University of Khartoum
Faculty of Animal Production
M.Sc. Tropical Animal Production
Seminar about
Effect of Heat Treatments, Starter Culture and
Storage Temperature and Period on The Quality of
White Cheese (Gibna byda)
By
Hanaa Mohammed Abbas Salih
Supervisor
Mohamed Osman M. Abdalla
Introduction
 World
production of milk in 2008 is estimated at
576 × 106 tones (ZMP, 2008). Milk is a highly
perishable
food
material,
therefore,
its
transformation into cheese or other forms of
fermented dairy products, provides an ideal vehicle
to preserve its valuable nutrients, making them
available throughout the year (Kongo, 2013).
 White soft cheese 'Gebna Beyda' is the major type
of cheese in Sudan beside 'Mudaffara', and recently
'Gouda' and 'Muzzarella' cheeses are introduced
(Abdalla and Sulieman, 2010).
 Sudanese
white cheese falls into the family of soft
and semi-soft pickled cheeses of the East
Mediterranean region and North Africa (Abdalla,
1992).
 It is manufactured from raw or heated milk (El Owni
and Hamid, 2007). When manufactured from raw
milk no starter culture is added, only the natural lactic
acid bacteria present in the raw milk carry the
fermentation process required for the cheese
maturation (Omer and Hamid, 2013).
 Sudanese
white cheese is usually manufactured in
rural areas where hygienic conditions are poor in
addition to poor handling and packaging (Maher et
al., 2001; Hamid and El Owni, 2008).
 Elkhider et al. (2012) found high bacterial load in
Sudanese white cheese samples collected from
different producers in rural areas of New Halfa,
eastern of Sudan.
 The major factor that contributing to the presence of
S. aureus in cheese the use of un-pasteurized milk
(Santos and Genigeorg, 1981).
 Also
the use of raw milk leads to unpredictable
chemical or biological changes or possible survival
of various pathogens during manufacture and
repining (Pappa et al., 2006).
 Nowadays, pasteurized milk is used instead of raw
milk in organized cheese dairies making necessary to
the use of lactic acid bacteria (LAB).
 Lactic acid bacteria are a group of gram-positive,
non-spore forming, cocci or rods, which produce
lactic acid as the major end product during the
fermentation of carbohydrates.
 LAB
are important in cheese processing because they
increase food safety through the release of lactic acid
and bacteriocins, produce aromas and flavors,
accelerate the maturation process of cheese via their
proteolytic and lipolytic activities and contribute in
food texture via release of polysaccharides that
increase the viscosity and firmness, and reduce
susceptibility to syneresis (kongo, 2013).
The objectives of the study are:
 Evaluation
of the effect of starter culture on white
cheese quality.
 Determination of the quality of cheese as affected by
heat treatments of cheese milk.
 Determination of the effect of storage period on the
quality of white cheese.
 Determination of the effect of storage temperature on
the quality of white cheese.
 The
present study was conducted at Department of
Dairy Production, Faculty of Animal Production,
University of Khartoum during the period October to
December, 2014.
 Fresh cow’s milk was brought from Sudan
University farm at kuku, Rennet powder and a
Thermophilic yoghurt culture (Code : CH1) were
obtained from Cher. Hansen’s Laboratory (Denmark)
and salt was purchased from the local market.
Cheese manufacture
 Cow
milk was used for the manufacture of white
cheese (Gibna Bayda) to which a starter culture (2%
w/w of a 1:1 combination of Streptococcus
thermophilus and Lactobacillus bulgaricus) was
added.
 Four treatments were prepared as fallow:
 Treatment
1 (T1 control): milk was only warmed to
45⁰C.
 Treatment 2 (T2): milk was warmed to 45⁰C, starter
culture (2% w/w) was added and left for 30 min to
develop acidity.
 Treatment 3 (T3): milk was heat treated at 72⁰C for
1 min, cooled to 45⁰C and CaCl2 (0.02% w/w) was
added.
 Treatment 4 (T4): milk was heat treated at 72⁰C for
1 min, cooled to 45⁰C, starter culture (2% w/w)
was added and left for 30 min to develop acidity,
followed by addition of CaCl2 (0.02% w/w).
