Journal of Food Engineering 100 (2010) 490–495

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Journal of Food Engineering

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Influence of brine salting prior to pickle salting in the manufacturingof various salted-dried fish species

Ana Brás, Rui Costa *

Food Science and Technology Department, College of Agriculture of the Polytechnic Institute of Coimbra, 3040-316 Coimbra, Portugal

a r t i c l e i n f o a b s t r a c t

Article history:Received 18 February 2010Received in revised form 20 April 2010Accepted 21 April 2010Available online 4 May 2010

Keywords:SaltingDryingFishTextureColor

0260-8774/$ - see front matter � 2010 Elsevier Ltd. Adoi:10.1016/j.jfoodeng.2010.04.036

* Corresponding author. Tel.: +351 239804940; faxE-mail address: ruicosta@esac.pt (R. Costa).

In Portugal, the production of salted-dried cod and similar species is a relevant fish industry. Pickle salt-ing is the most common salting method in this industry. The objective of this work was to study the influ-ence of brine salting before pickle salting in the characteristics of the final salted-dried product ofdifferent fish species. Three salting methods were studied: only pickle salting, brine salting at 16�Bauméfollowed by pickle salting and brine salting at 25�Baumé followed by pickle salting. Fish species studiedwere Gadus morhua, Gadus macrocephalus, Theragra chalcogramma. The results showed from 4.7% to 9.2%significant higher yields of salted-dried fish when using the lower salt content brine, but drying timeincreased from 32 to 45 h (35–65%), depending on size of the fish, and texture became significantly softer,what may imply that salted-dried fish using lower salt content brines may be perceived by consumers asa different product. No significant differences of color were obtained.

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1. Introduction

Cod is a highly appreciated fish in Portugal and also in the Med-iterranean countries and South American countries. Even with thedevelopment of other preservation techniques (like freezing) andcorrespondent facilities, the gastronomic culture of Portugal main-tains the need of the supply of salted-dried cod.

This product is mainly commercialized in the form of watercontent below 47% and a salt content higher than 16%. Almost noneis consumed in the salted-dried state being practically all of it de-salted prior to cooking. Gadus morhua is the main cod species usedbut the industry is not limited to it, using also Gadus macrocephalusand Gadus ogac. Other species are allowed to be commercialized as‘‘similar species”, like Theragra chalcogramma, among others.

Salted cod products have a long shelf life due to the low wateractivity – 0.75 if salt saturated or lower if dried (Andrés et al.,2005; Rodrigues et al., 2003) – and due to the flora selection thata high salt content media implies, only halophilic microorganismsare able to develop in salted-dried cod. Compositional changes insalting consist not only in salt gain but also in water loss, togetherwith some loss of other soluble components and proteins (Ismailand Wootton, 1992; Thorarinsdottir et al., 2004), contributingto a completely different flavour and texture of cooked cod whencompared to cod prepared from the raw fish. Other changes,such as protein denaturation, are also important chemical changes

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that have a strong influence in the texture of this product(Thorarinsdottir et al., 2004).

In the production of salted fish, the raw fish is headed, gutted,butterfly split, deboned and washed, and then heavily salted bypickle, brine or kench salting. Pickle salting consists of alternatelayers of split fish and salt in a tank, where the liquid leaving thefish muscle dissolves the solid salt and forms a brine that immersesthe fish. Kench salting also consists of piles of alternate layers offish and salt but where the liquid leaving the fish muscle is allowedto drain away. Brine salting is the immersion of the split fish in pre-pared brine (Ismail and Wootton, 1992; Horner, 1992). Salting maybe done using only one or a combination of these methods. In allthese methods the fish is disposed in piles of approximately 1 mhigh creating an overpressure that increases water loss kinetics(Andrés et al., 2005). Making use of even higher piles for this pur-pose is called water-horsing (van Klaveren and Legrende, 1965).Salting time depends on the thickness of the fish and the curing(period after salting where fish is maintained without further pro-cessing) may last from less than a month to 6 months.

