Chemical composition of camel skim milk concentrated by ultrafiltration

Inf. Dairy Journal 6 (1996) 141-152 Copyright @ 1996 Elsevier Science Limited Printed in Ireland. All rights reserved 0958-6946/96/%15.00+0.00 ELSEVIER

0958-6946(95)00063-l

Chemical Composition of Camel Skim Milk Concentrated by Ultrafiltration

Mohamed A. Mehaia Dairy Technology Laboratory, College of Agriculture and Veterinary Medicine, King Saud University-Qassim, Buriedah P.O. Box 1482, Saudi Arabia (Received 12 July 1995; accepted 9 October 1995)

ABSTRACT Camel skim milk was concentrated by ultrafiltration (UF) to volume concentration ratios (VCR) of 2,3,4 and 5. Gross composition and mineral contents of skim milk and retentates, as well as retention and recovery of components were studied. All fat, CN, WPN, 13-18% of NPN and about 1% of lactose were retained during UF of camel skim milk. Recovery of these components were 6.2, 17.3 for NPN, lactose and 100% for fat, WPN or CN, respectively. For all minerals, retention was increased by increasing the VCR. The retention of Zn, Fe, Cu, Ca, P, Mg, K and Na in the j-fold retentate were 99,99,99,98,91,86,37 and 32%, respectively. The corresponding values for recovery were 97, 96. 93, 87, 70, 60, 24 and 23%, respectively. Copyright 0 1996 Elsevier Science Limited

INTRODUCTION

Application of ultrafiltration (UF) in the dairy industry has been reviewed by several authors (Glover, 1985; Cheryan, 1986; Pal & Cheryan, 1987; El-Gazzar & Marth, 1991; Renner & Abd El-Salam, 1991). The use of UF to concentrate and separate cow milk constituents is widely recognized and could have far-reaching effects, especially for milk destined for cheese-making (Moubois and Mocquot, 1975; Zall, 1984; Kosikowski, 1986; Lelievre & Lawrence, 1988), production of low-sodium and low-lactose milk products (Kosikowski, 1979, 1983; Edelstein et al., 1983), and increased utilization of whey for human food (Renner & Abd ElSalam, 1991). During ultrafiltration of milk, non-protein nitrogen and soluble components, such as lactose, salts and some vitamins, pass through the membrane, whereas milk fat, proteins and colloidal salts are retained (Glover, 1971; Peri et al., 1973; Covacevich & Kosikowski, 1977; Green et al., 1984; Premaratne & Cousin, 1991; Bastian et al., 1991). However, the changes that 741

742

hf. A. Mehaia

occur in the chemical composition of milk during UF must be considered before retentates are used in the manufacture of various cultured dairy products (Premaratne & Cousin, 1991). Camel milk plays an important role in the human diet in many hot and arid countries. In Saudi Arabia, the camel population (Camelus dromedurius) is estimated to be about 600,000 (Chapman, 1991); most of their milk is consumed fresh (Mehaia et al., 1995). Recently, however, camel milk is gaining more popularity and several commercial farms are being established to supply fresh pasteurized milk to consumers. Moreover, a recent study by Mehaia (1993a, b) in Saudi Arabia, on the manufacture of cheese from camel milk showed that fresh soft white cheese with good acceptability could be made from low-fat camel milk with lactic cultures. Camel milk, owing to its different physco-chemical properties, probably will behave differently than cows’ milk during processing and product manufacture (Farah, 1993; Mehaia, 1993a, b, 1995). Although data in the chemical composition of cows’ milk concentrated by UF have been reported by several workers (Glover, 1971; Peri et al., 1973; Covacevich & Kosikowski, 1977; Green et al., 1984; Renner & Abd El-Salam, 1991; Premaratne & Cousin, 1991; Bastian et al., 1991), there is limited information on the chemical composition of camel milk concentration by UF except for the recent report of Mehaia (1994) on the rennet coagulation studies of UF-concentrated camel milk. However, as UF is increasingly being considered and applied in dairy processing, there is a growing need for compositional data for different kinds of milk, such as camel milk. The present investigation was undertaken to study changes in the concentrations of milk protein, fat, lactose, ash, total solids and minerals during concentration of camel skim milk to 2-, 3-, 4- and 5-fold by ultrafiltration.

