The study was based on surveying thirty six samples of Sudanese white cheese from restaurants, supermarkets and groceries (Khartoum North). The comparison of the chemical composition (total solids, total protein, fat, ash and acidity) and some of the microbial hazards (E. coli, Salmonella spp. and Staphylococcus aureus) associated with cheese were estimated. The means of total solids, ash, fat, protein and acidity for the samples were 47.8, 6.2, 14.0, 15.9 and 0.04%, respectively. The result indicated that there was non significant differences between total solids, ash, fat, acidity and protein in all batches in different sources. Positive isolates for E. coli (4), Salmonella typhi (4), Salmonella paratyphi (4) and S. aureus (8), were found in restaurants. Similarly 4, 4, 0 and 4 and 2, 2, 0 and 2 isolates of Salmonella typhi, Salmonella paratyphi, S. aureus and E. coli were found, respectively in supermarkets and groceries. The log counts of coliforms bacteria was 6.56006±0.52936, 6.5423±0.24873 and 6.4856±0.23278 and the log counts of total bacteria (SPC) was 9.46956±0.58882, 9.02652±0.01826 and 8.9713±0. 44743 for cheese samples collected, respectively from restaurants, supermarkets and groceries. Similarly, the log of Salmonella spp. counts was found to be 4.0612±0.0629, 2.0037±2.8337 and 4.97803±1.1807; the log count of Staphylococcus aureus was 3.40887±4.82087, 4.90646±6.93878 and 0 and the log of E. coli counts was 5.23337±0.53085, 0 and 5.33815±0.771346, respectively from restaurants, supermarkets and groceries.
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Cheese was originally developed as a mean of preserving raw milk in time of excess production and cheese is generally considered to be relatively safe food. It contains high quality proteins, vital minerals and vitamins (Ibrahim, 1971). However, the spread of some diseases by cheese have been demonstrated and as a result, most cheese is now produced from milk that has been pasteurized (Anonymous, 1998). It is indisputable that some outbreaks of food borne illness have been clearly linked with the consumption of cheese, the majority of those reported being associated with cheese made from unpasturized milk. Whilst pathogens can gain access to cheese after curd formation, it is clear that many food borne pathogens are feacal in origin (Rampling, 1996).
One of the most frequent foods borne microbial disease is staphylococcal food poisoning, which is caused by S. aureus metabolites (Holeckova et al., 2002). Similarly it was reported that several pathogenic bacteria (Salmonella spp., Bracella spp., Compylobacter spp. and Listeria spp.) can survive in cheese made from raw milk and may not be destroyed by some heat process (Ibrahim et al., 1981). It was also investigated that the presence of some pathogenic bacteria in soft cheese were found to be Staphylococcus aureus and it was found in about 20% of the samples and Escherichia coli that was isolated from 21.1% of the samples (Araujo et al., 2002). Salmonella spp. was responsible for 29 outbreaks, Listeria monocytogenes for 10 outbreaks, E. coli for 11 outbreaks and Staphylococcus aureus for 10 outbreaks in France (De Buyser et al., 2001). Moreover 600 cases of salmonella outbreaks in south West Germany were reported to be due to contaminated cheese (Geiss et al., 1993). However the incidences of coliforms, B-glucuronidase positive E. coli and S. aureus were higher in soft than in blue veined, semi hard, hard and fresh cheeses (De Reu et al., 2002). Moreover it has been shown that curd at 8°C, for 5 min resulted in the loss of culture ability of E. coli O157: H7 during the production of mozzarella cheese (Spano et al., 2003).
Hence, the present study was undertaken to estimate the chemical composition and the hygienic quality and to determine some food borne diseases associate with Sudanese white cheese from some markets in Khartoum North.
MATERIALS AND METHODS
Source of Cheese Sample
Thirty six samples of Sudanese white cheese were collected from Khartoum North. The survey involved restaurants, groceries and supermarkets. The collection of the samples was done in duplicate.
