Combined Effects of Temperature, Acidification, and Diafiltration on Composition of Skim Milk Retentate and Permeate

Combined Effects of Temperature, Acidification, and Diafiltration on Composition of Skim Milk Retentate and Permeate

Combined Effects of Temperature, Acidification, and Diafiltration on Composition of Skim Milk Retentate and Permeate DANIEL ST-GELAIS,' SYLVIE HACHE, ...

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Combined Effects of Temperature, Acidification, and Diafiltration on Composition of Skim Milk Retentate and Permeate DANIEL ST-GELAIS,' SYLVIE HACHE, and MICHEL GROS-LOUIS Agriculture Canada Food Research and Development Centre S I 0 Casavant Boulevard West St-Hyadnthe, PQ. Canada J2S 8E3 ABSTRACT

INTRODUCTION

Commercial pasteurized skim milk was concentrated five times by UF with a Romicon membrane of .56 m2 having a molecular weight cutoff of 50,000 Da Ultrafiltration was conducted under various pH and temperature conditions and could be followed by a diafiitration step. Skim milk ultrafiltered at 50'C was used for control. For each UF treatment, the composition and buffer capacity of the five times retentate and the permeation flux during concentration were determined. The fiial composition of the retentate was different for each UF treatment. Retentate obtained after diafiltration at 4°C and pH 5.3 had the highest protein content and the lowest ash. Under these conditions, 78.3% of the Ca, 93.9% of the P, 75% of the Mg, and 95.3% of the K were removed from skim milk compared with 17.5% of the Ca, 45.4% of the P, 60.4% of the Mg,and 79.1% of the K for the control retentate. The removal of these minerals lowered the buffer index from .E1 for the control retentate to .063 for the retentate after treatment. Permeation flux was affected by temperature and acidification. These retentates with different buffering capacities could be dried and used to standardize or to enrich milk used for cheese making. (Key words: acidification, buffer capacity, retentate, temperature)

The use of UF to separate and to concentrate milk constituents is widely recognized and can be applied to manufacture various cultured dairy products. Changes in chemical composition of skim milk occur during UF and have to be considered (19). Minerals associated with casein are concentrated during UF and increase buffering capacity of retentate (4, 23). Minerals can contribute to more than 35% of the buffering capacity in the retentate concentrated 5 times (x) (23). The high mineral content and buffering capacity of mi& retentate, compared with skim milk (5, 9, 15, 23), contribute to body, textural, and flavor defects of many hard cheeses (6, 16, 24). However, because minerals in milk are more soluble at low pH (4, 27), high buffer capacity of UF retentate can be overcome by reducing its mineral content by acidification of milk coupled with diafiltration (3, 4, 8, 12). Minerals in milk and retentate are also more soluble at low than at high temperatures (4,27, 28). Ultrafiltration and diafiltration at low temperatures could modify mineral content and buffering capacity of retentate. However, UF of milk at 4'C is rarely used because it is known that permeation flux decreases with low temperatures (14, lS), so available information on the effects of low temperature during UF and diafiltration of s k i m milk is limited. The objective of this study was to determine the combined effects of temperature, acidification, and diafiltration on chemical composition of 5x retentate and permeate and on buffering capacity of 5x retentate.

Abbreviation key: x = times.

MATERIALS AND METHODS

Preparatlon of Mllk

Received August 19, 1991. Accepted January 15, 1992. 'Corresponding author. 1992 J Dairy Sci 75:1167-1172

Each UF treatment consisted of 35 kg of pasteurized skim milk obtained from the 1167

