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International Dairy Journal 31 (2013) 29e33

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International Dairy Journal

journal homepage: www.elsevier .com/locate/ idairyj

The effect of dry matter and salt addition on cheese wheydemineralisation

Lenka Diblíková a,*, Ladislav �Curda a,b, Jan Kin�cl b

aDepartment of Dairy, Fat and Cosmetic Sciences, Institute of Chemical Technology Prague, Technická 5, 166 28 Prague, Czech RepublicbMemBrain s.r.o., Pod Vinicí 87, 471 27 Strá�z pod Ralskem, Czech Republic

a r t i c l e i n f o

Article history:Received 11 November 2011Received in revised form14 December 2012Accepted 28 December 2012

* Corresponding author. Tel.: þ420 220 443274.E-mail address: lenka.diblikova@vscht.cz (L. Diblík

0958-6946/$ e see front matter � 2013 Elsevier Ltd.http://dx.doi.org/10.1016/j.idairyj.2012.12.008

a b s t r a c t

The high mineral load of whey limits its utilisation. Demineralisation is needed for further processingand food applications. We used a lab-scale electrodialysis unit to remove ions from ten model solutionsof fresh or reconstituted whey with increased dry matter and sodium content. The drop of main wheycations (Kþ, Naþ, Ca2þ, Mg2þ) was measured by capillary electrophoresis. Whey solutions with 7, 14, 21%(w/w) dry matter were demineralised in 35, 60 and 95 min, respectively. The total salt content decreasedby 90e95%. After NaCl addition at 1, 2, 3% (w/w), more than 95% of all cations were removed in 45, 65and 90 min, respectively. Kþ and Naþ were removed the fastest in all solutions, their concentrationdecreased by 83e100%, Ca2þ and Mg2þ content decreased by 61e96%. These results demonstrate thatmineral salts are effectively removed from whey even if it is concentrated and highly salted.

� 2013 Elsevier Ltd. All rights reserved.

1. Introduction

The global production of cheese and casein whey is around 180million tonnes per year (IDF, 2009). The three most common waysof whey utilisation in the food industry are lactose production,production of whey powders and individual whey proteins, andanimal feedstocks preparation (Sienkiewicz & Riedel,1990). Twentyone percent of whey powders are used in feed production, 36% infood, but at 43% utilisation applications in nutrition/pharmaceuti-cals predominate (Visser, 2008). However, the utilisation of cheesewhey in human-food products is limited by several factors: i)a small protein/sugars ratio together with the low sweetening po-wer of lactose (Coughlin & Charles, 1980); ii) the low solubility oflactose (Baret, 1982); iii) a high mineral load (8e10% on a dryweight basis; Gernigon, Schuck, Jeantet, & Burling, 2011).

An excessive saline taste is undesirable especially in dietetic orbaby foods (Siso, 1996), and furthermore the quality and func-tionality of whey products may be affected by high salts content(Greiter, Novalin,Wendland, Kulbe, & Fischer, 2002). Desalination istherefore required in several whey processing technologies; thiscan be carried-out by electrodialysis (ED), ion exchange, nano-filtration either alone or in combination (Gernigon et al., 2011).

ED with ion-exchange membranes represents one of the mostconsiderable separation methods with a great potential of

ová).

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application in dairy industry (Casademont, Araya-Farias, Poucelly, &Bazinet, 2008). Researchers have been interested in this topic formore than 15 years, but mainly from an economic point of view.Many studies have been carried-out to compare demineralisationof whey by ED, ion exchange or nanofiltrationwith regards to costs,energy demand or amount of waste water produced (Greiter et al.,2002; Houldsworth, 1980; Strathmann, 2010). Several articles andpatents have been published reporting the possibility of multistagedesalination of whey performed to reach higher demineralisationdegree (Casademont, Sistat, Ruiz, Pourcelly, & Bazinet, 2009;Chavéron, Sihver, & Duperrex, 1979). However, the efficiency of theED process depends predominantly on the properties of semi-permeable membranes used.

