Comparison of Chemical Composition and Microbial Profile of Raw and Pasteurized Milk of the Western Cape, South Africa
Ibtisam E.M. El Zubeir,
During the present study raw and pastuerized milk samples
were collected from the three major dairy factories during March- August
2001. The raw milk supplied by farmers to the selected factory was collected
from bulk tank. Similarly pasteurized milk samples, processed and distributed
by those factories, were randomly collected from three different food
stores and retailers of the Western Cape of South Africa. The frequency
of the isolation of the microorganisms, from both raw and pasteurized
milk, revealed a higher prevalence of S. aureus in the raw milk
(15.38%) followed by those of E. coli (14.3%) that was also isolated
at a rate of 3.6% form pasteurized milk. Also, other mastitis-isolated
pathogens found were Streptococcus agalactiae (8.79%), Streptococcus
dysglactiae (12.09%), Streptococcus uberis (6.72%), Enterococcus
faecalis (8.35%) which was also found in 2.2% of the pasteurized milk
samples and Staphylococcus epidermidis (8.79%) that were also found
in pasteurized milk (2.2%). Other identified isolates, were also represented.
However, all samples revealed negative results for the growth of Salmonella
and Listeria monocytogenes. Descriptive and frequency analysis
showed higher means, standard error of means and standard deviation for
the somatic cell counts, total bacterial counts, coliform counts and E.
coli counts, although their minimum values revealed a negative or
a very low levels. A lower level was also obtained for the chemical content
(fat, protein, lactose, SNF and total solids) of the pasteurized milk
compared to the raw milk samples for all studied companies. Also the percentage
of the added water was very high in the processed milk compared to the
samples from herd raw bulk milk. Moreover the significant variation between
the measurements were estimated.
Food production processes are increasingly influenced by quality and
safety concerns, for dairy production, one of the food quality outcomes
is low level of bacteria in unprocessed milk (Finger and Sischo, 2001).
Milk and dairy products are the major sources of nutrition and energy;
however, it is well known that they can become sources of zoonotic infections
(Mohamed and El Zubeir, 2007a). They recommended that milking should be
done under hygienic conditions and milk should be cooled immediately after
milking and should be heat treated to control bacteriological quality.
This to ensure that milk is produced, distributed, handled and marketed
under the control of milk commission and the commission must have a sanitary
inspector and veterinarian to enforce its methods and standards (Mohamed
and El Zubeir, 2007b).
The microbiological contents of raw milk affect quality, shelf life and
safety of processed milk and other dairy products (Gunasekera et al.,
2000). Mohamed et al. (1997) reported the effect of mastitis on
the compositional quality of milk and concluded that mastitis has a great
influence on milk composition. Infection and disease are the results of
failures in proper application of milk production hygiene (El Zubeir et
al., 2006). However, independently to the milk production situation
in any place, milk should not be drunk or used to manufacture of any products
without previous pasteurization or boiling (Giovannini, 1998). Moreover,
pasteurization of milk provides protection for the consumers against pathogens
that might be present in the raw milk and improves its keeping quality
Gunasekera et al. (2000) reported that several methods available
for detection and enumeration of microorganisms in raw and processed milk.
However, as they reported culture techniques are the most common. Similarly,
somatic cell counts (SCC) are widely used to predict the mammary health
status of quarters and cows, the suitability of milk for human consumption
(Heeschen, 1996). On the other hand, Berning and Shook (1992) cited that
infections by major pathogens are often associated with SCC below the
threshold for mastitis diagnosis (500,000 cell mL-1). Moreover,
Dekkers et al. (1995) indicated that efforts to reduce bulk milk
Somatic Cell Count (SCC), resulted in substantial extra milk revenues.
Further, a bulk SCC target of 250,000 cells mL-1 was advocated.
Since they estimated a level 200,000 and 450,000 cells mL-1
in Ontario, Canada. However, Ma et al. (2000) stated that in general
standard plate counts, coliform counts and psychrotrophic bacterial counts
of both high and low SCC milk remained low (<100,000 cfu mL-1)
during 5 °C storage.