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Laiterie Mont-St-Hilaire (St-Hyacinthe, PQ, Canada). Temperature and pH of the skim milk were adjusted before UF. Twenty-five kilograms of the prepared skim milk were concentrated 5x by UF. The control skim milk (sample T-50) was heated and kept at 50'C in a hot water double wall tank. Ultrafiltration was performed at 50'C. Skim milk sample T 4 was maintained at 4'C before and during UF. Skim milk sample T-A50, maintained at 4'C, was adjusted to pH 5.6 with concentrated hydrochloric acid The next day, pH was verified and corrected to 5.6, and UF was performed at 50'C. Skim milk sample T-A4 was adjusted to pH 5.3, and UF was performed at 4'C. Dalgleish and Law (1l ) did not observe a universal relation between the dissociation of minerals and casein from the micelles at different temperatures and pH. In this study, two pH were used at different temperatures because the dissociation of casein micelles at 4'C was maximum at pH 5.2 to 5.3 and for higher temperatures at pH 5.5 to 5.6 (10). To prepare diafiltration samples (T-50D, T4D, T-MOD, and T-A4D), UF retentates obtained previously (acidified or not, at 4 or 5 0 ' 0 were reconstituted with deionized water of the desired temperature (4 or 50'C) and concentrated 5x by UF. Treatments without diafiltration were repeated four times. Diafidtration treatments were performed in triplicate. UF Process

The UF system consisted of a double wall tank in which milk was kept at a constant temperature, a positive pump for recycling milk, a UF membrane (Romicon M O , 5 6 m2, Romicon Inc., Woburn, MA), and a container placed on a scale to collect and weigh the permeate. The milk was pumped through the membrane module, and the pressure was adjusted and controlled to 1.8 bar with a backpressure valve at the outlet. Permeate weight was monitored continuously to determine the weight reduction by 2-, 3-, 4-, and 5x concentration. Samples of permeate and retentate were taken at the membrane autlet and weighed in order to adjust the weight reduction. Chemical analyses were performed the same day as the UF process. As the concentration reached 5x, UF was stopped.For diafiltration, deionized water was added to the retenJournal of Dairy Science Vol. 7.5, No. 5, 1992

tate, and another UF was performed. After each run, the membrane was cleaned and sanitized according to the manufacturer's instructions. Chemical Analyses

Samples of skim milk, retentate, and permeate were analyzed for DM, total protein, fat, and ash. Dry matter was determined by the hot air oven method (1). Fat content was determined by the Mojonnier extraction procedure (2). Ash was determined by heating samples at 550'C overnight in a muffle furnace. Total protein was measured using the macroKjeldahl method. An N to protein conversion factor of 6.38 was applied. Lactose was determined by difference. All chemical analyses were performed in triplicate. Minerals (Ca, P, Mg, and K) were determined with an ICP Spectrometer (model 3510, Applied Research Laboratories, Sunland, CA). Minerals were extracted from samples by precipitating proteins with TCA solution. To 1 0 4 samples, 30 ml of pure water (Milli-Q Water System, Millipore, Milford, MA) and 10 ml of TCA (20%. wt/vol) were added, and the mixture was vortexed for 2 min. After 15 min, 1 ml of a 1OOO-ppm Cu solution (Anachemia, Mantreal, PQ, Canada) was added (internal standard). The volume was adjusted to 100 ml with pure water (final dilution was 1Ox for skim milk and permeate samples and 25x for retentate samples), and the samples were left overnight at room temperature for sediment to settle. The supernatant was filtered on .45-pm filters (Millipore), and 10 ml were used for analysis on the CP system. Analyses were done in triplicate extracts. Buffering Capacity

Buffer index of the 5x retentates were determined by titration according to the method described by Van Slyke (26) and Mistry and Kosikowski (15). Only the higher buffer index values between pH 4.8 and 5.2 were presented according to results obtained by Srilaorhl et al. (22, 23) and Mistry and Kosikowski (15). Permeatlon Flux

Permeation flux means were calculated according to formula of Cheryan (7): FM = FF +

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TABLE 1. Retentate buffer index (ABlApH) and composition of the different five-times retentates and permeates based on nonfat DM.

