cottage cheese whey ultrafiltrate produced by hollow fiber ultrafiltration,

Cot tage Cheese W h e y U l t r a f i l t r a t e Produced by H o l l o w

F iber U l t r a f i l t r a t i o n ~ ,2

J. T. BAKEL, H. A. MORRIS, S. H. RICHERT 3 , and C. V. MORR 4

Department of Food Science and Nutri t ion University of Minnesota

St. Paul 55108

ABSTRACT

The composit ion and volume of ultrafiltrate produced by hollow fiber ultrafiltration of cottage cheese whey with the Bio-Rad Bio-Fiber 50 Miniplant were studied and fi t ted to models. Tempera- ture, pH, and protein concentration of the feed cheese whey, the flow rate of the feed cheese whey through the Miniplant, and the pressure differential across the membranes were the independent variables in the model fitting. Feed whey temperature and pressure differential across the membranes were the most significant variables affecting the volume of ultrafil trate produced. Surface plots of response were generated.

INTRODUCTION

The problem of utilization of cheese whey has been approached from several perspectives. One such perspective has been the use of membranes to concentrate whey or to separate whey constituents. The two main membrane systems are reverse osmosis (6, 7, 9) and ultrafil tration (4, 5, 8). The Bio-Rad Bio-Fiber Miniplant is an uhrafi l t rat ion device utilizing cellulose formed into small hollow fibers as its membranes (2). The molecular weight cutoff of the cellulose membranes is approximately 10,000. The device consists of a large number of hollow fibers, each 20 cm in length and 180 /Ira internal diameter, having a total surface

Received March 3, 1975. Scientific Journal Series Paper No. 9013, Minne-

sota Agricultural Experiment Station, St. Paul 55108. 2 This work was taken from a thesis submitted by

J. T. Bakel to the faculty of the Graduate School of the University of Minnesota in partial fulfillment of the requirements for the degree of Master of Science.

3Massey University, Palmerston North, New Zea- land.

4 Ralston Purina Company, St. Louis, MO 55108.

area of about 15,000 cm 2. This configuration provides a high ratio of surface area to volume with respect to other ultrafi l tration units. The flow through the fibers is laminar in nature. This paper reports results of an experiment characterizing the response of the device to varying processing conditions, concentrating on the response of ultrafil trate flux across the membranes.

EXPERIMENTAL PROCEDURE

The experimental apparatus consisted of a pressurized reservoir, peristaltic pump, pressure and flow rate monitors, constant temperature water bath, the hollow fiber device, a syringe to return the ultrafiltrate to the system and to control pressure, and interconnecting plastic tubing. The pH, temperature, and protein concentration of the feed cottage cheese whey, the pressure differential across the membranes, and the rate of flow of the cheese whey through the device were controlled as independent variables. Table 1 lists the parameters and levels in the experiment. The quanti ty of ultrafiltrate produced per 3-min interval, and the phosphorus, ash, lactose, and nonprotein nitrogen contents of the ultrafihrate as percentages of the feed whey concentrations of those components, were determined as dependent variables.

Appropriate combinations of five independent variables, each at five different levels, shown in Table 1, were studied. A half-replicate central composite experimental design, des- cribed by Cochran and Cox (3), was used to estimate the regression coefficients of the experimental models. The models were 21-term equations of the type: Y = B0 + BIX1 + B2X2 + B3X3 + B4X4 + B5X5 + B l l X I X 1 + . . . + B45X4X5, where Y is the measured response, BO is a constant, B1 is the numerical coefficient for X1, B l l is the coefficient for the quadratic term of X1, B45 is the coefficient for the X4, X5 interaction, etc.

Experiments were designed to allow corn-

1794

HOLLOW FIBE R ULTRAFILTRATION 1795

TABLE 1. Parameters in the five factor experimental design.

Parameter Coded level

-2 -1 0 +I +2

x1 pH 4.0 X2 Pressure differential (mm Hg) 300 X3 Temperature (C) 30 X4 Protein concentration (X normal cone.) 1 X5 Flow rate of whey through device (ml/min) 100

4.5 5.0 5.5 6.0 395 490 585 680

35 40 45 50 2 3 4 5

275 450 625 800

purer analysis and model fitting by the UMST 500 statistical program of the University of Minnesota Computer Center (1). Thirty-two processing trials were performed with data collection for each dependent parameter at each trial. The trials included half-replicate 5 × 5 factorial design of +1 and - 1 (16 trials), 10 points outside the cubic surfaces to determine curvature (10 trials), and 6 replicate center points to estimate experimental error (6 trials). The order of the trials was randomized.

Cottage cheese whey was obtained from Minnesota Milk Company, St. Paul, and was separated twice in a Westphalia Milk Separator to remove residual fat and curd. Cheese whey was concentrated in a Calgon-Havens ultrafiltration unit to a protein concentration greater than that required for experimental trials and was diluted appropriately with ultrafiltrate. Feed whey pH was adjusted by appropriate addition of HC1 or NaOH.

