vol1-no2-4

30

Journal of Applied and Industrial Sciences, 2013, 1 (2): 30-37, ISSN: 2328-4595 (PRINT), ISSN: 2328-4609 (ONLINE)

Research Article

*Corresponding author: Adil Salman E-mail: [email protected]

Abstract- This study was designed to monitor some bacteriological

and physical quality of milk from two dairy factories before and after

pasteurization, and also to assess the compliance of this quality

detected with the standard set by the Sudanese Standards and

Meteorology Organization (SSMO). Two hundred and Twenty raw

and pasteurized milk samples were collected from dairy factories and

sale points in Khartoum State. The average total bacterial counts

before pasteurization was1×105-9×106 cfu/ml and after pasteurization

it was 0-9×104 cfu/ml. Most of the market samples in day 1,3 and

day 6 showed range of 0-1×104 cfu/ml. Staphylococci counts before

pasteurization were found in range of less than 1×104 cfu/ml and after

pasteurization were in the range of 0-9×10 cfu/ml. The Coliform

counts before pasteurization were in the range of 1×103-9×103 cfu/ml

and immediately after pasteurization the range was reduced to 5-

1×102 cfu/ml. E.coli was identified from24%of the samples before

pasteurization. Before pasteurization acidity was found to be 0.17%,

directly after pasteurization the acidity was 0.15-0.16% but it was

0.16-0.17% in market samples.

INDEX TERMS: Acidity, Bacteria, Pasteurized milk, Khartoum,

Sudan.

I. INTRODUCTION

ilk is a nutritious food for human beings. It also serves as

a good medium for the growth of many microorganisms

such as Staphylococcus and Coliform. Bacterial

contamination of raw milk can originate from different

sources, including low quality raw milk, improper refrigeration

and an inadequate packaging system [1,4]. Raw milk

deteriorates in few days and pasteurized milk with high

temperature short time system (HTST) has a shelf life of about

seven days ]5[.

Measurement of bacterial numbers in milk is of interest

because they are indicator of poor milk hygiene production or

ineffective pasteurization of milk. Some microbes such as

gram negative Psychrotrophs, Coliforms and other pathogenic

bacteria such as Escherichia Coli ,Staphylococcus aureus may

also be found in milk ]6[.The hygienic quality of milk at the

point of production is also of importance from both public

health and consumer perception points of view. For milk to be

produced with a low bacterial count the temperature must be

kept low until the point of processing ] 7].

Contaminations of raw milk and the consequent high

bacterial count in milk originates from milking wet dirty

udders, the milking system used, the cooling and storage

temperature and the holding time ]8[The bacterial count is a

useful method to measure milk quality, a bacterial count

ranging between 9×105 - 9×10

6 cfu/ml is acceptable [ 9] , and

the mean standard plate count of raw milk is 1.29×106 cfu/ml ,

[10] but when milk was pasteurized it was reduced to 1.2×104

cfu/ml. Grade A milk has a count less than 1×105 cfu/ml and

grade B milk has count with less than 3×105 cfu/ml [11] , but

the majority of pasteurized milk sample has a count of 1×103

cfu /ml. [12 ].

Milk is often contaminated by Escherichia coli under lack

of sanitary conditions which can affect public health. The

coliform count is related to the unsanitary milking process and

dirty cow`s environment [13]. E. Coli was isolated from 32%

of raw fresh milk with Coliform count of less than 100 cell/ml

in Khartoum state [14]. Many studies indicated that the

production of high quality liquid milk is dependent on the

microbiological quality of raw material. The spoilage of

processed milk is primarily due to bacterial activity, presence

and activity of post-pasteurization contaminations and types

and activity of pasteurization resistant micro-organisms which

are the main limiting factors in extending the shelf life of high

temperature short time (HTST) pasteurize milk [15,17].In

addition other factors which limit the shelf life of refrigerated

pasteurized milk include the time and temperature of

pasteurization, and storage temperature of milk after

pasteurization [2,18 ].

In the Sudan milk and milk products play an important role

in the family diet. Most of the milk produced in the Sudan is

consumed as raw in both rural and urban areas, while the rest

is processed into milk products in urban areas [9] . Therefore,

certain requirements should be fulfilled in order to produce

safe and clean milk.

