evolution of various salt concentrations in the moisture

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Evolution of various salt concentrations in the moistureand in the outer layer and centre of a model cheese

during its brining and storage in an ammoniacalatmosphere

Frédéric Gaucheron, Yvon Le Graët, Françoise Michel, Valérie Briard, MichelPiot

To cite this version:Frédéric Gaucheron, Yvon Le Graët, Françoise Michel, Valérie Briard, Michel Piot. Evolution ofvarious salt concentrations in the moisture and in the outer layer and centre of a model cheese duringits brining and storage in an ammoniacal atmosphere. Le Lait, INRA Editions, 1999, 79 (6), pp.553-566. �hal-00929672�

https://hal.archives-ouvertes.fr/hal-00929672

https://hal.archives-ouvertes.fr

Il

Lait (1999) 79, 553-566© Inra/Elsevier, Paris

553

Original article

Evolution of various salt concentrations in the moistureand in the outer layer and centre of a model cheese

during its briningand storage in an ammoniacal atmosphere

Frédéric Gaucheron *, Yvon Le Graët, Françoise Michel,Valérie Briard, Michel Piat

Laboratoire de recherches de technologie laitière, Inra,65 rue de Saint Brieuc, 35042 Rennes cedex, France

(Received 8 July 1998; accepted 20 May 1999)

Abstract - The evolution of various salt concentrations in moisture and in the outer layer and cen-tre of a model cheese during brining and storage in an ammoniacal atmosphere was studied. Duringbrining, calcium, magne sium, potassium, inorganic phosphate and citrate ions entered the. brine witha slight decrease in their contents in the moisture. In parallel, sodium and chloride were incorporatedin outer layer and in the moi sture of gel. Then, during storage of this model gel in an ammoniacal atmo-sphere, calcium, magnesium, inorganic phosphate and citrate ions migrated to the outer layer of geland consequently underwent a decrease in their concentrations in the moisture and the centre of thegel. These migrations are related to the formation of pH gradient in the gel which indu ce precipita-tions of these ions in the outer layer. In parallel, sodium, potassium and chloride were rapidly presentuniformly in the different parts of the gel. The model cheese potentialities are also discussed.© Inra/Elsevier, Paris.

model cheese / mineraIs / aqueous phase / pH / salt / brining / ripening

Résumé - Évolution des concentrations minérales dans la phase aqueuse, la partie centrale etla surface d'un fromage modèle durant son saumurage et son stockage en atmosphère ammo-niacale. Durant le saumurage, les ions calcium, magnésium, potassium, phosphate inorganique et citratepassent dans la saumure avec une légère diminution de leurs concentrations dans la phase aqueuse.En parallèle, les ions sodium et chlorure sont incorporésà la surface et dans la phase aqueuse du gel.Puis, durant le stockage en ambiance ammoniacale, les ions calcium, magnésium, phosphate inor-ganique et citrate migrent vers la surface du gel avec comme conséquence une diminution de leursconcentrations dans la phase aqueuse et dans la partie centrale du gel. Ces migrations sont dues à la

* Correspondence and reprints. [email protected]

mailto:[email protected]

554 F. Gaucheron et al.

formation d'un gradient de pH dans le gel qui entraîne une précipitation de ces ions en surface. En paral-lèle, les ions sodium, potassium et chlorure étaient rapidement répartis de façon uniforme dans les dif-férentes parties du gel. Les potentialités de ce fromage modèle sont également discutées. © InralElsevier, Paris.

fromage modèle 1 minéraux 1 phase aqueuse 1 pH 1 saumurage 1 affinage

1. INTRODUCTION

Cheese is composed of a paracaseinicnetwork, dispersed elements (cells, fat glob-ules, crystals and air) and interstitialliquidcontaining several dissolved compounds(proteins, sugar, lipids and minerals), Dur-ing its fabrication, physicochemical com-position of cheese varies as a function ofacidification, brining, alcalinisation, prote-olysis and lipolysis. Proteolysis and aminoacid catabolism, lipolysis and lactose break-down are relatively well described in theliterature [4-6, 11,32]. On the contrary,much less is known about the salt fractionevolution during brining and ripeningalthough this fraction plays a considerablerole in the texture elaboration and in the rhe-ological properties of cheese [6, 16,23,24,28,31,32]. Moreover, sorne ofthese mod-ifications are sequential and others can takeplace at the same time. So, for simultane-ous modifications, it is difficult to under-stand the fundamental phenomena.

