Effect of Moisture Content on the Quality of Process Cheese Spread.

Abstract

The objective of this research was to determine the effect of increasing
water amount added to the ingredients on chemical, microbial, organoleptic
properties and yield of processed cheese spread. Six treatments of cheese were
made by adding 25,26,27,28,29 and 30 % water to the ingredients. Resultant
cheese was stored for 3 months at 5-10°C or at 25-30°C. Increasing amount of
water added to the blend of processed cheese spread increased the yield and pH
values of resultant cheese while decreased TS, fat, salt, TN, WSN, NPN, total viable
bacterial count (TVBC) and sporeformes bacteria numbers. Storage processed
cheese spread at 25-30°C decreased pH and TN contents and increased TS, fat,
salt, WSN, NPN, TVBC and sporeformes bacteria numbers of cheese more than
that stored at 5-10°C. No significant differences (p> 0.001) were observed in
sensory scores of different treatments. From the results of feasibility study it
could appear that increasing the concentration of water added to the blend of
processed cheese spread raised the net profit.

Full text

Effect of moisture content on the quality of process cheese spread.
By
Hamad,M.N.* and Ismail,M.M.** 
*Food science and Dairy Department , Faculty of Agriculture "Qena" , South Vally University.
** Dairy Technology Department, Animal Production Research Institute, Agriculture Research
Center.
ABSTRACT
The objective of this research was to determine the effect of increasing
water amount added to the ingredients on chemical, microbial, organoleptic
properties and yield of processed cheese spread. Six treatments of cheese were
made by adding 25,26,27,28,29 and 30 % water to the ingredients. Resultant
cheese was stored for 3 months at 5-10°C or at 25-30°C. Increasing amount of
water added to the blend of processed cheese spread increased the yield and pH
values of resultant cheese while decreased TS, fat, salt, TN, WSN, NPN, total viable
bacterial count (TVBC) and sporeformes bacteria numbers. Storage processed
cheese spread at 25-30°C decreased pH and TN contents and increased TS, fat,
salt, WSN, NPN, TVBC and sporeformes bacteria numbers of cheese more than
that stored at 5-10°C. No significant differences (p> 0.001) were observed in
sensory scores of different treatments. From the results of feasibility study it
could appear that increasing the concentration of water added to the blend of
processed cheese spread raised the net profit.
Key ward: processed cheese spread- water- palm oil- Ras cheese.
Introduction
Processed cheese is a generic term used to describe 3 separate categories of
cheese. These categories are pasteurized processed cheese (PC), pasteurized
processed cheese food (PCF), and pasteurized processed cheese spread (PCS)
(Code of Federal Regulations, 2003). According to the Code of Federal
Regulations (2003), these 3 categories differ on the basis of the requirements for
minimum fat content on DM basis and the maximum allowed moisture content
as well as the quantity and the number of optional ingredients that can be used.
A typical processed cheese formulation contains substantial amounts of salt and
water, and it may be possible to replace the salt and water with salt whey. In

Egypt processed cheese is one of the most popular variety of cheese, particularly,
among the children due to its palatability, high nutritive value and spread
ability. The ingredients used in processed cheese manufacture different from
plan to other but they usually consists from aged cheese such as Ras cheese ,
Young cheese or Quark cheese, butter oil (anhydrous) , palm oil , skim milk
powder and emulsifying salts.
On the other hand, salt whey, unlike sweet whey, cannot be conveniently
processed because of its high salinity level (Sanderson et al., 1996). Moreover, it
has a high biological oxygen demand and chemical oxygen demand, which make
its disposal a problem (Zayed and Winter, 1995). One possible alternative for
salt whey is to use it as an ingredient in processed cheese as it is or after
filtration. The use of whey retentate in processed cheese spread has several
technological, nutritional and economical advantages. Form the economical
point of view, the use of the cheap whey retentate to replace the expensive cheese
would reduce the cost of production of this product, and in the mean time , offer
a feasible way for the utilization of whey retentate. The high biological value of
whey proteins would improve the nutritional value of processed cheese spread
containing whey retentate. The addition of whey proteins in processed cheese
spread can also modify the functional properties of the product for variable uses.
Yield of cheese is very important factor for cheese producers, increasing of
this yield means more profits and little costs, so that the objective of this study
was to evaluate the feasibility of increasing yield of processed cheese
manufacture using whey retentate by adding water to cheese ingredients and
determine any influences on the chemical , microbial and sensory properties of
the resulting processed cheese.
Materials and Methods
Materials:
Quark cheese used in the ingredient blends was prepared from skim milk
concentrates by ultrafiltration, so added 10% palm oil, so homogenization at 50
bar, so added citric acid and rennet at pH 5.2. Old Ras cheese (6-10 months) was
obtained from private Ras cheese production laboratory in Domiatt
Governorate. Precooked cheese was the residual of previous processed cheese