The present study is meant to evaluate and discuss the present hygenic
and compositional situation of milk produced and consumed in the Western
Cape of South Africa.
MATERIALS AND METHODS
Source of Milk Samples
The present study was conducted during March- August 2001 in the Western
Cape of South Africa. It involves 3 different dairy companies, with their
suppliers of the raw milk. Raw bulk tank milk samples were collected from
some of the farmers (30 samples) that supply their milk to the selected
dairy factories. The samples were collected in sterile Macarteny bottles
directly from the bulk tank supplying raw milk to the factory. Similarly
pasteurized milk samples, processed and distributed by three factories
(30; 10 samples from each), were randomly collected from the three different
food stores and retailers distributed in the different socioeconomical
groups of the Western Cape of South Africa.
Analysis of Milk Samples
The milk samples were first brought to the Laboratory of the Medical
Microbiology, University of Western Cape in an ice container. Part of
the milk samples were spilt aseptically into 40 mL sterile bottles, coded
and refrigerated over night for bacteriological analysis. All microbiological
evaluations were done at Provincial Veterinary Laboratory, Stellenbosch.
The somatic cell counts (SCC) were estimated using Coulter Counter (Beckman,
Z1 series, England) according to the manufacturers recommended procedures.
South African Bureau of Standards (SABS) methods were applied to the total
bacterial count (ISO 6222, 1999), enumeration of coliforms (SABS ISO 4831,1991),
detection of Escherichia coli (SABS ISO 7251, 1993), detection
of Salmonella (ISO 6579, 1993) and detection of Listeria monocytogenes
(SABS ISO 11290/ 1 and 2, 1996, 1998). The isolation and identification
of Staphylococcus spp., Streptococcus spp., Enterococcus
spp. and Bacillus cereus (their presence is coded as standard
cultures; in order to facilitate their statistical analysis) were also
done on blood agar according to Quinn et al. (1994) and Bergey`s
manual (Holt et al., 1994). Similarly another 50 mL of the same
milk samples were coded and brought to the ARC-Animal Nutrition and Product
Institutes, Elsenburg for the determination of chemical composition of
milk. Percentages of fat, protein, lactose and SNF were done using infrared
spectrophotometer (Milko Scan 133B analyzer, A/S N. Foss Electric, Hillerford,
Denmark), whereas total solids and ash contents were obtained by subtraction.
The freezing point, to detect the percentage of the added water was also
done by the Advanced Cryscope (Fiske, USA).
The rate of isolation of each organism in both raw and pasteurized
milk was calculated as a percentage of the total number of the isolates.
The isolated bacteria were grouped into three categories (major pathogens:
1; minor pathogens: 2 and negative: 0), according to Berning and Shook
(1992) to facilitate their statistical analysis. Due to the wide variation
of the counts, a logarithmic function was estimated; using the Microsoft
Excel computer program (2000) for SCC; TBC; E. coli count and coliform
count. Descriptive statistical (mean, standard deviation, variance, maximum
and minimum) and ANOVA test of the paired t-test analysis were also performed,
using the Statistical Packages for Social Science (SPSS, 10). Correlation`s
and their significant level among the measurements, were estimated using
Pearson correlation using the same program (SPSS, 10).
Comparison of Microbiological Contents of Raw and Pasteurized Milk
Table 1 shows the frequency of the isolation of
the microorganisms, from both raw and pasteurized milk, which are produced
and consumed in the Western Cape. The higher prevalence is that of S.
aureus in the raw milk (15.38%), followed by those of E. coli
(14.3%) that was also isolated at a rate of 3.6% form pasteurized milk.
