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Application of pulsed-vacuum on the salt impregnation process of pirarucu fillet
Food Research International 120 (2019) 407–414
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Application of pulsed-vacuum on the salt impregnation process of pirarucu fillet Mayara Galvão Martinsa, Paulo Sérgio Nunes Chadab, Rosinelson da Silva Penaa,b, a b
T
⁎
Postgraduate Program in Food Science and Technology, Technology Institute, Federal University of Pará (UFPA), Belém 66075-110, PA, Brazil Faculty of Food Engineering, Technology Institute, Federal University of Pará (UFPA), Belém 66075-110, PA, Brazil
A R T I C LE I N FO
A B S T R A C T
Keywords: Arapaima gigas Vacuum pulse Salting Diffusion Modeling
The influence of the pulsed-vacuum impregnation (PVI) and periodic pulsed-vacuum impregnation (PPVI), and the temperature, on the salting process of pirarucu fillet was studied. For this, the dorsal region of the fish in the slab-shaped (60 mm × 20 mm × 5 mm) and sodium chloride solution (30 g/100 g NaCl) were used. The process was conducted at different temperatures (10 °C – 40 °C) and the following pulsed-vacuum conditions: initial vacuum pulse (5 min at 10 kPa) and alternating periods of vacuum pulse (5 min at 10 kPa) and atmospheric pressure (101 kPa) for 5 min, 10 min and 15 min intermittently. The solid gain (SG) in the fillet was more pronounced in the first two hours of the salting process. The increase of salt content in the product (0.33 ± 0.02 to 0.43 ± 0.04 g/g db) promoted the gradual reduction of moisture (72.99 ± 1.27 to 57.1 ± 2.4 g/100 g) and water activity (1.00 ± 0.03 to 0.78 ± 0.05). PVI and PPVI processes can be used efficiently at room temperature or under refrigeration in the salting process of pirarucu fillet. On the other hand, at higher temperatures (> 30 °C), the effect of temperature prevails over the effect of vacuum. Peleg model satisfactorily explains the salting kinetics of the pirarucu fillet.
1. Introduction The Amazon is recognized worldwide for having a great diversity of fish species, which have social, cultural, environmental and economic relevance (Junk, Soares, & Bayley, 2007). In this context, pirarucu (Arapaima gigas) is one of the largest fish of the Amazonian ichthyofauna, which stands out for the great potential for sustainable exploitation, as it presents relevant nutritional aspects, high added values and characteristics that promote cultivation and industrialization (Castello, Stewart, & Arantes, 2011; Martins, Martins, & Pena, 2017; Martins & Pena, 2017; Núñez et al., 2011). Traditionally, pirarucu is marketed in dry-salted form, whose salting process is similar to that used for codfish, in which blankets are stacked and intercalated with different layers of salt crystals (Barat, RodríguezBarona, Andrés, & Fito, 2003). However, in the case of pirarucu, there are still no well-defined parameters for the salting process, as well as for the complementary drying. Salting is one of the oldest techniques of preservation of food, which is based on the principle of osmotic dehydration, where the diffusion of the salt into the tissues and the loss of free water by osmosis occurs (Gallart-Jornet et al., 2007; Martins, Martins, & Pena, 2015; Sobukola & Olatunde, 2011). Salt impregnation process using sodium chloride or brine can be
⁎
carried out at atmospheric pressure or as vacuum impregnation (VI), pulsed-vacuum impregnation (PVI) or periodic pulsed-vacuum impregnation (PPVI). PVI consists of product immersion in a hypertonic solution and the application of subatmospheric pressure at the beginning of the process, for a short time, with subsequent restoration of atmospheric pressure. In contrast, PPVI is characterized by intercalated periods of subatmospheric and atmospheric pressure, intermittently (Chiralt et al., 2001; Collignan, Bohuon, Deumier, & Poligne, 2001). In the PVI and PPVI, when the vacuum is applied, the expansion of the muscle fibers occurs, accompanied by the elimination of occluded gases in the pores. When the atmospheric pressure is restored, the osmotic solution is introduced into the pores of the product due to the macroscopic pressure gradients and the capillary effects (Chiralt et al., 2001; Deumier, 2004). The mass transfer is favored by the enhancement of the contact surface, due to the elimination of the air inside the pores (Deumier, 2004; Marouzé, Girox, Collignan, & Rivier, 2001). The use of vacuum in salting processes has been reported as an alternative to reduce the process time, as well as to promote a more homogeneous distribution of the salt in the product (Chiralt et al., 2001; Hofmeister, Souza, & Laurindo, 2005; Schmidt, Carciofi, & Laurindo, 2009). There are few reports in the literature involving vacuum application in fish salting processes (Corzo & Bracho, 2007; Corzo, Bracho,
Corresponding author at: Faculdade de Engenharia de Alimentos, Universidade Federal do Pará (UFPA), Rua Augusto Corrêa, 01, Belém 66075-110, PA, Brazil. E-mail address: [email protected] (R. da Silva Pena).
https://doi.org/10.1016/j.foodres.2019.03.016 Received 4 November 2018; Received in revised form 5 March 2019; Accepted 8 March 2019 Available online 09 March 2019 0963-9969/ © 2019 Elsevier Ltd. All rights reserved.
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the experiments were performed in triplicate.
Rodríguez, & González, 2007; Maciel, Rodrigues, & Pena, 2016; Martins & Pena, 2017; Rastogi & Raghavarao, 1996), as well as studies about the processing of pirarucu (Hernández, Carvalho Jr, Joele, Araújo, & Lourenço, 2017; Martins et al., 2015; Martins & Pena, 2017; Oliveira, Jesus, Batista, & Lessi, 2014). These facts motivated this research, whose objective is to study the influence of the application of pulsedvacuum and periodic pulsed-vacuum, as well as the temperature, in the salting process of the pirarucu fillet, by impregnation of sodium chloride.
2.3. Salt impregnation process kinetics The effect of the contact time (30, 60, 90, 120 and 180 min) on the solids gain (SG) was used to follow the evolution of the salting process, from salting kinetics, obtained for the different process conditions. The SG values were calculated according to Eq. (1).
SG = 2. Material and methods
SMt − SMo Mo
(1)
where SG: solid gain (g/g dry basis – db), Mo: initial mass of fish fillet slab (g), SMo: initial dry mass of fish fillet slab (g), SMt: dry mass of fish fillet slab (g) after impregnation time (t). The moisture and water activity profiles (aw), and the evolution of the salt content were also determined. Moisture was measured by gravimetry, aw was determined on a thermo-hygrometer (Aqualab 3TE, Decagon, USA) and the salt content was determined by the Mohr method (AOAC, 1997). All the determinations were performed in triplicate.
2.1. Raw material and sample preparation The pirarucu used in the research was acquired at an aquaculture farm located in Breu Branco (Pará, Brazil) (04°04′04″ S and 49°38′13″ W) and transported to the Federal University of Pará (Belém, Pará, Brazil) (01°27′21″ S and 48°30′16″ W), in an isothermic container containing ice. In the laboratory, the fish was sanitized, scales and skin were removed, and then filleting of the muscle was performed with stainless steel blades. The most representative fraction of the pirarucu muscle, the dorsal region (Martins et al., 2017), was used in the research, as slab-shaped samples (60 mm length, 20 mm width, and 5 mm thickness). In order to assure the microbiological quality of the raw material used, microbiological analyses were performed to investigate the absence or presence of Salmonella sp., the groups coagulase positive Staphylococcus, expressed as colony forming units per gram of fresh fish (CFU/g), and thermotolerant coliforms at 45 °C, expressed as the most probable number per gram of fresh fish (MPN/g) (APHA, 2015).
2.4. Salt impregnation process modeling Peleg (1988) proposed a two-parameter model (Eq. (2)), which can be used to describe the kinetics of a salting process. Thus, the parameters of the Peleg model for SG were estimated by linear regression, using the linear (k1) and angular (k2) coefficients of the t/SG versus t curve. The fit of the model to the experimental data was evaluated by the coefficient of determination (R2).