Analysis of Cheese Samples
The samples were collected in a clean sterile bottles and transported at 4°C to the laboratory of the Department of Dairy Production, Faculty of Animal Production, University of Khartoum, for chemical and microbiological examination.
The protein content was determined by Kjeldahl methods, the fat content was determined by Gerbers method and total solids was determined according to the modified method (Anonymous, 1990). Similary ash content and the titratable acidity were also determined according to the method of AOAC (1990).
The samples were enumerated for counting total bacteria (standard plate count) and some potential pathgenic bacteria (E. coli, Staphylococcus aureus, colifom and Salmonella spp.). Plate count agar, salmonella and shigella agar, mannitol salt agar, metachromgelb agar were the selected media for enumeration. All media were obtain in dehydrated forms and prepared according to the manufactures instructions. Sterilization, (Barrow and Felthman, 1993) dilution of the samples (Richardson, 1985) and purification and identification of the isolates (Barrow and Felthman, 1993) were done.
The data of the present study were analyzed statistically using Complete Randomized Design. ANOVA test and the least significant difference were used to determine the difference between means. The analysis was carried out using SAS (1989).
RESULTS AND DISCUSSION
The fat content revealed values of 19.9167±3.9802%, 17.7917±1. 9001 and 19.6667±2.8402% for cheese samples collected from restaurants, supermarkets and groceries, respectively. However values of 16.0 and 27%, 15.5 and 20% and 15 and 22.2% were reported for minimum and maximum values, respectively (Table 1). There was no significant differences between these values.
The law values of fat might be due to storage as it was indicated that fat content was high in the beginning of storage period, then gradually decreased towards the end of storage period of cheese (Nuser, 2001). Moreover, some fat must have leaked from curd into the brine solution, which partially might explain the decrease in fat content in curd during the storage period (Abdalla, 1992).
The average protein content recorded values of 13.6751±2.2600, 15.4083±3.62787 and 13.3917±2.03087% for cheese samples collected from restaurants, supermarkets and groceries, respectively. However, values of 11.5 and 17.5, 12.35 and 22.3, 11.7 and 16.3% were found for minimum and maximum, respectively (Table 1). All these values of protein, showed non significant differences between them.
Protein content in restaurants and groceries (Table 1) showed low values. This result agreed with the findings, which reported that protein decreased considerably due to degeneration of protein and loss in whey (Khalid, 1991; Abdel Razig, 1996).
The average acidity revealed values of 1.61±0.7731%, 1.5667±0.5930 and 1.52561±0.5672% for cheese samples collected from restaurants, supermarkets and groceries, respectively. Values of 1.05 and 3.15%, 1.0 and 2.7% and 1.15 and 2.65% were found for minimum and maximum values, respectively (Table 1). There was non significant differences between all values of the acidity. This was explained as that, the high acidity of raw milk cheese could be due to the fact that the storage temperature activated the natural microflora of raw milk to develop acidity as the result of lactose fermentation since the cheese was stored at room temperature (Hamed, 1998). Moreover it was reported that whether at room temperature or in the refrigerator about 45-80% of increase in the acidity was mainly due to lactic acid formed by the usually predominating lactic acid bacteria (Nofal et al., 1981).
The average ash content values were 8.0833±6.3306, 6.95±3.7303 and 8.2667±5.4458% for cheese samples collected from restaurants, supermarkets and groceries, respectively. Values of 4.2 and 20.45%, 4.05 and 14.15% and 5.25 and 19.3% were reported for minimum and maximum values, respectively (Table 1). There were non significant differences between values of ash content. The increase in ash content during picking might be due to decrease in moisture content or absorption of salt by curd (Abdel Razig, 1996).
