (p 0.05) (Table 3). As previously discussed, Choi
and Okos equation is more suitable to predict the thermophysical
properties of ideal mixture model such as brined escamoles. In the
literature, some authors have reported values for the thermal proper-
ties of various canned foods (Boz Erdogdu, 2013; Kannan
Gourisankar, 2008), and some of them are similar to those reported
in this study.
Experimental and calculated process time
The process time is an important parameter that must be care-
fully determined for foods requiring a canning and sterilization
process because it depends on the type of food and experimental
conditions. This parameter is widely used to ensure the absence
of pathogens in food, which can cause an effect on the human
health. Therefore, process time must be also validated through
microbiological tests such as that used in this study, which were
negative for all experiments. The experimental and predicted
process time for each experimental condition investigated are
also given in Table 3. According to ANOVA (p = 0.0001,
r2
= 0.998), the process time was affected by the product type
(pickled or brined escamoles), by the temperature and by the
product type × heating medium and product type × temperature
interactions (Table 4). Pickled escamoles required less process
time than brined escamoles regardless of the heating medium
suggesting that there is greater heat transfer in pickled esca-
moles. Processing times estimated by nlr were closer to the
experimental processing times than those estimated by Choi
and Okos due to the lack of fit of the experimental data observed
during the simulation.
Chemical composition and physicochemical properties
of processed escamoles
Fresh escamoles constitute a good source of protein (10.15%
wet basis), carbohydrates (10%) and lipids (6%). Data on the
protein content in processed escamoles showed that this com-
pound was sensitive to heat, and the remaining percentage of
protein varied from 4.2% to 6.0%. It was observed that the
remaining percentage of protein was higher in brined esca-
moles than pickled escamoles. This protein degradation can
be attributed to protein denaturalization during thermal ster-
ilization as well as to hydrolysis of proteins induced by the
pH value. Even taking into account the maximum loss of
protein observed in pickled escamoles, the remaining is high
compared to other Mexican pickles products such as pickled
mushroom whose protein content is around 1.1% (wet basis).
With respect to physicochemical parameters of products,
Table 3 shows the average results of water activity (Aw) and
pH for each experiment. Aw values ranged between 0.98 and
Figure 4. Comparison between experimentally measured and simulated cold point temperatures for sterilization carried out at 121°C. (a) Exp. 6, (b) Exp. 8,
(c) Exp. 5, (d) Exp. 7 from Table 2, nlr = nonlinear regression.
Figura 4. Comparación entre los resultados experimentales y simulados de la temperatura en el punto frio durante la esterilización realizada a 121°C,
(a) Exp 6, (b) Exp 8, (c) Exp 5, (d) Exp 7 de la Tabla 2, nlr = regresión no lineal.
CyTA – Journal of Food 5
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7. 0.99, which were very similar to the water activity
(0.98 ± 0.05) for fresh escamoles, suggesting that the factors
evaluated (product type, heating medium, temperature and
their respective interactions) caused no significant effect
(p = 0.548, r2
= 0.37) on the Aw value. According to
ANOVA, the pH was affected only by the product type
Maximum 122.05°C
Minimum 59.07°C
117
107
97
87
77
67
t = 150 s t = 300 s t = 450 s
t = 900 s t = 1050 s t = 1200 s
t = 1500 s t = 1800 s t = 2100 s
Figure 5. Temperature contours at different heating times for brined escamoles treated with saturated steam at 121°C.
Figura 5. Evolución de la temperatura a diferentes tiempos de calentamiento para escamoles en salmuera tratados con vapor saturado a 121°C.
Table 3. Thermophysical and physicochemical properties and process time for canned escamoles products.
Tabla 3. Propiedades termo-físicas y fisicoquímicas y tiempo de proceso para los productos de escamoles enlatados.
Experiments
hnlr × 10−9
(W/m2/°C) knlr (W/m/°C)
K (W/m/
°C)
(Equation
(7))
Cp (kJ/kg/°C)
(Equation (8))
ρ (kg/m3
)
(Equation
(9)) pH Aw
Experimental
process time
(min)
Choi and
Okos
process
time (min)
Nonlinear
regression
process
time (min)
1 10.078 3.006 0.643 3.77 987.95 4.26 0.992 17.44 40.5 19.0
2 10.019 0.590 0.635 3.77 987.65 6.22 0.988 54.85 45.5 55.3
3 6.501 3.668 0.635 3.76 976.6 4.40 0.975 17.9 53.5 19.1
4 9.628 0.726 0.636 3.74 992.24 6.24 0.987 52.44 53.0 53.5
5 9.679 1.983 0.645 3.76 976.82 4.36 0.984 11.65 27.0 20.4
6 9.638 1.259 0.645 3.79 977.55 6.29 0.983 31.59 38.0 32.0
7 9.969 2.318 0.643 3.77 975.94 4.99 0.987 12.36 40.0 16.4
8 10.849 0.995 0.639 3.74 981.88 6.09 0.985 28.35 39.5 28.5
9 8.654 0.801 0.637 3.76 981.62 4.21 0.983 17.19 44.0 18.6
10 8.743 0.624 0.636 3.77 987.58 6.27 0.982 55.12 49.0 55.0
11 11.765 5.508 0.640 3.76 980.01 4.65 0.979 18.50 43.5 18.3
12 10.219 0.674 0.633 3.74 990.32 6.34 0.985 53.82 54.0 54.2
13 9.623 1.484 0.642 3.76 978.87 4.32 0.986 12.2 30.0 12.5
14 9.726 0.615 0.641 3.79 982.24 6.18 0.988 31.79 32.0 31.5
15 9.539 2.884 0.642 3.77 976.81 4.29 0.998 13.02 33.0 14.0
16 8.706 0.791 0.637 3.73 979.17 6.19 0.982 31.94 36.0 33.4
Notes: hnlr = heat transfer coefficient obtained by nonlinear regression, knlr = thermal conductivity obtained by nonlinear regression, k = thermal conductivity obtained by
Equation (7), Cp = specific heat obtained by Equation (8), ρ = density obtained by Equation (9), Aw = water activity.
