Effect of moisture, salt content and pH on the microbiological  quality of traditional Egyptian Domiati cheese

By

Salwa, A. Aly*  Morgan, S. D.* Moawad, A. A.* and Metwally, B.N.**

*Food Hygiene Department, Faculty of Veterinary Medicine

Cairo University

**MVSC, Food Hygiene Department, Faculty of Veterinary Medicine

Cairo University

Abstract

This study was performed to investigate chemical and microbiological characteristics of 40 random samples of traditional white soft Domiati cheese purchased from various markets in Cairo and Giza Governorates, Egypt. The mean gross composition of Domiati cheese samples was 62.9% ± 0.09 moisture; 6.6% ± 0.30 salt and 4.1 ± 0.05 pH. The highest frequency distribution (47.5%); (45%) and (70%) lies within the range of 50-55% moisture; 3-4% salt content and 4-5 pH. Variations between the samples in terms of their gross composition suggested a lack of quality standards in cheese milk, cheese making procedure and ripening conditions. The levels of main microbial groups including total mesophilic, Coliform bacteria, mold, yeast and the presence of some potentially pathogenic microorganisms (Salmonella spp.) was determined. The mean total mesophilic, mold, yeast, Coliform, Enterobacteriacae and  Staphylococci counts were 0.26x10⁶ ± 0.14x10⁵; 3.1x10⁵ ±9.2x10⁴; 1x10⁴ ±0.25x10³; 0.13x10³ ±0.15x10²; 8.9x10⁴ ±0.19x10³ and 1.3x10⁴ ± 1.1x10² respectively. Salmonella was not detected in any of the examined samples. There was correlation coefficient between moisture, salt content, pH and the isolated microorganisms. Our results suggested that moisture, salt content and pH applied to Domiati cheese did not constitute an effective barrier to microorganisms.

Key Words: Cheese, Domiati, microbial flora, chemical characteristics

INTRODUCTION

          Domiati cheese is the most popular type of pickled soft cheese by all socioeconomic classes in Egypt due to its nutritional value, convenience and good taste. When fully ripened it has strong sharp flavor as well as smooth body and texture (Yousef et al., 2001 and Kepary et al., 2007). 

          It is commonly made from whole or partially skimmed raw, pasteurized or sub-pasteurized milk. Although, Domiati cheese production should employs the full pasteurization process, there is a long standing tradition of making cheese from raw milk. The tendency to reduce the heat treatment of milk is due to the believe of cheese manufacture that this enhance the rate of ripening and produces cheese with full ripened flavor at much shorter time and higher intensity (Metwally, 2007). Because of raw milk utilization, some preventive measures have to be taken to assure elimination of manufactured Domiati cheese from undesirable bacteria. It is usually held at least 60 days to allow a time for inactivation of pathogens during ripening process but these conditions do not cause reduction of all pathogen specially, if present in a high count, so outbreaks of food borne illness have been associated with cheese made from raw or sub-pasteurized milk. Low pH and salt content are two factors contributing to the inactivation of bacterial pathogens during 60 days ripening period (Abdelhady and Elassar, 2001; Hamed et al., 2006 and Shehata et al., 2007).

          In addition to the microbial load present in raw milk, other organisms may gain entrance to Domiati cheese during different stages of processing, handling and storage. Such contamination may induce objectionable changes rendering the product unmarketable or even unfit for consumption. Some of the spoilage microorganisms have a public health hazard as Staphylococci, and some types of mould & yeast (Badawi and Hussain 1999; El-Abd et al., 2003 and El-Baradei et al., 2007). As the successful methods of improving the quality of the produced Domiati cheese installs recognition of the prevalent existing microorganisms. So the object of the present study is to examine the Domiati cheese concerning its chemical and microbiological aspects that may be responsible for rapid deterioration as well as to study the correlation coefficient of moisture, salt content and pH on the existing microorganisms present in Domiati cheese.

MATERIAL AND METHODS

Fourty random samples of Domiati cheese samples were collected from dairy shops in Cairo and Giza Governorates, Egypt, in sterile plastic bags and transferred directly to an insulated ice box.The samples (200 gm) were divided into two parts (100 gm each). The first part was examined for chemical analysis while the second part was examined microbiologically.

