Effect of freeze-drying on camel's milk nutritional properties

Abstract

The purpose of this research was to study the effect of freeze-drying process on camel's milk nutritional characteristics compared with fresh milk. The results showed that the protein, casein, whey proteins, lactose and ash percentage were significantly higher (P< 0.05) in freeze-dried skim milk than fresh milk. The average of mineral contents in reconstituted freeze-dried skim camel's milk was slightly higher than that of fresh camel milk except Ca, K and P contents. On the other hand, freeze-dried skim camel's milk had a slightly higher concentration of water-soluble vitamins except vitamin C. Vitamins B, A, D and E showed relatively stable values after freeze-drying treatment. Freeze-drying process skim camel's milk was characterized by slightly higher contents of all amino acids. Freeze-dried whole milk showed higher contribution of Protein efficiency ratio, Biological value and Net protein utilization than that of fresh whole milk. Freeze-dried process had a little effect on fatty acid profile in camel milk fat. Nutritional properties of lyophilized camel's milk remained basically unchanged compared with fresh milk.

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*Corresponding author.
Email: salaha.khalifa@gmail.com
Tel: 0020552282360; Fax: 0020552287567
International Food Research Journal 22(4): 1438-1445 (2015)
Journal homepage: http://www.ifrj.upm.edu.my
1Ibrahim, A. H. and 2*Khalifa, S. A.
1Department of Animal and Poultry Breeding, Desert Research Center, Cairo, Egypt
2Food Science Department, Faculty of Agriculture, Zagazig University, Zagazig 44519, Egypt
Effect of freeze-drying on camel’s milk nutritional properties
Abstract
The purpose of this research was to study the effect of freeze-drying process on camel’s milk
nutritional characteristics compared with fresh milk. The results showed that the protein, casein,
whey proteins, lactose and ash percentage were signicantly higher (P< 0.05) in freeze-dried
skim milk than fresh milk. The average of mineral contents in reconstituted freeze-dried skim
camel’s milk was slightly higher than that of fresh camel milk except Ca, K and P contents. On
the other hand, freeze-dried skim camel’s milk had a slightly higher concentration of water-
soluble vitamins except vitamin C. Vitamins B, A, D and E showed relatively stable values
after freeze-drying treatment. Freeze-drying process skim camel’s milk was characterized by
slightly higher contents of all amino acids. Freeze-dried whole milk showed higher contribution
of Protein efciency ratio, Biological value and Net protein utilization than that of fresh whole
milk. Freeze-dried process had a little effect on fatty acid prole in camel milk fat. Nutritional
properties of lyophilized camel’s milk remained basically unchanged compared with fresh milk.
Introduction
Camel milk is highly nutritious so that many
generations of our ancestors survived on this
beverage alone. Camel milk is almost a complete
food consisting of proteins (mainly casein), fat, salts
and lactose as well as vitamins and minerals (Sawaya
et al., 1984). Camel milk and bovine milk had
similar amino acid composition. Camel milk casein
contained most of the essential amino acids in high
ratios. Glutamic acid was the most abundant amino
acid followed by Leucine, Lysine and Aspartic acid
(Abu-Tarboush and Ahmed, 2005). In Africa and
the Middle East, camel milk is used therapeutically
against dropsy, jaundice, problems of the spleen,
tuberculosis, asthma, anemia, piles, diabetes and
against Hepatitis C Virus (Rao, et al., 1970; El-
Fakharany et al., 2008). Benecial role of raw camel
milk in chronic pulmonary tuberculosis patients has
been observed (Mal et al., 2001). Treatment of type–I
diabetes with oral supplementation of raw camel milk
was reported to be effective and reduces the insulin
daily doze from 30 to 35% (Agrarwal et al., 2003).
Research has demonstrated the presence of potent
anti-bacterial and anti-viral factors in camel milk.