XS − X S0 = 2.2. Salt impregnation procedure
t k1 + k2 t
(2)
where XS: product's solid content at a time t (h) of impregnation (g/g db), Xs0: product's initial solid content (g/g db), XS – Xs0 = GS: solid gain (g/g db), k1: Peleg rate constant (h/(g/g db)), k2: Peleg capacity constant (1/(g/g db)).
Salt impregnation process with sodium chloride (NaCl) solution was conducted by pulsed-vacuum impregnation (PVI) and periodic pulsedvacuum impregnation (PPVI). All experiments were performed in a covered system to allow the recirculation of the thermal fluid (water), which was coupled with a vacuum pump and an ultra-thermostatic bath (Q214M2, Quimis, Brazil) to assure pressure and temperature controls inside the system. The covered system was maintained on a shaker table to ensure a constant stirring at 60 rpm, sufficient to promote the circulation of the solution and remove the surface layer around the sample (Maciel et al., 2016; Martins & Pena, 2017). In the impregnation experiments it was used an osmotic solution with 30% NaCl (w/v), prepared by dissolving the NaCl analytical grade in distilled water. A ratio of mass sample/volume of the osmotic solution of 1:20 (w/v) was used to ensure a constant concentration of the osmotic solution throughout the process. The slab-shaped samples (≈ 7 g) were weighed in an analytical balance (AY220, Shimadzu, Brazil) and immersed in the osmotic solution. The system was immediately closed and subjected to different temperature conditions (10, 20, 30 or 40 °C) and at 10 kPa absolute pressure (vacuum), according to the process conditions. After the processing times (30, 60, 90, 120 and 180 min), the samples were removed from the osmotic solution, washed with 20 mL of water and dried with absorbent paper to remove excess salt and water from the surface. Finally, the samples were weighed again on the analytical balance. In the PVI process, during the first 5 min, the system was maintained at 10 kPa, then system's vacuum condition was interrupted and the system was maintained at atmospheric pressure (101 kPa – Belém, PA, Brazil) until the end of the process (1st condition). In the PPVI process, alternating periods of vacuum pulse (5 min at 10 kPa) and atmospheric pressure (101 kPa) were used until the end of the process. In this case, the system was maintained at atmospheric pressure for 5 min (2nd condition), 10 min (3rd condition) e 15 min (4th condition). A graphical scheme of these process conditions used is shown in Fig. 1. All
2.5. Prediction of effective diffusivity Based on Fick's second law, Crank (1975) proposed an equation for unidirectional diffusion in a sample with flat slab geometry in contact with an infinite amount of solution, used to describe the osmotic dehydration kinetics. The simplified form of this model (Eq. (3)) for short contact times (t) is applied to the initial phase of the process, when diffusion is assumed to occur in a semi-infinite medium. 1/2
Deff ⋅t SGt ⎞ = 2⋅⎛ 2 SG∞ ⎝ π ⋅L ⎠ ⎜
⎟
(3)
where SGt: amount of SG the product at a given time (t), WS∞: amount of SG the product after an infinite time (equilibrium), Deff: effective diffusivity (m2/s), L: half-thickness of the sample (m). Considering Eq. (3), the effective diffusivity (Deff) was calculated for each process condition and time interval (t) of the kinetics (Eq. (4)), as a function of the angular and linear coefficients of the t/SG versus t curves (Eq. (5)).
Deff =
∞ π⋅t ⎡ ⎛ Si⋅L ⎞ ⎛ SGpred ⎞ ⎤ ⋅⎜ ∞ ⎟ ⎥ ⎢ 4 ⎝ 1 + Si⋅t ⎠ ⎝ SGexp ⎠ ⎦ ⎣ ⎜
⎟
(4)
1 1 t = + SG Si (SG∞) SG∞
(5) 2
where Deff: effective diffusivity (m /s), t: contact time (s), L: halfthickness of the sample (m), SG: solid gain (g/g db), SGpred∞: predicted solid gain for the product after an infinite time (equilibrium) (1/angular coefficient), SGexp∞: experimental solid gain for the product after an 408
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Fig. 1. Graphical scheme of pulsed-vacuum processes.
infinite time (equilibrium), Si: (1/(linear coefficient × SGpred∞)).
(Fig. 2); conditions in which the influence of the vacuum pulse on the mass transfer mechanisms that favor the salting process, were more representative. During the application of vacuum pulses, initial SG rates are affected by pressure gradients called hydrodynamic mechanisms (HDM) (Andrés, Rodríguez-Barona, Barat, & Fito, 2002). Due to the pressure changes that the system undergoes, the HDM favors the increase of the driving forces responsible for the mass transfer, promoting the exchange of gas or liquid occluded in the pores of the product by an external liquid phase. Additionally, the relaxation of the cellular network occurs slightly deformed due to the reduced pressure level (Fito, Andrés, Chiralt, & Pardo, 1996). The HDM can occur concomitantly with the deformation-relaxation phenomenon (DRP), which affects not only the kinetics and equilibrium condition of the system but also the physical, mechanical and microstructural properties of porous solids (Fito et al., 1996). According to these authors, in plant tissues, the DRP promoted by the vacuum pulse is more affected when higher temperatures are employed. For the salting of the pirarucu fillet (animal tissue), it was also observed an increase in the salt impregnation rates, as the temperature increases. This is evidenced by the increase in the tangent of the curve (Fig. 2), especially in the first hour of the process, and can be attributed to DRP. In general, the results of the research indicate that, in the experimental domain, pirarucu salting process does not need to exceed two hours. In addition, when PVI or PPVI are used, the salting process can be conducted efficiently at room temperature or under refrigeration (< 30 °C). These conditions are favorable from the point of view of product quality because they minimize the negative effects of oxidative processes, the development of halophilic bacteria and other degradation processes to which the pirarucu muscle is susceptible. On the other hand, when higher temperatures are used (> 30 °C) the PVI and PPVI process are not recommended, since the effect of temperature prevails over DRP, favoring the mass transfer rates, regardless of whether or not the vacuum is used. The salt gain during the impregnation process of the pirarucu fillets followed the same behavior observed for the SG, and the maximum salt levels observed in the product at the end of the salting process varied from 0.33 ± 0.02 to 0.43 ± 0.04 g/g db. These salt levels are in agreement with those observed in other researches, which involved the fish salting process (Corzo, Bracho, & Rodríguez, 2015; Gallart-Jornet et al., 2007; Nguyen, Arason, Thorarinsdottir, Thorkelsson, & Gudmundsdóttir, 2010). In addition to changing the sensorial characteristics of the product, the salt concentration in the salting process has a direct influence on the functional properties of the proteins, texture of the product and viscosity of the osmotic solution (CostaCorredor, Muñoz, Arnau, & Gou, 2010; Fito et al., 2001; Nguyen et al., 2010). The increase of the salt content, during the salting process,
2.6. Statistical analysis For evaluate the isolated effects of temperature and vacuum pulse conditions, and the combined effect of these variables on the experimental results was used Statistica 7.0. For this, the experimental data were submitted to analysis of variance using factorial ANOVA, and the means were compared by Tukey's test at 95% significance. The parameters of the Peleg model and the effective diffusivity values were predicted by linear regression. 3. Results and discussion The results of the microbiological analyzes indicated that the hygienic-sanitary procedures used during capture, slaughter, and evisceration, as well as in the manipulation of the fish muscle used were adequate. Values of 2.3 × 101 MPN/g were observed for thermotolerant coliforms at 45 °C, 1 × 101 CFU/g for Coagulase-positive Staphylococcus and the absence of Salmonella sp. in fish muscle. The kinetics of the solids gain (SG) during the salt impregnation process of the pirarucu fillet, under the different temperature and vacuum pulse conditions are presented in Fig. 2. Regardless of the experimental condition, a gradual increase of SG was observed, which was more pronounced in the first two hours, for the processes carried out at 10 °C, 20 °C and 30 °C, and in the first hour for the processes carried out at 40 °C. The increase of the SG at the beginning of the salting process is attributed to the driving force, which is responsible for the diffusion of solids between the hypertonic solution and the product. At the beginning of the process, the osmotic pressure and concentration gradient between the osmotic solution and the product are higher, favoring higher SG rates. As the process progresses, these gradients gradually decrease until the equilibrium condition is reached (Medina-Vivanco, Sobral, & Hubinger, 2002; Rastogi & Raghavarao, 1996). The salting process is characterized by a dynamic period and by equilibrium. In the dynamic period, mass transfer rates increase or decrease until equilibrium is reached; when the net mass transportation rate becomes insignificant (Rahman, 2007). After the first two hours of the process, SG levels practically stabilized, regardless of the temperature and vacuum pulse conditions used; indicating that there is no salt concentration and osmotic pressure gradients between solution and product (equilibrium). Then, the migration of the salt from the solution to the product and from the product to the solution occurs concurrently (Erikson, Veliyulin, Singstad, & Aursand, 2004). The effect of the vacuum pulse conditions applied to the salting was more evident in the processes conducted at temperatures until 30 °C 409
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Fig. 2. Kinetics of solid gain during the salting process of pirarucu fillet at 10 °C, 20 °C, 30 °C and 40 °C using pulsed-vacuum impregnation (PVI) and periodic pulsedvacuum impregnation (PPVI) (markers) and fit of the model proposed by Peleg (lines): 1st condition (◯, ──), 2nd condition (□, ——), 3rd condition (◇, ····) and 4th condition (Δ, – · –).