I. Chemical examination

1.1. Determination of moisture contentwas applied according to Guinee and Fox, (1993).

1.2 Determination of salt content according to AOAC, (2003)

1.3 Determination of pH value according to Kosikowski and Mistry (1997).

2. Microbiological examination

2.1.Preparation of decimal dilutions according to APHA, (2003)

2.2.Total mesophilic countaccording to Swanson et al.,(1992)

2.3.Total mold count according to APHA, (2003)

2.4. Total yeast count according to APHA (2003)        

2.5.Coliform count “MPN /g according to  APHA, (2003)     

2.6.Total Enterobacteriaceae count according to APHA, (2003)     

2.7 Total Staphyloccus count according to Lancette & Tatini (1993)

2.8 Isolation and identification of Salmonella according to Krieg & Holt

 (1986).

RESULTS and DISCUSSION

Table (1): Statistical analytical results of chemical analysis in examined

Domiati cheese samples (N=40)

*N: Number of samples

Fig. (1) Frequency distribution of moisture % in examined Domiati cheese samples

Fig. (2):Frequency distribution of salt % in examined Domiati cheese samples

Fig. (3):Frequency distribution of pH value in examined Domiati cheese samples

Table (2): Statistical analytical results of microbiological analysis in examined Domiati cheese samples (N=40)

*N: Number of samples

Table 3: Correlation between the chemical composition and  microorganisms in examined Domiati cheese samples (N =40).

*Correlation coefficient, significant at P<0.05 level

T.M.C.: Total mesophilic  count

M.C.: Total mold count

T.Y.C.: Total yeast count

According to the Egyptian Standard, (EGSQ, 2005), the moisture content of Domiati cheese must not higher than 60% and the salt content must be not more than 9%. The moisture, salt and pH content of the examined Domiati cheeses samples ranged from; 51.26 to 70% with a mean value of 62.9 ± 0.09; 3.1 to 9.0 with a mean values of 6.6 ± 0.30 and 2.51 to 5.75 with a mean value of 4.1± 0.05 respectively (Table 1). The highest frequency distribution (47.5%); (45%) and (70%) of the examined Domiati cheese samples lies within the range of 50-55% moisture; 3-4% salt content and 4-5 pH respectively (Fig. 1, 2 & 3). The chemical characteristics of Domiati cheese in this study did not met the necessary Egyptian standard (EGSQ, 2005). These results were in good agreement with those reported by Badawi and Hussain (1999) and Elzayat and Osman (2001). Lower percentage were recorded by Mehanna and Rashed (1990); Ordoney (1999) and El-Abd et al. (2003), while higher percentages were reported by Ibrahim (1991) and Mahmoud (1993). Variations between the samples in terms of their gross composition suggested a lack of quality standards in cheese milk, cheese making procedure and ripening conditions (El-Baradei et al., 2007). The pH of Domiati cheese samples were not only contribute the flavor and taste of the cheese but also maintain its convenient texture and protect it against spoilage microorganisms (Araujo et al., 2002 and Turkoglu et al., 2003). The higher moisture content, the more potential off flavors and over ripening which results in many soluble breakdown products of acids, sugars, proteins and lipids (Cakmakci, et al., 2000; Ceylan et al., 2003 and Morales, et al., 2003). Salt concentration in cheese influences many of the chemical, enzymatic, and microbiological processes that occur during cheese aging that create the typical flavor and texture of cheese (Fox, et al., 2000; Melilli, et al., 2003 and Battistotti, and Cocconcelli, 2004). Addition of salt to cheese decreases water activity and has an inhibitory effect on both desirable and undesirable bacteria present in cheese. Generally, cheeses with very high salt content remain firmer during aging (Candioti et al., 2001; Turkoglu et al., 2003 and Ismail, 2005). The high salt content in some of the investigated samples may be due to the poor quality of the manufactured raw milk to prevent the formation of gas holes and abnormal flavor. The apparent variation among chemical examination of examined cheese samples may be due to the variation in composition and properties of the milk used for production of Domiati cheese.