Similarly, other mastitis-isolated pathogens were Streptococcus agalactiae
(8.79%), Streptococcus dysglactiae (12.09%), Streptococcus uberis
(6.72%), Enterococcus faecalis (8.35%) that were also found in
pasteurized milk (2.2%) and Staphylococcus epidermidis (8.79%)
that were also found in pasteurized milk (2.2%). Other identified isolates,
were represented in the same Table. However, all samples revealed negative
results for the growth of Salmonella spp. and Listeria monocytogenes.
Descriptive and frequency analysis of the different measurements (Table
2), showed higher means, standard error of means and standard deviation
for the somatic cell counts, total bacterial counts, coliform counts and
E. coli counts, although their minimum values revealed a negative
or a very low levels.
Comparison of the Chemical Composition of Raw and Pasteurized Milk
The comparison of different levels of the bacteriological quality
on milk constituents (Table 3), revealed significant
differences in the fat % for the somatic cell counts (p<0.05), coliform
counts (p<0.01) and bacteriological status (standard cultures) of the
milk (p<0.001). However protein %, lactose %, total solids % and solids
not fat % revealed significant differences only for the bacteriological
status (standard cultures) at p<0.001. The only significant difference
obtained for the ash % was due to the variation of the SCC (p<0.05).
However the added water showed significant differences due to E. coli
|| Frequency of the isolation of microbial organisms from
raw and pasteurized milk in Western Cape, South Africa
||Descriptive statistical analysis of some quality control
tests on raw and pasteurized milk produced and consumed in the Western
|SD = Standard Deviation, ND = Not Detectable
||Comparison of the significant differences of bacteriological
quality on raw and pasteurized milk constituents, using t-test analysis
|NS = Non Significant, * = p≤0.05, ** = p≤0.01,
*** = p≤0.001
Correlation Between Milk Constituents and Microbiological Contents
of Raw and Pasteurized Milk
The log SCC revealed a positive correlation with log total bacterial
counts; log coliform counts; standard cultures; fat %; protein %; lactose
%; total solids % and solids not fat % (p<0.001) and log E. coli
counts (p<0.01). Positive correlation`s were found for the log E.
coli counts and each of the total solids % (p<0.001), log SCC;
solids not fat % and protein % (p<0.01) and fat %; lactose %; ash %
and standard cultures at p<0.05. Similarly, the standard culture showed
a positive correlation (p<0.01) towards log SCC.
The present research is done as a trial to estimate the bacteriological
and the chemical composition of the market milk, following its distribution
and comparing that with the raw original milk supply. As represented in
Table 1, a high frequency of pathogens were isolated
from the raw milk and this confirmatory results for the presence of mastitis
pathogens as stated by Berning and Shook (1992) and Gunasekera et al.
The higher level of the SCC in most of the bulk tank milk (Table
2), which exceeded the threshold, were also indicative of the presence
of the infection within the herd as it was confirmed by the presence of
mastitis pathogens (Table 1). This was in accord to
Berning and Shook (1992) who demonstrated that log SCC was discriminate
infected from non-infected quarters of cows. Hence, the present study
suggested that the quality control authority of each factory should inform
and train their farmers to apply the proper hygienic practices. However,
as represented in Table 2 that some of the farms yield
very satisfactory milk as represented by the low SCC, TBC and coliform
There is no evidence that any particular cell count per se has any significant
effect on human health. However, the higher the cell count the greater
the risk of raw milk contamination with pathogens and antibiotic residues
(Savelle et al., 2000); toxins (Tood, 1992) and the resistant bacteria
that could also be transfer to human (Manie et al., 1999). The
risk of milk contamination was confirmed by the present findings as shown
in Table 3, that significant differences and a positive
correlation were obtained for the different bacteriological measurements.