Some Bacterial and Physical Quality of Pasteurized

Milk in Khartoum

Adil, M. A. Salman *1 and Eltaf, M. Hagar

2

1Department of Preventive medicine, College of Veterinary Medicine, University of Bahri

2 Preimer Company for dairy processing- Khartoum – Sudan

(Received: March 19, 2013; Accepted: May 29, 2013)

M

mailto:[email protected]

31


These requirements include: clean milking and cooling of

milk immediately after transference of milk to processing in

ideal plants with stick quality control. Handling of raw milk is

a big problem in the Sudan as the dairy farms are located in

different remote areas with minimum infra-structure in

addition to the prevailing hot climate of the country with lack

of cooling and transportation facilities, appreciable amount of

milk is spoiled even while in transit. The main objective of this

study is to estimate acidity and bacterial quality of

1- raw milk intended for pasteurization.

2- pasteurized milk immediately after processing in the factory

3- pasteurized market milk at different time interval .

II. MATERIAL & METHODS

Milk samples were collected from two factories and

different sale points in Khartoum State- Sudan. The factories

are located in Khartoum North, while market samples were

collected from the three municipalities Khartoum, Khartoum

North and Omdurman.

Sample collection

A total of 220 milk samples were collected from two

factories (A &B). Factory A has its own dairy farms and use

their own milk for processing, while factory B purchases milk

from local market.

Market samples were collected at three different levels in

different batches as follows:

1- Fresh milk samples: Fifty samples were collected from raw

fresh milk supplied to factory A and B in clean and sterile

bottles.

2- After pasteurization samples: Fifty samples from the milk

tanks of two factories A and B were collected immediately

after pasteurization in clean and sterile bottles.

3- The market samples (shelf life): one hundred twenty

samples were collected from pasteurized milk produced by the

two dairy factories from different sales points in Khartoum

state at days 1, 3and 6.

Laboratory tests

1- Acidity: The test was performed according to the method

described by [19]

2-Bacteriological analysis

a) The Total bacterial count (T.B.C) was performed according

to[20 ]

b)The Coli form Count and E.Coli identification were carried

out using Violet Red Bile agar (VRB) and Eosin Methylene

Blue Agar (EMB agar) [21].

c)The Staphylococci count was done was done using the Baird

Parker Agar [21 ] .

Statistical analysis

SPSS 12 analysis packages and One-Sample t test was used for

comparison of milk samples

III. RESULTS

Most milk samples of both factory A (88%) and B (87.5%)

showed a range of 1×105-9×10

6cell/ml of total bacteria count

before pasteurization, 80% of the samples from factory A showed

a range of more than 1×107

cell/ml while 12.5% in factory B

showed a range of 0-9x104cell/ml (Fig. 1a and Fig. 1b).

After pasteurization 96% of the samples were in the range of 0-

9x104cell/ml

. in factory A and 43.5% were in the same range in

factory B, while a range of 1x105 -9x10

5 was 56.5% in factory B.

(Fig.1a and Fig.1b). Statistically, the difference in Total Bacterial

Count between factory A and B was significant for both factories

before and after pasteurization at P<0.05 (Table 1).

32


Table (1). One-Sample Statistics (One-Sample Test) of Total Bacterial Count For milk samples from factory A&B before and

after pasteurization.

N

Mea

n

Std.

Deviation Std. Error Mean

Before Pasteurization A 25 2.04 .35 7.02E-02

Before Pasteurization B 25 1.88 .34 6.90E-02

After Pasteurization A 25 1.04 .20 4.00E-02

After Pasteurization B 25

1.57 .51 .11

Test Value = 0

T Df

Sig

(2-tailed)

Mean

Difference

95% Confidence Interval

of the Difference

Lower Upper

Before Pasteurization A 29.04 24 .000 2.04 1.90 2.18

Before Pasteurization B 27.19 23 .000 1.88 1.73 2.02

After Pasteurization A 26.00 24 .000 1.04 .96 1.12

After Pasteurization B 14.81 24 .000 1.57 1.35 1.78

The difference is significant in the bacterial count between the two factories before and after pasteurization at P<0.05

