8/19/2019 Effect of Temperature on Nitrite and Water Diffusion in Pork Mea

http://slidepdf.com/reader/full/effect-of-temperature-on-nitrite-and-water-diffusion-in-pork-mea 1/7

Effect of temperature on nitrite and water diffusion in pork meat

J. Gómez a , N. Sanjuán b , J. Bonb , J. Arnau c, G. Clemente b ,⇑

a Universidad De La Salle Bajío, Avenida Universidad 602, Lomas del Campestre, 37150 León de los Aldama, Guanajuato, Mexicob Food Technology Department, Universitat Politècnica de València, C/ Camí de Vera s/n, 46022 València, Spainc Institut de Recerca i Tecnologia Agroalimentàries (IRTA), Food Technology Center, Finca Camps i Armet, 17121 Monells, Girona, Spain

a r t i c l e i n f o

Article history:Received 24 January 2014Received in revised form 20 September2014Accepted 5 October 2014Available online 14 October 2014

Keywords:NitriteWaterMeatTemperatureDiffusionModelling

a b s t r a c t

Nitrites are important food additives. The nitrite movement in meat is assumed to occur by means of a dif-fusion process. The objective of this study was to investigate theeffect of temperature on nitrite and waterdiffusionmechanisms in meat samples during the curing of pork meat.For this purpose,cylinders of Semi-membranosus muscle were salted with sodium nitrite (NaNO 2) a t 2 C, 7 C and 12 C. Experimental curingand water loss kinetics were modelled by means of a diffusion model. As the curing time lengthened, thewater content fell and the nitrite content increased. The values for the nitrite and water diffusion wereestimated to be in the range of 4.58 10 12 –1.02 10 12 m 2 /s and 5.96 10 9–9.82 10 9 m 2 /s respec-tively, and they increased as the temperature went up. The activation energy was 32.24 kJ/mol for waterdiffusion and 60.32 kJ/mol for nitrite diffusion.

2014 Elsevier Ltd. All rights reserved.

1. Introduction

Meat products are preserved by means of different methods,salting and curing being one of the most commonly used. Sodiumchloride (NaCl) is an ingredient which, among other things,enhances the avour and decreases the water activity of the prod-uct. Nitrite is an additive giving the cured products their character-istic red colour and avour ( Flores and Toldrá, 1993 ). Nitrite,together with sodium chloride, inhibits the production of theneurotoxin produced by Clostridium botulinum , thus preventingfood poisoning and botulism. Although the positive effect of nitrites on meat has been agged, this curing agent involves thepotential formation of nitrosamines through the reaction with sec-ondary amines, which are compounds with teratogenic, mutagenicand carcinogenic effects ( Cassens, 1997 ). Previously, Bogovski andBogovski (1981) investigated the risk of cancer induced by thenitrouscompounds in animal species, concluding that these sub-stances are potent carcinogens.

In the last few years, there have been proposals put forward tocontrol and reduce the maximum authorized amount of nitritespermitted in meat products. In the EU, potassium and sodiumnitrite and nitrate are authorized for use in different meat products(Commission Regulation (EC) No 1129/2011 ). Maximum added orresidual amounts are established depending on the meat product

(Directive 2006/52/CE ). When the maximum amount of addednitrite is regulated it should not exceed 150 mg/kg, however, insome products nitrite is added by rubbing on the surface manuallyor in a tumbler (e.g. dry-cured ham maximum residual 100 mg/kgor dry-cured bacon 175 mg/kg) or brine-cured (Wiltshire baconand toucinho maximum residual 175 mg/kg). Thus, it meansthat nitrite is at very high concentrations on the surface untilequalization.

Since it is difcult to control the level of endogenous factors,such as amino acids and amines, it would be necessary to evaluatethe effect of the reduction in the nitrite added to products and togain greater knowledge of the reaction and process conditionswhile preserving the product safety. For this reason, it is essentialto control the curing process, i.e. the amount of nitrites, the curingtime and the main factors governing nitrite penetration into meat.The transfer mechanismof both nitrite ionand sodium through themeat structure is an interesting aspect in meat processing technol-ogy. The transport phenomenon in the meat brining operation,dened by the transfer of salts and water, is complicated anddepends on aspects such as salt concentration, temperature, pHand meat bre direction ( Barat et al., 2011; Boudhrioua et al.,2009; Gravier et al., 2006, 2009 ).

One of the best ways to learn about the factors governing thisprocess is by using mathematical models, which may representthe process, explain the observed data and predict the behaviourunder different conditions ( Mulet, 1994 ). Diffusion models are usu-ally applied to describe mass transfer in food. Diffusion is the most

http://dx.doi.org/10.1016/j.jfoodeng.2014.10.008

0260-8774/ 2014 Elsevier Ltd. All rights reserved.

⇑ Corresponding author. Tel.: +34 96 387 91 48; fax: +34 96 387 98 39.E-mail address: gclemen@tal.upv.es (G. Clemente).