The objective of this work was to developa model gel to study the salt behaviour dur-ing brining and storage under ammoniacalatmosphere; model gel was chosen to limitthe numerous other changes that occur dur-ing brining and ripening of cheese, i.e. lac-tose degradation, proteolysis and lipolysis.Two approaches were used. The first onewas the determination of salt contents in themoisture obtained by gel pressing [22, 27],after brining and as a function of time ofstorage in ammoniacal atmosphere. It isnoteworthy that most of the few studiesrelated to the characterization of the moistureextracted from chee se concem hard cheeses

[22, 27]. The second approach was the directdetermination of the total mineral contentin the outer layer and in the centre of thegel before and after brining and as a functionof storage time.

2. MATERIALS AND METHODS

2.1. Experimental protocol

The experimental protocol is schematicallypresented in figure 1. This protocol and subse-quent analyses were carried out in triplicate.

2.2. Milk epuration by cross-Dowmicrofiltration

Raw skim milk from Triballat (Noyal-sur-Vilaine, France) was used. Before microfiltra-tion, the skim milk was preheated to 50 oc. Then,cross-flow microfiltration was used to eliminatebacteria [30]. The membrane module in alumineSterilox (Société des céramiques techniques,Tarbes, France) had 19 channels, each with aninner diameter of 4 mm, and a total membranearea of 0.2 m-. The average nominal pore sizewas 1.4llm. The temperature was 50 oc. Underthese conditions almost aIl of the whey proteinsand casein micelles pass through the membranewhile 99.99 % ofbacteria are retained [30]. Thepermeate was then concentrated by ultrafiltra-tion (UF).

2.3. Ultrafiltration

The preparation of the UF retentate was car-ried out as previously described by Maubois &Mocquot [20]. The membrane Ml (Carbosep",Orelis, France) was used (molecular mass eut-off: 150000 g·mol-') at 50 "C. Under these con-

Evolution of various salt concentrations in a model cheese

Day 0

Day 1

Figure 1. Experi-mentai protocol forthe preparation ofthe model chee se.Figure 1. Protocoleexpérimental pour lapréparation de fro-mage modèle.

555

Skim milk

11Milk purification by cross-tlow microliltration

11Milk protein concentration by ultrafiltration

(UF retentate)

11Addition 01 antibiotics, fungicide and lactic acid

11Addition of glucono-delta·lactone (40g.kg-')

11Renneting al 30 ·C

(0.1 g.kg-' of rennet)

11Cooling at 20 ·C

Spraying 01 pimaricine solution

Storage at 12 ·C in ammoniacal atmosphere du ring 13 d

Brining at 12 ·C for 30 min

11

Day 1 before and alter brining, 3 , 6, 9, 11 and 13.

11Extraction and physlco-chemlcal analyses 01 the gel moisture

Physico-ehemical analyses of surface and centre of gels

ditions, whey proteins can pass slightly throughthe membrane (rejection of 75 %) while caseinmicelles are retained. To limit bacterial growthand contamination, nisin, penicillin Gand strep-tomycin (Sigma, MO, Saint-Louis, USA) wereadded to the UF retentate at the following finalconcentrations: 100 UI ml.:'. 12 UI mL -1 and12 mg-L':' [17]. A final concentration of10-4mol-L'! OfE amino caproic acid was addedto inhibit residual plasmin activity. The proteinconcentration was about 19 g-kg'".

2.4. Acidification and renneting

A lactic acid (Sigma, France) solution(1 mol-L -1 dissolved in UF permeate) was addedunder stirring to the UF retentate to have a pHvalue of about 6.3. A glucono-delta-Iactone(GDL) (Lysactone, Roquette, Lestrem, France)concentration of 40 g-kg! was added to the UFretentate previously incubated at 30 "C to havepH value of about 4.75 after 24 h. Immediately

after GDL addition, 0.10 g-kg'" of rennet solution(1/10 000) (laboratoire Granday-Roger, Beaune,France) was added to the UF retentate. The ren-net coagulation time was about 20 min. The gelsobtained were left standing ovemight at roomtemperature. The rate of cooling to 20 "C after gelformation was less than one hour. Afterwards,a slight syneresis, with a loss of about 20 g for atotal weight of 370 g of gel, was observed. Thecharacteristics of the model gel are indicated intable J.