proteins, causing them to lose the capacity of water retention, due to the weakening of the forces of protein-water binding (Thorarinsdottir, Arason, Bogason, & Kristbergsson, 2004; Thorarinsdottir, Arason, Geirsdottir, Bogason, & Kristbergsson, 2002). The curves estimated by the Peleg model are presented in Fig. 2 and the statistical parameters of the mathematical modeling, as well as the constants of the model adjusted to the experimental data, are presented in Table 1. The values of the coefficient of determination (0.99 > R2 > 0.85) indicate that the Peleg model is able to satisfactorily explain the kinetics of the salting process of the pirarucu fillet in the experimental domain. Corzo et al. (2015) observed that the Peleg model described with good precision the SG kinetics of catfish fillet in osmotic solutions with different chloride mixtures. Good adjustments for the Peleg model were also observed by Corzo et al. (2007), for the SG kinetics of sardine fillet, using a vacuum pulse. The value of the Peleg rate constant (k1) is related to the initial mass transfer rate, and the lower the value of k1, the higher the initial solids gain rate (Peleg, 1988). Based on the k1 values (Table 1) it is possible to
promoted the gradual reduction of moisture content and, consequently, of the product aw, as can be observed in the Fig. 3. In the first hour of the process there was a marked reduction of aw, which remained practically constant from that time, reaching values varying from 0.78 ± 0.05 to 0.84 ± 0.07 at the end of the process. Similar behavior was observed for fresh pirarucu muscle moisture (72.99 ± 1.27 g/ 100 g), which reduced to 57.1 ± 2.4 g/100 g after the salting process. In addition, regardless of the temperature and the vacuum pulse condition used, no significant difference was observed between the moisture content and aw values (p ≤ 0.05) of the product. The replacement of gases or liquids occluded in the pores of the product by saline solution, due to the application of the vacuum pulse, increases the mass transfer pathways, especially those related to solute absorption, due to the absence of cell membranes in these spaces (Fito et al., 2001). The influence of salt on water loss (reduction of moisture) can also be attributed to protein denaturation promoted by salt during the fish salting process (Sannaveerappa, Ammu, & Joseph, 2004). Along with the denaturation occurs the reduction of the solubility of the 410
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Fig. 3. Moisture content and water activity profiles during the salting process of pirarucu fillet at 10 °C, 20 °C, 30 °C and 40 °C using pulsed-vacuum impregnation (PVI) and periodic pulsed-vacuum impregnation (PPVI): 1st condition (◯), 2nd condition (□), 3rd condition (◇) and 4th condition (Δ).
Table 1 Parameters of the Peleg model to the experimental data for the solid gain kinetics during the salting process of pirarucu fillet at different temperatures and with the application of pulsed-vacuum impregnation (PVI) and periodic pulsed-vacuum impregnation (PPVI).⁎ Temperature
Condition
k1
10 °C
1st 2nd 3rd 4th 1st 2nd 3rd 4th 1st 2nd 3rd 4th 1st 2nd 3rd 4th
1.72 0.84 0.34 0.22 0.25 1.13 0.24 0.35 2.04 1.37 0.47 0.26 0.06 0.16 0.19 0.34
20 °C
30 °C
40 °C
SG∞
k2 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
0.14b 0.06e 0.02fg 0.01gh 0.02gh 0.09d 0.02gh 0.03fg 0.14a 0.09c 0.03f 0.02g 0.01h 0.01gh 0.01gh 0.02fg
1.39 1.69 1.34 1.72 1.70 1.31 1.92 1.81 0.72 1.17 1.19 2.57 1.72 1.34 1.43 1.27
± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
0.11cd 0.13bc 0.06d 0.10bc 0.12bc 0.10d 0.14b 0.14b 0.05e 0.08d 0.07d 0.21a 0.12bc 0.07d 0.08cd 0.09d
0.72 0.59 0.75 0.58 0.59 0.76 0.52 0.55 1.39 0.85 0.84 0.39 0.58 0.75 0.70 0.79
R2 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
0.06bcd 0.05def 0.04bc 0.03def 0.04def 0.06bc 0.04fg 0.04ef 0.10a 0.06b 0.05bc 0.03g 0.04def 0.04bc 0.04cde 0.06bc
0.886 0.994 0.993 0.993 0.977 0.903 0.990 0.970 0.865 0.953 0.982 0.852 0.995 0.999 0.988 0.998
k1 = Peleg rate constant (h/(g/g db)); k2 = Peleg capacity constant (1/(g/g db)); SG∞ = SG of the product after an infinite time (equilibrium) (g/g db); R2 = Coefficient of determination. ⁎ Means ( ± standard deviations) with different superscript letters in the same column are statistically different (p ≤ 0.05, Tukey test). 411
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Fig. 4. Effective diffusivity for the salting process of pirarucu fillet at 10 °C, 20 °C, 30 °C and 40 °C using pulsed-vacuum impregnation (PVI) and periodic pulsedvacuum impregnation (PPVI). 1st condition (◯), 2nd condition (□), 3rd condition (◇) and 4th condition (Δ).
condition, for the studied temperature range (10 °C to 40 °C) (Table 1). Thus, the results allow affirming that the higher levels of salt impregnation in the pirarucu muscle were observed in this condition. The behavior of the effective diffusivity (Deff) during the salting process of the pirarucu fillet is presented in Fig. 4. The Deff values confirm that from two hours of contact of the fish fillet with the osmotic solution, the vacuum pulse and temperature conditions no longer interfere on SG rates. The higher Deff values at the start of the salting process are attributed to the low molecular weight of NaCl and to the high osmotic pressure and concentration gradients between the product and the osmotic solution. With the evolution of the process, the Deff values reduce gradually, due to the decrease of these gradients, until they reach a constant value, when the system reaches the equilibrium condition. Structural changes in tissues due to the salt action may also promote the reduction of Deff (Telis, Murari, & Yamashita, 2004). In addition, the heterogeneity of food composition, a compacted network of fibers and proteins, high lipid content and low water content are other factors that may reduce the value of Deff (Gallart-Jornet et al., 2007).