Journal of Food Engineering 149 (2015) 188–194

Contents lists available at ScienceDirect

Journal of Food Engineering

j ou rna l homepage : www.e l sev i e r. com/ loca t e / j foodeng

8/19/2019 Effect of Temperature on Nitrite and Water Diffusion in Pork Mea

http://slidepdf.com/reader/full/effect-of-temperature-on-nitrite-and-water-diffusion-in-pork-mea 2/7

important mass transfer mechanism during salting ( Barat et al.,2003; Wang et al., 2000 ). Effective diffusivity, which includes theeffect of known hypotheses and unknown phenomena which are

not included in the model, can be calculated by means of diffusionmodels. When modelling, this parameter can be considered con-stant (e.g. Gou et al., 2003; Gravier et al., 2006 ) or dependent onsome process or product conditions. For example, Gravier et al.(2009) in a study on pork meat salting with a mixture of NaNO 2 ,KNO3 , and NaCl considered that the effective diffusion coefcientdepended on NaCl concentration.

The diffusivity is a parameter to consider in the curing processsince it affects the water content and, in turn, the salt penetrationinto the meat. It is signicantly affected by operating tempera-tures. An increase in temperature raises the thermal energy of mol-ecules, resulting in an increase in the diffusion rate of themolecules ( Gou et al., 2003; Pinotti et al., 2002 ). Thus, the depen-dence of diffusivity on temperature is generally described by the

Arrhenius equation.The diffusion of sodium chloride (NaCl) and the inuence of itsconcentration on the diffusivity of a mixture of salts (NaCl, NaNO 2

and KNO 3 ) in pork, beef and sh has been studied by differentresearchers ( Graiver et al., 2006; Sabadini et al., 1998; Siro et al.,2009; Wang et al., 2000 ). Likewise, studies have been performedon the kinetics of the diffusion of sodium chloride during chickenmeat curing ( Volpato et al., 2007 ). Other studies show the inu-ence of curing salts on the macro and microstructure of the treatedproduct: for example pork meat immersed in NaCl brines of differ-ent concentrations ( Graiver et al., 2005, 2009 ) or pork meat saltedby immersion in brines of different compositions (NaNO 2 , KNO3

and NaCl) ( Pinotti et al., 2000 ). Nevertheless, neither has the diffu-sive behaviour of sodium nitrite inside the meat been published,nor the effect of the curing temperature on the diffusion of this salt.On the other hand, due to the increase of the interest about reduc-ing NaCl in meat products ( Stollewerk et al., 2012 ), it is importantto know the behaviour of isolated salts in the curing process, forbetter understanding the diffusion process of a mixture of salts.Therefore, for the purposes of contributing to an improvement inham processing, the objective of this research was to study theeffect of temperature on the diffusion kinetics of sodium nitriteand water in the Semimembranosus muscle of pork leg.

2. Materials and methods

2.1. Raw material

Six pork legs, with an average weight of 9.6 ± 1.2 kg and apH 45 > 6.0 and pH 24 of 5.9 ± 0.1, were selected from a local

slaughterhouse. All the pork legs came from different animalsobtained at a commercial slaughterhouse the day before the curingprocess began. The legs were packed in plastic lm and stored at

2 ± 1 C for between 13 and 14 h before separatingthe Semimembr-anosus muscle (SM). The SM muscle was separated from each legand fourteen cylinders, 8.4 cm in height and 2.4 cm in diameterwere obtained from each muscle, keeping the orientation of themeat bres parallel to the cylinder axis ( Fig. 1 ). Thirteen of thefourteen cylinders obtained from each muscle were used for curingwith sodium nitrite (NaNO 2 ) and the remaining cylinder was usedto characterize the initial conditions of the meat.

2.2. Experimental conditions

The cylinders were weighed and their side faces were subse-quently coveredwith a PVC lmto prevent moisture loss. Each cyl-inder was hung from one of its bases and the other one was in

contact with a brine saturated with sodium nitrite (NaNO 2 ). Thebrine was prepared with an excess of NaNO 2 in order to compen-sate the amount absorbed by the meat. The saturated brine andthe cylinders were placed randomly into curing chambers at 2, 7and 12 C (thirteen cylinders per chamber) with 95 ± 1.5 % relativehumidity.