Notas: hnlr = coeficiente de transferencia de calor obtenido por regresión no lineal, knlr= conductividad térmica obtenida por regresión no lineal, k = conductividad térmica
obtenida por la Ecuación (7), Cp = calor especifico obtenido por la Ecuación (8), ρ = densidad obtenida por la Ecuación (9), Aw = actividad de agua.
6 M.A. Ruiz-Cabrera et al.
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8. (p = 0.0001, r2
= 0.98) (Table 4). A decrease of pH was
observed in the sterilized products (Table 3) due to the fact
that the pH value of fresh escamoles varies between 6.5 and
6.7, the lowest pH value was 4.21 ± 0.03 (pickled escamoles
heated with steam at 115°C) and the highest value was
6.29 ± 0.06 (brined escamoles heated with water immersion
at 115°C). pH values decreased more drastically in the
pickled escamoles because acetic acid (vinegar) was used in
its formulation. Therefore, pickled escamoles may be classi-
fied as high-acidity products and brined escamoles as low-
acidity products.
Sensory quality in finished product
Figure 6 shows the results of overall quality (taste, color,
texture and appearance) for finished products. The product
with highest score was pickled escamoles heated with steam
at 115°C (A) where the average score was approximately of 6.0,
according to the hedonic scale, it means “like moderately”. This
score can be considered satisfactory because these products are
new and exotic and some judges have never tasted them. The
other escamoles products such as pickled-immersion at 115°C
(B), pickled-immersion at 121°C (C), pickled-steam at 121°C
(D), brined-immersion at 121°C (G) and brined-steam at 121°C
(H) obtained an score of 5.0, which is equivalent to “like
slightly” these products were statistically different (p 0.05)
to product A. The score for brined-steam at 115°C (E) and
brined-immersion at 115°C (F) was of 4.0, which was equiva-
lent to “neither like nor dislike”. These results suggest that the
overall quality of these products was satisfactory because all
samples received a positive score. The final comment from the
judges was that all products had a good taste and a very good
appearance.
Conclusions
Sterilization process can be used to give added value to esca-
moles without damaging its nutritional and sensory characteris-
tics. Conduction was the main heat transfer mechanism during
the sterilization process in pickled and brined escamoles; how-
ever, pickled products required less process time than brine
products. Sterilization process conditions and thermal properties
of canned escamoles determined in this study can be used to
generate new products based on escamoles in different geome-
tries and sizes of the can without the need for further experi-
ments. Good agreement between the experimental and simulated
temperature profiles was observed using either the nlr or Choi
and Okos procedures in brined escamoles. Therefore, Choi and
Okos equation was more suitable to predict the thermophysical
properties of ideal mixture model.
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Figure 6. Overall quality scores for sterilized escamoles products.
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Coefficients p(t) Coefficients p(t) Coefficients p(t) Coefficients p(t) Coefficients p(t)
b0 Constant 1.106 0.0002 982.078 0.0001 3.7612 0.0001 5.33 0.0001 28.76 0.0001
b1 Pickled escamoles 0.965 0.0007 −2.750 0.0022 0.0024 0.2125 −0.895 0.0001 −13.725 0.0001
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b5 Pickled × temperature −0.334 0.120 1.20 0.0982 −0.0012 0.519 0.048 0.319 4.422 0.0001
Brined × temperature 0.334 0.120 −1.20 0.0982 0.0012 0.519 −0.048 0.319 −4.422 0.0001
b6 Steam × temperature 0.243 0.236 −0.2468 0.7133 0.0012 0.519 0.015 0.739 −0.0237 0.9223
Immersion × temperature −0.243 0.236 0.2468 0.7133 −0.0012 0.519 −0.015 0.739 0.0237 0.9223
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Nomenclature
Aw water activity
ρ density (kg/m3
)
Cp specific heat (kJ/kg/°C)
F0 Lethality sterilization value (min) at 115°C or 121°C
h heat transfer convective coefficient (W/m2/°C)
k thermal conductivity (W/m/°C)
L height of the can (mm)
R radius of the can (mm)
r radial dimension
nlr nonlinear regression
SSE sum of squared error
T Experimental temperature in cold point (°C)
Tref reference temperature (115°C or 121°C)
Tsimulated simulated temperature (°C)
Xm
mass fraction
Xv
volume fraction
z temperature sensitivity for Clostridium botulinium (°C)
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