Pasteurization as a practice has a positive effect on the bacteriological
contents of milk since it improve the TBC, coliform and other pathogenic
organisms (Table 1). Moreover, as stated by Hayes et
al. (2001) that increase in TBC can reduce the price that farmer receives
for milk. The presence of E. coli and other pathogens in pasteurized
milk (Table 1) was either due to insufficient pastuerization
or indication of post pastuerization contamination of milk, since as stated
by Manie et al. (1999) that the Enterobacteiaceae do not survive
pasteurization but contamination can be due to poor post pasteurization
control. Moreover, the bacteriological content was found to influence
the milk constituents (Table 3), which was in agreement
to Mohamed et al. (1997). Lower levels of all the chemical compositional
estimated in the pasteurized milk, compared to the original raw milk from
all tested milk samples of the different companies. This might be due
to either adulteration of milk by the addition of water and /or the steam
that used as an indirect method of pasteurization. Since some of the factories,
used the direct steam, as stated earlier by Lombard (1976) that systems
in operation in South Africa use steam injection for heating and sterilizing
temperature was the reason of this due to some technical faults. Regardless
of the reason of the high percentage of the added water, the lower level
of lactose (Table 2) also reflected the adulteration.
Since the lactose level is the most non-variable of the milk constituents
as stated by Mitchel et al. (1978). However, it is well known that
it is influenced by bacterial status as demonstrated by Mohamed et
The present study suggested that monitoring program for evaluation and
grading of milk is urgently needed for the consumed dairy products, since
in those factories they pay for milk according to its quality including
the somatic cell count. However, the lack or inefficiency of the quality
assurance programs at factories may lead to production of law quality
products. Similarly more attention should be directed towards the producers
to ensure safety supply of milk. This could be a chivied by application
of quality control at farm as well. The absence of Salmonella spp.
and Listeria monocytogenes in both raw and pasteurized milk, during
the present study was indication that the herds and the labors; deal with;
are free from those pathogens. This was cope well with the results of
the questionnaire that addressed the farmers` knowledge and practices
(data not shown) that no entry for the person with such illness as stated
by the farmers involved in the present study.
The present study concluded that milk is a vulnerable product, which
in some cases may become dangerous to human health if it was subjective
to adulteration and/or health hazards. Hence a quality assurance programs
are essential for monitoring its quality at all steps from production
to consumers. Training and education is also needed for all persons who
deal with milk production and processing. Further research and extension
is urgently needed to characterize critical quality points and hazards
in order to ensure that good quality dairy products are produced and consumed.
The present study was conducted through the UNESCO Pilot African Academic
Exchange Program (UPAAE). The fund from the Royal Society/NRF of South
Africa was also appreciated. The authors would also like to thank all
factories` mangers, quality control supervisors, dairy advisers and their
farmers who allowed and facilitate collection of data and samples for
the present study. The effort of the International office of the University
of the Western Cape and the other departments was also acknowledged. The
technical help of the staff of ARC-Animal Nutrition and Product Institutes,
Elsenburg and Provincial Veterinary Laboratory, Stellenbosch were also
appreciated with thanks.
1: Berning, L.M. and G.E. Shook, 1992. Prediction of mastitis using milk somatic cell count, N-acetyl-β-D-glucosaminidase and lactose. J. Dairy Sci., 75: 1840-1848.
CrossRef | Direct Link |
2: Dekkers, J.C., T. Van Erp and Y.H. Schukken, 1995. Economic benefits of reducing somatic cell count under the milk quality program of Ontario. J. Dairy Sci., 79: 396-401.
CrossRef | Direct Link |
3: El Zubeir, I.E.M., P. Kutzer and O.A.O. El Owni, 2006. Frequencies and antibiotic susceptibility patterns of bacteria causing mastitis among cows and their environment in Khartoum State. Res. J. Microbiol., (2): 101-109.
4: Finger, R. and W.M. Sischo, 2001. Bioluminescence as a technique to evaluate udder preparation. J. Dairy Sci., 84: 818-823.
Direct Link |
5: Giovannini, A., 1998. Importance of milk hygiene to public health. MZCP/workshop on the management of milk-borne zoonoses surveillance and control in the MZCP countries, Cephalonia Island, Greece.