state that until 30 °C the mass transfer rates in the initial period of the pirarucu salting process increased with the increasing system maintenance time at atmospheric pressure, between vacuum pulses (p ≤ 0.05). In turn, when the process was conducted at 40 °C an inversion of this behavior was observed, confirming that in this condition the effect of temperature on the mass transfer is preponderant. Peleg capacity constant (k2) is related to the SG value in equilibrium (SG∞ = 1/k2) (Peleg, 1988). Although the k2 values varied from 0.72 ± 0.05 to 2.57 ± 0.21 g/g db, a standard behavior of this parameter was not observed as a function of the temperature and vacuum condition. The lowest and highest values of k2 were observed for the processes performed at 30 °C, in the 1st and 4th vacuum pulse conditions, respectively. On the other hand, in general, maximum values of SG observed experimentally (0.47 ± 0.03–0.73 ± 0.04 g/g db) are in agreement with the SG∞ estimated values (0.52 ± 0.04–1.39 ± 0.10 g/g db). As mentioned, the higher levels of salt impregnation are expected for the conditions with the lowest values of k1 and higher values of SG∞. Based on the statistical analysis, the best combination of these values was observed in the 3rd vacuum pulse 412
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The values of Deff observed for the salting process of the pirarucu fillet, under the different vacuum pulse and temperature conditions (Fig. 4), are in the range of values observed for the salting processes of tilapia fillet (Medina-Vivanco et al., 2002), sardine (Corzo & Bracho, 2007), and codfish and salmon (Gallart-Jornet et al., 2007) (10−10–10−12 m2/s). As the main objective of this research was to evaluate the effect of the vacuum pulse and temperature conditions on the salt impregnation of process, we chose to use a single arbitrary salt concentration and samples with slab-shaped. However, if the salting process is performed at different temperatures and osmotic solution concentrations, and with samples with different shapes, it is possible to calculate additional mass transfer parameters (e.g. profile of solid density distributions within the sample), which are important for a better control of the process (Fabbri, Cevoli, & Troncoso, 2014; Schmidt et al., 2009; Singh, Kumar, & Gupta, 2007; Vatankhah & Ramaswamy, 2019).
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Innovative Food Science & Emerging Technologies, 39, 94–100. https://doi.org/10.1016/j.ifset.2016.11.009. Hofmeister, L. C., Souza, J. A. R., & Laurindo, L. B. (2005). Use of dyed solutions to visualize different aspects of vacuum impregnation of Minas cheese. Food Science Technology, 38, 379–386. https://doi.org/10.1016/j.lwt.2004.05.019. Junk, W. J., Soares, M. G. M., & Bayley, P. B. (2007). Freshwater fishes of the Amazon River basin: Their biodiversity, fisheries, and habitats. Aquatic Ecosystem Health & Management, 10, 153–173. https://doi.org/10.1080/14634980701351023. Maciel, R. A., Rodrigues, A. M. C., & Pena, R. S. (2016). Influence of the process parameters on osmotic dehydration of mapará (Hypophthalmus edentatus) fillet. Journal of Food Science and Technology, 53, 676–684. https://doi.org/10.1007/s13197-0151999-5. Marouzé, C., Girox, F., Collignan, A., & Rivier, M. (2001). Equipment design for osmotic treatments. Journal of Food Engineering, 49, 207–221. https://doi.org/10.1016/ S0260-8774(00)00217-X. Martins, M. G., Martins, D. E. G., & Pena, R. S. (2015). Drying kinetics and hygroscopic behavior of pirarucu (Arapaima gigas) fillet with different salt contents. Food Science and Technology, 62, 144–151. https://doi.org/10.1016/j.lwt.2015.01.010. Martins, M. G., Martins, D. E. G., & Pena, R. S. (2017). Chemical composition of different muscle zones in pirarucu (Arapaima gigas). Food Science and Technology, 37, 651–656. https://doi.org/10.1590/1678-457x.30116. Martins, M. G., & Pena, R. S. (2017). Combined osmotic dehydration and drying process of pirarucu (Arapaima gigas) fillets. Journal of Food Science and Technology, 54, 3170–3179. https://doi.org/10.1007/s13197-017-2755-9. Medina-Vivanco, M., Sobral, P. J. A., & Hubinger, M. D. (2002). Osmotic dehydration of tilapia fillets in limited volume of ternary solutions. Chemical Engineering Journal, 86, 199–205. https://doi.org/10.1016/S1385-8947(01)00290-X. Nguyen, M. V., Arason, S., Thorarinsdottir, K. A., Thorkelsson, G., & Gudmundsdóttir, A. (2010). The effects of salt concentration on conformational changes in cod (Gadus morhua) proteins during brine salting. Journal of Food Engineering, 100, 225–231. https://doi.org/10.1016/j.foodchem.2010.09.109. Núñez, J., Chu-Koo, F., Berland, M., Arevalo, L., Ribeyro, O., Duponchelle, F., & Renno, J. F. (2011). Reproductive success and fry production of the paiche or pirarucu, Arapaima gigas (Schinz), in the region of Iquitos, Peru. Aquaculture Research, 42, 815–822. https://doi.org/10.1111/j.1365-2109.2011.02886.x. Oliveira, P. R., Jesus, R. S., Batista, G. M., & Lessi, E. (2014). Sensorial, physicochemical and microbiological assessment of pirarucu (Arapaima gigas, Schinz 1822) during ice storage. Brazilian Journal of Food Technology, 17, 67–74. https://doi.org/10.1590/ bjft.2014.010. Peleg, M. (1988). An empirical model for the description of moisture sorption curves. Journal of Food Science, 53, 1216–1217. https://doi.org/10.1111/j.1365-2621.1988. tb13565.x. Rahman, M. S. (2007). Handbook of food preservation. United States of America: Taylor & Francis850. Rastogi, N. K., & Raghavarao, K. S. M. S. (1996). Kinetics of osmotic dehydration under vacuum. Food Science and Technology, 29, 669–672. https://doi.org/10.1006/fstl. 1996.0103. Sannaveerappa, T., Ammu, K., & Joseph, J. (2004). Protein-related changes during salting
4. Conclusions The study of salting process of the pirarucu fillets using pulsed-vacuum impregnation (PVI) and periodic pulsed-vacuum impregnation (PPVI), with vacuum pulse of 5 min at 10 kPa and different temperatures (10 °C–40 °C) showed that the PVI and PPVI processes favor the solid gain (salting) when low or moderate temperatures are used (10 °C at 30 °C). The lowest mean moisture (58.8 g/100 g) and aw (0.80) were observed when the salting process was accomplished using PPVI for 5 min at 10 kPa (vacuum pulse) and 10 min at atmospheric pressure, intermittently, regardless of the temperature. In this condition, the product presented 0.43 ± 0.04 g/g db salt content. On the other hand, if the salting of pirarucu is accomplished at temperatures higher than 30 °C, the PVI and PPVI processes are not recommended, since in this condition the effect of temperature under the SG prevails regardless of vacuum application. Additionally, the salting of the pirarucu fillet using PVI and PPVI can be considered a fast process, since it demanded only two hours, in the experimental domain. As it is a fast process and it can be carried out at ambient or lower temperature, which favors the maintenance of product quality, the PVI and PPVI processes are considered as promising alternatives for the salting of the pirarucu muscle. Finally, Peleg model satisfactorily explain the salting kinetics of the pirarucu fillet in the experimental domain. Acknowledgements The authors acknowledge Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq, Brazil) for the financial support (311067/2015-8) and Coordenação de Pessoal de Nível Superior (CAPES, Brazil) for the scholarship of M. G. Martins. The authors have no conflict of interest. References Andrés, A., Rodríguez-Barona, S., Barat, J. M., & Fito, P. (2002). Mass transfer kinetics during cod salting operation. Food Science and Technology International, 8, 309–314. https://doi.org/10.1106/108201302031117. AOAC (1997). Official methods of analysis (16th ed.). Gaithersburg: Association of Official Analytical Chemists. APHA (2015). Compendium of methods for the microbiological examination of foods (5th ed.). Washington: American Public Health Association995. Barat, J. M., Rodríguez-Barona, S., Andrés, A., & Fito, P. (2003). Cod salting manufacturing analysis. Food Research International, 36, 447–453. https://doi.org/10. 1016/S0963-9969(02)00178-3. Castello, L., Stewart, D. J., & Arantes, C. C. (2011). Modeling population dynamics and conservation of arapaima in the Amazon. Reviews in Fish Biology & Fisheries, 21, 621–640. https://doi.org/10.1007/s11160-011-9241-7. Chiralt, A., Fito, P., Barat, J. M., Andrés, A., González-Martı́nez, C., Escriche, I., & Camacho, M. M. (2001). Use of vacuum impregnation in food salting process. Journal of Food Engineering, 49, 141–151. https://doi.org/10.1016/S0260-8774(00)00219-3. Collignan, A., Bohuon, P., Deumier, F., & Poligne, I. (2001). Osmotic treatment of fish and meat products. Journal of Food Engineering, 49, 153–162. https://doi.org/10.1016/ S0260-8774(00)00215-6.