 Table
salt (NaCl) was added to all treatments at the
rate of 2% (w/w), rennet powder (1.3 gm) was
dissolved in 50 ml distilled water and added (1 ml/1
L milk). Milk was stirred for 5 min and left to
develop a curd. After coagulation, the curd was cut
by a sterile stainless steel knife and left for 5 min to
separate the whey, which was collected for further
use in preservation. The curd was transferred into
clean wooden moulds lined with clean cloth and
pressed overnight (1 kg weight).
 Next
day the curd was cut into cubes (2.5x2.5x2.5
cm), weighed and preserved in the heat treated
(72⁰C/1 min) salted (2% w/w) whey for 24 hr.
 For each treatment, the curd was divided into two
batches: first batch was stored without whey at 8⁰C,
while the second was stored in the whey at 25oC and
both were stored for 45 days.
 Chemical, microbiological and sensory characteristics
were determined at 1, 15, 30 and 45 day intervals. In
addition coagulation time was recorded and cheese
yield was determined immediately after processing.
Milk
Raw
With Starter
30⁰C
8⁰C
Heat treated
Without starter
30⁰C
8⁰C
With Starter
30⁰C
8⁰C
Without starter
30⁰C
8⁰C
Physiochemical
analysis
 Fat,
protein, total solids, ash contents and titratable
acidity) for milk and cheese samples were determined
according to AOAC (2000).
 Cheese yield was determined immediately after
processing in (kg cheese/100 kg milk).
 Coagulation time was recorded (min).
Microbiological
analysis
 Total
viable bacterial count and Staphylococcus
aureus count were determined according to
(Houghtby et al., 1992).
 E. coli most probable numbers per ml of sample were
determined according to (Marshall, 1992; Thatcher
and Clark, 1986).
 Yeasts and moulds enumeration was carried
according to Frank et al. (1992).
Sensory evaluation
A
panel of 10 untrained panelists were chosen to
judge on the quality of cheese (color, flavor, texture
and saltiness) using a sensory evaluation sheet.
Statistical analyses
 Statistical
analyses were performed using the
Statistical Analysis Systems (SAS, ver. 9). Factorial
design (2x2x2x4) was used to determine the effect of
heat treatment of milk, starter culture, and storage
temperature and storage period on physiochemical,
microbiological and sensory characteristics of cheese.
Means separation was carried out using Duncan
Multiple Range Test (p<0.05).
Table 1. Yield and coagulation time of cheese
Type of cheese
Coagulation time (min)
Weight/7L
T1
60
952g
T2
45
850g
T3
90
975g
T4
75.5
1200g
T1= cheese made with raw milk without starter culture.
T2 =cheese made with raw milk with starter culture.
T3 =cheese made with heat treated milk without starter culture.
T4 =cheese made with heat treated milk with starter culture.
Table 2. Effect of heat treatments of cheese milk on the physiochemical
characteristics of white soft cheese
Physiochemical
characteristics (%)
Fat
Protein
Total solid
Moisture
Ash
Acidity
Type of milk
Raw
Heat treated
25.07a
24.20a
18.33a
18.16a
44.25b
47.36a
55.73a
53.11b
6.45a
5.92b
0.57a
0.57a
SE
SL
0.972
2.328
4.488
2.486
0.151
0.006
NS
NS
***
***
***
NS
Means in the same row bearing similar superscripts are not significantly
different (P>0.05)
*** = P<0.001
NS = Non significant
SL = Significance level
SE = Standard error of means
Table 3. Effect of addition of starter culture on the physiochemical
characteristics of white soft cheese
Physiochemical
characteristics (%)
Fat
Protein
Total solid
Moisture
Ash
Acidity
Starter culture1
1
24.79a
18.36a
45.88a
54.57a
6.36a
0.55a
2
24.48a
18.13a
45.73a
54.27a
6.01b
0.58a
SE
SL
0.972
2.328
4.488
2.486
0.151
0.006
NS
NS
NS
NS
*
NS
Means in the same row bearing similar superscripts are not significantly
different (P>0.05)
* = P<0.05
NS = Non significant
SL = Significance level
SE = Standard error of means
1
= Treatment No. 1 cheese made with starter culture, and treatment