In order to control the temperature, the curing chambers wereplaced inside a chamber with controlled temperature and relativehumidity. Inside the curing chambers, the relative humidity wasmaintained at around 95% by means of a saturated brine of KNO3 . The measurement of temperature and relative humidity

Nomenclature

C concentration of nitrite or water (kg/m 3)C e equilibrium concentration of nitrite or water (kg/m 3)C s average nitrite concentration (kg/m 3)C 0 initial concentration of nitrite or water (kg/m 3)C se average equilibrium nitrite concentration (kg/m 3)C s0 average initial nitrite concentration (kg/m 3)C w average moisture content (kg water/kg dry matter)C we average equilibrium moisture content (kg water/kg dry

matter)C w0 average initial moisture content (kg water/kg dry

matter)De effective diffusivity of nitrite or water (m 2 /s)DNe effective diffusivity of nitrite (m 2/s)

DN0 pre-exponential factor in equation 11 (m 2/s)Dw0 pre-exponential factor in equation 12 (m 2/s)Dwe effective diffusivity of water (m 2/s)E Na activation energy for nitrite (kJ/mol)E wa activation energy for water (kJ/mol)L length of the cylinder (m)R ideal gas constant (8.31 J/mol K)R2 explained varianceT temperature (K)t time (s) x cartesian coordinate (m)

Fig. 1. Meat bre orientation in the samples from the Semimembranosus muscle.

J. Gómez et al. / Journal of Food Engineering 149 (2015) 188–194 189

8/19/2019 Effect of Temperature on Nitrite and Water Diffusion in Pork Mea

http://slidepdf.com/reader/full/effect-of-temperature-on-nitrite-and-water-diffusion-in-pork-mea 3/7

inside the curing chambers was carried out by TFG80Exi sensors(Gall Tech Mess und Regeltechnik GmbH, Bondorf, Alemania).These parameterswere monitored and controlledby means of soft-ware developed in LabView (National Instruments, USA). In orderto avoid air stratication, a fan was installed inside each curingchamber.

The curing process lasted 21 days to obtain enough experimen-tal points for modelling. The cylinders obtained from two of themuscles were used at each experimental temperature. At regularintervals, every 12 h during the rst two days of curing, and every24 and 48 h after the third day, a cylinder was taken out from thechamber, weighed and cut into four slices (A, B, C and D), 2.4 cm indiameter and 2.1 cm in length, perpendicular to the cylinder axis(Fig. 2 ). The nitrite content of each slice was determined.

The curing experiments were carried out in duplicate.

2.3. Analytical techniques

2.3.1. pH determinationThe pH was measured using a Mattäus model pH-STAR CPU lab

pH-meter (Pötmes, Germany).

2.3.2. Water content The initial water content was determined by drying the samples

until constant weight at 103 ± 2 C (AOAC, 1997 ). The evolution of the water content of each cylinder over time was determinedthrough weight difference, based on the initial moisture content.

2.3.3. Nitrite determinationThe procedure for nitrite determination was performed from

the modication of the AOAC methodology ( AOAC, 2000 ). Thismethod is based on the colorimetric reaction between the nitritein the sample and the reagents sulphanilamide and N-(1-naphthyl)ethylenediamine dihydrochloride (NED), which produce an azo-dyaminethat is detected spectrophotometrically at 520–540 nm(Ruiz-Capillas et al., 2007 ). To determine the quantity of nitrites,5 g of meat tissue which had previously been triturated in Mini-mixer equipment (Ufesa BP4530) and 200 ml of water from a Mil-liQ plus system (Millipore, Billerica, MA, USA) were placed in a300 ml volumetric ask. The ask containing the mixture wasput into a bath at 100 C and heated for 10 min. The suspensionwas homogenized for 10 min at 9000 rpm using an Ultra-turraxT25 (IKA Labortechnik, Janke & Kunkel GMBH & Co, Staufen,Germany), maintaining the temperature of the bath constant.Afterwards, the homogenate was diluted with water and ltered

(Waterman #1) to obtain the meat extracts. From the nal solu-tion, 10 ml were taken and mixed with the reagents, sulphanila-mide and N-(1-naphthyl) ethylenediamine dihydrochloride(NED). After reacting for 15 min, the nitrite concentration wasmeasured at 540 nm using a Helios Gamma + spectrophotometer(Thermo Spectronic, Cambridge, UK). At least 4 replications werecarried out for each measurement.

The method was validated by injecting a known amount of NaNO 2 into small pieces of meat, and comparing those quantitieswith the values obtained following the extraction and determina-tion procedure described above. The method was successfully val-idated; R2 was 0.99.

2.4. Modelling

The mass transport of a solute from the surface towards thecentre of the food tissue is affected both by the nature of the foodtissues and the different parameters that affect the diffusion. Inthis research, the modelling of the mass transfer during the meatcuring was based on the analytical solution of Fick’s second lawof diffusion. Specically, the penetration of nitrite and the outowof water during the process were modelled.