blend. The chemical composition of quark, old Ras cheese and precooked cheese
was indicated in Table (1). The emulsifying salts used were No emulsifier
(consists of sodium diphosphate, sodium polyphosphate and sodium
orthophosphate) and S9 emulsifier (consists of sodium diphosphate, sodium
polyphosphate and sodium triphosphate) which obtained from Benckiser
Knapsaek Gmb H, Lodenburg, Germany. Other ingredients were butter oil
(imported from France by Flecgard, S.A., Importer, Arab Trading Company),
palm oil (Misr Oil and Soap Company, Zagazig Factory) , skim milk powder
(low heat) (imported from USA by Egyptian Company for Trad , Industry
"Zahran") and potassium sorbate and nisin (Pharmacentical Company, Pfizer).
Methods:
Preparation of whey retentate:
Ras cheese whey was pasteurized to 72°C/15 sec., then ultrafiltered at 45°C using
the ultrafiltration unit (Carbo-Sep unit type 25 151, France). The whey retentate
was heated at 60°C/15 sec., cooled to 45°C followed by homogenization using a
one stage homogenizer ( Rannie, Copenhagen, Denmark) at 50 kg/ cm2 . The
prepared ultrafiltrated whey retentate had 36% TS.
Table (1): Chemical composition of ingredients used in processed cheese making.
Ingredients
pH
TS %
Fat %
Protein
%
Salt %
Quark
5.20
31.50
11.50
13.20
0.22
Ras cheese
4.90
70.00
35.00
30.14
2.90
Precooked cheese
5.75
49.50
26.50
-
2.70
Whey
6.02
8.76
0.10
3.44
0.22
Whey retentate
5.75
36.00
2.10
28.75
1.00
Manufacture of processed cheese spread:
The manufacture of processed cheese spread was carried out as described
by Meyer (1973). The detailed ingredients blends and formulations for six cheese
treatments are indicated in Table (2). From pervious study (Hamad 1997), we
added whey retentate to the blend of processed cheese by 7.5% and different

amounts of water were used as mentioned in Table (2). Processed cheese was
made as follows:
Ras cheese was cut into small-pieces with a sharp knife. The pieces were fed into
electric mincer to convert them into finally minced cheese. Each formulation of
blends (except nisin) was placed in a 40 kg processing kettle ( Kustner, SA
Geneva – 22H 210 986), closed and heated by direct steam injection at pressure
of 3-5 kg/cm2 under continuous stirring, at a temperature of 90-94°C for 10
minutes, and the melted cheese was maintained at such temperature for 3
minutes and then nisin was added. The resultant processed cheese spread of all
treatments were filled in 160 g glasses and stored for 3 months at 5-10°C
(refrigerator) or at 25-30°C (room temperature). The processed cheese were
chemically, microbiologically and organoleptically analyzed while fresh at zero
time and then after 1,2, and 3 months of storage.
Table (2): Processed cheese formulation.
Ingredients
%
Control
(A)
Treatments
B
C
D
E
F
Quark
Whey retentate
Ras cheese
Palm oil
Butter oil
Skim milk powder
Precooked cheese
Emulsifying salts
Added water
25.0
7.5
12.5
8.5
8.5
5.0
5.0
3.0
25.0
25.0
7.5
12.5
8.5
8.5
5.0
5.0
3.0
26.0
25.0
7.5
12.5
8.5
8.5
5.0
5.0
3.0
27.0
25.0
7.5
12.5
8.5
8.5
5.0
5.0
3.0
28.0
25.0
7.5
12.5
8.5
8.5
5.0
5.0
3.0
29.0
25.0
7.5
12.5
8.5
8.5
5.0
5.0
3.0
30.0
Total
100
101
102
103
104
105
Preservatives
0.1% potassium sorbate + 12.5 ppm nisin
Cheese analyses :
Quark, Ras cheese, precooked cheese, whey and whey retentate samples were
analyzed for total solids (TS), fat and total protein contents according to Ling
(1963). The pH values were estimated using a pH meter type CG 710. Cheese was
analyzed for total solids (TS), pH, fat, total nitrogen (TN), water soluble nitrogen