In sales point samples obtained from factory A 100%, 95% and 90% of the samples were in range 0-9×104 cfu in day 1, 3 and

day 6 respectively (Fig. 2a).While in sales point samples obtained from factory B 70%, 80% and 60% of T.B.C was found in the

range of 0 - 9X104 cfu in day 1, 3 and 6 respectively. Only 10% of samples collected in day 6 showed a range between 1×10

5-

9×106 cfu from factory A (Fig.2a). The difference was also significant for TBC between day 1 and day 6 in factory A at P<0.05.

(Table 2).

Table (2): One-Sample Test of factory A for sale points in day 1 and day 6.

Test Value = 0

T df Sig. (2-tailed)

Mean

Difference

95% Confidence Interval of the

Difference

Lower Upper

TBC 12.365 19 .000 1.30 1.08 1.52

coliform 15.280 18 .013 1.11 .95 1.26

Staphylococci 11.059 17 .000 2.39 1.93 2.84

The difference is significant in the bacterial count between day 1 and 6 in factory A after pasteurization, at 95% confidence

interval.

In factory A and factory B, 80% and 52% of the samples showed a Coliform count in the range of 1×103

cfu before

pasteurization. After pasteurization 80% and 40%of the samples in factory A and B were in the range of 1-102

cfu. (Fig 2a and

Fig.2b).

33


In day 1, day3, and day 6, 50%, 40% and 20% were in the range of 1-102 cfu in factory A, and 40%, 50% and 20% samples

from factory B respectively (Fig 2a and Fig. 2b). The difference in Coliform counts between day 1 and day 6 was statistically

significant (Table 2) E. Coli were detected from 24%and 12% of Coliform positive milk samples from factory A and factory B

respectively before pasteurization. In factory A and factory B 15% of the Coliform positive samples at the sales point in day 6

were E. Coli positive, but in day 3, 15% of the samples from factory B at the sales point were also positive (Tab

Table (3). E.coli detection from coliform positive milk samples.

E.Coli test +ve -ve

Total number of

Samples

A 6 19 25

Before 24% 76%

pasteurization B 3 22 25

12% 88%

A 0 25 25

After 100%

pasteurization B 0 25 25

100%

A 0 20 20

Day3 80%

Day6 A 3 17 20

15% 85%

Day3 B 3 17 20

15% 85%

Day6 B 3 17 20

15% 85%

34


The range of Staphylococci counts in all milk samples

before pasteurization in both factories A and B were more

than1×104

cfu in about 76% and 88% in the two factories

respectively. After pasteurization the counts were 0 - 9×10 cfu

in about 72% and 100% in the two factories respectively. In

day 3 almost all sales point samples from factory B showed a

range of 0 - 9X10 cfu/ml while 61% of the samples were in the

range of 1×102

-9×103 cfu/ml in the same factory in day 6 (Fig

3).

As for factory A the count of Staphylococci of range of 0 -

9×10 cfu was found to be 85%,50% and 40% in day 1,3 and 6,

respectively , and the range of 1 ×102 -9×10

3 cfu/ml was

10.5%,10.5% and 61.1% in days 1,3 and 6 respectively,

statistically there was a significant difference in Staphylococci

count between day 1 and 6 in factory A at 95% confidence

interval, (Table 2). At the sale points the acidity within the

range of 0.14%-0.18%, were 40% and 20% in factory A and

factory B in day six. (Table 4)

Table (4): Acidity of milk samples of factory A&B before and after Pasteurization

Table (5) Acidity range at sale points

Acidity Range Factory A Factory B

Before pasteurization After pasteurization Before pasteurization After pasteurization

15%- 18% 15(60%) 20 (80%) 14 (56%) 20 (80%)

19% 7 (28%) 3(12%) 7 (28%) 00

20%- 21% 3 (12%) 2 (8%) 4 (16%) 5 (20%)

Total 25 25 25 25

Acidity range Factory A Factory B

Day

one

Day

Three

Day

Six

Day

One

Day

Three

Day

Six

14%-18%

15 (75%) 16

(80%)