In developing the model, the following assumptions weremade: one-dimensional transport parallel to direction of the meatbre (semi-innite slab geometry), negligible external resistanceto mass transfer, homogeneous and isotropic meat, constant effec-tive diffusivity and constant dimensions of the samples throughoutthe experiment. With these considerations, the governing equa-tion, Eq. (1) , the initial condition, Eq. (2) , and the boundary condi-tions, Eqs. (3) and (4) , were formulated:

@ C ð x; t Þ@ t

¼ D e@ 2 C ð x; t Þ

@ x2" # ð1Þ

C ð x; 0Þ ¼C 0 ð2Þ@ C

@ t ð x ¼ 0Þ ¼0 ð3ÞC ðLÞ ¼C e ð4Þ

By considering the above conditions and solving the governingequation (Eq. (1) ), a function was obtained which permits the cal-culation of the local concentration of nitrite or water in the wholesample, Eq. (5) :

C ð x; t Þ C eC 0 C e

¼ 2X1

n ¼0

ð 1Þn

k nL e D e k n 2 t cos ðk nx Þ ð5Þ

where k n

L

4 ¼ ð2n þ 1Þp

8; n ¼ 0; 1; 2 . . .

The average nitrite content for each slice at a given time t , C s,was calculated by integrating Eq. (5) between 0 and L/4 (Eq. (6) )for slice D, L/4 and L/2 (Eq. (7) ) for slice C, L/2 and 3L/4 (Eq. (8) )for slice B, and 3L/4 and L (Eq. (9) ) for slice A ( Fig. 2 ).

C s 0 L

4;t ð Þ C se

C s0 C se¼ 8X

1

n ¼0

ð 1Þn

ðk nL Þ2 e D Ne k n 2 t sen kn

L

4 ð6Þ

C s L

2L4;t ð Þ C se

C s0 C se¼ 8X

1

n ¼0

ð 1Þn

ðk nL Þ2 e D Ne k n 2 t sen kn

L

2 sen kn L

4 ð7Þ

C s 3L

4L2;t ð Þ C se

C s0 C se¼ 8X

1

n ¼0

ð 1Þn

ðk nL Þ2 e D Ne k n 2 t sen kn

3L

4 sen kn L

2 ð8Þ

C s L 3L

4 ;t ð Þ C se

C s0 C se ¼ 8X1

n ¼0

ð 1Þn

ðk nL Þ2 eD Ne k n 2 t

sen ðk nL Þ sen kn3L

4 ð9Þ

SampleFilm PVC

Saturated brineDiffusion of nitrite (parallel to meat fibre)

Slice D

Slice C

Slice B

Slice A

x L/4L/2

3L/4L

Fig. 2. Sections into which the meat cylinders were divided to analyse nitritecontent.

190 J. Gómez et al./ Journal of Food Engineering 149 (2015) 188–194

8/19/2019 Effect of Temperature on Nitrite and Water Diffusion in Pork Mea

http://slidepdf.com/reader/full/effect-of-temperature-on-nitrite-and-water-diffusion-in-pork-mea 4/7

The equilibrium concentration of nitrites was considered as themaximum nitrite concentration of a cylinder during long-timeimmersion in the saturated brine. It was experimentally deter-mined by leaving a cylinder in contact with the saturated brineuntil the equilibriumconcentrationwas achieved. The time neededfor that was determined in preliminary experiments as 30 days.

The average moisture content ðC w Þ in the sample at a given timet , was calculated by integrating Eq. (5) for the whole volume of thesample, Eq. (10) :

C w ð0 L; t Þ C we

C w 0 C we¼ 2X

1

n ¼0

ð 1Þn

ðk nL Þ2 e D we k n 2 t ð10 Þ

The equilibrium moisture content of the samples under theexperimental conditions was calculated using Peleg’s model(Peleg, 1988 ).

To estimate the effective diffusivity, an optimization problemwas formulated. The SOLVER tool of EXCEL™ (Microsoft Excel)was applied to solve the optimization problem, which uses anon-linear optimization method ‘‘Generalized Reduced Gradient’’.DNe and Dwe values were calculated by minimizing the mean of the squared differences between the experimental and calculated

concentrations using the model.The goodness of t was evaluated by means of the explainedvariance, and the graphical representation of the calculated vsexperimental results.

2.5. Temperature effect on effective diffusivity

The Arrhenius equation was applied for nitrite, Eq. (11) , andwater, Eq. (12) , in order to analyse the inuence of the processtemperature on the diffusion coefcients.

D Ne ¼ D N 0 exp E Na

RT ð11 Þ

D we ¼ D w 0 exp E wa

RT

ð12 Þ

3. Results and discussion

The main components transferred between the meat and thesaturated brine during the curing process were sodium nitriteand water. Sodium nitrite was transferred from the brine into themeat, while water owed out from the meat and it was transferredinto the surrounding brine.

3.1. Water content

The initial water content of the cylinders was 73% on wet basis.The water content of meat is an important factor to take into

account, because nitrite, due to its high solubility, is mobilized intothe meat in the aqueous phase ( Honikel, 2008 ).