2.5. Brining

A saturated brine (330 g-kg'" of NaCI) wasprepared from distilled water and dairy salt(Compagnie saline du midi, Dax, France). Theconditions of the brining were 30 min at 12 "Cwith a ratio of 2 L of brine per gel. Brining wasdone under manual stirring to maintain the brineconcentration constant throughout the experi-ment.


Table I. Characteristics of the model chee sebefore brining.Tableau I.Caractéristiques du fromage modèleavant saumurage.

DiameterHeightSurfaceVolumeWeightPHG1ucono- Delta- LactoneTotal Nitrogen X 6.38Non Casein Nitrogen X 6.38Non Protein Nitrogen X 6.38FatLactoseCalciumMagnesiumSodiumPotassiumChlorideInorganic phosphateCitrateDry matter

11.0 cm3.7 cm318 cm?351 cm!370 g4.7540 g·kg-I208 g-kg"28.9 g·kg-I4.8 g·kg-Io g-kg!39 g·kg-I5.700 g·kg-I0.300 g-kg "0.450 g·kg-I1.740 gkg!0.800 g·kg-I6.700 g·kg-1

1.950 g·kg-I29.23 %

2.6. Storage conditions

The gels obtained were sprayed with a 5 gL-1pimaricine solution (Delvocid'", Gist-brocades,Seclin, France) and stored in an ammoniacalatmosphere for 13 days. Storage in ammoniacalatmosphere was necessary to create a pH gradi-ent in the model gel. The NH, diffusion was donefrom a vessel containing 2 mol·L-1 (day 1) andthen 0.3 mol-Lr! (day 2 to day 13) ammoniacalsolution in a ripening box (volume 0.75 m ').Temperature and relative humidity were 12 "Cand 95 %, respectively.

2.7. Moisture extraction

The extraction protocol used was the onedescribed by Salvat-Brunaud et al. [27] forcooked hard cheese of the Emmental type andadapted to soft cheese by Pierre et al. [26]. Themethodology of this extraction has the advan-tages of preserving the minerai equilibrium andobtaining sufficient quantities of moi sture forphysicochemical analyses without use of chern-ical compounds or dilution. The quantity of gelwas 1.2 kg and the ratio sand/gel was about 1.211.

The extractions of moisture were carried out onday 1 (before and after brining), 3, 6, 9, Il and 13(day 0 = renneting day). Before minerai analysesof moisture, samples were ultrafiltered on Cen-triflo CF 25 membrane (molecular mass eut-off:25 000 g-rnol ", Amicon, Epernon, France)(800 g, 30 min, 12 OC).

2.8. Zone preparation

The preparations of the outer layer and centreof the gel were carried out on day 1 (before andafter brining), 3, 6, 9, Il and 13 (day 0 = ren-neting day) [18, 19]. The depth and weight ofeach zone of the gel were about 2 mm and 65 g,respectively.

2.9. Analyses

The pH values were measured with a Por-tamess pH-meter.

The contents in total protein were determinedaccording to the lOF method (standard20B:1993).

For minerai content determination in differentzones of the gel, about 1g of gel was homogenisedin 30 g of 0.02 rnol-L -1 nitric acid solution. Then,after standing overnight at room temperature,the solution was filtered on Whatman 42.

On the filtrates, cation (calcium, magnesium,sodium and potassium) and anion (chloride, phos-phate, citrate) concentrations were determinedusing atomic absorption spectrometry (Varian,Les Ulis, France) [2] and ion chromatography(Dionex, Jouy-en-Josas, France) [7], respectively.The accuracies of the cation and anion determi-nations were about ± 2 %. The concentrationunits were expressed in mg per kg of material(moisture or gel).

2.10. Theoretical calculationof calcium phosphate saturationindexes in a pH range between4.8 and 6.5.

From initial composition of moisture (day 1after brining) and with a NaCI concentration of4 moIL-I, calcium phosphate saturation indexesin a pH range between 4.8 and 6.5 were calcu-lated. The saturation indexes with respect to agiven calcium phosphate phase were defined asthe ratio: ionie activity product in solution/solu-


bility product. Calculations were performed by aniterative method described by Holt et al. [13].Although calcium is bound more strongly to glu-conate than to lactate, we have assimilated boththese ions. It is noteworthy that the results ofthese theoretical calculations indicated tendenciesand were of semi-quantitative significance.