6: Gunasekera, T.S., P.S. Attfield and D.A. Veal, 2000. A flow cytometry method for rapid detection and enumeration of total bacterial in milk. Applied Environ. Microbiol., 66: 1228-1232.
Direct Link |
7: Hayes, M.C., R.D. Ralyea, S.C. Murphy, N.R. Carey, J.M. Scarlett and K.J. Boor, 2001. Identification and characterization of elevated Microbial counts in bulk tank raw milk. J. Dairy Sci., 84: 292-298.
Direct Link |
8: Heeschen, W.H., 1996. Mastitis: The disease under aspects of milk quality and hygiene. Mastitis Newsletter, Newsletters of the IDF No. 144, pp: 16.
9: Holt, J.G., R.N. Krieg, P.H.A. Sneath, J.T. Staley and S.T. Willims, 1994. Bergey's Manual of the Determinative Bacteriology. 9th Edn., Williams and Wilkins, USA
10: IDF, 1994. Recommendations for the hygienic manufacture of milk and milk based products. International Dairy Federation, Document No. 292. Brussels, Belgium.
11: ISO 4831, 1991. Microbiology: General guide for enumeration of coliform. Most probable number technique.
12: ISO 7251, 1993. Microbiology: General guide for enumeration of presumptive Escherichia coli. Probable number technique.
13: ISO 11290-1, 1996. Microbiology of food and animal feeding stuff. Horizontal method for enumeration of Listeria monocytogenes. Part 1 Detection Method.
14: ISO 11290-2, 1998. Microbiology of food and animal feeding stuff. Horizontal method for enumeration of Listeria monocytogenes. Part 2 Enumeration Method.
15: ISO 6222, 1999. Water quality. Enumeration of culture microorganisms. Colony counts by incubation in nutrient agar culture medium.
16: Lombard, S.H., 1976. UHT-behanding van melk. J. S. Afr. Vet. Assoc., 57: 101-104.
17: Ma, Y., C. Ryan, D.M. Barbano, D.M. Galton, M.A. Rudan and K.J. Boor, 2000. Effect of somatic cell count on quality and shelf life of pasteurized milk. J. Dairy Sci., 83: 264-274.
Direct Link |
18: Manie, T., V.S. Brozel, W.J. Veith and P.A. Gouws, 1999. Antimicrobial resistance of bacterial flora associated with bovine products in South Africa. J. Food Prot., 62: 615-618.
Direct Link |
19: Mitchel, E.G., A. Lyall and K.D. Shackel, 1978. Milk composition in Queenland. Aust. J. Dairy Technol., 33: 80-84.
20: Mohamed, I.E., O.A.O. El Owni and G.E. Mohamed, 1997. Effect of bacteria causing mastitis on milk constituents. Sudan J. Vet. Sci. Anim. Husb., 36: 125-136.
Direct Link |
21: Mohamed, N.N.I. and I.E.M. El Zubeir, 2007. Evaluation of the hygienic quality of market milk of Khartoum State (Sudan). Int. J. Dairy Sci., 2: 33-41.
CrossRef | Direct Link |
22: Mohamed, N.N.I. and I.E.M. El Zubeir, 2007. Evaluation of the hygienic quality of market milk of Khartoum State (Sudan). Int. J. Dairy Sci., 2: 33-41.
CrossRef | Direct Link |
23: Quinn, P.J., M.E. Carter, B. Markey and G.R. Carter, 1994. Clinical Veterinary Microbiology. 1st Edn., Mosby-Yearbook Europe Ltd., UK.
24: Savelle, W.J., T.E. Wittum and K.L. Smith, 2000. Association between measures of milk quality and risk of violative antimicrobial residues in grade-A raw milk. J. Am. Vet. Med. Assoc., 217: 541-545.
Direct Link |
25: Todd, E.C.D., 1992. Foodborne disease in Canada-a 10-year summary from 1975 to 1984. J. Food Protect., 55: 123-132.
CrossRef | Direct Link |