Fig. 3 shows the evolution of the experimental average moisturecontent of the whole cylinder samples during the curing process atdifferent temperatures. As can be observed, the longer the curingtime, the lower the moisture content. During the rst 5 days of cur-ing, a rapid drop in the water content was observed at the threeexperimental temperatures (2, 7 and 12 C), which then decreasedand tended towards the equilibrium value (1.4 kg water/kg drymatter at 2 C and 0.89 and 0.75 kg water/kg dry matter at 7 and12 C, respectively). These results are typical of meat salting andcuring, where the decrease in water content is faster during theearly days of the process due to osmotic dehydration ( Baratet al., 2011; Grau et al., 2008 ). The drop in moisture content was

faster during the entire curing process for the samples salted at12 and 7 C than for those salted at 2 C.

3.2. Nitrite content

The results for the nitrite gain in both replications are shown inFig. 4 . As can be observed, the nitrite concentration was inuencedby salting time and position. Slice A (closest to the brine) showed atendency to reach maximum concentration at the three experi-mental temperatures. Slice B also presented an increase in nitritecontent, although it reached a lower concentration than slice A.As expected, the lowest nitrite concentration was that of slices Cand D, which were the furthest from the brine. In the slice closestto the brine (A), the nitrite concentration increased rapidly duringthe rst 5 days of salting at 2 C, while at 7 C and 12 C thisincrease was observed around the ninth day of salting. The highwater content at 2 C (Fig. 3 ) favours a faster penetration of nitriteinto meat samples. The difference between the nitrite concentra-

tion in the different sections of the samples was more evident atthe end of the salting period. After 21 days of salting, the nitritecontent for slice A was close to 1720.5, 2287.45, and 2834.9 mg/L at 2 C, 7 C and 12 C, respectively. In comparison, the nitrite con-tent in slice D after 21 days was 37.3, 51.9 and 135.3 mg/L at 2 C,7 C and 12 C, respectively, which is more than 20 times lower.During the rst days of salting, there was a steep concentrationgradient between the meat and the brine, leading to a fast penetra-tion of nitrite into slice A, while for the other slices it occurred atslower rates. The same behaviour was observed by other authorswhen salting with sodium chloride, such as Grau et al. (2008)studying the salting of fresh and thawed Iberian hams, Telis et al.(2003) working on salt diffusion in farmed pantanal caiman muscleand Wang et al. (2000) analysing the salting of farmed Atlantic

salmon.When analysing these results and how they relate with the

temperature, it can be observed that the nitrite content values inevery slice were higher at 12 C than at 7 C and 2 C. This temper-ature effectwas more evident for slice A, due to its high nitritecon-tent. The temperature increase, together with a rapid nitritesaturation on the surface of the meat sample in contact with thesaturated brine (section A), causes a decrease in the water contentthereof. This decrease could hinder the nitrite mobility in the meat,leading to a lower nitrite concentration in the successive sectionsof the cylinder, especially in the one farthest from the brine (sec-tion D).

In order to study the effect of temperature on the average nitritecontent of all the samples, the experimental average nitrite content

of the samples was plotted versus time ( Fig. 5 ). As can be observedin Fig. 5 , therewas no observed effect of salting temperature on the

0.0

0.3

0.6

0.9

1.2

1.5

1.8

2.1

2.4

2.7

3.0

0 5 10 15 20 25

w a t e r c o n t e n t

( k g w a t e r / k g

d r y m a e r )

sa ng me (days)

T2ºC

T2ºC

T7ºC

T7ºC

T12ºC

T12ºC

model

Fig. 3. Kinetics of waterloss in cylindrical samples during salting andt of modeltoexperimental data.

J. Gómez et al. / Journal of Food Engineering 149 (2015) 188–194 191

8/19/2019 Effect of Temperature on Nitrite and Water Diffusion in Pork Mea

http://slidepdf.com/reader/full/effect-of-temperature-on-nitrite-and-water-diffusion-in-pork-mea 5/7

nitrite content during the rst 4 days. According to Fig. 4 , samplespresented a high water content during the same salting period,favouring the ow of nitrite in the aqueous medium of the meat.During this period, the nitrite diffusion was mainly inuenced bythe water content in the sample and the concentration gradientbetween the sample and the brine. After the fth day, the nitritediffusion appeared to be inuenced by temperature, and the aver-age nitrite content increased as the curing temperature went up.Boudhrioua et al. observed that temperature had a similar effecton salting kinetics (2009). The combined effect of temperatureand high salt concentration induces the movement of water fromthe samples towards the surrounding medium. Likewise, this effectcauses an opposite movement: the nitrite gain from the surround-

ing medium towards the samples, until equilibrium concentrationis reached.

3.3. Mathematical modelling

Table1 shows the average values of the effective diffusivity of nitrite and water in cylinders of Semimembranosus muscle at thestudied temperatures. The values obtained for the diffusion coef-cient of water were comparable to thoseobtained by other authors,such as Ruiz-Cabrera et al. (2004) when analysing the drying of Semimembranosus muscle in pork (3.45 10 11 –2.45 10 9 m 2/s)and Boudhrioua et al. (2009) when studying the diffusion of sodium chloride in sardine llets (2.43 10 10 –1.9 10 8 m 2/s).