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of milkfish (Chanos chanos). Journal of Science and Food Agriculture, 84, 863–869. https://doi.org/10.1002/jsfa.1682. Schmidt, F. C., Carciofi, B. A. M., & Laurindo, J. B. (2009). Salting operational diagrams for chicken breast cuts: Hydration–dehydration. Journal of Food Engineering, 88, 36–44. https://doi.org/10.1016/j.jfoodeng.2007.12.005. Singh, B., Kumar, A., & Gupta, A. K. (2007). Study of mass transfer kinetics and effective diffusivity during osmotic dehydration of carrot cubes. Journal of Food Engineering, 79, 471–480. https://doi.org/10.1016/j.jfoodeng.2006.01.074. Sobukola, O. P., & Olatunde, S. O. (2011). Effect of salting techniques on salt uptake and drying kinetics of African catfish (Claris gariepinus). Food and Bioproducts Processing, 89, 170–177. https://doi.org/10.1016/j.fbp.2010.06.002. Telis, V. R. N., Murari, R. C. B. D. L., & Yamashita, F. (2004). Diffusion coefficients during osmotic dehydration of tomatoes in ternary solutions. Journal of Food Engineering, 61,
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Food Research International journal homepage: www.elsevier.com/locate/foodres
Application of pulsed-vacuum on the salt impregnation process of pirarucu fillet Mayara Galvão Martinsa, Paulo Sérgio Nunes Chadab, Rosinelson da Silva Penaa,b, a b
T
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Postgraduate Program in Food Science and Technology, Technology Institute, Federal University of Pará (UFPA), Belém 66075-110, PA, Brazil Faculty of Food Engineering, Technology Institute, Federal University of Pará (UFPA), Belém 66075-110, PA, Brazil
A R T I C LE I N FO
A B S T R A C T
Keywords: Arapaima gigas Vacuum pulse Salting Diffusion Modeling
The influence of the pulsed-vacuum impregnation (PVI) and periodic pulsed-vacuum impregnation (PPVI), and the temperature, on the salting process of pirarucu fillet was studied. For this, the dorsal region of the fish in the slab-shaped (60 mm × 20 mm × 5 mm) and sodium chloride solution (30 g/100 g NaCl) were used. The process was conducted at different temperatures (10 °C – 40 °C) and the following pulsed-vacuum conditions: initial vacuum pulse (5 min at 10 kPa) and alternating periods of vacuum pulse (5 min at 10 kPa) and atmospheric pressure (101 kPa) for 5 min, 10 min and 15 min intermittently. The solid gain (SG) in the fillet was more pronounced in the first two hours of the salting process. The increase of salt content in the product (0.33 ± 0.02 to 0.43 ± 0.04 g/g db) promoted the gradual reduction of moisture (72.99 ± 1.27 to 57.1 ± 2.4 g/100 g) and water activity (1.00 ± 0.03 to 0.78 ± 0.05). PVI and PPVI processes can be used efficiently at room temperature or under refrigeration in the salting process of pirarucu fillet. On the other hand, at higher temperatures (> 30 °C), the effect of temperature prevails over the effect of vacuum. Peleg model satisfactorily explains the salting kinetics of the pirarucu fillet.
1. Introduction The Amazon is recognized worldwide for having a great diversity of fish species, which have social, cultural, environmental and economic relevance (Junk, Soares, & Bayley, 2007). In this context, pirarucu (Arapaima gigas) is one of the largest fish of the Amazonian ichthyofauna, which stands out for the great potential for sustainable exploitation, as it presents relevant nutritional aspects, high added values and characteristics that promote cultivation and industrialization (Castello, Stewart, & Arantes, 2011; Martins, Martins, & Pena, 2017; Martins & Pena, 2017; Núñez et al., 2011). Traditionally, pirarucu is marketed in dry-salted form, whose salting process is similar to that used for codfish, in which blankets are stacked and intercalated with different layers of salt crystals (Barat, RodríguezBarona, Andrés, & Fito, 2003). However, in the case of pirarucu, there are still no well-defined parameters for the salting process, as well as for the complementary drying. Salting is one of the oldest techniques of preservation of food, which is based on the principle of osmotic dehydration, where the diffusion of the salt into the tissues and the loss of free water by osmosis occurs (Gallart-Jornet et al., 2007; Martins, Martins, & Pena, 2015; Sobukola & Olatunde, 2011). Salt impregnation process using sodium chloride or brine can be
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carried out at atmospheric pressure or as vacuum impregnation (VI), pulsed-vacuum impregnation (PVI) or periodic pulsed-vacuum impregnation (PPVI). PVI consists of product immersion in a hypertonic solution and the application of subatmospheric pressure at the beginning of the process, for a short time, with subsequent restoration of atmospheric pressure. In contrast, PPVI is characterized by intercalated periods of subatmospheric and atmospheric pressure, intermittently (Chiralt et al., 2001; Collignan, Bohuon, Deumier, & Poligne, 2001). In the PVI and PPVI, when the vacuum is applied, the expansion of the muscle fibers occurs, accompanied by the elimination of occluded gases in the pores. When the atmospheric pressure is restored, the osmotic solution is introduced into the pores of the product due to the macroscopic pressure gradients and the capillary effects (Chiralt et al., 2001; Deumier, 2004). The mass transfer is favored by the enhancement of the contact surface, due to the elimination of the air inside the pores (Deumier, 2004; Marouzé, Girox, Collignan, & Rivier, 2001). The use of vacuum in salting processes has been reported as an alternative to reduce the process time, as well as to promote a more homogeneous distribution of the salt in the product (Chiralt et al., 2001; Hofmeister, Souza, & Laurindo, 2005; Schmidt, Carciofi, & Laurindo, 2009). There are few reports in the literature involving vacuum application in fish salting processes (Corzo & Bracho, 2007; Corzo, Bracho,
Corresponding author at: Faculdade de Engenharia de Alimentos, Universidade Federal do Pará (UFPA), Rua Augusto Corrêa, 01, Belém 66075-110, PA, Brazil. E-mail address: [email protected] (R. da Silva Pena).
https://doi.org/10.1016/j.foodres.2019.03.016 Received 4 November 2018; Received in revised form 5 March 2019; Accepted 8 March 2019 Available online 09 March 2019 0963-9969/ © 2019 Elsevier Ltd. All rights reserved.
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the experiments were performed in triplicate.
Rodríguez, & González, 2007; Maciel, Rodrigues, & Pena, 2016; Martins & Pena, 2017; Rastogi & Raghavarao, 1996), as well as studies about the processing of pirarucu (Hernández, Carvalho Jr, Joele, Araújo, & Lourenço, 2017; Martins et al., 2015; Martins & Pena, 2017; Oliveira, Jesus, Batista, & Lessi, 2014). These facts motivated this research, whose objective is to study the influence of the application of pulsedvacuum and periodic pulsed-vacuum, as well as the temperature, in the salting process of the pirarucu fillet, by impregnation of sodium chloride.
2.3. Salt impregnation process kinetics The effect of the contact time (30, 60, 90, 120 and 180 min) on the solids gain (SG) was used to follow the evolution of the salting process, from salting kinetics, obtained for the different process conditions. The SG values were calculated according to Eq. (1).
SG = 2. Material and methods
SMt − SMo Mo
(1)
where SG: solid gain (g/g dry basis – db), Mo: initial mass of fish fillet slab (g), SMo: initial dry mass of fish fillet slab (g), SMt: dry mass of fish fillet slab (g) after impregnation time (t). The moisture and water activity profiles (aw), and the evolution of the salt content were also determined. Moisture was measured by gravimetry, aw was determined on a thermo-hygrometer (Aqualab 3TE, Decagon, USA) and the salt content was determined by the Mohr method (AOAC, 1997). All the determinations were performed in triplicate.