The typical salting process in Portugal consists of pickle saltingas the main salting step, followed by kench salting before drying.Other salting steps have been used specially in Iceland, with a firststep consisting of brining and a second step of kench salting(Thorarinsdottir et al., 2004). Single salting methods or a combina-tion of different salting methods have been studied (Barat et al.,2002, 2003; Andrés et al., 2005; Thorarinsdottir et al., 2004).Differences found are related to the kinetics of salting, yield ofthe process and visual quality for producers, which the late twoare important aspects from the commercial point of view.

Nomenclature

PS pickle salting for 13 daysBS16 brine salting with 16�Baumé for 2 days followed by

pickle salting for 11 daysBS25 brine salting with 25�Baumé for 2 days followed by

pickle salting for 11 daysL* lightness valuea* greenness–redness valueb* blueness–yellowness value

A mass of ashes (g)NAS mass of non-ash solids (g)W mass of water (g)mi mass after salting or drying (g)m0 mass before salting (g)Y yield (g per 100 g)F firmness (N)

A. Brás, R. Costa / Journal of Food Engineering 100 (2010) 490–495 491

However, studies have been limited both in terms of fish species(to G. morhua) and combinations of salting methods and, specially,no study about the influence on the drying step after salting isknown.

The objective of this work was to study the influence of a brin-ing step before pickle salting in the characteristics of the finalsalted-dried products of different fish species, in terms of yield,drying time, color and texture.

2. Materials and methods

2.1. Raw material

The fish used in this is work was in the frozen state, the mostcommon state of the raw material used by the Portuguese industry.Fish species used were of G. macrocephalus, captured in the PacificOcean (FAO 67) with an average weight of 2.7 ± 0.30 kg; G. morhua,captured in the Northeast Atlantic Ocean (FAO 27) with an averageweight of 2.06 ± 0.21 kg; T. chalcogramma, captured in the North ofthe Pacific Ocean (FAO 67) with an average weight of 0.54 ±0.10 kg. All the species where frozen in the sea at �18 �C and trans-ported and kept at �18 �C.

Main composition of fishes presents similar values of water andashes for G. morhua and T. chalcogramma, and a higher water con-tent of G. macrocephalus (Table 1). The salt used had a content ofsodium chloride higher than 99.0%.

In each experiment (combination of fish species and saltingmethod), 10 fishes were used, in a total of 30 fishes for each spe-cies. Each fish was identified and weighed individually after eachprocessing step. Mass of split fish includes tail, spines and skin.Chemical analyses were done taking samples from two fishes ofeach batch, texture analysis and color analysis was done on twofishes of each batch.

2.2. Fish preparation

The experiments were done in industrial facilities, using theusual processes. In the normal production line, headed and guttedfish were defrosted with running water at 10–15 �C overnight.Then it was butterfly split and partly deboned, leaving the tailand part of the bone close to the tail. Fishes were then salted anddried.

Table 1Average and standard deviation of determined water content and ashes content ofraw fish.

Fish species Water content(%; total basis)

Ashes content(%; total basis)

G. macrocephalus 82.4 ± 0.7 0.9 ± 0.1G. morhua 80.6 ± 0.8 1.2 ± 0.1T. chalcogramma 80.0 ± 0.4 0.9 ± 0.1

2.3. Salting

Salting was carried out at ambient temperatures between 12and 18 �C for 13 days in total. Salting methods used where: picklesalting, where fishes were covered with salt at a ratio of 0.5 kg/kgof fish; brine salting, where fishes were immersed in brines of 16 or25�Baumé, at a ratio of 1.6 and 4 L/kg of fish, respectively. Thefishes were kept submerged with the help of a net.

Three salting methods used were: pickle salting for 13 days(PS), brine salting with 25�Baumé for 2 days followed by picklesalting for 11 days (BS25) and brine salting with 16�Baumé for2 days followed by pickle salting for 11 days (BS16). After salting,fish was left at refrigeration temperatures for 2 days for draining.