As regards the values of the diffusion coefcient of nitrite, thesewere comparable to those obtained by Barat et al. (2011) for NaCland KCl in pork meat brining. The authors obtained values for thediffusion coefcient of these salts of between 4.98 10 12 and2.48 10 9 m 2 /s by tting a diffusionmodel to experimental saltingkinetics and assuming diffusion to be time-dependent. However, inthe same study, when the authors included other aspects, such asequilibriumconditions andthedeterminationof thesalt concentra-tions in the liquid phase of the meat in the model, the diffusioncoefcientswere higherthan those obtained in this study, with val-ues of between 1.12 10 8 and 5.33 10 10 m 2/s.

0

200

400

600

800

1000

1200

0 5 10 15 20 25

N O

2 - c o n

t e n

t ( m g

/ L )

N O

2 - c o n

t e n

t ( m g

/ L )

N O 2 - c o n

t e n

t ( m g

/ L )

sal ng me (days)

0 5 10 15 20 25

sal ng me (days)

0

500

1000

1500

2000

2500

0 5 10 15 20 25

sal ng me (days)

0

500

1000

1500

2000

2500

3000

3500

(2)(1)

(3)

Fig. 4. Kinetics of nitrite gain of the samples during the salting process at: (1) 2 C, (2) 7 C and (3) 12 C. slice A, h d slice B, D + slice C and ; slice D.

0

200

400

600

800

1000

1200

1400

0 5 10 15 20 25

N O

2 - c o n t e n t

( m g / L )

sal ng me (days)

Fig. 5. Average experimental nitrite content of samples versus salting time.

Table 1

Values of the effective diffusivity of NO 2 and water in Semimembranosus muscleparallel to meat bres at different temperatures. Different letters in the same columnindicate signicant differences ( p < 0.05).

Temperature ( C) DNe (m 2/s) 10 10 % var. Dwe (m 2/s) 10 10 % var.

2 0.04 a 90.7 59.40 A 95.87 0.07 b 94.8 90.60 B 98.4

12 0.11 c 94.8 97.73 C 95.2

192 J. Gómez et al. / Journal of Food Engineering 149 (2015) 188–194

8/19/2019 Effect of Temperature on Nitrite and Water Diffusion in Pork Mea

http://slidepdf.com/reader/full/effect-of-temperature-on-nitrite-and-water-diffusion-in-pork-mea 6/7

Similarly, the values of the diffusion coefcient of nitrite werelower than those obtained by other authors, such as Pinotti et al.(2002) when studying the diffusion of nitrite in Longissimus dorsimuscle (3.8 10 10 –9.5 10 10 m 2/s) and Graiver et al. (2006)when working on the diffusion of sodium chloride in pork meat(0.6 10 10 –5.0 10 10 m 2 /s). Low values of the diffusion coef-cient of nitrite may be related to a decrease in the water contentof the sample ( Fig. 3 ), because the nitrites are mobilized into themeat in the aqueous phase, and a low water content hinders theirmobility in the meat.

As shown in Fig. 3 , a good t was obtained between the exper-imental and calculated data for the water content. This result wasconrmed by the percentage of explained variance, which washigher than 95% for every experiment.

In Fig. 5 the experimental and calculated nitrite mean content isrepresented. A good agreement between experimental and calcu-lated values for nitrite gain is shown, being the correlation coef-cient higher than 0.90 for all the temperatures. Fig. 6 shows thecalculated nitrite content versus the experimental values for thefour slices (A, B, C and D) at the three temperatures considered,where a correlationcoefcient of 0.94 is achieved, which is an ade-quate correlation between both values. Furthermore, the percent-age of explained variance (% var) was over 90% ( Table 1 ).

3.4. Temperature effect on diffusion coefcients

The inuence of temperature on the effective diffusivity wassignicant ( p < 0.05), as canbe observed from the diffusivity valuesshown in Table 1 . Nitrite and water effective diffusivities increasedwhen the temperature rose. Other authors reported a similar effectof temperature on the effective diffusivity of salts, such as sodiumchloride ( Chiralt et al., 2001; Telis et al., 2003 ), or on a mixture of curing salts ( Pinotti et al., 2002 ) and also on the effective diffusivityof water ( Gou et al., 2003; Clemente et al., 2007 ).