(WSN) and non-protein-nitrogen (NPN) contents according to Ling (1963). Salt
contents of processed samples were estimated using Volhard method according
to Richardson (1985).Cheese samples were analyzed for total viable bacterial
count (TVBC); colifom bacteria; staphylococci; moulds and yeast counts
according to the methods described by the American Public Health Association
(1992). The cheese samples were scored for outer appearance (20 points), inner
appearance (40 points) and flavour (40 points) by ten panelists according to
Meyer (1973).The obtained results were statistically analyzed using a software
package (SAS, 1991) based on analysis of variance. When F-test was significant,
least significant difference (LSD) was calculated according to Duncan (1955) for
the comparison between means. The data were presented, in the Tables, as the
mean (± standard deviation) of 3 replicate experiments.
Results and Discussion
Chemical composition of Processed cheese spread:
Compositional analyses of the fresh processed cheese spread and during
storage period are given in Table (3). An increase in water concentrations added
to the cheese ingredients caused a proportional increase in the final pH values of
the cheese. This may be due to dilution of ingredients acidity (especially old Ras
cheese) by added water. Gradual decrease in pH values was noticed in both
cheese stored at 7 and 25°C for three months. However, great decrease occurred
in cheese stored at 25°C so these cheese treatments had the lowest pH values at
the end of storage time. The observed differences in cheese pH between
treatments stored at refrigerator and others stored at room temperature may be
related to a difference in bacterial growth and enzymatic activation rates in both
cheese treatments which happened slowly in cold storage cheese.
Changes in pH depend on change in lactose, protein and fat in cheese during
storage. Lactose plays an important role in this respect. Similar results were
reported by Emara (1984), El-Neshawy et al.,(1987), Farahat et al., (1993), Omar
(1994) and Hamad (1997).
As it is expected, by increasing concentrations of water added to processed
cheese spread formula, TS, fat, Fat/DM and salt contents of the resultant cheese
significantly (P< 0.001) decreased. Also, as water levels increased from 25 to
30% in cheese blend, TN and TN/DM contents reduced. Prolongation of the

storage period resulted higher contents of TS, fat and salt in all cheese variants
at room temperature than at refrigerating temperature. On contrast, storing
cheese samples at 5-10°C or 25-30°C decreased the total nitrogen content of
cheese by advancing the period of storage. The lowest TN concentrations were
observed in cheese samples stored at 25-30°C.
Water soluble nitrogen (WSN) and non-protein-nitrogen (NPN) contents for
the various process cheese spread samples had the same trend of total nitrogen
values (Table 3). Both WSN and NPN contents influence the total nitrogen
concentrations in cheese which significantly (P< 0.001) decreased by adding
water to the blends of these cheese. On the other side, gradual and slight increase
in WSN and NPN contents of the variants of processed cheese spread was
observed during storage period either in refrigerator or in at room temperature.
The higher values of WSN/TN and NPN/TN obtained in cheese stored at room
temperature might be explained by the retarding effect of refrigerator on the
activity of proteolytic organisms or enzymes during storage time (Hamad 1997).
All processed cheese spread met the legal standards of identity as specified
by the Egyptian Standards, Processed Cheese (2002).
Microbiological quality of processed cheese spread:
Total viable bacterial count (TVBC) and sporeformes bacteria numbers of
processed cheese spread were different with significant (p 0.001) effects of both
adding water and storage temperature and their interaction (Tables 4 and 7).
The TVBC and sporeformes bacteria contents decreased with an increase in the
level of water added to the blends of cheese. At the end of storage time at 5-
10°C, treatment F (30% water) had the lowest TVBC (1.82 x103) whereas
treatment C (27% water) possessed the lowest number of sporeformes bacteria
(1.50 x103). It could also be appeared that TVBC and sporeformes bacteria
numbers were lower in cheese treatments stored at 5-10°C than that of stored at
25-30°C, which is mainly due to the retarding effect of low temperature upon the
growth and activity of these bacteria. During storage period there was
significantly (p< 0.001) increase in the TVBC and sporeformes bacteria numbers
in all processed cheese spread samples. The maximum growth of TVBC for
treatments stored at 5-10°C or 25-30°C was achieved at the end of second month
of storage period and then it decreased, sporeformes bacteria numbers in all