2.1. Raw material and sample preparation The pirarucu used in the research was acquired at an aquaculture farm located in Breu Branco (Pará, Brazil) (04°04′04″ S and 49°38′13″ W) and transported to the Federal University of Pará (Belém, Pará, Brazil) (01°27′21″ S and 48°30′16″ W), in an isothermic container containing ice. In the laboratory, the fish was sanitized, scales and skin were removed, and then filleting of the muscle was performed with stainless steel blades. The most representative fraction of the pirarucu muscle, the dorsal region (Martins et al., 2017), was used in the research, as slab-shaped samples (60 mm length, 20 mm width, and 5 mm thickness). In order to assure the microbiological quality of the raw material used, microbiological analyses were performed to investigate the absence or presence of Salmonella sp., the groups coagulase positive Staphylococcus, expressed as colony forming units per gram of fresh fish (CFU/g), and thermotolerant coliforms at 45 °C, expressed as the most probable number per gram of fresh fish (MPN/g) (APHA, 2015).
2.4. Salt impregnation process modeling Peleg (1988) proposed a two-parameter model (Eq. (2)), which can be used to describe the kinetics of a salting process. Thus, the parameters of the Peleg model for SG were estimated by linear regression, using the linear (k1) and angular (k2) coefficients of the t/SG versus t curve. The fit of the model to the experimental data was evaluated by the coefficient of determination (R2).
XS − X S0 = 2.2. Salt impregnation procedure
t k1 + k2 t
(2)
where XS: product's solid content at a time t (h) of impregnation (g/g db), Xs0: product's initial solid content (g/g db), XS – Xs0 = GS: solid gain (g/g db), k1: Peleg rate constant (h/(g/g db)), k2: Peleg capacity constant (1/(g/g db)).
Salt impregnation process with sodium chloride (NaCl) solution was conducted by pulsed-vacuum impregnation (PVI) and periodic pulsedvacuum impregnation (PPVI). All experiments were performed in a covered system to allow the recirculation of the thermal fluid (water), which was coupled with a vacuum pump and an ultra-thermostatic bath (Q214M2, Quimis, Brazil) to assure pressure and temperature controls inside the system. The covered system was maintained on a shaker table to ensure a constant stirring at 60 rpm, sufficient to promote the circulation of the solution and remove the surface layer around the sample (Maciel et al., 2016; Martins & Pena, 2017). In the impregnation experiments it was used an osmotic solution with 30% NaCl (w/v), prepared by dissolving the NaCl analytical grade in distilled water. A ratio of mass sample/volume of the osmotic solution of 1:20 (w/v) was used to ensure a constant concentration of the osmotic solution throughout the process. The slab-shaped samples (≈ 7 g) were weighed in an analytical balance (AY220, Shimadzu, Brazil) and immersed in the osmotic solution. The system was immediately closed and subjected to different temperature conditions (10, 20, 30 or 40 °C) and at 10 kPa absolute pressure (vacuum), according to the process conditions. After the processing times (30, 60, 90, 120 and 180 min), the samples were removed from the osmotic solution, washed with 20 mL of water and dried with absorbent paper to remove excess salt and water from the surface. Finally, the samples were weighed again on the analytical balance. In the PVI process, during the first 5 min, the system was maintained at 10 kPa, then system's vacuum condition was interrupted and the system was maintained at atmospheric pressure (101 kPa – Belém, PA, Brazil) until the end of the process (1st condition). In the PPVI process, alternating periods of vacuum pulse (5 min at 10 kPa) and atmospheric pressure (101 kPa) were used until the end of the process. In this case, the system was maintained at atmospheric pressure for 5 min (2nd condition), 10 min (3rd condition) e 15 min (4th condition). A graphical scheme of these process conditions used is shown in Fig. 1. All
2.5. Prediction of effective diffusivity Based on Fick's second law, Crank (1975) proposed an equation for unidirectional diffusion in a sample with flat slab geometry in contact with an infinite amount of solution, used to describe the osmotic dehydration kinetics. The simplified form of this model (Eq. (3)) for short contact times (t) is applied to the initial phase of the process, when diffusion is assumed to occur in a semi-infinite medium. 1/2
Deff ⋅t SGt ⎞ = 2⋅⎛ 2 SG∞ ⎝ π ⋅L ⎠ ⎜
⎟
(3)
where SGt: amount of SG the product at a given time (t), WS∞: amount of SG the product after an infinite time (equilibrium), Deff: effective diffusivity (m2/s), L: half-thickness of the sample (m). Considering Eq. (3), the effective diffusivity (Deff) was calculated for each process condition and time interval (t) of the kinetics (Eq. (4)), as a function of the angular and linear coefficients of the t/SG versus t curves (Eq. (5)).
Deff =
∞ π⋅t ⎡ ⎛ Si⋅L ⎞ ⎛ SGpred ⎞ ⎤ ⋅⎜ ∞ ⎟ ⎥ ⎢ 4 ⎝ 1 + Si⋅t ⎠ ⎝ SGexp ⎠ ⎦ ⎣ ⎜
⎟
(4)
1 1 t = + SG Si (SG∞) SG∞
(5) 2
where Deff: effective diffusivity (m /s), t: contact time (s), L: halfthickness of the sample (m), SG: solid gain (g/g db), SGpred∞: predicted solid gain for the product after an infinite time (equilibrium) (1/angular coefficient), SGexp∞: experimental solid gain for the product after an 408
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Fig. 1. Graphical scheme of pulsed-vacuum processes.
infinite time (equilibrium), Si: (1/(linear coefficient × SGpred∞)).
(Fig. 2); conditions in which the influence of the vacuum pulse on the mass transfer mechanisms that favor the salting process, were more representative. During the application of vacuum pulses, initial SG rates are affected by pressure gradients called hydrodynamic mechanisms (HDM) (Andrés, Rodríguez-Barona, Barat, & Fito, 2002). Due to the pressure changes that the system undergoes, the HDM favors the increase of the driving forces responsible for the mass transfer, promoting the exchange of gas or liquid occluded in the pores of the product by an external liquid phase. Additionally, the relaxation of the cellular network occurs slightly deformed due to the reduced pressure level (Fito, Andrés, Chiralt, & Pardo, 1996). The HDM can occur concomitantly with the deformation-relaxation phenomenon (DRP), which affects not only the kinetics and equilibrium condition of the system but also the physical, mechanical and microstructural properties of porous solids (Fito et al., 1996). According to these authors, in plant tissues, the DRP promoted by the vacuum pulse is more affected when higher temperatures are employed. For the salting of the pirarucu fillet (animal tissue), it was also observed an increase in the salt impregnation rates, as the temperature increases. This is evidenced by the increase in the tangent of the curve (Fig. 2), especially in the first hour of the process, and can be attributed to DRP. In general, the results of the research indicate that, in the experimental domain, pirarucu salting process does not need to exceed two hours. In addition, when PVI or PPVI are used, the salting process can be conducted efficiently at room temperature or under refrigeration (< 30 °C). These conditions are favorable from the point of view of product quality because they minimize the negative effects of oxidative processes, the development of halophilic bacteria and other degradation processes to which the pirarucu muscle is susceptible. On the other hand, when higher temperatures are used (> 30 °C) the PVI and PPVI process are not recommended, since the effect of temperature prevails over DRP, favoring the mass transfer rates, regardless of whether or not the vacuum is used. The salt gain during the impregnation process of the pirarucu fillets followed the same behavior observed for the SG, and the maximum salt levels observed in the product at the end of the salting process varied from 0.33 ± 0.02 to 0.43 ± 0.04 g/g db. These salt levels are in agreement with those observed in other researches, which involved the fish salting process (Corzo, Bracho, & Rodríguez, 2015; Gallart-Jornet et al., 2007; Nguyen, Arason, Thorarinsdottir, Thorkelsson, & Gudmundsdóttir, 2010). In addition to changing the sensorial characteristics of the product, the salt concentration in the salting process has a direct influence on the functional properties of the proteins, texture of the product and viscosity of the osmotic solution (CostaCorredor, Muñoz, Arnau, & Gou, 2010; Fito et al., 2001; Nguyen et al., 2010). The increase of the salt content, during the salting process,