Under the salting conditions, the temperature dependence of both nitrite and water effective diffusivity was represented bythe Arrhenius equation ( Fig. 7 ). The E wa value (32.24 kJ/mol) forwater loss in the samples was similar to the values reported byother authors: 25.94–61.65 kJ/mol for Gluteus Medius musclesalted with NaCl ( Gou et al., 2003 ), 27.8 kJ/mol for Biceps femorisand Semimembranosus muscles salted with NaCl and dried(Clemente et al., 2007 ) and 22 kJ/mol for meat pork salted withNaCl ( Palmia et al., 1993 ). The E Na value (60.32 kJ/mol) for nitritediffusion was also comparable to the results reported by otherauthors who studied the diffusion of sodium chloride into shand caiman, with values ranging from 29.00 to 168.13 kJ/mol(Corzo and Bracho, 2008; Telis et al., 2003; Uribe et al., 2011;Zhang et al., 2011 ).

As can be observed, the activation energy for water is lowerthan the one for nitrite. According to these results, nitrites needmore energy than water to be mobilized into the meat. This is alsoconrmed by the high values of the diffusion coefcient of waterand the low values of the diffusion coefcient of nitrite mentionedabove.

4. Conclusions

During curing, the water content of meat decreased while thenitrite content rose. A good agreement was found between theexperimental kinetics (water loss and nitrite gain) and the diffu-sion model. In order to obtain a better understanding of nitrite dif-fusion in meat, it is important to include aspects such as thedependency of salt diffusion on moisture content in the modeland also to consider meat tissue as an anisotropic medium. Theeffective diffusivity of nitrite and water increased as the tempera-ture rose. The activation energy for water loss was lower than theone for nitrite gain.

Acknowledgements

The authors of this paper acknowledge the nancial supportfrom CONSOLIDER INGENIO 2010 (CSD2007-00016), Spain.

References

AOAC, 1997. Ofcial methods of analysis of the Association of Ofcial AnalyticalChemists International. 16th ed., 3rd revision, Gaithersburg, USA.

AOAC, Ofcial methods of analysis of the Association of Ofcial Analytical ChemistsInternational, 2000. In: Horwitz, W. (Ed.), Nitrites in Cured Meat, ColorimetricMethod, 17th ed. AOAC International, USA .

Barat, J.M., Baigts, D., Alino, M., Fernández, F.J., Pérez-García, V.M., 2011. Kineticsstudies during NaCl and KCl pork meat brining. J. Food Eng. 106 (1), 102–110 .

Barat, J.M., Rodríguez-Barona, S., Andrés, A., Fito, P., 2003. Cod salting

manufacturing analysis. Food Res. Int. 36 (5), 447–453 .Bogovski, P., Bogovski, S., 1981. Animal species in which n-nitroso compoundsinduce cancer. Int. J. Cancer 27 (4), 471–474 .

Boudhrioua,N., Djendoubi, N., Bellagha, S., Kechaou,N., 2009. Study of moistureandsalt transfers during salting of sardine llets. J. Food Eng. 94 (1), 83–89 .

Cassens, R.G., 1997. Residual nitrite in cured meat. Food Technol. 51 (2), 53–55 .Chiralt, A., Fito, P., Barat, J.M., Andrés, A., González-Martínez, C., Escriche, I.,

Camacho, M.M., 2001. Use of vacuum impregnation in food salting process. J.Food Eng. 49 (2–3), 141–151 .

Clemente, G., Bon, J., García-Pérez, J.V., Mulet, A., 2007. Natural convection drying atlow temperatures of previously frozen salted meat. Drying Technol. 25 (11),1885–1891 .

Commission Regulation (EC) No 1129/2011, 2011. Commission Regulation (EC) No1129/2011 of 11 November 2011 amending Annex II to Regulation (EC) No1333/2008 of the European Parliament and of the Council by establishing aUnion list of Food Additives.

Corzo, O., Bracho, N., 2008. Application of Weibull distribution model to describethe vacuum pulse osmotic dehydration of sardine sheets. LWT-Food Sci.Technol. 41 (6), 1108–1115 .

Directive 2006/52/CE, 2006. Directive 2006/52/EC of the European Parliament andof the Council of 5 July 2006 amending Directive 95/2/EC on food additives

0

1000

2000

3000

4000

0 1000 2000 3000 4000

C a

l c n i t r i t e c o n t e n t

( m g N O

2 - / L )

Exp nitrite content (mg NO2

-/L)

Fig. 6. Comparison between experimental and calculated data for nitrite uptakeduring salting at N 2 C, j 7 C and X 12 C (R2 = 0.98).

Fig. 7. Ln (De) versus 1/ T for samples during salting. Nitrite uptake and j waterloss.

J. Gómez et al. / Journal of Food Engineering 149 (2015) 188–194 193

8/19/2019 Effect of Temperature on Nitrite and Water Diffusion in Pork Mea

http://slidepdf.com/reader/full/effect-of-temperature-on-nitrite-and-water-diffusion-in-pork-mea 7/7

other than colours and sweeteners and Directive 94/35/EC on Sweeteners forUse in Foodstuffs.

Flores, J., Toldrá, F., 1993. Curing. In: Macrae, R., Robinson, R.K., Sadler, M.J. (Eds.),Encyclopedia of Food Science, Food Technology and Nutrition. Academic PressInc, New York, pp. 1277–1282 .