Membranes for whey desalination have to meet the followingdemands: high permeability for mineral ions and at the same timehigh resistance to the diffusion of electrolytes, low permeabilityin relation to lactose, minimal electric resistance and good reten-tion properties in relation to milk proteins and lipids (Bleha,Tishchenko, �Sumberová, & K�udela, 1992).

It is well known that the membrane fouling is one of the com-mon problems in ED. To optimise the process, numerous studieshave been carried-out to understand fouling formation. Thesestudies dealt with the precipitation of milk proteins at the mem-brane surface and the sorption of whey components withinmembranes and the microbial fouling of membranes. The effect ofdifferent factors such as pH, temperature, ionic strength, magne-sium/calcium ratio etc., on membrane fouling was investigated(Ayala-Bribiesca, Araya-Farias, Pourcelly, & Bazinet, 2006; Bazinet &

Table 1Composition of model whey solutions before ED.

Modelsolutiona

Drymatter (%)

Protein(%)

Ash(%)

Freezingpoint (�C)

pH Conductivity(mS cm�1)

FW7-0 5.45 0.714 0.50 �0.445 6.5 5.15FW7-1 6.27 0.588 1.26 �1.004 5.6 19.10FW7-2 6.95 0.554 2.20 �1.514 5.2 33.10FW7-3 8.34 0.580 3.32 �2.041 5.3 46.10RW7-0 6.62 0.894 0.58 �0.528 6.5 5.88RW7-1 7.71 0.707 1.28 �1.139 5.7 19.16RW7-2 8.50 0.760 2.45 �1.719 5.5 33.90RW7-3 9.45 0.750 3.41 �2.315 5.4 46.50RW14-0 12.83 1.771 1.06 �1.133 6.5 9.66RW21-0 19.86 2.647 1.63 �1.813 6.4 12.12

a Model nomenclature: FW, fresh whey; RW, reconstituted whey; first numberreflects dry matter (7, 14 or 21%, w/w), second number gives percentage of saltaddition (0, 1, 2 or 3%, w/w).

L. Diblíková et al. / International Dairy Journal 31 (2013) 29e3330

Araya-Farias, 2005; Casademont, Pourcelly, & Bazinet, 2007; LingTeng Shee, Angers, & Bazinet, 2005; Strathmann, 2010).

Most researchers studied the ED process onmilk, caseinwhey ormodel solutions with whey proteins. There is still a little knowledgeabout ED of highly salted or concentrated cheese whey. The mainsource of saltywhey is Cheddar production,whichmakes up to5% oftotal Cheddar whey (Blaschek, Wendorff, & Rankin, 2007). As worldCheddar production can be estimated at 18 million tonnes, theamount of salty whey is considerable. Another component of cur-rentwheyprocessing technologies is concentrationbefore transportto further processing; it will therefore be helpful to obtain the dataabout this process to extend the application of ED in dairy industry.

The objective of this study was to evaluate the use of ED for thedemineralisation of fresh or reconstituted cheese whey with differ-ent dry matter and sodium chloride addition, which has to simulatethe salty whey from processing of cheddar or blue-veined cheeses.

2. Materials and methods

2.1. Whey

FreshEdamwheywasprovidedbya local dairy (Moravia Lacto a.s.,Jihlava, Czech Republic). Raw material was microfiltrated on a filtra-tion unit ARNO 700 (Mikropur a.s., Hradec Králové, Czech Republic)with ceramic membranes (TAMI-Industries, Hermsdorf, Germany)under followingconditions: tubularmembranewithpore size1.4mm,membrane length 550 mm, diameter 10 mm, channel diameter3.5 mm, effective filtration area 0.02 m2, zirconium oxide separationlayer, pressure 0.125 MPa, temperature 35 �C. Permeate after micro-filtration was stored at 4 �C. Whey powder (Moravia Lacto a.s.) wasreconstituted in distilled water to obtain 7%, 14% and 21% (w/w) so-lutions,whichwere left to stand for at least 1h tohydrate theproteinsand subsequently treated exactly the same way as fresh whey.