No. 2 cheese made without starter culture
Table 4. Effect of storage temperature on the physicochemical characteristics
of white soft cheese
Physiochemical
characteristics (%)
Fat
Protein
Total solid
Moisture
Ash
Acidity
Storage temperature (⁰C )
8
30
23.24b
26.03a
17.98a
18.51a
44.10b
47.51a
60.00a
52.84b
7.03a
5.34b
0.38b
0.75a
SE
SL
0.972
2.328
4.488
2.486
0.151
0.006
***
NS
***
***
***
***
Means in the same row bearing similar superscripts are not significantly
different (P>0.05)
*** = P<0.001
NS = Non significant
SL = Significance level
SE = Standard error of means
Table 5. Effect of storage Period on the physiochemical
characteristics of white soft cheese
Physiochemical
characteristics (%)
Fat
Protein
Total solid
Moisture
Ash
Acidity
Storage period (days)
1
15
30
45
22.47b
21.63a
39.12c
61.28a
8.01a
0.25c
25.70a
18.18b
49.50a
50.50c
5.33b
0.54b
25.50a
16.99b
47.99ab
52.01bc
5.70b
0.72a
24.88a
16.17b
46.61b
53.89b
5.72b
0.77a
SE
SL
1.374
3.291
3.517
3.514
0.214
0.002
***
***
***
***
***
***
Means in the same row bearing similar superscripts are not
significantly different (P>0.05)
*** = P<0.001
SL = Significance level
SE = Standard error of means
Table 8. Effect of heat treatments of cheese milk on the microbiological
quality (log10 cfu/gm) of white soft cheese
Microorganism
Type of milk
Raw
Heat treated
TVB count
S. aureus count
E. coli count
Yeasts and moulds count
6.68a
2.26a
0.56a
6.02a
6.72a
1.40b
0.76a
5.95a
SE
SL
0.017
0.208
0.410
0.037
NS
***
NS
NS
Means in the same row bearing similar superscripts are not significantly
different (P>0.05)
*** = P<0.001
NS = Non significant
SL = Significance level
SE = Standard error of means
Table 9. Effect of addition of starter culture on the microbiological
quality (log10 cfu/gm) of white soft cheese
Microorganism
TVB
S. aureus count
E. coli count
Yeasts and moulds
Starter culture1
1
2
6.63b
6.77a
1.73a
1.94a
0.38a
0.94a
5.91a
6.06a
SE
SL
0.017
0.208
0.410
0.037
*
NS
NS
NS
Means in the same row bearing similar superscripts are not significantly
different (P>0.05)
* = P<0.05
NS = Non significant
SL = Significance level
SE = Standard error of means
1
= Treatment No. 1 cheese made with starter culture, and treatment
No. 2 cheese made without starter culture
Table 10. Effect of storage temperature on the microbiological quality
(log10 cfu/gm) of white soft cheese
Microorganism
TVBC
S. aureus count
E. coli count
Yeasts and moulds
Storage temperature (⁰C )
8
30
6.72a
6.68a
2.37a
1.30b
0.95a
5.87b
0.36a
6.10a
SE
SL
0.017
0.208
NS
***
0.410
0.037
NS
*
Means in the same row bearing similar superscripts are not significantly
different (P>0.05)
*** = P<0.001
* = P<0.05
NS = Non significant
SL = Significance level
SE = Standard error of means
Table 11. Effect of storage Period on the microbiological quality
(log10 cfu/gm) of white soft cheese
Microorganism
Storage period (days)
SE
SL
6.89a
0.024
***
1.95a
1.92a
0.294
***
1.12a
0.36ab
1.15a
0.579
*
5.93b
6.14b
6.54a
0.052
***
1
15
30
45
TVB count
6.97a
6.51b
6.43b
S. aureus count
2.57a
0.89b
0b
5.33c
E. coli count
Yeasts and moulds count
Means in the same row bearing similar superscripts are not significantly
different (P>0.05)
*** = P<0.001
* = P<0.05
SL = Significance level
SE = Standard error of means
Table 14. Effect of heat treatments of cheese milk on sensory characteristics
of white soft cheese
Character
Color
Flavor
Taste
Body
Saltiness
Overall acceptability
Type of milk
Raw
Pasteurized
3.23a
3.31a
2.61a
2.72a
2.25a
2.20a
2.06b
2.31a
1.36b
1.54a
3.00a
2.52b
SE
SL
0.038
0.039
0.031
0.033
0.019
0.046
NS
NS
NS
***
***
***
Means in the same row bearing similar superscripts are not significantly
different (P>0.05)
*** = P<0.001
NS = Non significant (P>0.05)
SL = Significant level
SE = Standard error of means
Table 15. Effect of addition of starter culture on sensory characteristics
of white soft cheese
Character