Antimicrobial properties were partially attributed
to well characterize proteins, such as lactoferrin,
lactoperoxidase, lysozyme and immunoglobulin
G. These proteins were shown to have higher
concentrations or higher activity in camel milk (El-
Agamy et al., 2009). In addition, camel milk could
have signicant therapeutic attributes such as anti-
cancer (Magjeed, 2005).
Egypt considered as one of the world’s highest
Hepatitis C. There are several traditional medicines
used by different Egyptian patients sectors. The most
popular one is the camel milk, 50% of the patients
shown a marked improvement in general fatigue (El-
Fakharany et al., 2008). Considering the health effect
of camel milk proteins and its bioactive peptides, it
could be the ‘super food’ of the future. Traditional
dehydration processes usually cause physical and
structural changes in the dried products due to heat
application. In fact, caramelization, discoloration,
loss in texture and physical form, loss of volatile
flavoring characteristics, and poor rehydration ability
of many dried foods have left an imprint on the
mind of consumers (Desrosier, 1977). Freeze-drying
or lyophilization is a process in which a solvent is
removed from a frozen solution by sublimation.
This process minimizes the degradation reactions
and maintains adequate physical, chemical, and
biological stability of the product during long-
term storage at ambient temperature (Fonseca et
al., 2004). Being a cold process, freeze-drying is
especially useful for drying heat sensitive foods.
Freeze-drying is recognized as the best method of
producing drier material of high quality. The dried
products obtained from freeze-drying processes have
good flavour appearance, and a high preservation of
Keywords
Camel milk
Freeze-drying
Lyophilization
Nutritive value
Article history
Received: 24 July 2014
Received in revised form:
27 November 2014
Accepted: 10 December 2014

1439 Ibrahim, A. H. and Khalifa, S. A./IFRJ 22(4): 1438-1445
nutrition. Moisture level as low as 2% can be reached
with freeze-drying. It can be benet to produce
freeze-dried camel milk to take advantage of its
nutritional and therapeutic properties. In spite of all
these nutritional and therapeutic properties of camel
milk, the changes in physical and chemical properties
of freeze-drying camel milk is still unknown. The
objective of this study was to investigate the effects
of the lyophilization (freeze-drying) treatment on
physical, chemical and nutritional characteristics of
camel’s milk.
Materials and Methods
Camel’s milk
Fresh whole camel milk from healthy and
uninfected Magrabi camels (Camelus dromedarius)
was obtained from Sidi-Barani areas Matrouh
Governorate, North West Coast, Egypt. The
udder was cleaned and washed with disinfectant
solution (Safflon 20%), before collection of milk.
Autoclaveable plastic containers (1000 mL) were
used for the collection of samples. Containers were
sterilized at 120°C for 15 min and kept ready for milk
collection from different sites (Omer and Eltinay,
2009).
Preparation of freeze-dried camel’s milk samples
Batches of skimmed milk were prepared from
fresh camel milk by centrifugation at 4000 g for 10
min at 15°C. Freeze-drying of whole and skim camel
milk was performed in a Freeze Dryer (Thermo-
Electron Corporation-Heto power dry LL300 Freeze
Dryer, Czech Republic). The freeze-dryer was
programmed to operate for 1 h initial freezing at
-45°C followed by primary drying at 30°C at 0.10
mbar pressure for 48 h and secondary drying at 5°C
for 3 h at the same pressure. After the end of freeze-
drying cycle, the vials were sealed under vacuum and
stored at 5°C until analyzed (Ivanova, 2011).
Raw whole and skimmed milk - freeze-dried whole
and skimmed milk
Proximate analysis (total solids, fat, total nitrogen,
ash content and titratable acidity %) for raw whole
and skimmed milk was determined as described
by Ling (1963). The casein and whey protein was
determined by micro Kjeldahl method as mentioned
by Rowland (1938). Lactose content was determined
by the phenol-sulfuric spectrophotometeric method
as reported by Barnett and Abd-El-Tawab (1957).
The total solids in freeze-dried whole and
skimmed milk was determined according to the
IDF procedure (1993), fat (Rose Gottlieb method),
ash content, titratable acidity and total protein
(Kjeldahl) in freeze-dried whole and skimmed milk
were determined as mentioned in AOAC, (1997).