Sodium chloride, which is commonly used for the industrialsalting of cheeses (Guinee & Fox, 2004), was added to selectedsolutions (7%, w/w, reconstituted whey and fresh whey) in therange of 1e3% (w/w). In the end, ten model whey solutions wereprepared for demineralisation by ED.

2.2. Electrodialysis

A lab-scale electrodialysis unit ED-Z mini, consisting of twentyheterogeneous ion-exchange Ralex� membranes AMH-PES andCMH-PES (Mega a.s., Strá�z pod Ralskem, Czech Republic) witheffective surface area of 64 cm2, effective membrane dimensions40 � 160 mm, channel diameter 6 mm and current density 150e160 A m�2, was kindly lent by MemBrain s.r.o. (Strá�z pod Ralskem,Czech Republic). The conditions used for whey desalination were asfollows: constant voltage (20.0 � 0.1 V), laboratory temperature(25.0 � 2.0 �C), electrolyte: anhydrous sodium sulphate (10 g L�1),concentrate: distilled water acidified with HNO3 (pH 2). Electricalconductivity, pH, temperature, voltage and current intensitiesapplied at the electrodes were registered throughout every EDexperiment. Samples of the diluate were taken as 25, 50, 75, 85 and95% conductivity decrease was reached and also every 10 min of ED.Collected samples were deep-frozen (�80 �C) and analysed later formineral salt content. EDprocesswas stopped as selected conductivitylimitwas reached (0.25mS cm�1). After eachexperiment EDunitwascleaned chemically using following sequence: water, 10 min; 5%NaOH, 60 min; water, 10 min; 5% HNO3, 60 min; water, 2 � 10 min.

2.3. Capillary electrophoresis

The concentration decrease of the main whey cations (Kþ,Naþ, Ca2þ, Mg2þ) was measured by capillary electrophoresis

PrinCE-C750 (Prince Technologies B.V., Emmen, The Netherlands)according to Suaréz-Luque, Mato, Huidobro, and Simal-Lozano(2007). This method is rapid, reliable and does not requirecomplicated sample preparation (i.e., mineralisation). The accu-racy and precision data are described in the relevant literature(Suaréz-Luque et al., 2007). We performed several modificationsin the analytical process: ions were detected at 206 nm insteadof 185 nm because of less signal noise; internal standard (lithiumchloride, 0.02 g L�1) was added to correct for matrix effects;a higher temperature was applied due to problems with coolingthe device. The conditions used were as follows: 60 cm fusedsilica capillary, inside diameter 75 mm, electrolyte: imidazole(10 mmol L�1), hydrodynamic injection 34 Pa, 0.4 min, temper-ature 30 �C, diode array detector at 206 nm. Each analysis tookup to 8 min and was repeated at least twice. Cations wereidentified by their relative migration times calculated as the ratiobetween their migration times and the migration time of Liþ

used as reference compound. Anions were not determined.

2.4. General samples analysis

All final products, by-products as well as raw materials wereanalysed for dry matter, protein and ash content, pH, conductivityand freezing point. Conductivity and pH values were measuredusing a pH/Cond 340i (WTWGmbH, Weilheim, Germany). Freezingpoint was determined by cryoscope (Marcel, Warsaw, Poland). Totalprotein content was assessed according to Kjeldahl method onKjeltec Auto Plus device (Marshall, 1992). Dry matter and ashcontent were analysed as described by (Marshall, 1992). Eachanalysis was repeated three times.

3. Results and discussion

3.1. Characterisation of model solutions

Pasteurised skimmed cows’ whey, as well as reconstitutedwhey, was treated as described above to remove residual fat,casein and cheesemaking foulants, and mainly to prevent thegrowth of undesirable microorganisms. Permeates of 14 and 21%(w/w) reconstituted whey were demineralised without furthermodification. Permeates of fresh and 7% w/w reconstitutedwhey were divided into four 1 L batches. Each time, one batchremained without salt addition, in the others NaCl was addedto a concentrations of 1, 2, and 3% (w/w). As a result, 6 saltedand 4 non-salted solutions were prepared for ED. Theaverage composition of model whey solutions is shown inTables 1 and 2.