2.4. Drying

The salted fishes were dried in an industrial drier at a relativehumidity close to 60%, at a temperature of 19–20 �C and an airvelocity of 2–2.6 m/s. The end of drying was determined by anexperienced production manager using the usual production crite-rion: fish is considered dried when it stays flat when hold by theloin (Fig. 1). This assures that the water content is well below47%, the limit imposed by law to commercialize the fish assalted-dried fish.

2.5. Chemical analysis

Water and ashes were determined cutting slices of 2 g of 1–2 mm thickness. Six replicates were done for each analysis, takenfrom 2 fishes. Water content was determined by oven drying untilconstant weight (AOAC, 1996b) 950.46. Ashes content were deter-mined by 923.03 AOAC (1996a). These contents are defined as themass of water (W) or mass of ashes (A) per mass of non-ash solids(NAS).

The ashes and salt contents of heavily salted fish are similarsince almost all the ashes in the salted fish correspond to the saltthat entered to the fish muscle and since the ashes determinationinvolves a smaller experimental error, discussion of salt contents isthus based in ash content basis as elsewhere (Lauritzsen et al.,2004a).

The drying operation has to guarantee that the water content ofthe salted-dried fish that, apart from muscle includes some skinand some spines, must be less than 47% for commercial purposes.The water content presents a high variation between the dried sur-face and the inner tissue, especially in normal industrially driedsplit fish. As an example, when measuring the water content ofsome samples cut from the surface in the same fish, water contents(total basis) presented large variation, ranging from 24% to 40%,reaching 55% just 2 mm below the surface. If sampling from the in-ner tissue, more uniform values are obtained. Also, if different salt-ing procedures give origin to different salted muscle watercontents, larger differences will be found in the inner tissues of

Fig. 1. Manufacturing criterion for the end of drying of salted fish: fish staysstraight when hold by the loin.

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T. Chalcogramma G. morhua G. macrocephalus

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T. Chalcogramma G. morhua G. macrocephalus

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Fig. 2. Yield of the different treatments for each fish species: (a) after salting and (b)after drying.

492 A. Brás, R. Costa / Journal of Food Engineering 100 (2010) 490–495

fishes salted by different methods, than in the overall water con-tent, since each fish must be dried to similar overall water contentswhatever the salting method. Therefore, the chemical analyseswere done taking samples from the inner tissue.

2.6. Color measurements

The color of the muscle surface was measured using a MinoltaChromameter, model CR-200b (Minolta Camera Co. Ltd., Osaka, Ja-pan) after calibration with a white standard (L* = 98.0; a* = �0.3;b* = 2.4). After exceeding salt have been removed, the measure-ments were done in four points of each of two fishes, equallyspaced from the loin to the tail end, next to the central line. CIEL*a*b* values were recorded.

2.7. Texture measurements

Texture was analyzed with a texture analyzer TA.XT Express(Stable Micro Systems, Surrey, UK), through a compression testto simulate the test that the consumer does when evaluating theproduct. The probe had a diameter of 5 mm, the probe rate was1 mm/s and the compression length was 10 mm. Depending onthe size of the fish, from 7 to 12 measurements, spaced 1 cm fromeach other along the central line of the split fish, and were done intwo fishes.

2.8. Statistical analyses

Statistical analysis was performed with SPSS version 17 (SPSSInc., Chicago), to evaluate the influence of the salting method onthe yield, drying time, color and texture at the end of salting andof drying. Analysis of variance, Tukey’s least significant difference,Spearman correlation and linear regression were used to analyzethe data. The level of significance was set at p = 0.05 for all analysis.

3. Results and discussion

3.1. Yield

Yield (%) was determined as the total mass of the fish after anoperation (salting or drying) per 100 g of mass before salting. Meanyield values after salting varied between 75.7% and 89.6% and afterdrying varied between 60.4% and 67.6 % (Fig. 2). The values aftersalting are of the same level as the reported by Andrés et al.(2005) and Thorarinsdottir et al. (2004), that working with fresh

(not frozen) G. morhua, obtained values close to 75% for pickle salt-ing and for brine salting followed by kench salting.