2.6. Statistical analysis For evaluate the isolated effects of temperature and vacuum pulse conditions, and the combined effect of these variables on the experimental results was used Statistica 7.0. For this, the experimental data were submitted to analysis of variance using factorial ANOVA, and the means were compared by Tukey's test at 95% significance. The parameters of the Peleg model and the effective diffusivity values were predicted by linear regression. 3. Results and discussion The results of the microbiological analyzes indicated that the hygienic-sanitary procedures used during capture, slaughter, and evisceration, as well as in the manipulation of the fish muscle used were adequate. Values of 2.3 × 101 MPN/g were observed for thermotolerant coliforms at 45 °C, 1 × 101 CFU/g for Coagulase-positive Staphylococcus and the absence of Salmonella sp. in fish muscle. The kinetics of the solids gain (SG) during the salt impregnation process of the pirarucu fillet, under the different temperature and vacuum pulse conditions are presented in Fig. 2. Regardless of the experimental condition, a gradual increase of SG was observed, which was more pronounced in the first two hours, for the processes carried out at 10 °C, 20 °C and 30 °C, and in the first hour for the processes carried out at 40 °C. The increase of the SG at the beginning of the salting process is attributed to the driving force, which is responsible for the diffusion of solids between the hypertonic solution and the product. At the beginning of the process, the osmotic pressure and concentration gradient between the osmotic solution and the product are higher, favoring higher SG rates. As the process progresses, these gradients gradually decrease until the equilibrium condition is reached (Medina-Vivanco, Sobral, & Hubinger, 2002; Rastogi & Raghavarao, 1996). The salting process is characterized by a dynamic period and by equilibrium. In the dynamic period, mass transfer rates increase or decrease until equilibrium is reached; when the net mass transportation rate becomes insignificant (Rahman, 2007). After the first two hours of the process, SG levels practically stabilized, regardless of the temperature and vacuum pulse conditions used; indicating that there is no salt concentration and osmotic pressure gradients between solution and product (equilibrium). Then, the migration of the salt from the solution to the product and from the product to the solution occurs concurrently (Erikson, Veliyulin, Singstad, & Aursand, 2004). The effect of the vacuum pulse conditions applied to the salting was more evident in the processes conducted at temperatures until 30 °C 409
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Fig. 2. Kinetics of solid gain during the salting process of pirarucu fillet at 10 °C, 20 °C, 30 °C and 40 °C using pulsed-vacuum impregnation (PVI) and periodic pulsedvacuum impregnation (PPVI) (markers) and fit of the model proposed by Peleg (lines): 1st condition (◯, ──), 2nd condition (□, ——), 3rd condition (◇, ····) and 4th condition (Δ, – · –).
proteins, causing them to lose the capacity of water retention, due to the weakening of the forces of protein-water binding (Thorarinsdottir, Arason, Bogason, & Kristbergsson, 2004; Thorarinsdottir, Arason, Geirsdottir, Bogason, & Kristbergsson, 2002). The curves estimated by the Peleg model are presented in Fig. 2 and the statistical parameters of the mathematical modeling, as well as the constants of the model adjusted to the experimental data, are presented in Table 1. The values of the coefficient of determination (0.99 > R2 > 0.85) indicate that the Peleg model is able to satisfactorily explain the kinetics of the salting process of the pirarucu fillet in the experimental domain. Corzo et al. (2015) observed that the Peleg model described with good precision the SG kinetics of catfish fillet in osmotic solutions with different chloride mixtures. Good adjustments for the Peleg model were also observed by Corzo et al. (2007), for the SG kinetics of sardine fillet, using a vacuum pulse. The value of the Peleg rate constant (k1) is related to the initial mass transfer rate, and the lower the value of k1, the higher the initial solids gain rate (Peleg, 1988). Based on the k1 values (Table 1) it is possible to
promoted the gradual reduction of moisture content and, consequently, of the product aw, as can be observed in the Fig. 3. In the first hour of the process there was a marked reduction of aw, which remained practically constant from that time, reaching values varying from 0.78 ± 0.05 to 0.84 ± 0.07 at the end of the process. Similar behavior was observed for fresh pirarucu muscle moisture (72.99 ± 1.27 g/ 100 g), which reduced to 57.1 ± 2.4 g/100 g after the salting process. In addition, regardless of the temperature and the vacuum pulse condition used, no significant difference was observed between the moisture content and aw values (p ≤ 0.05) of the product. The replacement of gases or liquids occluded in the pores of the product by saline solution, due to the application of the vacuum pulse, increases the mass transfer pathways, especially those related to solute absorption, due to the absence of cell membranes in these spaces (Fito et al., 2001). The influence of salt on water loss (reduction of moisture) can also be attributed to protein denaturation promoted by salt during the fish salting process (Sannaveerappa, Ammu, & Joseph, 2004). Along with the denaturation occurs the reduction of the solubility of the 410
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Fig. 3. Moisture content and water activity profiles during the salting process of pirarucu fillet at 10 °C, 20 °C, 30 °C and 40 °C using pulsed-vacuum impregnation (PVI) and periodic pulsed-vacuum impregnation (PPVI): 1st condition (◯), 2nd condition (□), 3rd condition (◇) and 4th condition (Δ).
Table 1 Parameters of the Peleg model to the experimental data for the solid gain kinetics during the salting process of pirarucu fillet at different temperatures and with the application of pulsed-vacuum impregnation (PVI) and periodic pulsed-vacuum impregnation (PPVI).⁎ Temperature
Condition
k1
10 °C
1st 2nd 3rd 4th 1st 2nd 3rd 4th 1st 2nd 3rd 4th 1st 2nd 3rd 4th
1.72 0.84 0.34 0.22 0.25 1.13 0.24 0.35 2.04 1.37 0.47 0.26 0.06 0.16 0.19 0.34
20 °C
30 °C
40 °C
SG∞
k2 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
0.14b 0.06e 0.02fg 0.01gh 0.02gh 0.09d 0.02gh 0.03fg 0.14a 0.09c 0.03f 0.02g 0.01h 0.01gh 0.01gh 0.02fg
1.39 1.69 1.34 1.72 1.70 1.31 1.92 1.81 0.72 1.17 1.19 2.57 1.72 1.34 1.43 1.27
± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
0.11cd 0.13bc 0.06d 0.10bc 0.12bc 0.10d 0.14b 0.14b 0.05e 0.08d 0.07d 0.21a 0.12bc 0.07d 0.08cd 0.09d
0.72 0.59 0.75 0.58 0.59 0.76 0.52 0.55 1.39 0.85 0.84 0.39 0.58 0.75 0.70 0.79
R2 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
0.06bcd 0.05def 0.04bc 0.03def 0.04def 0.06bc 0.04fg 0.04ef 0.10a 0.06b 0.05bc 0.03g 0.04def 0.04bc 0.04cde 0.06bc
0.886 0.994 0.993 0.993 0.977 0.903 0.990 0.970 0.865 0.953 0.982 0.852 0.995 0.999 0.988 0.998
k1 = Peleg rate constant (h/(g/g db)); k2 = Peleg capacity constant (1/(g/g db)); SG∞ = SG of the product after an infinite time (equilibrium) (g/g db); R2 = Coefficient of determination. ⁎ Means ( ± standard deviations) with different superscript letters in the same column are statistically different (p ≤ 0.05, Tukey test). 411
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Fig. 4. Effective diffusivity for the salting process of pirarucu fillet at 10 °C, 20 °C, 30 °C and 40 °C using pulsed-vacuum impregnation (PVI) and periodic pulsedvacuum impregnation (PPVI). 1st condition (◯), 2nd condition (□), 3rd condition (◇) and 4th condition (Δ).