3.1. Brining effects

3. RESUL TS AND DISCUSSION

The comparison of results before and afterbrining on day 1 of model chee se showedthat this step has multiple physicochemicaleffects. Firstly, the sodium and chloride con-centrations in the moisture and in the outerlayer increased strongly (figures 2A, 3A,respectively). In the centre of the gel, con-

Figure 2, Sodium concentra-tion in the moi sture and in twozones of the gel before (whitehistogram) and after brining(black histogram) (A) and as afunction of storage time inammoniacal atmosphere (H):moi sture; (C): outer layer (+)and centre (.) of gel.Figure 2. Concentration ensodium de la phase aqueuse etde deux parties du gel avant(histogramme blanc) et aprèssaumurage (histogramme noir)(A) et en fonction du temps destockage en atmosphèreammoniacale (H) : phaseaqueuse; (C) : surface (+) etcentre (.) du gel.

35000

30000

~ 25000

~ 20000

W 15000

~ 10000

5000

o

557

centrations of these ions were unaffected,indicating that the diffusions of ionie sodiumand chloride were not immediate. Secondly,the pH (figure 4A) and the concentrations ofcalcium (figure 5A), magnesium (figure 6A),potassium (figure 7A), inorganic phosphate(figure SA) and citrate (figure 9A) in moistureand the outer layer decreased while those ofthe centre were not modified. The variationsin the outer layer of the ratio concentrationbefore brining/concentration after briningexpressed in % were 32, 36,45, 28 and 36 %for calcium, magnesium, potassium, inor-ganic phosphate and citrate, respectively. Inparallel, low decreases were observed in themoisture: 9.6, 9.5, 13, 1 and 1.5 % for cal-cium, magnesium, potassium, inorganicphosphate and citrate, respectively. Thesedifferences in variations between the outer

A

12000

~Ol 10000"'"~ 8000

E 6000:J

] 4000~

moisture outer layer centre

B•. •. •.... rncisture

2000

o +---t---+--+~-I---+---t---i.o 2 4 6 8 10 12 14

Days

c35000

30000

~ 25000cilE 20000

W 15000'ë~ 10000

5000

O+-.a::..+---t---+---+--+--t---io

centre

2 4 6 8 10 12 14Days


layer and the moi sture showed that the saltabsorption is essentially a surface phe-nomenon.

To approximate the diffusion coefficientof NaCl, these results were compared withthose obtained on model chee se containing70 % of moisture [9]. A value close to0.4 cm-/d was found. In previously pub-lished works, Geurts et al. [9, 10] and Hardy[12] described the salt diffusion respectively,in model chee se and Camembert cheese, asa process derived from Fick's law and deter-mined a diffusion coefficient of about0.2 cm-/d. Three reasons can explain thesediscrepancies between both determinations.Firstly, the technologies to prepare our curdswere not those used for traditional cheese.Secondly, our model has a higher moisturecontent (about 70 % against 55 % in mould-

ripened cheeses). Thirdly, fat was absent inour gel.

In parallel to the absorption of salt, thesedecreases of ion concentration in the outerlayer are due to ion transfers by diffusionfrom the gel surface towards the brine. It isnoteworthy that using a freshly made NaCIsolution, rather than used brine, leads to amarked loss of soluble components. Indeed,the mineraI transfers during brining wereless important when brine was old or whencalcium chloride was added to the brine [3,8,29].

The other consequence of brining is aloss of aqueous phase. In our case, no dataconcerning water loss was determined.However, this well-known phenomenon isdescribed by several authors [3, 8-10, 12,29, 32]. Geurts et al. [9] and Hardy [12]

50000 A7 400000)-'"

~ 30000ID:g 200000z8 10000

0moisture outer layer centre

20000 B70) 16000 •-'" • •ci>E 12000 • moisture

ID"0 8000'§:c8 4000

00 2 4 6 8 10 12 14

Days

50000 C45000 outer layer., 400000)

.-'" 35000ci>E 30000 Figure 3. Evolution of chlo-ID 25000"0 20000 ride concentration. Same sym-o§:c 15000 bols asfigure 2.8 10000

Figure 3. Évolution de la5000 centre

0 concentration en chlorure.0 2 4 6 8 10 12 14 Mêmes symboles que pour la

Days figure 2.


found a constant ratio of 2.5 between theabsorption of salt and the loss of moisture ina soft cheese. In our case this ratio is prob-ably different because: a) our curds havesurfaces different from those of Camembertcheese (table 1); b) the chemical compositionof our brine (only NaCI) was different fromthose used in chee se making (NaCI, miner-ais, organic compounds coming from whey)[3, 8].