treatments stored at 25-30°C had the same trend while they reached to the
highest levels at the end of storage period after three months in cheese
treatments stored at 5-10°C. In spite of treatment A (control) had the highest
TVBC and sporeformes bacteria numbers but the rates of increasing in these
microbial groups throughout the different examined periods were higher in
other treatments as compared with treatment A. The increasing rates of TVBC
from beginning and end of storage period at 5-10°C were
13.69,13.75,14.29,18.06,19.61 and 21.33% for treatments A,B,C,D,E and F
respectively.
Coliform bacteria, molds and yeast and Staphylococcus aureus were not
detected in all treatments of fresh processed cheese and during storage period
due to good hygienic condition during manufacturing and storage period.
Table (4): Effect of adding water to ingredients and storage temperature on some
microbial groups of processed cheese spread.

Treatments
Storage
time
(month)
TVBC
(x103)
Coliform
bacteria
(x102)
Spore-
forms
bacteria
(x103)
Moulds 
Yeast
(x102)
Staph.
aureus
(x102)
Storage temperature °C
7±2
25±3
7±2
25±3
7±2
25±3
7±2
25±3
7±2
25±3
A
(25% water)
0
1
2
3
1.68
1.50
2.35
1.91
1.68
3.70
6.00
5.15
-
-
-
-
-
-
-
-
1.10
1.30
1.43
1.56
1.10
2.30
4.80
3.30
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
B
(26% water)
0
1
2
3
1.60
1.49
2.00
1.82
1.60
2.53
6.00
5.00
-
-
-
-
-
-
-
-
0.99
0.84
1.33
1.52
0.99
2.00
4.10
2.99
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
C
(27% water)
0
1
2
3
1.61
1.50
1.95
1.84
1.61
2.71
6.00
5.10
-
-
-
-
-
-
-
-
1.01
1.07
1.28
1.50
1.01
2.00
3.83
2.99
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
D
(28% water)
0
1
2
3
1.55
1.50
1.99
1.83
1.55
2.18
6.01
5.11
-
-
-
-
-
-
-
-
1.00
1.10
1.31
1.56
1.00
1.85
4.23
3.01
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
E
(29% water)
0
1
2
3
1.53
1.40
1.98
1.83
1.53
2.58
6.00
5.00
-
-
-
-
-
-
-
-
1.00
1.15
1.35
1.55
1.00
1.99
4.00
3.01
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
F
(30% water)
0
1
2
3
1.50
1.38
2.10
1.82
1.50
2.63
5.90
5.00
-
-
-
-
-
-
-
-
0.98
1.20
1.50
1.67
0.98
1.89
4.10
3.00
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
Processed cheese spread sensory properties:
No significant differences (p> 0.001) were observed in sensory scores of
different treatments (Tables 5 and 7). It is obvious that the total score gained by
the examined cheese, generally, decreased by advancing the storage period. Such
decrease, however, was more noticeable when storage was carried out at higher
than at lower temperature. Outer and inner appearances were perceived to be
similar in the control (treatment A) and other treatments of processed cheeses.
Overall flavour scores were slightly higher for processed cheese made using 29
and 30% water (treatments E and F) than those made using 25,26, 27 and 28%

water (treatments A,B,C and D respectively). However, samples E and F
obtained the same higher scores than the rest samples but the most panelists
preferred sample E than F. From the results of sensory evaluation, it seems that
adding 29% water to blend of processed cheese spread improves sensory
properties of the resultant cheese by improving flavour.
Table (5): Sensory scores of processed cheese spread.
Treatments
Storage
time
(month)
Outer
Appearance
(20)
Inner
Appearance
(40)
Flavour
(40)
Total
(100)
Storage temperature °C
7±2
25±3
7±2
25±3
7±2
25±3
7±2
25±3
A
(25% water)
0
1
2
3
18
18
17
17
18
18
17
16
37
36
36
36
37
37
35
35
37
37
36
35
37
35
35
34
92
91
89
88
92
90
87
85
B
(26% water)
0
1
2
3
18
18
17
17
18
18
17
16
37
37
36
36
37
37
36
35
37
37
36
35
37
35
35
35
92
91
89
88
92
90
88
86
C
(27% water)
0
1
2
3
18
18
17
17
18
18
17
16
38
37
36
36
38
37
36
34
37
37
36
35
37
36
36
35
93
92
89
88
93
91
89
87
D
(28% water)
0
1
2
3
18
18
17
17
18
18
18
17
38
37
36
36
38
37
36
34
38
37
36
35
38
37
36
36
94
92
89
88
94
92
90
87
E
(29% water)
0
1
2
3
18
18
17
17
18
18
18
17
38
37
37
36
38
38
37
35
39
37
37
36
39
37
37
36
95
93
91
89
95
93
92
88
F
(30% water)
0
1
2
3
18
18
17
17
18
18
18
17
38
37
37
36
38
38
37
35
39
37
37
36
39
37
37
36
95
93
91
89
95
93
92
88
Feasibility study:
Tables (6a and b) show the simple economic analysis for increasing amount
of water in processed cheese spread manufacture. The cost of the ingredients