                   From the summarized  data given in Table (2) it is evident that the total mesophilic, mold, yeast, Coliform, Enterobacteriacae and Staphylococcus counts  of the examined Domiati cheese samples were ranged from 50 to 0.7x10⁸ with a mean value of 0.26x10⁶± 0.14x10⁵;   100 to 1.9x10⁸ with a mean value of  3.1x10⁵ ± 9.2x10⁴; 50 to 0.2x10⁶ with a mean value of 1.0x10⁴± 0.25x10³; 10 to 0.2x10⁵  with a mean value of 0.13 x 10³ ± 0.15x10²;   20 to 6.9x10⁵ with a mean value of 8.9x10⁴ ± 0.19x10³ and 10 to 0.2x10⁶ with a mean value of 1.3x10⁴ ± 1.9x10² respectively. Salmonella species could not be isolated from any of the examined samples. The high numbers of all microbial groups in the examined samples suggested that the production and maturation of Domiati cheese should be improved by better hygiene (El-Baradei et al., 2007). As shown in Table (3) there was significant positive correlation between total mesophilic count and moisture content. A negative correlation was found between total mesophilic count; salt and pH in the examined Domiati cheese samples which reflect their  inhibitory effect. A significant (p<0.05) positive correlation was found between moisture content as well as mold, yeast and Coliform count. A significant (p<0.05) positive correlation was found between salt content and Staphylococcus count which reflect its high salt tolerance due to its rigid cell wall and higher internal turgor pressure (.Kunin and Rudy, 2007). A significant negative correlation (p<0.05) was found between pH and mold, yeast and Coliform count in the examined Domiati cheese samples. This result could be account for the fact that yeast and mould could metabolize the lactic acid and lowered pH (Wang et al., 2007). The results were well in line with those reported by Farag (1991); El-Gamal and Abdel-Khalek (1997); Abd El-Tawab et al., (1998); Ahmed and Saad, (1999); EL-Menshawi and Eid (2000); Sabreen, and Zaky, (2001); EL-Abd et al. (2003); Abd El-Hakeem, (2006) and El-Baradei et al., (2007). Higher results were reported by Allam (1995) while lower results were obtained by Halawa (1991);Abd El-Haleem, (1999); Nassib et al. (2003) and Metwally (2007). From the obtained results, it is obvious that most of the examined cheese samples had yeast and mold counts higher than the Egyptian Standards Limits (mold  content must not exceed 10 cfu /g , while yeast must not exceed 400cfu/g) and should be rejected (EGSQ, 2005). The high incidence may be attributed to the numerous sources of cheese contamination. It may be contaminated through milk used, washing water, environment, utensils and equipment, as well as through persons taking part in manufacturing and handling the product (Mace et al., 2004 and Mullan, 2007). The public health importance of molds has been emphasized as certain species can produce mycotoxins, which may induce food poisoning and neoplastic diseases including leukemia and other cancers among consumers.  Also, some species of Penicillium have been associated with pulmonary and urinary tract infections in man (Saleh, 1989; Papageorgiou, et al., 1998; El-Menshawi & Eid, 2000; Bockelmann, et al., 2003; Cousin, 2005 and Brown,et al., 2007). The obtained results indicated that most of the examined cheese samples had Coliform count higher than the Egyptian standards limitswhich suggested that the Coliform content must not exceeds10 cfu/g of soft cheese. The presence of Coliform in cheese is supposed to indicate unsanitary conditions or practices during production, processing or storage. Coliform counts are traditional indicator of possible faecal contamination, microbial quality and wholesomeness and reflect the hygienic standards adopted in the dairy processing (Cakmakci et al., 1995; Ozdemir et al., 1998). A lake of good sanitary practices may result in a loss of quality, spoilage or, in some cases, create a health hazard. It has been suggested that the entire family Enterobacteriaceae  used as indicator organisms for assessing the hygienic quality of food that because the enteric bacteria that fail to ferment lactose are of more public health than those that ferment lactose (Aman et al., 1998; Niad, 2000 and  Morales, et al., 2003). The high rate of contamination of the examined cheese samples with Enterobacteriaceae is indicative for direct or indirect faecal pollution of milk used, neglecting of hygienic measures during production and handling and possible presence of enteric pathogens (Soomro et al., 2002 and Ceylan et al., 2003). Staphylococci exist in air, dust, sewage, water, milk and food equipment, environmental surfaces, humans and animals. Humans and animals are the primary methods of transport (Delbes et al., 2006). Staphylococcal food poisoning is being reported with increasing frequency specially in developing countries where food hygiene is still underway (Eid, 1997; Bakheit et al., 1998; Ingham et al., 2000; Loir et al., 2003 and Anne-Galle et al., 2005).