3.2. Effects of storagein an ammoniacal atmosphere

3.2.1. Calcium, magnesium, inorganicphosphate and citrate ions

In the absence of ammonia, no signifi-cant variation of pH and ion concentrations

I0.

4.90

559

was observed [results not shown and 18,19]. Conversely, during storage in an ammo-niacal atmosphere, the pH of the moisture(figure 4B), in the outer layer and in the cen-tre increased (figure 4C). The calcium (fig-ure 5B), magnesium (figure 6B), inorganicphosphate (figure SB) and citrate (figure 9B)concentrations in the moi sture decreased.In parallel, the concentrations of these ionsincreased in the outer layer and decreased inthe gel centre (figure 5C, 6C, SC, 9C,respectively).

These variations of concentrations inmoisture, outer layer and centre of gel wererelated to migrations of calcium, magne-sium and inorganic phosphate ions from thecentre to the outer layer during storage inammoniacal atmosphere of model gel.Moreover, in this work, we first observed

A

4.60moisture outer layer centre

6.00 B

5.50

Ia.5.00

•4.50

0 2 4 6 8 10 12 14Days

7.00 C6.50 •• •6.00

outer layer

Ia.

Figure 4. Evolution of pH. 5.50

Same symbols asfigure 2. 5.00

Figure 4. Évolution du pH.centre

4.50Mêmes symboles que pour la0 2 4 6 8 10 12 14

figure 2. Days

4.80

4.70


a citrate migration. However, it is probablethat, in cheese, this citrate migration wasnot observed because of its degradation bylactic acid bacteria [4]. These phenomenaof migration take place subsequent to theformation of pH gradient in the gel. Theincrease in pH value in the outer layer ofthe gel due to storage in ammoniacal atmo-sphere leads to the precipitation of differ-ent possible salts at the gel surface. Thesesalts can be calcium phosphate, magnesiumphosphate, calcium citrate and magnesiumcitrate which have low solubilities [14].From initial composition of moi sture pressedout (after brining) and with a NaCI concen-tration of 4 moIL-I, theoretical calculationsof calcium phosphate saturation indices in apH range between 4.8 and 6.5 were carriedout (figure 10). Thus, during pH increase,

the supersaturation of calcium phosphatesalts (octacalcium phosphate OCP and tri-calcium phosphate TCP) increased stronglyand explain the precipitation of calciumphosphate salts especially in the outer layer.Similar behaviours of both calcium phos-phate salts were determined.

Evolution of calcium was similar to thatobtained with magnesium because at 13 d ofstorage in an ammoniacal atmosphere, thecation concentration ratio between the outerlayer and the centre was about 6 for bothcations. These similar behaviours are prob-ably due to the same low solubilities forsalts of calcium and magnesium. In milk,calcium-citrate, by surpassing its solubilitylimit, is supersaturated and no precipitationof calcium-citrate is observed [32]. How-ever, in our case, the citrate concentration

8000 A7000

~~ 6000

~ 5000

E 4000::J

3000<:;êiiQ 2000

1000


B80007000

œ 6000.x:œ 5000E •E 4000::J 3000<:; moisture

êii 2000Q

10000

0 2 4 6 8 10 12 14Days

21000 C18000 •• •~ 15000 • • outer layer

œ Figure 5. Evolution of cal-E 12000E 9000 cium concentration. Same::J symbols asfigure 2.." 6000 centre

êiiFigure 5. Évolution de laQ

3000 •concentration en calcium.0Mêmes symboles que pour la0 2 4 6 8 10 12 14

Days figure 2.