MATERIALS

AND METHODS

Preparation of milk for ultrafiltration For each UF run, 15 kg of raw camel (Mujaheim) milk were obtained from King Saud University Farm, Buriedah, Saudi Arabia. The milk was warmed to 4145°C in a water bath and then skimmed, weighed, and pasteurized at 72°C for 20 s. Samples for chemical analyses were taken and refrigerated for subsequent analysis. The pasteurized skim milk was cooled to 50°C before UF. Ultrafdtration

process

The bench-scale UF system consisted of a feed tank for holding the milk, a Masterflex peristaltic pump (Cole-Parmer Instrument Co., Chicago, IL, USA) for recycling milk, two pressure gauges to monitor inlet and outlet pressures, a hollow fibre UF module with a polysulphone membrane of 30,000 molecular weight cut-off (MWCO) (Model UFP-30-C-4) obtained from A/G Technology, Needham, MA, USA, and a container to collect and measure the permeate. The UF process was started by pumping the milk at 50°C through the membrane module while maintaining inlet and outlet pressures of 137 and 35 kPa, respectively. Permeate volume was monitored continuously to determine reduction in milk volume to 2, 3, 4 and 5 volume concentration ratios (VCR).

Chemical composition of camel skim milk

143

At different VCR, retentate and permeate samples were taken and refrigerated for subsequent analysis. When the concentration reached 5 (VCR = 5), the UF system was stopped and the retentate stored at 4°C. After each run, the membrane module was cleaned and sanitized according to the manufacturer’s instructions and stored in a 5°C cooler. The experiment was repeated five times. Chemical analysis Skim milk, retentate and permeate samples were analysed for total solids, fat and ash according to procedures outlined in AOAC (1980). Lactose was determined by difference. Nitrogen was determined by the standard micro-Kjeldahl method (AOAC, 1980). A nitrogen conversion factor of 6.38 was used to calculate protein content. Milk samples were fractionated for total nitrogen (TN) and non-casein nitrogen (NCN) by the method of Rowland (1938) with the following modification. Retentate samples were diluted, before analysis, with distilled water to VCR = 1. Non-protein nitrogen (NPN) was determined in the supernatants produced by addition of 40 mL 15% trichloroacetic acid to 10 mL milk or diluted retentate, as outlined by Cerbulis and Farrell (1975). Nitrogen fractions were calculated as follows: protein nitrogen (PN) = TN - NPN, casein nitrogen (CN) = TN - NCN, and whey protein nitrogen (WPN) = NCN - NPN. For elemental (calcium, phosphorus, sodium, potassium, magnesium, zinc, copper, and iron) analysis, the ash was dissolved in 2% HCl; the amount of ash dissolved was adjusted to compensate for the increased concentration. The final diluted solution for calcium and magnesium determination contained 1% lanthanum chloride to overcome phosphate interference. All elements except phosphorus, were determined with an atomic absorption spectrophotometer Model 1lOOB (Perkin-Elmer Corp., Analytical Instruments, Norwalk, CT, USA). Phosphorus was determined spectrophotometrically using the procedure of Watanabe and Olson (1965). All chemicals were of reagent grade. All analyses of skim milk, retentate and permeate samples were performed in duplicate. Expression of results The volume concentration (1986) as follows: VCR =

ratio (VCR) was calculated as reported by Cheryan

Initial volume of milk Concentrate (retentate) volume

The concentration factor (CF) of a component Green et al. (1984), as follows: CF=

(1) was calculated as reported by

Concentration of a component in retentate Concentration of a component in the original milk

(2)

The percentage retention (Rt%) was calculated according to Bastian et al. (1991) as follows:

where Y = percentage of any component in retentate (r) or permeate (p).

M. A. Mehaia

744

Because the concentration of components in the final retentate is important for cheese-making, Bastian et al. (1991) defined a new term, percentage recovery (Rc%). This term is similar to percentage retention reported by Glover (1971) and is shown in Equation [4]: Rc% =

kg component in retentate x 100 kg component in original milk

(4)

RESULTS AND DISCUSSION Gross composition Gross compositional changes in the camel skim milk concentrated by UF are shown in Table 1. In Fig. 1, the changes in the composition of some constituents of skim milk during UF are expressed as the increase or decrease of the CF of the individual components as a function of the VCR. As the VCR of skim milk was increased by 2-, 3-, 4- and 5-fold, protein and fat concentrations increased proportionally. The fat content of skim milk increased from an initial average of 0.28 to 1.41 g/100 g in the 5-fold retentate, reflecting total (100%) retention (Table 2). The protein content increased from an initial value of 3.22 to 15.06 g/ 100 g in the 5-VCR retentate, indicating a 4-7-fold increase in concentration and 98% retention (Table 2). Total solids and ash contents increased from initial values of 8.64 and 0.69 g/100 g in skim milk to 21.94 and 1.65 g/lOOg in the 5VCR retentate, respectively. These increases were proportional to the CF of the retentates, but to a lesser degree, indicating the loss of small molecular weight components such as lactose, soluble salts, vitamins and NPN. These observations were comparable with those reported for camel skim milk by Mehaia (1994) and for cows’ milk by Ernstrom et al. (1980), Green et al. (1984), Srilaorkul et al. (1989), Premaratne & Cousin (1991) and St-Gelais et al. (1992). However, the lactose content of camel skim milk decreased from an initial value of 4.45 to 3.85 g/lOOg in the 5-VCR retentate. The CF of lactose was reduced from an initial 1.0 to 0.87 in the 5-VCR retentate (Fig. 1); because lactose is present in a