condition, for the studied temperature range (10 °C to 40 °C) (Table 1). Thus, the results allow affirming that the higher levels of salt impregnation in the pirarucu muscle were observed in this condition. The behavior of the effective diffusivity (Deff) during the salting process of the pirarucu fillet is presented in Fig. 4. The Deff values confirm that from two hours of contact of the fish fillet with the osmotic solution, the vacuum pulse and temperature conditions no longer interfere on SG rates. The higher Deff values at the start of the salting process are attributed to the low molecular weight of NaCl and to the high osmotic pressure and concentration gradients between the product and the osmotic solution. With the evolution of the process, the Deff values reduce gradually, due to the decrease of these gradients, until they reach a constant value, when the system reaches the equilibrium condition. Structural changes in tissues due to the salt action may also promote the reduction of Deff (Telis, Murari, & Yamashita, 2004). In addition, the heterogeneity of food composition, a compacted network of fibers and proteins, high lipid content and low water content are other factors that may reduce the value of Deff (Gallart-Jornet et al., 2007).
state that until 30 °C the mass transfer rates in the initial period of the pirarucu salting process increased with the increasing system maintenance time at atmospheric pressure, between vacuum pulses (p ≤ 0.05). In turn, when the process was conducted at 40 °C an inversion of this behavior was observed, confirming that in this condition the effect of temperature on the mass transfer is preponderant. Peleg capacity constant (k2) is related to the SG value in equilibrium (SG∞ = 1/k2) (Peleg, 1988). Although the k2 values varied from 0.72 ± 0.05 to 2.57 ± 0.21 g/g db, a standard behavior of this parameter was not observed as a function of the temperature and vacuum condition. The lowest and highest values of k2 were observed for the processes performed at 30 °C, in the 1st and 4th vacuum pulse conditions, respectively. On the other hand, in general, maximum values of SG observed experimentally (0.47 ± 0.03–0.73 ± 0.04 g/g db) are in agreement with the SG∞ estimated values (0.52 ± 0.04–1.39 ± 0.10 g/g db). As mentioned, the higher levels of salt impregnation are expected for the conditions with the lowest values of k1 and higher values of SG∞. Based on the statistical analysis, the best combination of these values was observed in the 3rd vacuum pulse 412
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The values of Deff observed for the salting process of the pirarucu fillet, under the different vacuum pulse and temperature conditions (Fig. 4), are in the range of values observed for the salting processes of tilapia fillet (Medina-Vivanco et al., 2002), sardine (Corzo & Bracho, 2007), and codfish and salmon (Gallart-Jornet et al., 2007) (10−10–10−12 m2/s). As the main objective of this research was to evaluate the effect of the vacuum pulse and temperature conditions on the salt impregnation of process, we chose to use a single arbitrary salt concentration and samples with slab-shaped. However, if the salting process is performed at different temperatures and osmotic solution concentrations, and with samples with different shapes, it is possible to calculate additional mass transfer parameters (e.g. profile of solid density distributions within the sample), which are important for a better control of the process (Fabbri, Cevoli, & Troncoso, 2014; Schmidt et al., 2009; Singh, Kumar, & Gupta, 2007; Vatankhah & Ramaswamy, 2019).
Corzo, O., & Bracho, N. (2007). Determination of water effective diffusion coefficient of sardine sheets during vacuum pulse osmotic dehydration. Food Science and Technology, 40, 1452–1458. https://doi.org/10.1016/j.lwt.2006.04.008. Corzo, O., Bracho, N., & Rodríguez, J. (2015). Modeling mass transfer during salting of catfish sheets. Journal of Aquatic Food Product Technology, 24, 120–130. https://doi. org/10.1080/10498850.2012.762703. Corzo, O., Bracho, N., Rodríguez, J., & González, M. (2007). Predicting the moisture and salt contents the sardine sheets during vacuum pulse osmotic dehydration. Journal of Food Engineering, 80, 781–790. https://doi.org/10.1016/j.jfoodeng.2006.07.007. Costa-Corredor, A., Muñoz, I., Arnau, J., & Gou, P. (2010). Ion uptakes and diffusivities in pork meat brine-salted with NaCl and K-lactate. Food Science and Technology, 43, 1226–1233. https://doi.org/10.1016/j.lwt.2010.03.018. Crank, J. (1975). The mathematics of diffusion. Oxford: Clarendon Press. 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Journal of Food Engineering, 49, 207–221. https://doi.org/10.1016/ S0260-8774(00)00217-X. Martins, M. G., Martins, D. E. G., & Pena, R. S. (2015). Drying kinetics and hygroscopic behavior of pirarucu (Arapaima gigas) fillet with different salt contents. Food Science and Technology, 62, 144–151. https://doi.org/10.1016/j.lwt.2015.01.010. Martins, M. G., Martins, D. E. G., & Pena, R. S. (2017). Chemical composition of different muscle zones in pirarucu (Arapaima gigas). Food Science and Technology, 37, 651–656. https://doi.org/10.1590/1678-457x.30116. Martins, M. G., & Pena, R. S. (2017). Combined osmotic dehydration and drying process of pirarucu (Arapaima gigas) fillets. Journal of Food Science and Technology, 54, 3170–3179. https://doi.org/10.1007/s13197-017-2755-9. Medina-Vivanco, M., Sobral, P. J. A., & Hubinger, M. D. (2002). Osmotic dehydration of tilapia fillets in limited volume of ternary solutions. 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4. Conclusions The study of salting process of the pirarucu fillets using pulsed-vacuum impregnation (PVI) and periodic pulsed-vacuum impregnation (PPVI), with vacuum pulse of 5 min at 10 kPa and different temperatures (10 °C–40 °C) showed that the PVI and PPVI processes favor the solid gain (salting) when low or moderate temperatures are used (10 °C at 30 °C). The lowest mean moisture (58.8 g/100 g) and aw (0.80) were observed when the salting process was accomplished using PPVI for 5 min at 10 kPa (vacuum pulse) and 10 min at atmospheric pressure, intermittently, regardless of the temperature. In this condition, the product presented 0.43 ± 0.04 g/g db salt content. On the other hand, if the salting of pirarucu is accomplished at temperatures higher than 30 °C, the PVI and PPVI processes are not recommended, since in this condition the effect of temperature under the SG prevails regardless of vacuum application. Additionally, the salting of the pirarucu fillet using PVI and PPVI can be considered a fast process, since it demanded only two hours, in the experimental domain. As it is a fast process and it can be carried out at ambient or lower temperature, which favors the maintenance of product quality, the PVI and PPVI processes are considered as promising alternatives for the salting of the pirarucu muscle. Finally, Peleg model satisfactorily explain the salting kinetics of the pirarucu fillet in the experimental domain. Acknowledgements The authors acknowledge Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq, Brazil) for the financial support (311067/2015-8) and Coordenação de Pessoal de Nível Superior (CAPES, Brazil) for the scholarship of M. G. Martins. The authors have no conflict of interest. References Andrés, A., Rodríguez-Barona, S., Barat, J. M., & Fito, P. (2002). Mass transfer kinetics during cod salting operation. Food Science and Technology International, 8, 309–314. https://doi.org/10.1106/108201302031117. AOAC (1997). Official methods of analysis (16th ed.). Gaithersburg: Association of Official Analytical Chemists. APHA (2015). Compendium of methods for the microbiological examination of foods (5th ed.). Washington: American Public Health Association995. Barat, J. M., Rodríguez-Barona, S., Andrés, A., & Fito, P. (2003). Cod salting manufacturing analysis. Food Research International, 36, 447–453. https://doi.org/10. 1016/S0963-9969(02)00178-3. Castello, L., Stewart, D. J., & Arantes, C. C. (2011). Modeling population dynamics and conservation of arapaima in the Amazon. Reviews in Fish Biology & Fisheries, 21, 621–640. https://doi.org/10.1007/s11160-011-9241-7. Chiralt, A., Fito, P., Barat, J. M., Andrés, A., González-Martı́nez, C., Escriche, I., & Camacho, M. M. (2001). Use of vacuum impregnation in food salting process. Journal of Food Engineering, 49, 141–151. https://doi.org/10.1016/S0260-8774(00)00219-3. Collignan, A., Bohuon, P., Deumier, F., & Poligne, I. (2001). Osmotic treatment of fish and meat products. Journal of Food Engineering, 49, 153–162. https://doi.org/10.1016/ S0260-8774(00)00215-6.
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