Evolution of various salt concentrations in a model cheese 561

350

~'" 300-x:~ 250

E 200.~ 150Q)

§, 100<Il

~ 500-+---+----+----1--+---+----+----1

o

was higher in the aqueous phase (about3 100 mg-kg:") (table /) than in milk (about1500 mg-kg:') [32]. This high concentrationof citrate was due to the release of citrateinitially bound to casein (about 10 % of totalcitrate) during the acidification of the reten-tate. So, these high contents in citrate andcalcium contributed to a slight precipitationof calcium citrate in the outer layer. It isnoteworthy that in one-month-old Cheddarcheese, Morris et al. [22] observed the pres-ence of crystals. These authors suggestedthat these crystals were calcium-phosphateand calcium-citrate. On the other hand, pres-ence of calcium and magnesium carbonatewas unlikely bec ause there is no microbialmetabolism which produces CO2• In the pre-sent work, the nature of the precipitated saltswas not precisely determined. However, the

400_ 350~ 300cr,E 250

'[ 200,il~ 150œ

:E1 100~ 50

o

massic ratio Ca/P calculated at the gel sur-face after 13 d of storage in an ammoniacalatmosphere was about 2. This ratio sug-gested the presence of tricalcic phosphate(theoretical massic ratio Ca/P = 1.93) in theouter layer of the gel. Brooker [1] identi-fied using transmission electron microscopy,the presence of calcium phosphate in therind of mould-ripened cheese (Coulom-miers). However, this Brooker's methodcannot determine the exact nature of thisprecipitated salt. In this sense, it would beinteresting to determine the nature of pre-cipitated salts at the chee se surface by othermethods such as polarising microscopy.

Taking into account the weight of theouter layer (about 65 g i.e. 18 % of the totalweight), the % of total calcium, magnesium,inorganic phosphate and citrate present in

A

moisture outer layer centre

B

•

rrcisture

2 4 12 146 8Days

10

Figure 6. Evolution of mag-nesium concentration. Samesymbols asfigure 2.Figure 6; Évolution de laconcentration en magnésium.Mêmes symboles que pour la

figure 2.

1200

~1000

~ 800'[ 600,il~ 400œi 200

o+---t---t---t----t----t---t--.Jo

c: ~~

centre

2 12 144 6 8Days

10


the outer layer after 13 d of storage in anammoniacal atmosphere were 58, 56, 73and 42 %, respectively. Precipitation ofthesesalts in the outer layer of gel led to deple-tions in soluble calcium, magnesium, inor-ganic phosphate and citrate ion concentra-tions in the moi sture and in the outer layerand consequently induced their migrationstowards the gel surface. During their migra-tions, calcium, magnesium, inorganic phos-phate and citrate are not dissociated in thegel. The forms of association are not deter-mined but it is probable that soluble saltsof calcium and magnesium phosphate andcalcium and magnesium citrate existed.

Similar results were observed in differentmould-ripened cheeses such as Camembert,Coulommiers, Brie and Pont l'Evêque [l,15, 18, 19,21,25]. In industrial cheeses,

ion accumulation at the cheese surface coin-cides with the surface flora growth, whichgenerates a basic pH at the surface of thecheese by its metabolism [l , 15, 18, 19,21,25].

3.2.2. Sodium, chlorideand potassium ions

During storage in an ammoniacal atmo-sphere, the sodium, chloride and potassiumconcentrations in moisture increased slightly(figures 2B, 3B, 7B, respectively). In paral-lei, the large difference observed in sodiumchloride content between the centre and theouter layer before and after brining on day 1(figures 2A, 3A, respectively) disappearedafter 5 d of storage in an ammoniacal atmo-sphere because in this period, their concen-

3000 A-t 2500Cl~0> 2000EE 1500;J·inU) 1000lU

ë~ 500

0moisture ouler layer centre

3000 Br: 2500Cl . • •~ •0> • •E 2000 moisture

E 1500;J·inU) 1000lU

ë~ 500

00 2 4 6 8 10 12 14

Days

3000 C., 2500Cl~ centre0> 2000E :;:er~Yer ! :==-- • Figure 7. Evolution of potas-E 1500 • • ===::e;J sium concentration. Same

·insymbols asfigure 2.U) 1000lU

ë Figure 7. Évolution de la~ 500

0 concentration en potassium.0 2 4 6 8 10 12 14 Mêmes symboles que pour la

Days figure 2.


10000r: 8000Cl-'"ci>E 6000Qj'iiis: 4000a.'"0s: 2000~


10000 Br:Cl 8000-'"ci>E 6000Qj'iii 4000s:a. moisture'"0 2000r.~ 0

0 2 4 6 8 10 12 14Days

30000 C-; 25000Cl •-'" • outer layerci>

Figure 8. Evolution of inor- E 20000ganicphosphateconcentration. Qj' 15000iiiSame symbols asfigure 2. s: 10000a.