8

(40%)

18 (90%) 10 (50%) 4 (20%)

19%-21%

5 (25%) 4

(20%)

12

(60%)

2 (10%)

10 (50%) 16

(80%)

Total 20 20 20 20 20 20

35


IV. DISCUSSION

Milk processing was practiced since the early sixties in

Sudan by the government sector but still most of the milk is

consumed as raw. Recently the private sector contributed to

this business by establishing many milk plants in Khartoum

state. In this study a range of 1×105-9×10

6 cfu/ml TBC for

raw milk was found to be 87.5%, and 88% in factory B and A

respectively. This range was almost in agreement with the

range required by the Sudanese Standards and Metrology

Organization, ]22[ for raw milk which was 5X105-

1X106cfu/ml. The range is comparable to that obtained by

similar studies where a range of 1×106

-9×106

cfu/ml in

Khartoum State was reported ]9,23[. The acceptable limit of

TBC of the European Union ]24[ of raw milk was reported to

be 1x104

cfu/ml . The findings in this study were comparable

to that of ]25[ who reported a range of 4×105cfu/ml.

High bacterial count is expected under tropical conditions

such as the Sudan due to the fact that high temperature

enhances growth and multiplication of bacteria in addition to

absence of sanitary conditions and unavailability of cooling

facilities during handling and transportation of milk ]9[.

In pasteurized milk the total bacterial count of less than or

equal to 9×104cells/ml was the lowest range, 43.5% and 96%

of the samples in factory B and A were in this range

respectively. This range was in compliance with what was

recommended by the Sudanese Standards and Metrology

Organization, ]22[ for pasteurized milk which was 1×104

-

9×104

cfu /ml, and higher than was reported by the European

Union which was 3x104. The data obtained during this study

showed that 56.4% of the pasteurized milk samples were in the

range of 1×105-9×10

6 cfu /ml in factory B while it was 4% in

factory A. This higher count might be due to higher TBC count

of the raw milk used in factory B, or recontamination from

equipment during and after pasteurization.

The findings in this study were in agreement to that reported

by ]26[ who reported that about 70% of the pasteurized milk

samples tested had aerobic bacteria count exceeding the

regulatory limit of 2×104cfu/ml for grade ‘A’ pasteurized milk

set by the United States Food and Drug Administration (FDA)

PMO ]27 [ .

Statistically the difference in the count before and after

pasteurization was significant, a high count of TBC before

pasteurization may affect the count of the bacteria after

pasteurization. The data obtained from the sales point showed

discrepancy between various samples. This may be attributed

to inadequate cooling systems at the sale points, improper

pasteurization or recontamination after pasteurization. In

factory A, 90% of the samples from different batches at day 6

conform with the limits set by SSMO (9×104

cells/ml), while

only 20% from factory B were within these limits. Although in

factory B, milk was collected from their own farm, in cans,

but their cans may not be well washed and disinfected

regularly. The load of bacteria in raw milk in transporting cans

and residues of milk in tanks is one of the important reasons

for recontamination of raw milk and this affect the load of

pasteurized milk ] 9[. Also this high total bacteria count might

be due to improper pasteurization and contamination of

packaging materials.

Coliform in milk is one of the best indices for judging

sanitation ]28[ .In this study, 76% and 32% of raw milk

samples in factory A and B were in the range of 1×103-9×10

4

respectively. This range is higher than that reported by

American Public Health Association, less than 102]

29[. The

higher Coliform count in raw milk used in factory B may be

due to the unsatisfactory milking practices in the farm from

which the milk was collected. A similar count of 9×103 cfu

/ml in Khartoum state was reported ]14,30[.In Jordan a higher

range of 2.5×104-1.4×10

6 was reported ]31[. In this study

lower TBC value was obtained for pasteurized milk compared

to what reported by]32[ who showed a range of 6.5×105 to

6.5×1014

cfu.