The average total solids content revealed values of 44.0792±11.4859, 43.975±5.7403 and 47.4833±7.9743% for cheese samples collected from restaurants, supermarkets and groceries, respectively. However values of 22.425 and 56.15%, 39.15 and 54.85% and 41.6 and 53.6% were reported for minimum and maximum values, respectively (Table 1). This values agreed with previous reports by Nuser (2001) and Hamed (1998).
|Table 1:||Comparison of the hygienic and compositional quality of Sudanese white soft cheese in Khartoum North|
|Table 2:||The prevalence of some pathogens in white soft cheese collected from Khartoum North|
Bacteriology of Isolated Pathogens from Sudanese White Cheese
Incidence of Food Borne Pathogens Isolated from Sudanese White Cheese
In the present survey three different types of the potentially food borne diseases (E. coli, Salmonella spp. and S. aureus) were found in Sudanese white cheese (Table 2).
A total of 38 food borne pathogens were found in the samples of Sudanese white cheese. Of these 10 (26.32%) isolates were identified for each of S. aureus, Salmonella typhi and Salmonella paratyphi and 8 (21.05%) isolates of E. coli (Table 2). In restaurants and groceries 8, 4, 4 and 4 and 0, 4, 4 and 4 isolates of each of S. aureus, E. coli, Salmonella typhi and Salmonella paratyphi were identified, respectively. However the supermarkets samples revealed 2, 0, 2 and 4 isolates of those organisms, respectively (Table 2).
The Counts of Food Borne Pathogens Isolated from Sudanese White Cheese
The log of Salmonella spp. counts was found to be 4.0612±0.0629, 4.0167 and 4.1056, for cheese samples collected from restaurants; for mean + standard deviation, minimum and maximum level, respectively (Table 1). However Salmonella spp. in cheese samples collected from supermarkets showed the log counts of 2.0037±2.8337, 0 and 4.0075, respectively (Table 1). The log of salmonella counts was found to be 4.97803±1.1807, 4.1431 and 5.8129 for cheese samples collected from groceries, respectively (Table 1).
Positive isolation of Salmonella spp. specially in the restaurants suggusted that large numbers of people were at high risk for subjecting to those food borne disease. This might be due to mishandling or improper hygiene as raw milk contamination usually takes place by salmonella from external sources (feaces, the farmer, water pollution and dust) (Asperger, 1994). Similarly it was reported that Salmonella food poisoning can occur when some one drinks unpasteurized milk or eat any food contaminated during preparations, poor hygiene can also allow such carrier to spread the infection to others (Carson and Dewitt, 2002). However the present result disagreed with the findings that Salmonella spp. was absent in the Sudanese white soft cheese (Ahmed, 1997). Hence the present study supported the study which reported that salmonellae continue to be a major concern for the dairy industry (El-Gazzar and Marth, 1992). Since these bacteria have caused recent outbreaks of illness and have been isolated from various dairy products in the market places (De Buyser et al., 2001; Geiss et al., 1993; El-Gazzar and Marth, 1992). Moreover Salmonella can survive a prolong time in frozen foods and that Salmonella are readily destroyed at milk pasteurization temperatures (Vlaemynck, 1994).
The log count of Staphylococcus aureus was found to be 3.40887±4.82087, 0 and 6.81774 for cheese samples collected from restrant, for mean + standard deviation, minimum and maximum values, respectively (Table 1). However the cheese samples collected from supermarkets revealed log counts of 4.90646±6.93878, 0 and 9.8129, respectively (Table 1). However, the present survey revealed a negative isolation for Staphylococcus aureus in cheese samples collected from groceries.
This result is higher compared with the report which found that the maximum log counts of Staphylococcus aureus in Sudanese white soft cheese was 3.500 (Asperger, 1994; Johnson et al., 1990). Moreover, Staphylococcus aureus have been found in various types of cheese and involved in outbreaks of food poisoning (De Buyser et al., 2001; De Reu et al., 2002). Similarly it was reported that of 450 volunteers, 131 (29%) were Staphylococcus aureus carriers, mostly at the mucosal membrane (Bischoff et al., 2004).
The log mean + standard deviation, minimum and maximum values of Eschriechia coli counts were found to be 5.23337±0.53085, 4.8580 and 5.60874, respectively for cheese samples collected from restaurants (Table 1). Similarly the log counts of E. coli were 5.33815±0.77134, 4.79273 and 5.88358, respectively for cheese samples collected from groceries (Table 1). However E. coli during the present survey revealed a negative value (0) for cheese samples collected from supermarkets (Table 1).