Color
Flavor
Taste
Body
Saltiness
Overall acceptability
Starter culture1
1
2
3.30a
3.24a
2.66a
2.68a
2.36a
2.09b
2.22a
2.15a
1.45a
1.46a
2.63b
2.88a
SE
SL
0.038
0.039
0.031
0.033
0.019
0.046
NS
NS
***
NS
NS
***
Means in the same row bearing similar superscripts are not significantly
different (P>0.05)
*** = P<0.001
NS = Non significant (P>0.05)
SL = Significant level
SE = Standard error of means
1
= Treatment No. 1 cheese made with starter culture, and treatment No. 2
cheese made without starter culture
Table 16. Effect of storage temperature on sensory characteristics of
white soft cheese
Character
Color
Flavor
Taste
Body
Saltiness
Overall acceptability
Storage temperature (⁰C )
8
30
3.25a
3.29a
2.55b
2.78a
2.01b
2.44a
1.90b
2.47a
1.33b
1.57a
2.49b
3.02a
SE
SL
0.038
0.039
0.031
0.033
0.019
0.046
NS
***
***
***
***
***
Means in the same row bearing similar superscripts are not significantly
different (P>0.05)
*** = P<0.001
NS = Non significant (P>0.05)
SL = Significant level
SE = Standard error of means
Table 17. Effect of storage Period on sensory characteristics of
white soft cheese
Character
Storage period (days)
SE
SL
1
15
30
45
Color
3.33a
3.34a
3.32a
3.09b
0.053
*
Flavor
2.44b
2.46b
2.83a
2.94a
0.055
***
Taste
1.86c
2.32ab
2.25b
2.47a
0.044
***
Body
1.61c
2.26b
2.42ab
2.44a
0.047
***
Saltiness
1.20c
1.63a
1.48b
1.50ab
0,026
***
Overall acceptability
2.63b
2.94a
2.79ab
2.68b
0.66
*
Means in the same row bearing similar superscripts are not significantly
different (P>0.05)
*** = P<0.001
* = P<0.05
SL = Significant level
SE = Standard error of means
conclusion
conclusion
 The
total solids, moisture and ash contents were
significantly (P<0.001) affected by heat treatment of
milk, while fat, protein contents and acidity were not.
 Body
and saltiness of white cheese were significantly
better in cheese produced from heat treated milk,
while color, flavor and taste were not.
 Staphylococcus
aureus count was significantly lower
in cheese made with heat treated milk.
 Starter
culture added had no effect on
physiochemical characteristics of white cheese. On
other hand ash content was significantly higher in
cheese made with starter culture added.
 Total
viable bacteria count was significantly lower in
cheese made with starter culture. Although other
microbiological characteristics were not significantly
affected by starter culture added, lower load was
observed in cheese made with starter culture added.

Higher physiochemical characteristics, lower
microbial load except yeasts and moulds count and
better sensory characteristics were observed in cheese
stored at 25⁰C .

The total viable bacteria increased at the end of
storage period and yeasts and moulds counts increased
as the storage period progressed.
 During
storage the saltiness and overall acceptability
of cheese improved till day 15 then deteriorated, while
color, flavor, body and taste improved.
Although
body was not affected by starter culture
addition, the higher score was in cheese with
starter culture addition.
 The
taste was significantly more acidic in cheese
made with starter culture and this affected the overall
acceptability.
 The
highest yield and the shortest coagulation time
were obtained from cheese made with heat treated
milk with starter culture.
The
use of starter cultures is recommended for
cheese making.
Heat treatment of milk is necessary for the
manufacture of safe product for consumption.
Storage at room temperature (25C) is suitable for
favourable growth of thermophilic lactic acid
bacteria which lead to production of lactic acid
that suppresses the growth of undesirable
bacteria.
Since high acidic taste was observed for cheese it
is recommended to use lower concentrations of
starter cultures.
Table 7. Effect of addition of starter culture and storage temperature
on the physiochemical characteristics of white soft cheese