A two-way analysis of variance (ANOVA) was carried out todetermine the effects of the salting method and the fish specieson yield after salting and after drying. Highly significant differ-ences (p < 0.01) were obtained for both yields and for both vari-ables. The results of yield after salting or after drying give thesame conclusions in terms of effects of treatment and fish species.

3.1.1. Salting methodsAlthough all the salting methods used in this work finished with

pickle salting, the first step made a difference in the final yield. Tu-key’s least significant difference analysis gave very significant pvalues (<0.02) for almost all comparison of treatments for each fishspecies, except when comparing with single pickle salting andimmersion in a 25�Baumé brine (plus pickle salting) for G. macro-cephalus (p > 0.05). For all fish species, salting with a 16�Baumé(plus pickle salting) gave the highest yield. For G. morhua and Ther-agra chalcograma, salting with a 25�Baumé brine (plus pickle salt-ing) gave the second highest yield and single pickle salting gave thelowest yield (Fig. 2). These results are in accordance with previ-ously published results for G. morhua, where higher yields were ob-tained when using brine salting being higher the lower the saltcontent of the brine (Andrés et al., 2005; Barat et al., 2002; Martí-nez-Alvarez and Gómez-Guillén, 2005). Andrés et al. (2005) alsoobserved that yield differences obtained during the salting stepwere kept along drying.

A. Brás, R. Costa / Journal of Food Engineering 100 (2010) 490–495 493

3.1.2. SpeciesTable 2 presents Tukey’s least significant difference analysis be-

tween species, for the different salting methods. For the singlepickle salting method there were no significant differences be-tween species (p > 0.05). After salting, Theragra calchogramma gavesignificantly (p < 0.01) higher yields than G. morhua and G. macro-cephalus when using brine salting. After drying, G. macrocephalusgave significantly (p < 0.01) lower yields than G. morhua and T. cal-chogramma when using brine salting. This result could be due tothe higher initial water content of the G. macrocephalus fishes com-pared to the other species (Table 1), that is inversely proportionalto the protein content (Love, 1988a) and once the yields in saltingare highly influenced by the interaction of salt with proteins, asmaller amount of proteins would give origin to a lower yield.

Time (h) PS BS25 BS16

3.1.3. Water and salt contentsThe difference of yields between brine salting and other salting

methods has been attributed to a higher water holding capacity,especially higher in the case where different brine concentrationsof 20–25% were combined (Barat et al., 2002). This higher waterholding capacity is attributed to swelling of the fish muscle dueto salt uptake. The amount of swelling depends on the salt concen-tration. Muscle swelling has been found to be at a minimum at aconcentration of 0.1 M and a maximum at 1 M (5.8% salt). But, par-ticularly above 4.5 M, the muscle shrinks (Offer and Knight, 1988).Hamm (1960) suggested that at low salt concentrations, chlorideions bind to the proteins, causing repulsion in the protein matrix.At salt concentrations approximately above 2 M, protein dena-tures, resulting in cross-linking between proteins increasingshrinkage and consequently loss of water from the muscle.

In this work, only the water content and salt content of themuscle under the dried surface were measured. ANOVA of waterand salt contents showed significant (p < 0.01) variation withinsalting methods and species. Tukey’s test showed significant differ-ence (p < 0.01) between all comparisons between species and a sig-nificant lower water content of single pickle salting methodcompared with the salting methods that used brines. The compar-ison between the two methods that used brines did not present asignificant difference (p > 0.05).

A positive significant correlation (p < 0.01) between water con-tent (W/NAS) and salt content (S/NAS) is observed. No significantcorrelation (p > 0.05) of these variables with yield after dryingwas obtained. This may mean that changes in other components,such as protein or other nitrogenous soluble contents, may contrib-ute to justify the different yields. Loss of small nitrogenous com-pounds (Thorarinsdottir et al., 2004) and proteins during saltingwere measured in other works (Thorarinsdottir et al., 2004; Lau-ritzsen et al., 2004a). Protein losses from the muscle have beenshown to be a function of the salt concentration, with a maximumat 6–9% NaCl (Lawrie, 1998). Lauritzsen et al. (2004a) also mea-

Table 2Statistical effects on yield of the different salting treatments on salting yields anddrying yields, comparing species: p value for the Tukey’s least significant differenceanalysis.