Lactose determination in freeze-dried whole and
skimmed milk samples were estimted according
to the modied phenol-sulfuric acid procedures
described by Lawrence (1968) using a Jenway 6850
spectrophotometer (Jenway Instruments, Beacon
Road, Stone, Staffordshire, ST15 OSA, UK) at a
wave length of 490 nm . The casein and whey
proteins were determined by micro Kjeldahl method
as mentioned by Rowland (1938).
Vitamins determination
Water-soluble vitamins such as vitamin C and
vitamin B complex (B1, B2, B3, B5, B6, B9 and B12)
and fat soluble vitamins such as vitamins A, D and E
were determined by the method of Albala-Hurtado et
al. (1997) and Paixao and Campos (2003), respectively.
Prepared samples were analyzed for vitamins C, A,
D, E and B complex (B1, B2, B3, B5, B6, B9 and
B12) group by liquid phase chromatography HPLC
(Dionex™ UltiMate™ 3000 RS systems –Thermo
Scientic system). The sample (20 µL) was injected
into the HPLC with a syringe (Hamilton, Reno, NV,
USA). The HPLC column used was a reversed-phase
Discovery C18 (150 mm × 4.6 mm, 5 µm) from
Supelco (Bellefonte, PA, USA). The column eluate
was monitored with a photodiode-array detector at
265 nm for vitamins C, 325 for A, 295 for E, 260 for
D, 234 nm for thiamine, 266 nm for riboflavin, 324
nm for pyridoxine, 282 nm for folic acid, 204 nm
for cobalamin, 261 nm for niacin, and 204 nm for
pantothenic acid. Identication of compounds was
achieved by comparing their retention times and UV
spectra with those of standards stored in a data bank.
Concentrations of the water-soluble and insoluble
vitamins were calculated from integrated areas of the
sample and the corresponding standards.
Minerals determination
Minerals were determined in ash solution
(Srivastava, 2010). Calcium, magnesium, phosphorus,
manganese, cupper, iron and zinc concentrations were
determined using atomic absorption spectrophotometer
(Unicam Analytical System, Model 919, Cambridge,
UK) while sodium and potassium concentrations was
determined using flame photometer (Jenway PF7 Flame
Photometer, Essex, UK).
Amino acid composition
Milk samples were prepared by acid hydrolysis
(6N HCl) for 24 h at 110°C and the nal mixture was
ltrate using Whatman lter paper no. 42. About 0.2
mL of ltration was evaporated at 140°C for one hour

Ibrahim, A. H. and Khalifa, S. A./IFRJ 22(4): 1438-1445 1440
and nally adds 1ml of diluting buffer to the dried
sample. Hydrolyzes were analyzed by Beckman
Amino Acid Analyzer, Model 119CL as mentioned
by Nagasawa et al. (1970).
Analysis of fatty acids by Gas Chromatography
Fatty acid methyl esters FAMES were prepared
as described in AOAC (1990) method 969.33. A GC
equipped with a flame ionisation detector and an auto
sampler (model 7673, Hewlett–Packard, Palo Alto,
CA, USA), was used for analyzing FAMES. The GC
conditions were: column oven temperature was 70°C
for 1 min, increased to 200°C (20°C/min) and kept at
200°C for 1 min, then increased to 220°C (1°C/min)
and kept at 220°C for 20 min, Injector temperature
and detector temperature was 260°C, flow rate 1.1
ml/min (He) and the split ratio used was 1:25. A
FAME Standard (mixture 463) was used to identify
the FAME, and the FA amount was expressed as
percent of total FAs.
Nutritive value
Protein efciency ratio (PER) based on the
amino acid contents of camel milk were calculated
according to the recommendations of Alsmeyer et al.