used in the examined blend and the total price as well as the net profit are
illustrated in the mentioned tables. It could appear that increasing the
concentration of water added to the blend of processed cheese spread raised the
yield and net profit.
Conclusions
Levels of added water when increased in the blend have a direct impact on
chemical and microbial characteristics of process cheese spread. This study
indicates that adding 29% water to blend of processed cheese spread improves
sensory properties of the resultant cheese by improving flavour. Also, increasing
amount of water added to an ingredients in processed cheese spread increase
yield and so reduce costs and raised net profit.
Table (6a): Economical studies on processed cheese spread.
Ingredients
Price (Kg.)
(L.E.)
The amount of ingredient
used in making 100kg
cheese (kg)
Price of total amount
of ingredient
Quark cheese
8.00
25
200.00
Whey Retentate
5.00
7.5
37.50
Ras cheese
20.00
12.5
250.00
Skim milk powder
26.00
5.0
130.00
Precooked cheese
10.00
5.0
50.00
Palm oil
5.00
8.5
42.50
Butter oil
18.00
8.5
153.00
Emulsifying salt
14.00
3.0
35.00
0.1 % Potassium sorbate
40.00
100g
4.00
12.5 PPm (Nicin)/ kg cheese
3000
12.5ppm
3.75
Total Price of 100kg cheese
--
--
905.75 L.E.
Table (6b): Economical studies on processed cheese spread.
Treatments
Yield
(kg)
Cost of Production (100kg cheese)
Cheese
Price(100kg)*
(L.E.)
Gain
L.E
Gain
%
Ingredients
Processing
Total

38 %
A
100.00
905.75
344.18
1249.93
1875.00
625.07
33.33
B
100.80
905.75
344.18
1249.93
1890.00
640.07
33.86
C
101.25
905.75
344.18
1249.93
1898.44
648.51
34.16
E
102.75
905.75
344.18
1249.93
1926.56
676.63
35.12
F
103.50
905.75
344.18
1249.93
1940.63
690.70
35.59
D
104.00
905.75
344.18
1249.93
1950.00
700.07
35.90
* Cheese Price = 18.75 (price of 1 kg cheese) x yield.
Table (7): Statistical analysis of processed cheese spread treatments.
Analysis
Effect of cheese treatments