The log counts of E. coli in restaurants was very high and this might be due to post contamination of the product (Yang and Jones, 1969; Kosikowiski, 1982). Similarly this result (Table 1) could be attributed to the traditional method used for the distribution of the product which subjecting it to contamination.
The log count of E. coli in groceries was high. This was in support to result, which stated that the manufacturing procedure encouraged some growth of E. coli O157:H7 (Maher et al., 2001). Moreover it was also reported that it might be due to mishandling and poor hygiene (Maher et al., 2001). Eschriechia coli in cheese samples from supermarkets (Table 1) were absent and had a negative result (0). This was a good result compared to those samples collected from restaurants and groceries which might be due to good quality and good hygiene. However the addition of type O lactic culture might be an additional safeguard to well established good manufacturing practices and hazard analysis control points programs in the control of growth of E. coli O157: H7 in cheese (Saad et al., 2001). Similarly the use of Lactobacilus paracasei spp. paracasei strains was suggested to increase the safety of cheese made from raw goats milk because these cultures strongly inhibited E. coli without adverse sensory changes (Caridi, 2002).
The log counts of coliforms bacteria was found to be 6.56006±0.52936, 6.18574 and 6.93438 for mean+standard deviation, minimum and maximum values respectively (Table 1), for cheese samples collected from restaurants. Similarly the log counts of coliforms bacteria was found to be 6.4856±0.23278, 6.32096 and 6.65016, respectively, for cheese samples collected from groceries (Table 1). Also the log counts of coliforms bacteria was found to be 6.5423±0.24873, 6.36642 and 6.718182 for mean + standard deviation, minimum and maximum values, respectively (Table 1), for cheese samples collected from suprmarkets.
This result agreed with the perivous reports (Kosikowiski, 1982; Coveney et al., 1994). Moreover, it was reported that coliforms bacteria grow well in cold or warm cheese causing slit eyes and that coliforms dont survive in pasteurized cheese milk but may be present as a result of post pasteurization contamination (Kosikowiski, 1982). Also the high concentration of feacal coliforms was observed in mozzarella cheese (Massa et al., 1992).
Total Bacteria Counts
The log counts of total bacteria was found to be 9.46956±0.58882, 9.05321 and 9.8859 for mean + standard deviation, minimum and maximum values respectively, for cheese samples collected from restaurants (Table 1). Total bacteria counts was found to be 9.02652±0.01826, 9.01361 and 9.03943, respectively (Table 1) for cheese samples collected from supermarkets. However the log counts of total bacteria was found to be 8.9713±0. 44743, 8.65492 and 9.28768, respectively (Table 1) for cheese samples collected from groceries.
The results indicated the presences of pathogenic bacteria (Salmonella and coliforms) as shown in Table 2 during the present survey. It is disagreed with the result, which demonstrated the absence of coliform and salmonella in Sudanese while soft cheese (Carson and Dewitt, 2002). Moreover, the high counts of pathogenes in cheese samples in the present survey (Salmonella, E. coli, Staphylococcus and coliforms) influence the counts of total bacteria (Table 1).
The present study concluded that there is non significant variation in the chemical content of the Sudanese white cheese marketed in Khartoum North. However, high bacterial load are found to be associated with cheese samples callected from different sources. Moreover, the study was able to identify some potentially foodborne pathogens; such as Staphylococcus aureus, E. coli, Salmonella typhi and Salmonella paratyphi. This might indicate that the level of hygiene and storage of the product and its handling which played a major role in the contamination of the cheese.
Hence it was recommended that processing of high quality milk, which produced from healthy animals and should be handled and processed, stored and marketed in a hygienic manner using hygeinic utensils. Periodic check out for all food distributing centers by the official authorities should be employed. Further study are needed to demonstrate the vehicles and sources of contaminations with food borne diseases and poisonings. Similarly molecular characterizations of those pathogens and their toxin is needed to determine the level of the health hazards that might a rise.
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