(1974) using the following equations:
PER1= -0.684+0.456 (leucine) – 0.047 (proline)
PER2= -0.468+0.454 (leucine) – 0.105 (tyrosine)
PER3= -1.816+0.435 (methionine) + 0.78 (leucine) +
0.211 (histidine) – 0.944 (tyrosine)
Biological value (BV) and net protein utilization (NPU)
were calculated using the equations suggested by
Block and Mitchell (1946): BV= 49.9 + 10.53 PER
NPU= BV× Digestibility (protein 95%).
Total energy in all sample of camel milk was
expressed in calories (Watt and Merrill, 1963), and
calculated using the following equation:
Calories= (protein × 4.27) + (fat × 8.78) + (lactose × 3.87).
Statistical analysis
Experimental data were analyzed as Complete
Random Design (CRD) according to SPSS package
(SPSS v.20, 2012). Standard error of the means
was derived from the error mean square term of
the ANOVA, which was used the least signicant
difference (LSD) test. Differences were considered
signicant at (P<0.05). All measurements were
performed in triplicate.
Results and Discussion
Data presented in Table (1) show the chemical
composition of fresh and freeze-dried camel’s milk.
The results indicated that the moisture content of
whole and skim freeze-dried camel milk was lower
as a result of freeze-drying. Thus, moisture level as
low as 2% can be reached with freeze-dried foods
(Dalgleish, 1990), this makes the products much
lighter than those dried by other drying methods and
they do not require refrigeration. In general, total
protein, caseins, whey proteins, lactose and ash %
were signicantly higher (P< 0.05) in freeze-dried
skim milk than freeze-dried whole camel milk.
Changes in the composition of some constituents in
freeze-dried milk can be explained as a function of
the freeze-dried process. These changes coincided
with changes in moisture content (Kumar and Mishra,
2004). However, no signicant differences in total
energy for both freeze-dried and fresh milk (Table 1).
Mineral content in camel milk were found here
(Table 1) was within the range with values reported
by various researchers (Elamin and Wilcox, 1992;
Gorban and Izzeldin, 1997; Haddadin et al., 2008).
The average of all major and trace element contents in
reconstituted freeze-dried camel’s milk was slightly
higher than those of fresh camel milk, thus might
be due to freeze-dried possess except Ca, K and P
contents were signicantly differences (P< 0.05). In
contrast, the influence of process of freeze-dried on
trace element was not signicant.
Milk is a valuable source for both water-soluble
and fat-soluble vitamins. Therefore, we compare the
concentration of vitamins in fresh and reconstituted
freeze-dried camel’s milk (Table 2). The results
showed that freeze-dried skim camel’s milk was
a slightly higher concentration of water-soluble
vitamins except vitamins C. Lyophilization process
signicantly affected the amount of vitamin C in
milk (Vincenzetti et al., 2011). Further, freeze-dried
yoghurt showed reduction in levels of ascorbic acid
(Karadimov and Karadimova, 1979). On the other
hand, vitamins B group were relatively stable in all
samples with no signicant differences (P< 0.05)
between all samples. Vitamins B group are relatively
stable to most food-processing operations and
storage (Fox and McSweeney, 1997). Fresh whole
camel’s milk had a slightly higher concentration of
fat-soluble vitamins (A, D and E) than freeze-dried
whole camel’s milk.
Table (3) shows the amino acid concentration
of fresh and reconstituted freeze-dried camel’s milk
(g/100 g protein). The results indicated that Glutamic
acid (Glu) was the major amino acid in all milk

1441 Ibrahim, A. H. and Khalifa, S. A./IFRJ 22(4): 1438-1445
Table 1. Chemical composition of fresh and freeze-dried camel's milk
*Reconstituted freeze-dried whole camel's milk (Dry matter 12.1%) and freeze-dried skim milk (Dry matter 9.3 %).