Storage at 7±2 °C
Storage at 25±3 °C
A
B
C
D
E
F
A
B
C
D
E
F
pH
5.78cd
5.86ab
5.86ab
5.84abc
5.89a
5.90a
5.76d
5.78cd
5.81bcd
5.78cd
5.78cd
5.78cd
TS
42.79ab
42.23abcd
41.39bcdef
41.11cdef
40.62ef
40.07f
42.97a
42.47abc
41.71abcde
41.43abcdef
40.77def
40.13def
Fat
24.50ab
23.90bc
23.22ed
22.62e
21.92fg
21.22h
24.56a
24.02ab
23.32cd
22.70c
22.00f
21.35gh
Salt
2.72abc
2.72abc
2.67cd
2.62de
2.57ef
2.54f
2.75a
2.77a
2.74ab
2.68bcd
2.63de
2.58ef
TN
2.00a
1.95b
1.92cd
1.85f
1.87e
1.74g
1.98a
1.93cb
1.90d
1.83f
1.84f
1.73g
WSN
1.04a
1.01bc
0.98d
0.94e
0.95e
0.88f
1.04a
1.02b
0.99cd
0.95e
0.94e
0.89f
NPN
0.54a
0.53ab
0.51bcd
0.50cd
0.50bcd
0.46e
0.53ab
0.52abc
0.51bcd
0.50d
0.49d
0.46e
TVBC
1.86e
1.75f
1.73f
1.71f
1.68f
1.72f
4.13a
3.83bc
3.86bc
3.89b
3.78cd
3.72cd
SBN*
1.35abc
1.17d
1.20d
1.24cd
1.27bcd
1.41ab
1.35abc
1.17d
1.42a
1.24cd
1.27bcd
1.44a
Oapp**
17.62a
17.75a
17.50a
17.50a
17.50a
17.25a
17.25a
17.25a
17.25a
17.75a
17.75a
17.75a
Iapp***
36.25a
36.25a
36.75a
37.75a
37.25a
37.25a
36.00a
36.25a
36.25a
36.25a
37.00a
37.00a
Flavor
36.25abc
36.25abc
36.25abc
36.50abc
37.00ab
37.25a
35.25c
35.50bc
36.00abc
36.75ab
37.00ab
37.25a
Effect of storage time (month)
0
1
2
3
pH
5.96a
5.88b
5.74c
5.69d
TS
41.19a
41.45a
41.56a
41.69a
Fat
22.87a
22.87a
22.96a
23.07a
Salt
2.62b
2.64b
2.69a
2.71a
TN
1.91a
1.88b
1.88b
1.84c
WSN
0.96a
0.97a
0.97a
0.97a
NPN
0.50a
0.50a
0.51a
0.51a
TVBC
1.58d
2.09c
4.08a
3.47b
SBN*
1.05d
1.16c
1.40b
1.57a
Oapp**
18.00a
18.00a
17.25a
16.79a
Iapp***
37.67a
37.17a
36.25b
35.33c
Flavor
37.67a
36.58b
36.17b
35.33c
*SBN : sporeformes bacteria numbers **Oapp : Outer appearances
*** Iapp : Inner appearances
For each effect the different letters in the means the multiple comparison are different from each. Letters a
is the highest means followed by b, c …..etc. References
American Public Health Association (1992): Standard Methods for the Examination of
ed., New York, USA.
th
Dairy Products. Amer. Publ. Health Assoc. Inc.12

Code of Federal Regulations. (2003): Section 133.169 US Dept. Health Human Services,
Washington, DC.
Duncan, D. B. (1955).Multiple Range and Multiple F-test.Biometrics,11:1– 42.
Egyptian Standards, Processed Cheese (2002): Part 2 , Spreadable Processed
Cheese. ES: 999-2/2002. I.C.S: 67.100.30.Egyptian Organization for
Standardization and Quality Control, Ministry of Industry and
technological Development.
El-Neshawy,A.A., Abdel-Baky,A.A., Farahat,S.M. and El-Desoki, M.E. (1987): Cheese
curd slurry in the manufacture of processed cheese spread. Egyptian J. Dairy
Sci.,15: 287-297.
Emara,H.M. (1984) : Effact of storage period on properties of processed cheese. M.Sc.
Thesis, . Zagazig Univ.
Farahat, S.M., Abdel-Baky,A.A., Aly, M.E. and Hana,U.B.B. (1993): The use of palm oil
in the manufacture of processed cheese spread. Zagazig J.Agric. Res., 20 (2A).
Hamad,M.N.(1997): Studies on the application of whey retentate produced by
ultrafiltration in process cheese manufacture. M.Sc. Thesis, . Mansoura Univ.
Ling, E. R. (1963). A text - book of Dairy Chemistry. Vol. 2, Practical, 3rd ed., Champan
and Hall, London, England.
Meyer,A. (1973): Processed Cheese Manufacture. Food Trade Press, Ltd, London.
Omar.M.A.M. (1994): A study on processed cheese. M.Sc. Thesis, . Al-Azhar Univ.
Richardson, G.H.(1985): Standard Methods of the Examination of Daity Products. 15th
ed. American Public Health Assocition. Washington, DC.
Sanderson, W. B., Brady, A. P., Whitehead, G. F., Oldham, I. J., and Brockwell, I. P.
inventors. (1996): Recycling salt solution in cheese processing and apparatus
therefore. Murray Goulburn Co-Operative Co. Limited, Australia, assignee. US
Pat. No. 5,73,237.
SAS (1991). SAS User’s guide: statistics. SAS Inst, Inc, Cary, NC.
Zayed, G., and Winter,J. (1995): Batch and continuous production of lactic acid from
salt whey using free and immobilized cultures of lactobacilli. Appl. Microbiol.
Biotechnol. 44:362–366.
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