X D z _

LL \

r~ J__J 41 ¸ LL

40

43-

4 2 -

\

0 G 12 18 24 3O 36 42

MINUTES

FIG. 1. Profile of ultrafihrate flux across the membranes in consecutive 3-min intervals during a wpical experimental trial.

Data on ultrafiltrate flux rate were obtained from multiple trials at each condition dictated by the experimental design. Ultrafihrate was collected in 15 consecutive 3-min intervals. After the volume of ultrafiltrate forced through the membrane was determined, that uhrafiltrate was returned to the system to maintain the system near steady state conditions. Fig. 1 shows the usual behavior of ultrafihrate flux rate during the 15 collection periods for all experimental conditions. The uhrafihrate flux rose to a "plateau" from which it began to decline after about 24 min, probably due to the development of solute polarization of protein, lactose, and possibly other constituents. The volume at the "plateau" was taken as the flux rate through the membrane for that trial. After each trial, the device was rinsed with water and back-flushed to remove polarized solutes. After each set of trials, the membranes were washed with enzyme detergent and stored in 1.5% formaldehyde.

RESULTS A N D DISCUSSION

Table 2 summarizes the models for the dependent variables. The square of the multiple correlation coefficient, R 2 , indicates the pro- portion of the experimental variability for which the model accounts. The small R 2 of the models of uhrafihrate lactose and ash content indicates that the models are not useful in the prediction of lactose and ash contents in the uhrafiltrate. The models of nonprotein nitrogen and phosphorus content are more useful, large R 2 values. The latter models account for large proportions of the experimental variability.

The equation for uhrafiltrate formation is the most important equation studied since the rate of protein concentration depends on the rate of uhrafiltrate formation and removal.

Journal of Dairy Science Vol. 58, No. 12

1796 BAKEL ET AL.

TABLE 2. The square of the multiple correlation coefficient, constants, and coefficients for linear model and quadratic models of dependent variables studied. BO is a constant, B1 is the numerical coefficient for X1, B l l is the coefficient for the quadratic term of X1, B45 is the coefficient for the X4, X5 interaction, etc.

Ultrafil- Ultrafil- Nonprotein trate flux trate flux Phosphorus Lactose Ash nitrogen

R 2 .780 .834 .805 .502 .549 .873 BO 30.27 29.43 92.22 94.48 93.70 63.85 B1 .281 .281 -.343 1.045 -.389 .115 B2 6.65* 6.65* -.094 .183 -.400 .312 B3 2.89* 2.89* -1.128" .592 -.124 .217 B4 -.744 -.744 -.557 -.351 -.188 4.030* B5 -.906 -.906 -.027 -.900 .722 .330 B l l .553 -1.980" 1.036 .342 -.042 B22 -.211 .284 -.671 -.623 -.558 B33 .159 1.415 -.882 .485 -.478 B44 .434 .356 -.652 -.472 -1.179 B55 .184 .068 .561 .065 -.449 B12 .996 .008 -1.144 -.383 -2.491" B13 -.622 -.801 .167 -.394 1.287 B14 .272 .676 1.561 1.256 -.508 B15 .441 -.235 -.292 -.161 -.816 B23 .766 -.561 1.366 1.706 -.072 B24 -.078 1.026 .494 .406 1.538 B25 -.759 1.085 .404 1.297 -2.574* B34 .234 .108 1.314 -1.361 2.483* B35 .803 1.106 .588 1.552 4.021" B45 .009 -1.344 -.044 -.899 .181

*P<.05.

Table 2 shows b o t h l inear and quadra t i c models. The pressure d i f fe ren t ia l and t e m p e r a t u r e t e rms are s ta t i s t ica l ly s igni f icant in b o t h models, s u p p o r t i n g the i m p o r t a n c e of these fac tors in d e t e r m i n i n g t he u l t ra f i l t r a te f lux ra te across t he m e m b r a n e s . These f indings agree wi th o t h e r s tudies of m e m b r a n e c o n c e n t r a t i o n (4, 9).

Tab le 3 is the analysis o f var iance for the quadra t ic m o d e l of u l t r a f i l t r a t e flux. T he second order t e r m s are nons ign i f i can t while the f irst order t e r m s are h ighly s ignif icant . This shou ld r e c o m m e n d the l inear mode l as shou ld

TABLE 3. Analysis of variance for the quadratic ultrafiltrate flux model.

Sums of Source df squares

First order terms 5 1238.34 Second order terms 15 149.83 Lack of fit 6 113.62 Experimental error 5 54.77 Total 31 1556.56

the l inear mode l ' s s implic i ty . With these mode l s and t he help of a com-

puter , surface plots of response can be gener- a ted fair ly easily. Fig. 2 shows the p lo t der ived f rom the l inear mode l , wi th p r o t e i n concen t r a - t ion, f low rate, a n d pH c o n s t a n t he ld a t levels ind ica ted . T h e l ines c o r r e s p o n d to ca lcu la ted vo lumes of u l t r a f i l t r a te fo rced t h r o u g h t he m e m b r a n e in 3-rain periods. By vary ing pressure and t e m p e r a t u r e wi th in the levels o f t he expe r imen t , changes of over 30 ml of ul t raf i l - t ra te cou ld be achieved theore t ica l ly .