Gross Composition

TABLE 1 (Mean f Standard Deviation)’ of Camel Skim Milk and Retentate Concentrated by UF (g/100 g).

VCR*

Fat

Protein3

Lactose

1 2 3 4 5

0.28ztO.08 0.58f0.10 0.86f0.12 1.12f0.10 1.41+0.12

3.22f0.09 6.25&O.15 9.14f0.10 12.06f0.11 15.06f0.12

4.45f0.07 4.28fO. 11 4.02&O. 11 3.95f0.08 3.85f0.10

’ Means of duplicate analyses on each of five runs. * VCR = Volume concentration ratio. 3 Protein = Total nitrogen x 6.38.

Ash

0.69f0.05 0.87f0.04 1.19f0.09 1.441!10.08 1.69fO. 10

Total solids

8.64f0.31 11.98+0.37 15.23f0.41 18.58f0.37 21.94f0.48

745

Chemical composition of camel skim milk

BTotal Solids

1

2

3

4

5

6

Volume Concentration Ratio (VCR) Fig. 1. Concentration

free state

in milk

factor of some constituents of camel skim milk as a function volume concentration ratio.

and

since

it has a molecular

weight

much

lower

than

of

the

MWCO of the UF membrane, it permeates freely. The decrease in its concentration closely followed the increase in VCR. Similar observations were made with cows’ skim milk (Premaratne & Cousin, 1991; St-Gelais er al., 1992). In fact, the percent lactose in the aqueous phase remained constant during UF. Brule et al. (1974) reported that the concentration of milk by UF does not change the aqueous phase and the concentration of its components. The percent retention and recovery of fat, lactose and protein fractions in camel skim milks during UF are presented in Table 2. Retention and recovery of fat and protein nitrogen were 100% in all milk retentates. This agrees with reported values for cows’ milk (Glover, 1971; Bundgaard et al., 1972; Green et al., 1984; Fischbach-Greene & Potter, 1986). The percent retention of lactose was 0.24.9%. This is lower than values reported for UF of cows’ skim milk using a different equation, which does not rely on concentration factor, to calculate percent retention (Peri et al., 1973; Covacevich & Kosikowski, 1977), but it agrees with the results of Green et al. (1984) and Bastian et al. (1991) who used a similar equation to that we have used here (Bastian’s equation). The recovery of lactose was reduced from 48% in the 2-VCR retentate to 17.3% in the 5-VCR retentate. Reported values of lactose recovery for 5-fold retentate cows’ milk were 12% for whole milk (Bastian et al., 1991) and 22% (Pompei et al., 1973) or 16% (Premaratne & Cousin, 1991) for skim milk. Nitrogen distribution Changes in the nitrogen distribution in concentrated camel skim milk during UF are presented in Table 3, and Fig. 2 shows typical changes in nitrogen fractions (as % of TN) of camel skim milk during UF processing. During UF, retention of TN increased from 96.5% in 2-VCR retentate to 98% in the 5-VCR retentate, whereas the recovery decreased from 97 to 93.5%. The corresponding figures for

746

M. A. Mehaia TABLE 2 Levels of Retention and Recovery (%) of Fat, Lactose and Protein Fractions in Camel Skim Milk Concentrated by UF’

VCR3

Component2 Fat: Retention Lactose: Retention TN: Retention

2

3

4

5

100 103

100 102

100 100

100 loo

0.9 48

0.2 30.1

0.9 22.2

0.4 17.3

96.5 97

97 95

97.5 93.6

98 93.5

PN: Retention Recovery

100 102

100 102

100 102

100 102

CN: Retention Recovery

100 102

100 102

100 102

100 102

NPN: Retention Recovery WPN: Retention Recovery

13 11.2

100 105

14 8

100 103

16 6.9

100 102

18 6.2

100 103

‘Means of duplicate analyses on each of five runs (calculated from mean values in Tables 1 and 3). %N = Total nitrogen, PN = protein nitrogen, CN = casein nitrogen, NPN = non-protein nitrogen, WF’N = whey protein nitrogen. 3VCR = Volume concentration ratio.