Retentates

UP

Permeates

Treatment AB/ApH DM

Protein

Ash

Lactose

T-50 T-4 T-A50 T-A4 T-SOD T-4D T-MOD T-A4D

70.2' 71.5' 69.1' 70.4' 83.3b 81.9b 88.1' 88.e

8.r 7.4' 6.2b 4.9 7.4' 5.4h 5.4bc 2.9

21.5' 21.1' 24.7' 24.7' 9.3h 12.7b 6.5' 9.1h

DM

Protein

Ash

Lactose

7.Sab 3.9h 4.5h 3.3' 9.6' 5.Ok 8 .Pb 6.1ah

6.8b 7.Zab 8Xab 9.gab 7.7ab 8.7ab ll.Sa 8.Yb

85.7'b 88.9' 86.7' 86.8' 82.7& 86.3' 80.2' 85.e

(96) .151' .1498 .12Sab .llSb .142' .lMb .lOZb 063'

22.6' 21.5' 20.6' 21.4' 16.4b 16.4b 17Ab 16.4b

6.3' 6.1' 6.1' 6.3' 2.0b 2.1b 1.3' 1.3c

4b*c7dDi€ferentsuperscript letters in the m e column indicate significant differences (P < .05).

higher (P < .05). The combined effects of acidification and diafiitration of the skim milk resulted in the highest concentration of proteins in the retentate (Table 1). Acidification of skim milk reduced significantly (P < .05) the Statistical Methods concentration of ash in 5x retentate. Ash conAnalysis of variance and least significant centration was significantly (P < .05) lower difference test were applied to determine sig- when diafiltration was performed at 4'C (T.4 nificant differences among treatment and vs. T 4 D and T-A4 vs. T-A4D); however, ash permeation flux means. Relationship between concentration reduction was not significant (P buffer index versus protein, ash lactose, and > .05) when diafiitration was conducted at minerals of the 5x retentates were examined 50°C (T-50 VS. T-50D and T-A50 VS. Tusing multiple regression analyses. These sta- MOD). Low temperature reduced sigmficantly tistical analyses were performed with the gen- (P < .05) the concentration of ash in retentate eral linear models procedure of SAS (20). only when it was combined with acidification or diafiitration. The effects of temperature, acidification, RESULTS AND DISCUSSION and diafjltration seemed to have the same inThe different prepared skim m i l k s were fluence on composition of the permeates, but concentrated to 5x by UF and by diditration. only some signrficant effects were observed During concentration, an increase in DM, pro- (Table 1). Dry matter was significantly (P < tein, fat, ash, and minerals and a decrease in .05) lower in permeate obtained by diafiltration lactose were measured in the retentate for all and especially with acidified skim milk. The eight UF treatments. Casein and fat were not permeate was signZicantly (P < .05) higher in detected in permeate, but a small increase in protein but significantly (P < .05) lower in other components was measured in all perme lactose only when diafiltration was performed ate. These observations were comparable with at 50°C. those presented by Premaratne and Cousin (19) Minerals in 5x retentate and permeate were and Srilaorkul et al. (23). However, the com- measured on a nonfat DM basis. Concentration position of retentates and permeates based on of Ca,P, Mg, and K and their amounts (pernonfat DM at 5x varied among UF treatments centage) removed from skim milk with perme(Table 1). ate are shown in Table 2.The overall recovery The concentrations of DM, ash, and lactose [(retentate + permeate)/skim milk] was excelwere significantly lower (P < .05) in retentate lent for all eight UF treatments (Ca = 96.6 f after diafilhation than after UF alone, whereas 4.7%, P = 99.1 f 5.9%. Mg = 97.8 f 6.1%, the concentration of protein was significantly and K = 102.5 f 7.1%). Temperature, acidifi-

.33(lF - FF), where FM, FF, and IF represent permeation flux means, final flux at 5x concentration, and initial flux, respectively.

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TABLE 2. Mineral composition of the different five-limes retentates and permeates based on nonfat DM. Permeates

UF

ca

Treatment Ca

RM%l P

T-50 T-4 T-A50 T-A4 T-50D T-4D T-MOD T-A4D

.47'

17.5' 26.6ab l.wb47.1' 1.46b 66.3d 1.03ab 31.9b .91ab 47SC 1.34b 54.3Cd 2 . 2 p 78.3=

P RM%

.82' 45.4' $7' 52.p .98& 62.5b 1.2@ 77.8' 1.lpbc 64.1b 1.48' 69.2b" 1.Bab" 69.gb" 1.41bc 93.9d