Table 2Mineral salts content in model whey solutions before ED.

Model solutiona Ion concentration (g L�1)

Kþ Naþ Ca2þ Mg2þ

FW7-0 1.988 � 0.096 0.546 � 0.032 0.513 � 0.056 0.180 � 0.013FW7-1 1.640 � 0.041 5.522 � 0.248 0.433 � 0.012 0.154 � 0.000FW7-2 2.195 � 0.004 12.827 � 0.071 0.504 � 0.086 0.180 � 0.011FW7-3 1.570 � 0.001 15.566 � 0.369 0.440 � 0.013 0.163 � 0.011RW7-0 1.323 � 0.104 0.431 � 0.004 0.469 � 0.022 0.186 � 0.008RW7-1 1.734 � 0.193 6.842 � 0.104 0.519 � 0.033 0.149 � 0.011RW7-2 1.778 � 0.102 13.819 � 1.305 0.461 � 0.044 0.197 � 0.042RW7-3 1.304 � 0.139 16.983 � 0.613 0.458 � 0.201 0.184 � 0.027RW14-0 2.708 � 0.007 0.842 � 0.059 0.736 � 0.072 0.259 � 0.053RW21-0 4.124 � 0.035 1.343 � 0.018 1.113 � 0.102 0.450 � 0.011

a Model nomenclature: FW, fresh whey; RW, reconstituted whey; first numberreflects dry matter (7, 14 or 21%, w/w), second number gives percentage of saltaddition (0, 1, 2 or 3%, w/w).

Fig. 1. Diluate conductivity changes during reconstituted whey demineralisation asa function of electrodialysis time. Line 1 (-), RW7-0; line 2 ( ), RW14-0; line 3 (A),RW 21-0; line 4 ( ), RW7-1; line 5 ( ), RW7-2; line 6 ( ), RW7-3, where RW isreconstituted whey, the first number refers to dry matter (7, 14 or 21%, w/w) and thesecond number refers to the percentage addition of salt (0, 1, 2 or 3%, w/w).

L. Diblíková et al. / International Dairy Journal 31 (2013) 29e33 31

3.2. Demineralisation

Model whey solutions were desalted in batch process using theED unit under conditions described in Section 2.2. Each time, 1 L ofwhey (diluate) was demineralised against 1 L of acidified distilledwater (concentrate). The flow rates of diluate and concentrate wereset at 30 L h�1, electrolyte flow rate was 50 L h�1. During demin-eralisation temperature, conductivity and pH values were meas-ured automatically in 1 min intervals using the pH/Cond 340i;voltage and current intensities werewritten down directly from thedevice. As the selected conductivity was reached 50 mL sample ofthe diluate was taken and analysed for ions composition, drymatter, protein and ash content, pH, conductivity and freezingpoint.

The duration of ED depends on the amount of salts that shouldbe removed; whey with increased dry matter or salt addition needslonger electrodialysis time. The specific ED times for studied modelsolutions along with the composition of final products are pre-sented in Table 3. As the consequence of ion transport throughmembranes a significant decrease in ash content (77.6e97.9%), drymatter (10.9e41.0%) and freezing point (36.5e85.8%) was observed.Conductivities of diluates were reduced from the initial values setin Table 1 below the selected limit (0.25mS cm�1). Conductivities ofconcentrates increased over a wide range of 6.4e55.4 mS cm�1.

Diluate conductivity declined as a function of ED time as shownon Fig. 1. The curves have an expected profile with a rapid con-ductivity decrease in the beginning (first 20 min) and very slowconductivity loss in the end (last 10e20 min, under 1 mS cm�1),which is a result of the process driving force gradual reduction asthe ions concentration in the solution became low (Klein, Ward, &Lacey, 1987). With increasing dry matter the steep conductivity

Table 3Composition of ED diluates after demineralisation.