abc.. Means followed by different letter in the same row are signicantly different. (P <0.05)
Table 2. Vitamin concentrations in fresh and reconstituted freeze-dried camel's milk*
*Reconstituted freeze-dried whole camel's milk (Dry matter 12.1%) and freeze-dried skim milk (Dry matter
9.3 %)
abc.. Means followed by different letter in the same row are signicantly different. (P<0.05)
**ND=Not determined

Ibrahim, A. H. and Khalifa, S. A./IFRJ 22(4): 1438-1445 1442
Table 3. Amino acid concentration of fresh and reconstituted freeze-dried camel's milk (g/100 g protein) *
*Reconstituted freeze-dried whole camel's milk (Dry matter 12.1%) and freeze-dried skim milk (Dry matter 9.3 %)
abc.. Means followed by different letter in the same row are signicantly different. (P<0.05)
Table 4. Nutritive value of fresh and reconstituted freeze-dried camel's milk*
*Reconstituted freeze-dried whole camel's milk (Dry matter 12.1%) and freeze-dried skim milk (Dry matter 9.3 %)

1443 Ibrahim, A. H. and Khalifa, S. A./IFRJ 22(4): 1438-1445
treatments. These values are in accordance with those
found by El-Agamy (2006), Kamal et al. (2007) and
Shamsia (2009). However, freeze-dried skim camel’s
milk was characterized by slightly higher contents
of all amino acids. The essential amino acids Ile,
Lys, Phe and Val were signicantly (P< 0.05)
higher in freeze-dried skim milk compared to their
amounts in the other milk treatments .In the case
of non-essential amino acids, all amino acids except
Glu and Ser were signicantly (P< 0.05) higher in
freeze-dried skim milk compared to their amounts
in the other milk treatments. Protein efciency
ratio (PER), biological value (BV) and net protein
utilization (NPU) of freeze-dried milk were higher
than those of fresh milk (Table 4). This result could
be attributed to the higher concentration of leucine in
the freeze-dried milk than in the fresh milk. On the
other hand, the nutritive values calculated for both
milk types using the third equation showed an equal
value. Data presented in (Table 5) shows the fatty
acid prole of whole fresh and freeze-dried camel’s
milk (g/100 g fat). In general, short-chain fatty acids
(C4:C12) in fresh and freeze-dried camel milk were
present in very small amounts compared with those
reported in cows’ milk (Abu-Lehia, 1989). However,
the concentrations of C14:0, C16:0, C18:0 and C18:1
is relatively high. Fresh and freeze-dried camel milk
has high amounts of linolenic acid (C18:3) and long-
chain polyunsaturated fatty acids compared with
those reported in cows’ milk. Our ndings are similar
to those reported by Abu-Lehia, (1989); Farah,
(1993). The main saturated fatty acids in freeze-dried
camel milk were 14:0 (12.2%), 16:0 (24.4%) and
18:0 acids (13.7%). The major unsaturated fatty acids
of fresh and freeze-dried camel milk triacylglycerol’s
were 18:1 and 16:1. The freeze-dried process had a
little effect on fatty acid prole in camel milk fat.
This result are in agreement with Karadimov and
Karadimova, (1976), who reported that there were
no changes in the fatty acids (C4: C12) of the dried
product.
Conclusion
Lyophilization of camel’s milk demonstrated that
the nutritional characteristics of this product remained
basically unchanged compared with fresh milk. The
results obtained also, conrmed the possibility of
producing freeze-dried camel milk with benecial
properties using camel’s milk as raw material and
lyophilized camel milk powder is easy to transport,
requires no special conditions for prolonged storage.
In addition, lyophilization of camel’s milk can help
in supplying camel’s milk on the market all-over the
year.
Acknowledgments
The present document was achieved in the frame
of PROCAMED project, supported by the European
Table 5. Fatty acid prole of whole fresh and reconstituted freeze-dried camel's milk (g/100 g fat)*
*Reconstituted freeze-dried whole camel's milk (Dry matter 12.1%) and freeze-dried skim milk (Dry matter 9.3 %)

Ibrahim, A. H. and Khalifa, S. A./IFRJ 22(4): 1438-1445 1444
Union (ENPI - Joint operational Programme of the
Mediterranean Basin -IEVP-CT). The contents of this
document are the sole responsibility of the ‘Division
of Animal Production, Animal Breeding Department,
Desert Research Center (Egypt) and can (under no
circumstances) is regarded as reflecting the position
of the European Union.