In Fig. 3, in which pressure, t e m p e r a t u r e , and pH were c o n s t a n t , a change of on ly 6 to 7 ml theore t i ca l ly cou ld be a t t a i n e d by vary ing p ro t e in c o n c e n t r a t i o n and f low rate. This is an ind ica t ion of the smal ler coef f ic ien ts for the la t ter two t e rms in the l inear mode l for pressure and t empera tu re .

Fig. 4 shows a p lo t whe re in t empe ra tu r e , p ro t e in c o n c e n t r a t i o n , and f low ra te are con- s tant . I t indicates t h a t chang ing pH whi le ho ld ing pressure c o n s t a n t has on ly negligible effects on u l t r a f i l t r a te flux. This, too , is a m a n i f e s t a t i o n of the small pH coef f ic ien t in t he


HOLLOW FIBER ULTRAFILTRATION 1797

50

eo 45

=- Iz: =)

40 n- W O.

W 35

50

15 \ 500 395 490

P R E S S U R E ,

45 \

35

58,5 680

mm Hg

FIG. 2. Surface response plot derived from linear uhrafiltrate flux model. Calculated ultrafiltrate volume forced through the membranes during 3-rain intervals (ml/3 min) under constant conditions of protein concentration (4 × normal concentration), pH of the feed cheese whey (5.5), and flow rate of the feed cheese whey through the device (625 ml/min).

linear model . Bio-Rad Bio-Fiber 50 Miniplant membranes

tended to rupture when consis tent ly exposed to

.ooL \ 37,

° t \ \ 625

I,IJ 450 4 0

O. Z75 42 % I.I.

100 IX 2X 5X 4X 5X

PROTEIN CONCENTRATION

FIG. 3. Surface response plot derived from linear model. Calculated ultrafihrate volume forced through the membranes during 3-rain intervals (ml/3 min) under constant conditions of temperature (45 C), pressure differential across the membranes (585 mm Hg), and pH of the feed cheese whey (5.5).

680

3:: 585

E E

d ~ 490 03 or; I.IJ IZ: a.

395

- - 4 0 - - -

2 0 -

30o4.0 415 510 515 eo

pH

FIG. 4. Surface response plot derived from linear model. Calculated uhrafihrate volume forced through the membranes during 3-rain intervals (ml/3 rain) under constant conditions of temperature (45 C), protein concentration (4 × normal concentration), flow rate of feed cheese whey through the device (625 ml/min).

pressure differentials across the membranes of more than 620 m m Hg. This t endency makes the device impractical for commerc ia l cheese whey processing. However , the device can be useful for laboratory-scale exper iments with water-protein systems.

These models should be used only as qualita- tive guides for designing exper iments uti l izing the Bio-Rad Bio-Fiber 50 Miniplant with water-protein systems. Varia t ion among individual membrane specimens precludes the use o f these models as quant i ta t ive guides. Any applicat ion of these models to similar systems under condi t ions beyond the l imits of these experiments would lead to serious reduc t ion of the applicabil i ty of the models .

ACKNOWLEDGMENTS

The authors acknowledge the assistance o f W. M. Breene and G. A. Reineccius in the preparat ion of this manuscr ip t and thank S. E. Fienberg for his statistical assistance.

REFERENCES

1 Anderson, D., and M. Frisch. 1971. UMST computer programs manual. University of Minnesota, Minneapolis.

2 Bio-Rad Laboratories. 1972. The new hollow fiber


1798 BAKEL ET AL.

technique for desalting, concentrating, fraction- ating. Bio-Rad Laboratories Tech. Bull. 1004.

3 Cochran, W. G., and C. M. Cox. 1957. Experimen- tal designs. J ohn Wiley and Sons, New York, NY.

4 Fenton-May, R. I., C. G. Hill, and C. H. Around- son. 1971. Use of ultrafiltration/reverse osmosis systems for the concentration and fractionation of whey. J. Food Sci. 36:14.

5 Madsen, R. F. 1967. Ultrafiltrierung und umge- kehrte Osmose. Dtsch Milchwirtsch. 22:727.

6 Marshall, P. G., W. L. Dunkley, and E. Lowe. 1968.

Fractionation and concentration of cheese whey by reverse osmosis. Food Technol. 22:969.

7 McDonough, F. E., and W. A. Mattingly. 1970. Pilot plant concentration of cheese whey by reverse osmosis. Food Technol. 24:194.

8 McDonough, F. E., W. A. Mattingly, and J. H. Vestal. 1971. Protein concentrate froln cheese whey by ultrafiltration. J. Dairy Sci. 54:1406.

9 Peri, C., and W. C. Dunkley. 1971. Reverse osmosis of cottage cheese whey. 1. Influence of composi- tion of the feed. J. Food Sci. 36:25.


cottage cheese whey ultrafiltrate produced by hollow fiber ultrafiltration,

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