'"Figure 8. Évolution de la 0 centres: 5000s,concentration en phosphate 0inorganique.Mêmessymboles 0 2 4 6 8 10 12 14que pour lafigure 2. Days

trations decreased in the outer layer andincreased in the centre (figures 2C, 3C,respectively). During this period, thesodium, potassium and chloride ions dif-fused in the gel matrix and at day 5 theywere uniformly distributed. This time was ingood accordance with a diffusion coeffi-cient of about 0.4 cm2/d previously deter-mined in this work for NaCl. Then, beyond5 d and up to the end of storage, the con-centration of sodium and chloride in the cen-tre increased slightly or was constant forpotassium.

It is noteworthy that the storage in a nonammoniacal atmosphere gave similar results[18, 19] which indicated that the presence ofammonia has no influence on the diffusionof sodium, chloride and potassium. InCamembert cheese, a reversible migration of

563

potassium in the cheese probably due to thedevelopment of surface flora was shown[19]. In our case, as the curd was poor inmicroorganisms due to the presence ofantibiotic and fungicide, which limited theirgrowth [17], no migration of potassium wasobserved.

5. CONCLUSION

In this study, we have prepared a modelcheese through the combined use of mem-brane technologies and different products(lactic acid, GDL, antibiotics, fungicide).This model has been successfully used toquantify ion transfers during its brining andstorage in ammoniacal atmosphere. Themultiple relationships between these trans-

564

35003000

~ 2500Cl.><dl 2000E

~ 1500

~ 1000500

0

F. Gaucheron et al.

A

moisture ouler layer centre

B--- .• •

moislure

3500_ 3000

]' 2500

~ 2000~ 1500r:6 1000- 500

O+---+--+---+---+---I----I~--Io

5000

2 4 6 B 10 12 14Days

C• Figure 9. Evolution of

iC • outer layer citrate concentration.Same symbols as figure2.

• • Figure 9. Évolution de lacentre concentration en citrate.

Mêmes symboles que2 4 6 8 la 12 14 pour lafigure 2.Days

4000~dl3000E~ 2000~Q. 1000

0+---+--+--+---+---+--+----;a

1.0E+061.0E+05

x 1.0E+04.gJ 1.0E+03.S;c 1.0E+02.2 1.0E+01ca::; 1.0E+OOJj 1.0E-01

1.0E-021.0E-03 +----+----+----1------1

4.5 5 5.5pH

6 6.5

10. Theoretical saturation indices of octacalcium phosphate (OCP) (Â) and tricalcium phosphate(TCP) (.) from pH 4.8 to 6.5. Calculations, from the initial minerai composition of the moisture witha NaCI concentration of 4 moIL-I, were carried out as described by Holt et al. [13].Figure 10. Index de saturation théoriques des phosphates octacalcique (OCP) (Â) et tricalcique(TCP) (.) entre pH 4,8 et pH 6,5. Les calculs, faits à partir de la composition minérale initiale de laphase aqueuse et une concentration en NaCI de 4 rnol-L -l, ont été réalisés comme décrit par Holt etal. [13].


fers and the physicochemical changes occur-ring in the model during brining and stor-age were not determined precisely becauseseveral factors such as pH, structure ofmatrix, state of water, ionie strength, saltsolubilities are involved at the same time.However, the se results show that globalphysicochemical changes of the moisturecan reflect sorne local changes in the cheese.Results are qualitatively in accordance withthose previously described [3, 9,12,15,18,19,21,25,29] although this model has sornedifferences in composition with industrialsoft cheeses. Indeed, it contained a high con-centration in gluconate and the fat contentwas close to zero. Moreover the initial lac-tose was not metabolised because it doesnot contain micro-organism. The potential ofthis model appears very interesting becauseit is now possible to study the influence ofdifferent factors on salt migrations. Thus,the salt migrations can be studied in gel con-taining more or less proteins, fat, with dif-ferent casein/whey proteins ratios, withphosphopeptides or with different initial pHvalues. The brining and the ripening condi-tions can also be studied. The consequencesof these physicochemical heterogeneities(pH, minerai composition) in the cheese onthe texture formation can be also investi-gated.

ACKNOWLEDGMENT

The authors thank Ll., Maubois for criticalreading of the manuscript.

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