Modelsolutiona

ED time(min)

Drymatter (%)

Protein(%)

Ash(%)

Freezingpoint (�C)

pH

FW7-0 30 4.73 0.624 0.06 �0.253 4.5FW7-1 45 4.90 0.642 0.06 �0.239 4.2FW7-2 60 4.97 0.665 0.05 �0.276 4.1FW7-3 80 4.92 0.633 0.07 �0.289 4.0RW7-0 35 5.75 0.796 0.13 �0.313 4.4RW7-1 45 6.01 0.670 0.08 �0.332 4.3RW7-2 65 6.09 0.770 0.07 �0.332 4.1RW7-3 90 6.24 0.760 0.07 �0.345 4.1RW14-0 60 11.42 1.603 0.16 �0.675 4.6RW21-0 95 17.70 2.500 0.20 �1.152 4.6

a Model nomenclature: FW, fresh whey; RW, reconstituted whey; first numberreflects dry matter (7, 14 or 21%, w/w), second number gives percentage of saltaddition (0, 1, 2 or 3%, w/w).

decrease interval prolongs by 20 min on each multiple of the freshwhey weight basis. The profile is exponential (Fig. 1). With eachpercent of added NaCl this interval increases by 15e25 min. Theintrinsic decline of diluate conductivity is mostly linear.

A partial precipitation of whey proteins was observed at lowconductivities in diluate. It is known that b-lactoglobulin and im-munoglobulins show low solubility in the pH range 4e5 at lowionic strength (Sienkiewicz & Riedel, 1990). We also assume thatthe precipitation is a result of a-lactalbumin destabilisation due tothe decrease in Ca2þ concentration and decrease of pH. This pre-cipitation appears to be reversible when the initial conditions arerestored (Bramaud, Aimar, & Daufin, 1997). As negatively chargedwhey proteins are not able to go through anion-exchange mem-brane, they can also precipitate on the membrane surface and thuscontribute to membrane fouling (Ayala-Bribiesca et al., 2006; Blehaet al., 1992). This precipitation appears to be reversible until a cer-tain part of functional groups of the membranes becomes blockedby firmly sorbed whey components (Bleha et al., 1992).

The pH decreased during ED in the range 6.5e4.0; a proportionof the cations seem to be replaced by Hþ ions. This phenomenoncould be explained by the molar conductivity of Hþ ions, which isalmost five times higher than the conductivity of others cations tobe replaced (Bazinet et al., 2000).

3.3. Ion concentration analysis

All samples collected during ED were analysed for mineral saltcontent using capillary electrophoresis under conditions described

Fig. 2. The electrophoretogram of cations analysed in fresh whey at 206 nm; Liþ wasadded as reference compound for the calculation of the relative migration times.

Table 4Total ions concentration decrease in percentage in whey diluates after ED.

Modelsolutiona

Ion concentration decrease (%)

Kþ Naþ Ca2þ Mg2þ

FW7-0 96.8 � 0.6 86.5 � 0.6 80.1 � 1.3 74.1 � 2.9FW7-1 95.2 � 0.9 96.3 � 0.2 84.8 � 1.4 92.2 � 0.8FW7-2 95.6 � 0.3 97.5 � 0.0 78.7 � 0.1 93.6 � 0.6FW7-3 96.2 � 0.3 99.0 � 0.0 78.7 � 0.4 90.2 � 2.4RW7-0 98.8 � 1.7 85.4 � 0.6 74.0 � 1.1 76.4 � 1.9RW7-1 90.6 � 2.5 92.1 � 1.0 61.3 � 3.4 88.9 � 1.3RW7-2 94.9 � 0.2 98.1 � 0.1 89.2 � 2.1 93.9 � 2.3RW7-3 98.6 � 0.1 98.9 � 0.1 94.4 � 1.8 96.4 � 0.1RW14-0 99.0 � 1.4 84.0 � 1.3 78.6 � 0.1 78.4 � 2.7RW21-0 100.0 � 0.0 87.4 � 2.6 80.4 � 1.4 83.4 � 2.2

a Model nomenclature: FW, fresh whey; RW, reconstituted whey; first numberreflects dry matter (7, 14 or 21%, w/w), second number gives percentage of saltaddition (0, 1, 2 or 3%, w/w).