References
Abu-Lehia, I. H. 1989. Physical and chemical
characteristics of camel milk fat and its fractions.
Food Chemistry 34: 261-271.
Abu-Tarboush, H. M. and Ahmed, S. B. 2005.
Characterization of hydrolysates produced by
enzymatic of camel casein and protein isolates of
Al-Ban (Moringa peregrina) and Karkade (Hibiscus
sabderiffa) seeds. Journal of the Saudi Society of
Agricultural Sciences 2: 61–81.
Agarwal, R. P., Swami S. C., Beniwal, R., Kochar, D.K.,
Sahani, M. S., Tuteja, F.C. and Ghouri, S. K. 2003.
Effect on camel milk on glycemic control, risk factors
and diabetes quality of life in type –1 diabetes : A
randomised prospective controlled study. Journal of
Camel Practice and Research 10: 45-50.
Albala-Hurtado, S., Veciana-Nogues, M.T., Izquierdo-
Pulido, M. and Marine-Font, A. 1997. Determination
of water-soluble vitamins in infant milk powder by
high performance liquid chromatography. Journal of
Chromatography A 778: 247–253.
Alsmeyer, H. R., Caningham, A. E. and Happich, M. L.
1974. Equation predict PER from amino acid analysis.
Food Technology 28: 34-40.
AOAC 1990. Ofcial Methods of Analysis of AOAC
International, 16th ed., 3rd revision, Washington, DC,
USA.
AOAC 1997. Ofcial Methods of Analysis of AOAC
International, 16th ed., 3rd revision, Washington, DC,
USA.
Barnentt, J.G. and Abdel-El-Tawab, G. 1957. A rapid
method for determination of lactose in milk cheese.
Journal of the Science of Food and Agriculture 8: 437-
442.
Block, R.J. and Mitchell, H. H. 1946. The Correlation of
the Amino Acid Composition of Proteins with their
Nutritive Value. Nutrition abstracts and reviews 16:
249 - 278.
Desrosier, N.W. 1977. The Technology of Food
Preservation. The AVI Publishing Company, Inc.,
Westport, CT.
El-Agamy, E. I. 2006. Camel milk. In: Park YW, Haenlein
GFW, editors. Handbook of milk of non-bovine
mammals, pp 297–344. Oxford, U.K., Blackwell
Publishing.
El-Agamy, E. I., Nawar, M., Shamsia, S. M., Awada, S.
and Haenlein, F.W. 2009. Are camel milk proteins
convenient to the nutrition of cow milk allergic
children. Small Ruminant Research 82: 1-6.
Elamin, F. M. and Wilcox, C. J. 1992. Milk composition of
Majaheim camels. Journal of Dairy Science 75: 3155-
3157.
El-Fakharany, E. M., Abd El-Wahab A., Bakry, M. H. and
El-RRashdy, M. R. 2008. Potential Activity of Camel
Milk-Amylase and Lactoferrin against Hepatitis
C Virus Infectivity in HepG2 and Lymphocytes.
Hepatitis Monthly 8(2): 101-109.
Farah, Z. 1993. Composition and characteristics of camel
milk. Review article. Journal of Dairy Research 60:
603-626.
Fonseca, F., Passot, S., Cunin, O. and Marin, M. 2004.
Collapse temperature of freeze-dried Lactobacillus
bulgaricus suspensions and protective media.
Biotechnology Progress 20: 229-238.
Fox, P. F. and McSweeney, P. L. H. 1997. Advanced Dairy
Chemistry, Volumes 1, 2 and 3, Elsevier Applied
Science Publishers and Chapman & Hall, London.
Gorban, A. M. S. and Izzeldin, O. M. 1997. Mineral
content of camel milk and colostrum. International
Journal of Dairy Technology 64: 471-474.