TC–GMo TC–GMa GMo–GMa

After salting PS 0.518 0.603 0.624BS25 <0.001 <0.001 0.423BS16 <0.001 <0.001 0.724

After drying PS 0.462 0.189 0.823BS25 0.998 0.007 0.008BS16 0.489 0.036 0.002

TC – Theragra calchogramma.GMa – Gadus macrocephalus.GMo – Gadus morhua.

sured significant effects of muscle pH on protein yield. Less lossof proteins occurred at low muscle pH probably due to their dena-turation leading to decreased diffusion rates. However, Lauritzsenet al. (2004a) measured weight yields negatively correlated to pro-tein contents and positively correlated with the water content.

3.2. Drying time

In industrial practice and in this work, drying time was deter-mined by a simple criterion that assures a low enough water con-tent of salted-dried fish for commercial purposes. This criterion isalso indicative of the evaluation that consumers do, especiallythose that are accustomed to well stiff fish. Even if the a fish pre-sents a 47% water content or lower but bends in this test, the fishwill be considered insufficiently dried because it will present a dif-ferent and supposedly undesirable characteristic to the consumer.Also, a not enough dried product will present higher weight lossesduring the commercialization route, causing problems to retailersand the manufacturers themselves.

Drying time varied greatly between the species studied,increasing approximately linearly with the initial mass of fish(Fig. 3). This was expected due to the difference in mass of eachspecies used. Average mass was 2.7 kg, 2.1 kg and 0.5 kg, respec-tively, for G. macrocephalus, G. morhua and T. chalcogramma. A high-er mass of fish implies a higher thickness and if drying is controlledby diffusion of water in the fish, a thicker product will take longerto dry (Del Valle and Nickerson, 1968).

These data also shows that the drying time increases with thedecreasing salt content of the brine salting: drying of salted fishin 16�Baumé requires the longest time and salting only by picklerequires the shortest time. Particularly disappointing to manufac-turers is that the drying time increases with the yield after salting(Fig. 4). Therefore, what manufacturers may gain by the increasedyield after drying, they may loose it by having to dry the fish forlonger times and also, consequently, spending more energy todry it.

Drying time also presents a significant positive correlation(p < 0.05) with the water content of the inner tissue after drying,and once this water content is expected to be proportional to thewater content before drying, it simply confirms that a salted fishof higher initial water content requires more time to dry to approx-imately the same range of overall water content.

3.3. Color

Color results were analyzed in terms of CIE L*a*b* scale. An AN-OVA to L*, a* and b* parameters presented significant differences

y = 20.5x + 43.0R² = 0.967

y = 22.1x + 59.7R² = 0.9987

y = 24.3x + 73.5R² = 0.9979

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0.0 1.0 2.0 3.0 4.0Mass (kg)

Fig. 3. Relation of drying time with the average mass of raw fish by salting method.

y = 2.95x - 177R² = 0.9535

y = 4.53x - 252R² = 0.9978

y = 7.08x - 440R² = 0.8165

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T. Chalcogramma G. morhua G. macrocephalus

Fig. 4. Relation of drying time with the yield after salting for each fish species. (a)

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Fig. 5. Relation of L*, a* and b* values with the water content of raw, salted or salted-dried fishes (r = Spearman’s correlation coefficient): (a) L*, (b) a* and (c) b*.

494 A. Brás, R. Costa / Journal of Food Engineering 100 (2010) 490–495

(p < 0.01) between the phase of processing (before and after dry-ing) and no significant differences for salting method or species(p > 0.05).