Fig. 3. The decrease of sodium and calcium ion concentration during model solutionsdesalination as a function of ED time. Panel a: ( ) RW7-0Naþ, ( ) RW7-0Ca2þ,( ) RW14-0Naþ, ( ) RW14-0Ca2þ, ( ) RW21-0Naþ, ( ) RW21-0Ca2þ;Panel b: ( ) RW7-1Naþ, ( ) RW7-1Ca2þ, ( ) RW7-2Naþ, ( ) RW7-2Ca2þ,( ) RW7-3Naþ, ( ) RW7-3Ca2þ. RW is reconstituted whey, the first numberrefers to dry matter (7, 14 or 21%, w/w) and the second number refers to the percentageaddition of salt (0, 1, 2 or 3%, w/w). (For interpretation of the references to colour inthis figure legend, the reader is referred to the web version of this article.)

L. Diblíková et al. / International Dairy Journal 31 (2013) 29e3332

in Section 2.3. An example of the electrophoretogram obtained isgiven in Fig. 2.

The percentage drop in individual ions is shown inTables 4 and 5.Data are related to the initial cation concentrations in model solu-tions (Table 2). Migration priority is linked to the electrical charges,the electrical mobility of each ion, membrane selectivity, ion radius,etc. (Sadrzadeh, Razmi, & Mohammadi, 2007; Sata & Yang, 2002).During the skimmilk electroacidification process, it was shown thatthe first cation to migrate through cation-exchange membranes isKþ; Naþ, Ca2þ and Mg2þ cations migrate afterwards (Bazinet et al.,2000). Whey cation migration should follow the same trend. Theresults obtained agree with those found in the literature, whichreport faster migration rates for monovalent ions than divalent(Kabay et al., 2003; Pérez, Andrés, Alverez, Coca, & Hill, 1994);however, the trend was different: Kþ > Naþ > Mg2þ > Ca2þ. Thislower calcium separation is due to its incorporation in structures ofwhey proteins (Hiraoka, Segawa, Kuwajima, Sugai, & Murai, 1980),and it has also been reported that calcium can participate on

Table 5The percentage drop in cations of whey diluates as a function of conductivity decrease during ED.

Modelsolutiona

CDb

(%)Conductivity(mS cm�1)

TSRc

(%)Ion concentration decrease (%)

Kþ Naþ Ca2þ Mg2þ

RW7-0 25 4.41 23.6 � 2.6 26.3 � 3.6 22.8 � 1.6 15.2 � 1.1 19.3 � 2.350 2.94 49.4 � 2.1 60.6 � 1.1 42.0 � 2.5 19.8 � 3.2 28.8 � 0.575 1.47 69.4 � 1.1 82.1 � 1.8 61.7 � 2.6 36.8 � 0.1 37.8 � 3.1

RW7-1 25 14.37 24.1 � 0.5 27.1 � 0.5 29.9 � 0.7 2.3 � 0.9 19.5 � 2.550 9.58 47.7 � 5.4 52.0 � 3.2 50.1 � 2.8 4.7 � 0.2 37.6 � 1.475 4.79 72.9 � 1.0 87.5 � 4.1 72.4 � 3.3 21.9 � 1.7 48.7 � 2.2

RW7-2 25 25.42 7.6 � 3.3 26.2 � 1.2 9.3 � 0.8 20.7 � 2.3 16.9 � 1.550 16.95 58.1 � 2.4 56.4 � 3.6 63.4 � 4.2 30.0 � 1.1 33.2 � 1.575 8.48 69.3 � 0.8 56.6 � 2.8 75.5 � 3.1 41.8 � 1.6 66.9 � 4.7

RW7-3 25 34.88 12.1 � 1.2 23.6 � 1.0 10.9 � 1.1 48.7 � 1.8 19.5 � 0.650 23.25 52.0 � 1.0 63.0 � 2.9 51.4 � 2.4 62.5 � 2.7 35.6 � 2.175 11.63 67.8 � 1.7 78.7 � 3.4 67.8 � 3.0 62.5 � 1.4 48.4 � 2.3