Gou, P., Comaposada, J., Arnau, J., 2003. NaCl content and temperature effects onmoisturediffusivityin the Gluteus medius muscle of pork ham. Meat Sci. 63(1),29–34 .

Graiver, N.,Pinotti, A., Califano, A., Zaritzky, N.,2005. Diffusionof sodiumchloride inmeat pork: inuence on its microstructure. Scanning 27 (2), 76–77 .

Graiver, N.,Pinotti, A., Califano, A., Zaritzky, N.,2006. Diffusionof sodiumchloride inpork tissue. J. Food Eng. 77 (4), 910–918 .

Graiver, N., Pinotti, A., Califano, A., Zaritzky, N., 2009. Mathematical modeling of theuptake of curing salts in pork meat. J. Food Eng. 95 (4), 533–540 .

Grau, R., Albarracín, W., Toldrá, F., Antequera, T., Barat, J.M., 2008. Study of saltingandpost-salting stagesof fresh andthawed Iberian hams. Meat Sci. 79 (4), 677–682 .

Honikel, K.O., 2008. The use and control of nitrate and nitrite for the processing of meat products. Meat Sci. 78 (1–2), 68–76 .

Mulet, A., 1994. Drying modeling and water diffusivity in carrots and patatoes. J.Food Eng. 22 (1–4), 329–348 .

Palmia, F., Pecoraro, M., Ferris, S., 1993. Essiccazione di prodotti carnei: calcolo delcoefciente di diffusione effettivo ( De) dell’acqua in fette di lombo suino. Ind.Conserve 68 (3), 238–242 .

Peleg, M., 1988. An empirical-model for the description of moisture sorption curves. J. Food Sci. 53 (4), 1216–1219 .

Pinotti, A., Califano, A., Zaritzky, N., 2000. Diffusion of curing salts in meat: effect of sodium chloride on tissue microstructure. Scanning 22 (2), 137–138 .

Pinotti, A., Graiver, N., Califano, A., Zaritzky, N., 2002. Diffusion of nitrite and nitratesalts in pork tissue in the presence of sodium chloride. J. Food Sci. 67 (6), 2165–2171 .

Ruiz-Cabrera, M.A., Gou, P., Foucat, L., Renou, J.P., Daudin, J.D., 2004. Water transferanalysis in pork meat supported by NMR imaging. Meat Sci. 67 (1), 169–178 .

Ruiz-Capillas, C., Aller-Guiote, P., Jiménez-Colmenero, F., 2007. Application of owinjection analysis to determine protein-bound nitrite in meat products. FoodChem. 101 (2), 812–816 .

Sabadini, E., Carvalho, B.C., Sobral, P.J.D., Hubinger, M.D., 1998. Mass transfer anddiffusion coefcient determination in the wet and dry salting of meat. DryingTechnol. 16 (9–10), 2095–2115 .

Siro, I., Ven, C., Balla, C., Jonas, G., Zeke, I., Friedrich, L., 2009. Application of anultrasonic assisted curing technique for improving the diffusion of sodiumchloride in porcine meat. J. Food Eng. 91 (2), 353–362 .

Stollewerk, K., Jofré, A., Comaposada, J., Arnau, J., Garriga, M., 2012. The effect of NaCl-free processing and high pressure on the fate of Listeria monocytogenesand Salmonella on sliced smoked dry-cured ham. Meat Sci. 90 (2), 472–477 .

Telis, V.R.N., Romanelli, P.F., Gabas, A.L., Telis-Romero, J., 2003. Salting kinetics andsalt diffusivities in farmed pantanal caiman muscle. Pesquisa AgropecuariaBrasileira 38 (4), 529–535 .

Uribe, E., Miranda, M., Vega-Galvez, A., Quispe, I., Claveria, R., Di Scala, K., 2011.Mass transfer modelling during osmotic dehydration of jumbo squid ( Dosidicus gigas): inuence of temperature on diffusion coefcients and kineticparameters. Food Bioprocess Technol. 4 (2), 320–326 .

Volpato, G., Michielin, E.M.Z., Ferreira, S.R.S., Petrus, J.C.C., 2007. Kinetics of thediffusionof sodiumchloride in chicken breast( Pectoralis major ) during curing. J.Food Eng. 79 (3), 779–785 .

Wang, D.H., Tang, J.M., Correia, L.R., 2000. Salt diffusivities and salt diffusion infarmed Atlantic salmon muscle as inuenced by rigor mortis. J. Food Eng. 43(2),115–123 .

Zhang, Q., Xiong, S., Liu, R., Xu, J., Zhao, S., 2011. Diffusion kinetics of sodiumchloride in grass carp muscle and its diffusion anisotropy. J. Food Eng. 107 (3–4), 311–318 .

194 J. Gómez et al. / Journal of Food Engineering 149 (2015) 188–194