Drying is, by definition, the loss of water, and this has beenpointed out as part of the reason of changes in color. Lauritzsenet al. (2004b) noted that the loss of water can reduce light scatter-ing and Stien et al. (2005) refers that it can lead to loss of transpar-ency, and the consequence of this is the increase of lightness (L*). Inorder to relate with water content, the water content of the surfaceis needed, but, as referred before, it is difficult to obtain experi-mentally a feasible value in samples like the split fish used in thiswork. However, some proportionality between the inner watercontent and the surface water content in dried fish is expected.Values of inner water content of salted muscle can be estimatedusing values of salt content of dried samples (S/NAS; this value isthe same before and after drying in the inner tissue) and assumingthat salt to water proportion on salted fish was 1:3, as confirmed inother works (Barat et al., 2002). If then L*a*b* values are plottedagainst the water content of the inner flesh of salted and driedsamples (Fig. 5), a strong correlation is obtained for parametersL* (p < 0.05) and b* (p < 0.01). The lightness (L*) and the yellowing(b*) increased inversely proportional to the water content. Theserelations should be explored in further studies.

Other factors are known to influence color of salted fish. Thepresence of calcium and magnesium ions present in the salt cancontribute to whitening of the muscle surface (Lauritzsen et al.,2004a; Horner, 1992; Martínez-Alvarez and Gómez-Guillén,2005). Since their cross-linking effect is used to prepare gels of var-ious food products (for example, in dairy products as yoghurt andcheese, and gelatins), retaining more water, the influence of theseions on color of salted fish may be explained by their effect onwater content.

Some reactions are also suggested to be a cause of a colorchange in salted fish such as the denaturation of proteins throughthe fast rate of pH decline during rigor mortis (Lauritzsen et al.,2004a; Stien et al., 2005), the pH of the salt used for salting (Lau-ritzsen et al., 2004a); the strong ionic force due to the salting (Lau-ritzsen et al., 2004a; Stien et al., 2005); oxidation of phospholipidsthough the low concentration of these in cod (Stien et al., 2005;Anon, 1967). Also, Anon (1967) observes that iron and copper saltsare known to yellow codfish and they are known catalysts of oxi-dation reactions. In fact, lipids were known to affect the qualityof fresh cod, since rancification in such a low lipid content fishwas really a problem noted in New Scotland where fish caughthad 1% lipid content, usually a maximum found in cod (Anon,1967). Anon (1967) also refers that mixtures of tryptophan, lysineand histidine and muscular cod lipids gave origin to a yellowsolution.

3.4. Texture

Texture was analyzed with a compression method to simulatethe compression that consumers do with the fingers when choos-ing the dried fish. The salting (Barat et al., 2002) and drying (Lau-ritzsen et al., 2004a) steps are known to increase firmness andprotein denaturation and a reduction of the hydration of proteinswere suggested to explain that effect on texture. ANOVA of firm-ness (maximum force) showed significant differences (p < 0.01)of salted-dried fish within salting methods. Tukey’s test showedsignificant differences (p < 0.05) between only pickle salting andthe salting methods involving brine salting, a similar result ob-

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Fig. 6. Relation of firmness of fish with the water content of raw, salted or salted-dried fish (r = Spearman’s correlation coefficient).

A. Brás, R. Costa / Journal of Food Engineering 100 (2010) 490–495 495

served with the water content. A correlation coefficient of �0.850at p < 0.01 with firmness and water content (W/NAS) of inner tissueexplains these differences (Fig. 6). Using brines leads to higherwater content of the inner tissue leading to smaller firmness.Therefore, using brines produces a different texture what may leadthe consumer to think that the fish is not sufficiently dried, if theirstandard is a stiff fish.

Other effects are usually attributed to increase the firmnesssuch as the presence of calcium and magnesium ions present inthe salt (Lauritzsen et al., 2004a; Horner, 1992) and the lower pHof the muscle (Lauritzsen et al., 2004a; Love, 1988b).

4. Conclusions

The yield is a very important aspect from an economic point ofview and this work confirmed that brine salting prior to pickle salt-ing improves the yield of salted and salted-dried fish. However,manufacturers should be reluctant in using this step because thisincreases costs in drying, through the increase of drying time andassociated higher energy costs. Using brines also gives less firmsalted-dried fish what may be perceived as a different product bythe consumer used to more stiffed products. No significant differ-ences of color were obtained.

Acknowledgment

The authors acknowledge Sueste Company (Gafanha da Nazaré,Portugal) for making this research possible.

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