The official limits set by the SSMO for pasteurized milk for

Coliform bacteria was 1x5 -1x102

cfu/ml ]22[ . The result of

this study showed that, 80%of the samples from factory A and

40% from factory B conform with this limits. The results were

in agreement with[ 27[who suggested a range of less than 102

cfu/ml. in Algeria [ 33[ stated that (31.5 %) and (6.5 %)

samples of milk from the two sources of samples at sales point

were not in compliance with the acceptability threshold fixed

at 10 cfu/ml. Coliform bacteria counts of pasteurized milk

showed lower numbers than these reported by ]32[ . The lower

Coliform counts might be due to hygienic quality of raw milk,

proper pasteurization process, good packaging and good

storage conditions. This agreed with] 27[who reported that the

total bacterial standards for grade A pasteurized milk should

be < 10 Coliform/ ml.

In this study, at the sale points samples of pasteurized milk,

50%, 40%,49% and 20% of samples from factory A comply

with the official standards. Towards the end of the validity,

both factories showed a lower compliance (20%). This might

be due to poor cooling efficiency at these points and variations

in samples that were collected from different batches.

Several workers isolated E.coli from milk and stated that it

might cause a potential risk particularly for children ]34,37[.

However, in this study, before pasteurization 24% of the

samples from factory A and 12% from B were positive ,

comparable to what was reported by ]14[ who reported about

32% of the raw bulk milk were E. coli positive in Khartoum

state. After pasteurization there was no growth of E.coli in the

samples obtained from both factories. The sale points samples

of factory A showed no E coli growth at day 3 while 15% of

the samples were positive in day 3 in factory B, but in day 6

both factory A and B showed positive E.coli results (towards

the end of shelf life).

36


This result was higher than what was reported by SSMO for

pasteurized milk of E.coli ]22[ which was Zero. In factory B

the early detection of E.coli may indicate flocculation in the

pasteurization process, since the samples were from different

batches.

In this study 76% and 88% of raw milk samples from

factory A and B had a Staphylococci count of more than

1×104

. These results are higher than those reported by ]38[

and ]39[ which were 45% and 68%,respectively. All these

counts are beyond bacterial safety limit recommended by ]40[

not to exceed 103.

After pasteurization 72% and 100% of the samples form

factory A and B had a count of 0-9×10. Several studies

showed a wide range of bacterial count, ] 33[ found that 20%

of the samples had a count of more than 10cfu/m. Laszlo

]12[reported the count of more than 103 cfu/ml . While ]39[

found that 30% of the samples were contaminated with

Staphylococcus aureus. The Staphylococci can contaminate

milk after milking or during processing ]9[ .

Raw milk acidity reported in this study was in the range of

0.15-0.18% lactic acid in 60% and 56% of samples from

factory A and B respectively. Which was better than what was

reported by ]9[ who reported acidity of less than 0.20% in raw

milk. It was also lower than that obtained by ]41[ who

reported raw milk acidity between 0.18-0.2 % lactic acid, but

in agreement with the result reported by ]42[ who reported an

acidity range of 0.14 -0.18%, and they reported that a high

acidity implies a high lactic acid content which, in turn,

implies a high bacteria count in the milk. But after

pasteurization, the acidity was in the range of 0.15-0.18% in

80% of the samples in both factories A and B which is in

accordance with SSMO standard ]22[ . These findings are

comparable to what is reported by ]23[ who showed that the

mean acidity of pasteurized milk was 0.143 in Sudan and it is

lower than 0.219% reported by ]43[ . The decrease of acidity

after pasteurization was also reported by ]44[. In sale points

pasteurized milk samples the acidity was stable till day 3, but

later on day 6 (towards the end of shelf life ) only 40% and

20% of the samples in factories A and B conform with SSMO

standards. Higher acidity reported here may be due to lack of

cooling facilities during transportation of raw milk or improper

storage.

V. CONCLUSION

1. The quality of pasteurized milk was not stable, different

batches were variable in their quality.

2. Albeit the good hygienic and controlled farm resulted in

acceptable bacterial quality of pasteurized milk in factory A,

the market samples showed unacceptable limits of bacteria.

3. Modern dairy farming coupled with efficient milk plants are

of importance for production of safe, clean and wholesome

milk.

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