In conclusion

This study clearly indicated the importance of production process, the amount of rennet used and the storage conditions should be standardized. The use of starter culture and nonstarter lactic acid bacteria should be investigated. On the other hand strict measures should be taken to prevent recontamination during production and storage.

REFERENCES

APHA, "American Public Health Association" (2003). Compendium of Methods for the Microbiological Examination of Foods. 3 ^rd Ed. (Vanderzant, C and Splittoesser, D. eds) Washington DC, USA, p.675-800.

Abdelhady, H. and Elassar, M. (2001). Impact of milk treatment, salting, and storage temperature on the survival of Staphylococcus aureus in Domiati cheese. 1^st Congress of Food hygiene& Human health 6-8 Feb 2001. Dept. Food Hygiene Fac. Vet. Med. Assiut, University, Egypt.p. 165-176.

Abd El-Hakeem, E.H. (2006). Incidence and public health importance of some food poisoning organisms in milk and some dairy products. Ph. D. Thesis, Fac. Vet. Med., Suez Canal Univ.

Abd El-Haleem, E.H. (1999). Occurrence of coliforms and entero-pathogenic Escherichia coli (EEC) in locally manufactured cheese. M.V.Sc. Thesis, Fac. Vet. Med., Assiut Univ.

Abd El-Tawab,  M.; Askar,A.; Hamzawi,L.; Alam Eldien,H. and Farrag, A. (1998). Compositional  quality of Domiati cheese as affected by lactose content in milk. Egyptian J. Dairy Sci. ,20(1),41-51.

Ahmed, A. and Saad, A. (1999). Incidence of slight and moderate halophiles in some selected food. Beni-Suef Vet. Med. J. Vol. 9, No.3, P. 37-49.

Allam, A. (1995). Enterobacteriaceae in Egyptian soft cheese. M.V.Sc.Thesis, Fac. Vet. Med. Moshtohor, Zagazig University , Benha branch.

Aman, I.; knappstein, k. and Hahn, G. (1998). Examination  of verotoxin producing Escherichia coli in some Egyptian dairy products with special reference to serotype O₁₅₇:H₇. Milchwissenschaft 53 (12) 676-679.

Anne-Galle L.; Katiana,S.;JoëL Dore,P.; Francois,C. and Tholozan,J. (2005). Development and validation of PCR primers to Asses the Diversity of Staphyloccoi in cheese by Temporal temperature Gradient Gel Electrophoresis. Applied Environ. Microbiol, 71(1) 29-38.

"AOAC"Association of Official Analytical Chemists (2003). Official analytical chemists. 15^th Ed., Inc. Arlington, Virginia, USA.

Araujo, V. ; Queiroz, M. and Freitaalmeida, A. (2002).Occurrence of Staphylococcus and Enteropathogens in soft cheese commercialized in the city of Rio de Janeiro, Brazil. J. Appl. Microbiol. 92 (6) 1172-1177.

Badawi, R.M. and Hussain, S.A. (1999). Survival of micro entrapped bifido bacteria during storage of white cheese and their effect on cheese quality. Monofia J. of Agricultural Research 24 (2) 493-513.

Bakheit, M.; Ahmed, H. and El-Amin, E. (1998). Isolation of Staphylococcus aureus from food poisoning of cheese. Bulletin of Animal Health and Production in Africa, 39,4,459. Dairy Sci. Abst., 55, 524 (1993).

Battistotti, B. and Cocconcelli, P. (2004). Safety of traditional food: regulations and technical aspects. Scienza Tecnica – Lattiero- Casearia,55 (3) 159-165.