NPN were 13 to 18 for percentage retention and 11.2 to 6.2 for percentage recovery. Similar observations were reported for whole cow milk by Bastian et al. (1991). Glover (1971) and Pompei et al. (1973) reported 96.4 and 89% TN recovery (calculated from their data using Equation [4]) for 1.6- and 5-fold retentate of cow skim milk, respectively. Casein and whey protein nitrogen were completely retained in the concentrates, i.e. retention was 100% (Table 2). The low molecular weight components, comprising the NPN fraction, were not concentrated at all, and their retention was only 13-18%. Pompei et al. (1973) reported that the retention of casein, whey protein and NPN were 100, 98 and 59%, respectively, for a 5-fold retentate of cows’ skim milk (calculated from their data using Equation 131).Both casein and whey proteins related to total nitrogen

Chemical composition of camel skim milk

747

TABLE 3 Nitrogen Distribution’ in Camel Skim Milk and Retentate Concentrated (Mean f Standard Deviation, mg/lOO g)’

by UF

VCR3

TN

PN

NPN

CN

WPN

1 2 3 4 5

505f17 980f23 1432rt18 189Ok19 2355f25

447614 920f19 1372f15 1831f14 2297f22

58f3 60f4 60f4 59f3 59f5

347f12 708f12 1062ztl3 1420f16 1781f16

lOOf 212f7 310f5 411f4 516f6

‘TN = Total nitrogen, PN = protein nitrogen, NPN = non-protein CN = casein nitrogen, WPN = whey protein nitrogen. ‘Means of duplicate analyses on each of five runs. 3VCR = Volume concentration ratio.

nitrogen,

increased from 68.7 and 19.8% in skim milk to 75.6 and 21.9% in 5-VCR retentate, respectively. NPN content decreased from 11.5 to 2.5% (Fig. 2). A similar observation was reported for cows’ whole milk by Green et al. (1984). Barbano et al. (1988), Bastian et al. (1991), Pompei et al. (1973) and Peri et al.

(1973) showed that less than 1% of bovine whey proteins passed through 10,000 and 20,000 MWCO membranes using Dorr-Oliver plate and frame and Abcor spiral wound membrane models, while Premaratne & Cousin (1991) reported 99% retention and 100% recovery of bovine total proteins using hollow fibre membranes with 30,000 MWCO. Our data for camel skim milk, however, showed 100% retention of whey proteins; this could be due to the fact that camel milk whey proteins exhibit comparatively large differences from the proteins of the other species (Beg et al., 1985, 1986, 1987; Farah, 1986). Passage of protein

i$

20f1

2

3

4

5

6

Volume Concentration Ratio (VCR) Fig. 2. Typical changes in nitrogen fractions (as % of TN) of camel skim milk during ultrafiltration.

748

M. A. Mehaia TABLE 4

Changes in the Concentration

of Elements in Camel Skim Milk during UF (mg/lOO g)’

VCR2

Ca

P

Na

K

A4g

Zn

cl4

Fe

1 2 3 4 5

110 195 286 370 480

86 135 186 240 300

70 73 75 77 80

140 152 160 167 170

13 18 24 31 39

0.6 1.1 1.5 2.1 2.9

0.14 0.25 0.36 0.49 0.65

0.20 0.36 0.50 0.70 0.96

‘Means of duplicate analyses on each of five runs. 2VCR = Volume concentration ratio. through a UF membrane pore could be dependent on several factors, such as: (a) molecular weight, charge, hydrodynamic size and shape, and hydrophobic or hydrophilic character of molecule; (b) type of membrane materials; (c) membrane configuration; (d) presence of other solutes; and (e) absorption of solutes by the membrane (Cheryan, 1986).

Concentration of minerals Milk constituents, such as minerals, that are smaller than the membrane pores and partly associated with proteins and fat demonstrate increased proportions in the retentate with an increasing degree of concentration (Glover, 1971; Green et al., 1984). The elements analysed in this study included major (i.e. Ca, P, Na, K and Mg) and trace elements (i.e. Zn, Cu and Fe). Changes in the concentrations of these minerals in camel skim milk during UF are shown in Table 4 and the typical concentration factors of the above minerals in skim milk as a function of VCR are shown in Fig. 3. The original concentrations of these elements in camel milk were 5 B 3 SE w s 5 z k z ‘= 6 b 2 s

4

3 2 1 0 1

2

3 Volume Concentration

Fig. 3. Concentration

4

5

6

Ratio (VCR)

factor of some elements in camel skim milk as a function of vohune concentration ratio.