Ms h4g

Retentates

K

RM%

K

1.39 1.48' .1pb 69.4ab 1 . 5 p .21ab 72.@ 1.58' .28abc 67.1ab 1.13' .3Pb" 74Sb ].Ma .42k 76.3b 1.66' .51' 75.0b 2.60b

.15' 60.4' .Nab 5 9 . p

Mg

RM%

Ca

P

79.1ab 75.1' 80.9b 82.9b 94.3' 94.6' 95.e 95.3'

2.29'b 2.03b 1.43' .87d 2.67' 1.90b 1.44' .72*

1.10' .llab .92ab .14' .7OC .lob .ad .Bb 1.03' .12ab .74bc .lob .6Zcd .OSb .He .lob

K .39ab .57' .46'

.aab .14' .13' .14' .20k

~

qb,c*d*%ifferent superscript letters in the same column indicate signifcant differences ( P < 1 ~ =% Percentage removed from skim milk with permeate.

cation, and diafiitration had a significant (P < .05) influence on Ca and P in 5x retentate and permeate. Temperature did not afFect Mg and K concentrations. Retentate with a low mineral content could be obtained by diafiltration of acidified skim milk at 4'C (T-A4D). This UF treatment removed from skim milk with permeate 78.3% of the Ca, 93.9% of the P, 75.0% of the Mg, and 95.3% of the K, compared with 17.5% of the Ca, 45.4% of the P, 60.4% of the Mg, and 79.1% of the K for the control retentate (T-50) (Table 2). The effects of temperature, acidification, and diafiitration seemed synergetic. Low temperature and low pH displaced the equilibrium of minerals from the colloidal fraction toward the soluble fraction (4, 27). During UF, soluble minerals went through the UF membrane and accumulated in the permeate. The loss in minerals could also be observed by the concentration of ash (Table 1)The buffering capacity of skim milk increased during UF (15, 23). Depending on the UF treatment, different buffering capacities were obtained (Table 1). Temperature (50 and 4'C) did not influence significantly (P > .05) the buffering capacity of the retentates except when low temperature was combined with diafiltration (T-50D vs. T 4 D and T-MOD vs. TA4D). In those cases, the reduction of buffer index was significant (P .05). Buffer index dropped significantly (P c .05) when acidified skim milk was concentrated. However, buffer index reduction at 50°C (T-50 vs. T-A50) was not significant (P > .05). Diafiltration significantly (P < .05) affected buffering capacity of Journal of Dairy Science Vol. 75, No. 5 , 1992

.a).

retentate except when diafiltration was conducted at 50°C (T-50 vs. T-50D). At 5WC, only combined effects of acidification and diafiltration (T-MOD) reduced buffering capacity significantly (P < .05). Srilaorkul et al. (23) demonstrated that the contribution of proteins and milk salts to the buffer system intensity of 5x retentate was 63.5 and 36.5%, respectively. However, in all 5x retentates, concentration of protein on wet basis was adjusted to 15% during UF and diafiltration. The role of protein on buffering capacity was made uniform. Multiple regression analysis of buffer index (ABlApH) versus protein, ash, and lactose confirmed this fact. Only ash concentration had a significant effect (P .01). Among minerals, multiple regression analysis showed that only P and Ca concentrations were significant (P < .OOO1 and P < .01, respectively) for buffer index. The statistical analysis of the data indicated that the dependence of the buffer index is given by the following relation: AB/ApH = .0616 R2 = .660

+

.1342 P - .0239 Ca

where P = P based on nonfat DM (percentage), and Ca = Ca based on nonfat DM (percentage). The buffer index (Table 1) fluctuated in the same way as the minerals, especially P and Ca (Table 2), showing the strong influence minera l s have on the buffering capacity of the 5x retentates. The correlation coefficient was low,

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TABLE 3. Permeation flux for each UP treatment.