Bockelmann,W.; Willems, P.; Rademaker, J.; Noordam ,W. and Heller,K. (2003). Culture for surface ripening of smeared softcheese. Milchwirtschaftliche 55(4) 277-299.

Brown, J.A.; Feegeding, E.A.; Drake, M. and Daubert, C. (2007). Microbial quality and presence of mold in soft cheese. Int. J. Food Microbiol. 115 (3) 376-380.

Candioti, M.; Palma, S. and Zalazar, C. (2001).  Influence of salting time on the salt concentration and during ripening of washed curd semisoft cheeses. J. Revista-Argentina de Lactologia, No.20 ,19-26

Cakmakci, S.; Engul, C. and Caglar, A. (1995). The chemical and microbiological properties of soft cheese. Milchwissenschaft, 50 (1) 622-625.

Ceylan, Z.; Turkoglu, H.         and Dayisoylu, S. (2003). The microbiological and chemical quality of soft cheese produced in Turkey. Pakistan J. of nutrition 33 (2) 95-97.  

Cousin, E. (2005). Incidence of pathogenic bacteria in unpasteurized soft cheese. Journal Dairy Sci., 76 (10) 3354-3361.

Delbes, C.; Alomar, J.; Chougui, V.; Martin, F. and Montel, M. (2006). Staphylococcus aureus growth and enterotoxin production during the manufacture of uncooked, semihard cheese from cows' raw milk. J Food Prot. 69 (9) 2161-2171.

 EGSQ, Egyptian Standards For Soft Cheese- Domiati Cheese (2005).  Part 3 Es.1008-3/2005.

Eid, A. (1997). Enteropathogenic Eschrichia coli in milk and some milk products. M. V. Sc., Thesis, Zagazig Univ.(Benha branch).

El-Abd, M.; El-Fattah,A.; Osman,S. and El-Kader,R. (2003). Effect of some lactic acid bacteria on properties of low salt Domiatti cheese. Egyptian J. of Dairy Sci., 31(1) 25-138.

El-Baradei, G.; Delacroix, B.A. and Ogier, J.C. (2007). Biodiversity of bacterial ecosystems in traditional Egyptian Domiati cheese. Appl. Environ. Microbiol. 73 (4) 1248-1255.

El-Gamal, A. and Abdel-Khalek , A. (1997). Quality control of Domiati cheese in El-Dakahlia province. Alex. Vet. Sci.,13 (6)784-790.

El-Menshawi, A. and Eid, S. (2000). Effect of handling methods on some chemical properties and microbiological quality of soft cheese at Al-Hassa local market, Kingdom of Saudi Arabia. Egyptian J. of Applied Sci.,15(8) 17-126.

El-Zayat, A.I and Osman, M.M. (2001). The use of probiotics in Tallaga cheese. Egyptian J. Dairy Science, 29(1) 99-106.

Farag, H. (1991). Microbiological quality of some Egyptian dairy products. Ph. D. Fac. Med. Moshtohor, Zagazig Univ., Benha Branch.

Fox, P.F.; Guinee, T.P.; Cogan, T.M., and McSweeney, P.L. (2000). Advanced Dairy Chemistry, Vol.1, Proteins.Kluwer Academic/Plenum Publishers, New York.

Guinee, T.P. and Fox, P. F. (1993). Fundamentals of Cheese Science. Gaithersburg, MD: 1^st Ed. Aspen Publishers, p. 200-233.

Halawa, M. (1991). Microorganisms causing defects in some dairy products. Ph.D. Thesis.,Fac. Of Vet. Med.,Cairo University.

Hamed, A.; Nafisa, A. ElSaify; Seham, I. Farag and Orsi, F. (2006). Effect of pasteurization and storage condition on the microbial, chemical and organoleptic  quality of Domiati cheese. Egyptian Journal Dairy Science 34 (1) 177-190.

Ibrahim, E. (1991). Bacteriological and chemical studies of soft cheese locally manufactured in Assuit Governorate. Annal of Agric. Sci. Moshtohor, 29(4) 19-23.

Ingham, S.; Reyes, J.; Schoeller, N. and Lang, M. (2000). Potential use of presumptive Enterococci and Staphylococci as indicators of sanitary condition in plants making hard Italian type cheese. J Food prot. 63 (12) 1697-1701.