Haddadin, M. S., Gammoh S.I. and Robinson, R. K. 2008.
Seasonal variations in the chemical composition of
camel milk in Jordan. Journal of Dairy Research 75:
8–12.
IDF (1993). IDF Standard 26A: 1993. Milk powder:
Determination of total solids.
Ivanova, S. 2011. Dynamical changes in the trace element
composition of fresh and lyophilized ewe’s milk.
Bulgarian Journal of Agricultural Science 17: 25-30.
Kamal, A. M., Salama, O. A. and El-Saied, K. M. 2007.
Changes in amino acid prole of camel milk protein
during the early lactation. International Dairy Journal
2: 226-234.
Karadimov, D. S. and Karadimova, Z. A. 1979. Changes in
yoghurt properties during freeze-drying and storage.
II. Changes in vitamin content, Nauchnye trudy 10:
53–58.
Karadimov, D.S. and Karadimova, Z.A. 1976. Losses
of volatile compounds during fluidized bed freeze-
drying of comminuted frozen yoghurt. Nauchnye
trudy 23(1): 305–313.
Kumar, P. and Mishra, H. N. 2004. Yoghurt powder- a
review of process technology storage and utilization.
Food and Bioproducts Processing 82 (C2): 133–142.
Lawrence, A. J. 1968. The determination of lactose in milk
products. Australian Journal of Dairy Technology 23:
103-106.
Ling, E.R. 1963. A text book of Dairy chemistry. Vol. 2
practical 3rd. Chapman and Hill.
Magjeed, N.A. 2005. Corrective effect of camel milk on
some cancer biomarkers in blood of rats intoxicated
with aflatoxin B1. Journal Saudi Chemical Society 9:
253–263.
Mal, G., Sena, D. S, Jain, V. K. and Sahani, M. S. 2001.
Therapeutic utility of camel milk as nutritional
supplement in chronic pulmonary tuberculosis.
Livestock International 7: 4-8.
Nagasawa, T., Kiyesawa, I. and Kuwahara, K. 1970.
Acrylamide gel electrophoresis and amino acid
compositions of human colostral casein. Journal of

1445 Ibrahim, A. H. and Khalifa, S. A./IFRJ 22(4): 1438-1445
Dairy Science 53: 92-94.
Omer, R. H., and Eltinay, A. H. 2009. Changes in chemical
composition of camel’s raw milk during storage.
Pakistan Journal of Nutrition 8: 607-610.
Paixao, J. A. and Campos, J. M. 2003. Determination
of Fat Soluble Vitamins by Reversed-Phase HPLC
Coupled with UV Detection: A Guide to the
Explanation of Intrinsic Variability. Journal of Liquid
Chromatography & Related Technologies 26: 641–
663.
Rao, M. B., Gupta R. C. and Dastur N. N. 1970. Camel’s
milk and milk products. Indian Journal of Dairy
Science 23: 71-78.
Rowland, S. J. 1938. The determination of the nitrogen
distribution in milk. Journal of Dairy Research 9: 42
- 46.
Sawaya, W.N., Khalil, J. K., Al-Shalhat, A. and Al-
Mohammad, H. 1984. Chemical composition and
nutritional quality of camel milk. Journal of Food
Science 49: 744–747.
SPSS package v.20 2012. Software package for Social
Science For windows.
Srivastava, M. K. 2010. Handbook on analysis of milk:
Chemical and microbiological analysis of liquid milk,
pp. 221-250, International Book Distributing Co.,
India.
Vincenzetti, S., Savini, M., Cecchini, C., Micozzi, D.,
Carpi, F., Vita, A. and Polidori, P. 2011. Effects of
Lyophilization and Use of Probiotics on Donkey’s
Milk Nutritional Characteristics. International Journal
of Food Engineering (7): 5 Article 8.
Watt, B. K. and Merrill, A. L. 1963. Composition of
Foods. Agriculture Handbook no. 8, 189 pp. USDA,
Washington, DC.