UP Treatment T-50 T-50D T-A50 T-MOD T-4D

T-4 T-A4D T-A4

Permeation flux’ (4m2 per h) m PM

IP

x

25.9 17.8 19.6 13.6 11.7 14.7 8.5 9.5

SE 10.0 .2 12.8 1.2 10.6 .7 11.3 1.1 10.4 .4 8.4 .4 7.3 .9 2.7 .4

SE 1.4 1.2

.9 1.3 .1 .8 .3 .1

X

SE 15.2’ .8 14.4ab .9 13.6ab .7 12.lh 1.0 10.8‘ .9 10.5‘ .8 7.6d .8 5.0d .7

“b,c.dDif€erent superscript letters in the same column indicate significant differences (P < .05). 1IF = Initial flux, PP = final flux, FM = flux mean = PP + [.33(IF - pp)].

but only four minerals were determined. Citrate and other minerals could affect buffer index of the 5x retentates and could modify the correlation coefficient. Alteration of UF parameters changed the concentration in minerals and the buffering capacity of retentates but also affected the permeation flux (Table 3). Low temperature caused a sigdicant (P < .05) reduction in permeation flux mean, which was also observed by Kapsimalis and Zall (14) and Pompei et al. (18). Acidification of skim milk decreased significantly (P < .05), especially the permeation flux mean when acidified skim milk was diafiitered at 4‘C. Diafiltration did not alter significantly (P > .05) the permeation flux mean; however, the UF membrane was not cleaned or sanitized between diafiltration and previous UF, and this could have affected permeation flux during diafiltration. Temperature and pH influence the salt system and the structure of casein micelles in milk (10, 11, 27). Temperature also influences the viscosity of retentate. In fact, viscosity of retentate is inversely proportional to temperature and directly proportional to protein concentration (21). Ultrafiltration of acidified skim milk at low temperature (4‘C) led to the dissociation of casein micelle and a solubility higher for the micellar minerals and caused an increase in viscosity. These effects led to membrane fouling because of adsorption and concentration polarization of milk components on membrane surfaces (12, 13, 17, 25) and reduced the permeation flux.

CONCLUSION

This study showed that mineral composition and buffering capacity of 5x skim milk retentate could be modified by adjusting the pH, the temperature, and the UF procedure (diafiltration or direct TJF). The 5x retentate differed in composition for each of the components according to the UF treatment received. Concentrations of proteins increased and minerals decreased with diafiltration, low temperature, and low pH. However, buffer index of the 5x retentates was related only to concentration of P and (2%Combined effects of temperature, acidification, and diafiltration affected permeation flux. These 5x retentates with different buffering capacities could be dried and used to standardize or to enrich milk used for cheese making. ACKNOWLEDGMENTS

The authors wish to thank Marco Lagimonihre, Jacinthe Larochelle, Elisabeth Gauthier, and Slobodan Levi for their technical assistance. They also thank Marie-Line Desjardin, Denis Roy, and Michel Britten, who reviewed this manuscript. This paper was issued as Food Research and Development Centre, Contribution Number 241. REFERENCES IAssociation of official Analytical Chemists. 1984. Official methods of analysis. 14th ed. AOAC, Wash-

in@&

Dc.

2Atherton, H. V., and J. A. Newlander. 1977. Test for Journal of Dairy Science Vol. 75, No. 5, 1992