Ismail, M. (2005). Microbiological and compositional status of Egyptian white soft cheeses.M. V. Sc. Thesis. Fac. Med. Vet. Cairo University.

Kepary, M.; Kamaly, K.; Zedan, N. and Zaghlol, A. (2007). Acceleration of ripening of Domiati cheese by accelase and lipozyme enzyme. Egyptian Journal of Dairy Science 35 (1)75-90.

Kosikowski, F.V. and Mistry, V.V. (1997). Cheese and Fermented Milk Foods, Vol. 2: Procedure and Analysis, 3^rd ed. (Kosikowski, F.V. Ed). USA, Academic press, p. 268-299.

Krieg, N. and Holt, J. (1986). Berge’s Manual of Systemic Bacteriology. Vol.2. USA.

Kunin, C. and Rudy, J. (2007). Effect of sodium chloride induced osmotic stress on intracelleular concentration of glycine betaine and potassium in Staphylococci, Escherichia coli and Enterococci. J. Lab. Clin. Med. 118 (3) 2133-2137.

Lancette, G. and Tatini,  S. (1993). Staph. aureus. Compendium of Methods for the Microbiological Examination of Food. INC 4^th Ed., New York. Vanderzantic ,C. and Splittstoesser, D.F.

Loir, Y.; Florence,  B. and  Gautier, M. (2003). Staphylococcal aureus food poisoning. Molecular Engeneering Research 2 (1) 63-76.

Mace, J.O.; Jovanovic, S. and Barac, M. (2004). The influence of different kinds of milk on quality of cheese. J.Biotechnol. 20 (2)109-117.

Mahmoud, M.D. (1993). Prevalence of food poisoning organisms in some dairy products in Beni-Suef Governorate. M.V.Sc. Fac. Vet. Med., Beni-Suef, Cairo University.

Mehanna, A.S. and Rashed, M.A. (1990). An attempt to improve the keeping quality of Tallaga cheese by using milk treated with carbon dioxide. Egyptian J. of Dairy Sci., 18 (2) 377-388.

Melilli, D. M.; Barbano2, G.; Licitra, G.; Tumino, G.; Farina, A. and Carpino, S. (2003). Influence of Presalting and Brine Concentration on Salt uptake by Ragusano Cheese. J. Dairy Sci. 86:1083–1100.

Metwally, B.N. (2007). Hygienic quality of soft cheese marketed in Cairo. M.V.Sc. Fac. Vet. Med. Cairo University.

Morales, P.; Fernandez, G. E. and Nunez, M. (2003): Caseinolysis in cheese by Enterobacteriaceae strains of dairy origin. Lett Appl. Microbiol.37(5)410-414.

Mullan, W. M. (2007). Classification of cheese types using calcium and pH.   J. Dairy Sci. and Food Technol. 28 (4) 200-209.

Nassib, T.; Seif El-Din, M. and El-Sharoud, W. (2003). Viability of some pathogenic organisms during preparation and cold storage of Egyptian soft cheeses and ice-cream. Int. J. Dairy Technol. 56 (1) 30-34.

Niad, S. (2000).  National Institute of Allergy and Infectious Diseases. National Institutes of Health U.S. Department of Health and Human Services Fact Sheet (Food Borne Diseases), Office of Communication and Public Liaison.

Ordoney, L. (1999). Effect of milk pretreatment and storage condition on the properties and keeping quality of cheese. Egyptian J. Dairy Sci. 27 (2) 153-166.

Ozdemir, S.; Celik, C. and Sert, M. (1998). The microbiological and chemical properties of orgu cheese produced in Karacadag region of Diyarbakir, Turkey. In National Productivity Center Publ. No.66.

Papageorgiou, D.K.; Abrahim, A. and Doundounakis, S. (1998). Chemical and bacteriological characteristics of Pichtogalo Chanion cheese and mesophilic starter cultures for its production. J. Food Protect., 61 (2) 688-692.

Sabreen, M. and Zaky, Z. (2001). Incidence of aflatoxigenic molds and aflatoxins in cheese. 1^st Congress of Food Hygiene and Human Health,6-8 Feb. p.241-257.