RW14-0 25 7.25 20.8 � 0.7 24.3 � 0.4 23.6 � 2.3 8.6 � 0.2 4.7 � 1.550 4.83 38.3 � 1.3 44.7 � 3.2 38.2 � 3.1 19.7 � 0.4 16.0 � 3.575 2.42 68.6 � 4.3 80.8 � 5.9 62.4 � 4.4 38.3 � 0.1 33.9 � 2.2

RW21-0 25 9.09 20.0 � 2.2 22.7 � 2.5 23.4 � 3.7 9.1 � 0.5 6.8 � 2.750 6.06 40.9 � 0.4 51.4 � 0.9 31.8 � 3.6 14.7 � 2.0 13.7 � 3.275 3.03 63.4 � 1.6 75.8 � 1.8 61.0 � 1.1 29.1 � 2.5 25.5 � 2.0

a Model nomenclature: RW, reconstituted whey; first number reflects dry matter (7, 14 or 21%, w/w), second number gives percentage of salt addition (0, 1, 2 or 3%, w/w).b CD, conductivity decrease.c TSR, total salt removal.

L. Diblíková et al. / International Dairy Journal 31 (2013) 29e33 33

membrane fouling as it is sorbed in the membrane stack, especiallyin presence of magnesium (Bazinet & Araya-Farias, 2005; Blehaet al., 1992; Casademont et al., 2007).

In all model solutions the total salt content decreased by 90e99%. The concentration of the fastest removed potassium and so-dium ions disposed exponentially with ED time in the range 83.0e100.0%. Calcium andmagnesium salts content decreased linearly by61e96%. The decline of the two nutritionally most relevant cationsconcentration in model solutions is demonstrated on Fig. 3. The Ca/Na ratio should be as high as possible to reduce dietary NaCl intake;this is especially important in infant nutrition (Andrés, Riera, &Alvarez, 1994).

As follows from Table 4, no significant differences were observedbetween fresh and reconstituted whey. However, dried whey pow-ders can differ substantially in composition or technological prop-erties from fresh whey (Jelen, 2002). Thus, their behaviour duringdemineralisation may be affected.

Increasing dry matter had no relevant impact on the final por-tion of individual ions eliminated. Terminal concentrations rose inthe same multiples as initial values. As the ED time was prolongedalmost 3 times, no operating difficulties were observed due tomembrane fouling or extensive protein precipitation.

The higher the sodium content in salted whey, the more effi-cient total salt removal because of greater driving force of theprocess and longer time. In the diluate with 3% (w/w) NaCl, con-ductivity was about 9 times higher and the sodium content 30times higher than in fresh whey. Despite this, the similar finalconcentration was reached after ED as in other final products.

4. Conclusions

The results showed that ED can be used for effective mineralsalts removal even from highly salted and concentrated whey so-lutions. The total salt content decreased in all model solutions by atleast 90% within 2 h, while no operating difficulties were observed.The concentrations of monovalent cations decreased exponentiallywith ED time by 83e100%, divalent ions were eliminated more orless linearly in the range of 61e96%. The difference betweenmigration of monovalent and divalent ions can be considered aspositive from the nutritional point of view as the decrease of so-dium content is desirable in human nutrition. This effect will behighlighted namely for salty whey and at partial demineralisation,e.g., 70%. ED of concentrated whey is favourable, because manycheese plants use reverse osmosis or evaporation to reduce trans-portation costs. The application possibilities in dairy industry arethus extended. Moreover, the stricter legislative requirements toeffluent quality can be reached easily even in Cheddar or blue-veined cheese production.

Increasing volumes of whey production represent a real prob-lem with process waste water elimination. Therefore, our furtherresearch will be focused on reducing water consumption duringwhey desalination and increasing salt concentration in concentrate.

Acknowledgements

Financial Support from Specific University Research (MSMT no.21/2011) and from the Ministry of Industry and Trade of CzechRepublic (MPO FR-TI1/470) is acknowledged.

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