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fat: Babcock, Gerber, and Mojonnier. Page 71 in Chemismy and testing of dairy products. 4th ed. AVI Publ. Co., Inc., Westport, CT. 3 Bastian, E. D., D. K. Cohge. and C. A. Emstrom. 1991. Ultrafiltration: partitioning of milk constituents into permeate and retentate. J. Dairy Sci. 742423. 4 Brule, G., and I. Fauquant. 1981. Mineral balance in skim milk and milk retentate: effect of physicochemical characteristicsof the aqueous phase. J. Dairy Res. 48:91. 5 Brule, G., J. L.Maubois, and J. Fauquaut. 1974. Etude de la teneur en 6lknents midram des produits obtenus lors de l'ultrafiltration du lait sur membrane. Lait 54600. 6 Casiraghi, E. M., C. Peri, and L. F'iazza. 1987. Effect of calcium equilibria on the rate of syneresis and on the firmness of curds obtained from milk Up retentates. Milchwissenschaft 42232. 7 C h e r y q M 1986. Rocess design. Wge 197 in Ultrafitration bandbook. Technonic Publ. Co., Inc., Lancaster, PA. 8 Covacevich, H. R.. and P.V. Kosikowski. 1977. Skim milk concentration for cheesemaking by alternative ultrafiltration procedures. J. Food Sci. 421359. 9Covacevich, H. R. and F. V. Kosikowski. 1979. Buffer, lactic fermentation, and rennet coagulation properties of skim milk retentates produced by ultrafiltration. J. Dairy Sci. 62204. 10 Dalgleish, D. G., and A.J.R. Law. 1988. pH-Wced dissociation of bovine casein micelles. I. Analysis of liberated caseins. J. Dairy Res. 55529. 11 Dal~leish,D. G.,and A.J.R. JAW. 1989. p H - L e d ~ d dissociation of bovine casein micelles. n. M solubilization and its relation to casein relase. J. Dairy Res. 56727. 12 Emstrom, C. A., B. 3. Sutherland, and G. W. Jamemn. 1980. Cheese base for processing. A high yield product from whole milk by ultrafiltration. J. Dairy Sci. 63228. 'jer. J. H.,T. Robbemen, T.van den Boom13 Hammaa~ gmd, and J. W.Grmninlc 1989. Fo~lingO f ultdiltration membranes. The role of protein adsorption and salt precipitation. J. Membr. Sci. 40.199. 14 Kapsimalis, D. J., and R R Zall. 1981. Ultrafiltratin of skimmilk at refrigerated temperatures.J. Dairy Sci. 64:1945. 15 Mistry. V. V., and F.V. Kosilrowski. 1984. Growth of

Journal of Dairy Science Vol. 75, No. 5, 1992

lactic acid bacteria in highly concentrated ultrafiite-d skim milk retentates. J. Dairy Sci. 68:2536. 16patel R. S., H.Reuter, and D. Prokopek. 1986. PIW duction of qua& by ultrafiltration. J. Soc.Dairy Techwl. 39:27. 17 Patocka, J., and P. Jelen. 1987. Calcium chelation and other pretreatments for flux improvement in ultrafiltration of cottage cheese whey. J. Food Sci. 52: 1241. 18 POmpei C., P. Reanbi, and C. Peri. 1973. Skim milk protein recovery and purification by ultrafiltration. Influence of temperaon permeation rate and retention. J. Food Sci. 38:867. 19Pmnaratne, R.J. and M. A. Cousin. 1991. changes in the chemical compositionduring ultrafiltration of skim milk. J. Dairy Sci. 74:788. 20SAS@ User's Guide: Statistics, Version 6 Edition. 1989. SAS Inst., Inc., C q , NC. 21 Setti, D., and C. Peri. 1976. Whey and skim milk ultrafiltration. 2. Parameters affecting permeation rate in skim milk ultratiitration. Milchwissenschaft 31:466. 22Srilaorkul, S., L. Ozimek, and M. E. Stiles. 1989. Growth and activity of Lactococcus lactis ssp. cremoris in ultrafiltned skim milk. I. Dairy Sci. 722435. 23Srilaorkul. S.,L. Ozimek, F. Wolfe, and 1. Dziuba. 1989. The effect of ultrafiitration on physicochemical properties of retentate. Can. Inst. Food Sci. Technol. 2256. 24 Sutherland, B. J., and G. W. Jameson. 1981. Composition of hard cheese manufactured by ultratiltration. Aust. J. Dairy Technol. 36:136. 25 Tong,P. S.,D. M.Barbano, and M. A. Rudan. 1988. Characterization of proteinaceous membrane foulants and flu.decline during the early stages of whole mik ultrafiltration. J. Dairy Sci. 71:604. 26 Van Slyke, D. D. 1922. On the measurement of buffer values and on the relationship of buffer value to the dissociation constant of the buffer and the concentration and reaction of the buffer solution. J. Biol. Chem. 52525. 27Visser, J., A. Minihan, P. Smits, S. B. Tjan, and I. Heertje. 1986. J3fects of pH aml temperatures on the milk salt system. Neth. Milk Dairy J. 40:351. 28znraW, J., Z. Smietana, J. Szpendowski, and W.Chojnowski. 1986. Influence de l'addition de sels de calcium et du chauffage sur les diverses formes de calcium dans le lait. Lait 66:421.