Saleh, O. (1989). Enterobacteriacae in some dairy products. M.V.Sc.Fac.Vet. Med., Alex. University.

Shehata, A.; Magdoub, M.; Fayed, E. and Hofi, A. (2007). Effect of salt on the properties of pickled Domiati cheese. Egyptian Journal Dairy Science 45 (1) 47-54.

Soomro, G.; Arain, M.; Khaskheli, A. S. and Bhutto, B. (2002). Isolation of Escherichia coli from raw milk and milk products in relation to public health sold under market conditions at Tandojam. Pakistan J. of Nutrition 11 (3) 151-152.

Swanson, K.; Busta, F.; Peterson, E. and Johnson, M. (1992): Colony count methods. Chapter 4. Compendium of Methods for Microbiological Examination of Food. (Vanderzant, C. and Splittoesser, D.F. Eds)  3^rd Ed. APHA, Washington D.C., USA.

Turkoglu, H.; Ceylan, Z. and Dayisoylu, K. (2003).The microbiological and chemical quality of orgu cheese produced in Turkey. Pakistan J. of nutrition 2 (2) 92-94.

Wang, J.; Ruan, H.; Zhang, H.; Hego, S. and Shen, R. (2007). Characterization of a thermostable and acidic tolerance beta gluconate from aerobic fungi.  J. Food Sci. 72 (9) 452-460.

Yousef, H.; Sobieh, M. and Nagedan, K.; (2001). Microbial status of Domiati cheese, at El-Gassiem area, Saudi Arabia. 8^th  Sci. Cong., Fac. Vet. Med., Assiut Univ., 91-97.

الملخص العربى

تاثير الرطوبة و الملح و الاس الهيدروجينى على الخواص الميکروبيولوجية للجبن الدمياطى المصرى

د. سلوى أحمد على* أ.د. صبرى درويش مرجان* أ.د. اشرف احمد معوض*و ط.ب. باسم نصر متولى**

*قسم الرقابة الصحية على الأغذية-کلية الطب البيطرى-جامعة القاهرة

**رسالة ماجستير بقسم الرقابة الصحية على ا لأغذية-کلية الطب البيطرى-جامعة القاهرة

يهدف البحث الى دراسة الخواص الکيميائية و الميکروبيولوجية لعدد اربعون عينة من الجبن الأبيض الدمياطى المتداولة فى الأسواق المحلية بالقاهرة و الجيزة. و قد تبين من فحص  العينات أن متوسط النسبة المئوية للرطوبة62,9 ± 0,09  و متوسط النسبة المئوية لملح الطعام هو6،6± 0،30و الأس  الهيدروجينى  کان 4،10 ± 0،05 ع في عينات الجبن  الدمياطي علي التوالي.وقد وجد ان اعلى نسبة  من العينات وهى 47,5%و 45% و 70% تقع بين 50-55%, 3-4% و 4-5% رطوبة و ملح و الأس الهيدروجينى على التوالى. کمـا أثبتـت النتائـج أن متوسـط العـدد الکلي للميکروبـات و الفطريات و الخمائرو ميکروب الکوليفورم و الميکروبات المعوية و کذلک المکور العنقودي  هو       26و0 Х ⁶10±       0،14 Х⁵10 و 3،1 Х ⁵10±       9.2 Х  ⁴10و  1 Х ⁴10   ±      25, Х    ³10   و 0،13 Х  ³10  ±   0,15 Х²10  و 8،9Х   ⁴10     ±  0،19    Х    ³10  و 1،3    Х     ⁴10  ±  9،1 Х   ²10 / جم من عينات الجبن الدميـاطى. کما لم يتم عزل  ميکـروب السالمـونيلا مـن جميع العينـات التي تم فحصها من الجبن الدميـاطي . و قد تبين وجود ترابط بين الترکيب الکيميائى و المحتوى الميکروبى لعينات الجبن الدمياطى. هذا وقد خلص البحث الى أن نسبة الرطوبة و الملح و الأس الهيدروجينى لعينات الجبن الدمياطى لا تمثل الحماية الفعالة ضد الميکروبات.