749

Chemical composition of camel skim milk

1

+Ca

100

+Zn *cu

80

-+Fe *P

60

+Mg +-K

40

t-Na

20 1

2

3

Volume Concentration Fig. 4. Typical percentage

retention

4

5

6

Ratio (VCR)

of some elements in camel skim milk during ultrafiltration.

similar to those reported in the literature (Sawaya et al., 1984; Abu-Lehia, 1987; Mehaia et al., 1995). During the concentration of skim milk to 5-VCR, the concentration of Ca, P, Na, K, Mg, Zn, Cu and Fe in skim milk increased by 4.4-, 3.5, l.l-, 1.2-, 3.0-, 4.8-, 4.6- and 4.8-fold, respectively. Mehaia (1994) reported a 4.1-fold higher Ca content in a 4.3-fold retentate of camel skim milk. Similar observations were reported for Ca, Mg, Zn, Fe and Cu in a 5-fold retentate of cows’ skim milk (Premaratne & Cousin, 1991). Pompei et al. (1973) observed a 4.3-, 2.8-, 2.2- and 1.05-fold higher concentration of Ca, P, Mg and K, respectively, in a 5-fold retentate of cows’ skim milk. Green et al. (1984) reported increases in the concentration of Zn, Fe and Cu proportional to, but less than CF for proteins and fat because a fraction of these minerals is soluble and is lost in the permeate. Typical changes in percent retention of minerals in camel skim milk during UF processing are shown in Fig. 4, while the percent recovery of these minerals in camel milk concentrated by UF to 5-VCR is shown in Fig. 5. For all minerals, retention increased with increasing VCR. Ca, Zn, Cu and Fe had the highest retention, while Na and K had the lowest values. This agrees with results reported for cows’ milk UF by Peri et al. (1973), Covacevich & Kosikowski (1977) Fischbach-Greene & Potter (1986), Bastian et al. (1991) and Premaratne & Cousin (1991). Retention of Zn, Fe, Cu, Ca, P, Mg, K and Na in the 5-fold retentate were 99, 99, 99, 98, 91, 86, 37 and 32%, respectively (Fig. 4). The corresponding values for recovery were 97, 96, 93, 87, 70, 60, 24 and 23%, respectively (Fig. 5). Recovery values for Zn, Fe, Cu, Ca, P, Mg, K and Na were very close to those obtained from the 5-fold retentate of cows’ milk by Pompei et al. (1973), Premaratne & Cousin (1991) and Bastian et al. (1991). Ca, P, Mg, Zn, Fe and Cu have been shown to be partly associated with the casein micelle (Lonnerdal et al., 1981; Green et al., 1984; Walstra & Jenness, 1984). Enzymes, including those associated with the casein micelle and milk fat globule membrane, contain such elements as Fe, Cu, P and Zn (Webb et al., 1978; Walstra & Jenness, 1984). Since macromolecules are retained during UF, high recoveries of many minerals were expected (Fischbach-Greene & Potter, 1986).

750

A4.A. Mehaia

100 80 60 40 20 0 3

ZII

Fe

Cu

Ca

P

Mg

K

Na

Milk Elements Fig. 5. Percentage recovery of some elements in camel skim milk concentrated filtration to 5-VCR.

by ultra-

CONCLUSIONS This study demonstrated that the fat and protein contents of camel skim milk increased proportionally with the VCR used for UF. All fat, CN, WPN, 1318% of NPN and about 1% of lactose were retained during UF of camel skim milk. The transfer of lactose through the membrane was similar to that for water. During UF of camel skim milk, retention of TN and minerals was increased by increasing VCR. This means that permeate to retentate ratios of these constituents did not remain constant during UF processing. However, the retention of the minerals depended upon their association with protein and fat globules membrane. Percentage retention and recovery of Na and K were lower than for Zn, Fe, Cu, Ca, P and Mg. Such data have relevance to questions of standards of properties and nutritional quality of UF camel milk products.

ACKNOWLEDGEMENTS This research was supported by the Center for Agriculture and Veterinary Research, College of Agriculture and Veterinary Medicine, Ring Saud University-Qassim, Buriedah, Saudi Arabia. The author is very grateful to Mr S. ElKhadragy for his technical assistance in chemical analysis. Also, the assistance provided in minerals analysis by the Department of Food Science, College of Agriculture, Ring Saud University, Riyadh is highly appreciated.

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Chemical composition of camel skim milk

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