EVALUATION OF HYGIENIC QUALITY OF LARGE SCALE MANUFACTURED YOGHURT SOLD IN SHARKIA GOVERNORATE

Dept. of Food Control,

Fac. of Vet. Med., Zagazig University, Egypt.

 

EVALUATION OF HYGIENIC QUALITY OF LARGE SCALE MANUFACTURED YOGHURT SOLD IN SHARKIA GOVERNORATE

(With 14 Tables)

 

By

Nesma I.S. Yasen; S.F.A. Abd El Aal;

M.A.H. Mansour and I.H. Amer

(Received at 1/3/2011)

 

تقييم الحالة الصحية للزبادي المصنع علي نطاق واسع والمباع

فى محافظة الشرقية

 

نسمة إبراهيم صالحيسن البياع ، صلاح فتحى احمد عبد العال ،

محمد احمد حسن منصور ، إبراهيم حسن عامر

 

تمثل الألبان المتخمرة أقدم منتجات الألبان. حيث استخدمها الانسان کغذاء لما لها من قيمة غذائية عالية لاحتوائها على المواد الغذائية الموجودة بالألبان بصورة ساعدت على سهولة الهضم وسرعة الامتصاص. وللالبان المتخمرة اهمية بالغة من حيث الناحية العلاجية نظرا لاحتوائها على حمض اللاکتيک الذى له اثر مثبط لنمو البکتريا فى الأمعاء. کما لجأ الکثيرون إلى الألبان المتخمرة کعلاج لبعض حالات أمراض الجهاز الهضمى کالامساک والاضطرابات المعوية. وبالرغم من أن الحموضة العالية نسبيا فى الألبان المتخمرة لها تأثير على حيوية بعض الميکروبات الا أن بعضها کانت سببا فى انتشار بعض الأمراض الوبائية. ونظرا لأهمية الألبان المتخمرة وانتشارها فى مصر کانت لهذه الدراسة أهميتها لتقرير حالتها الصحية وما قد تنقله من ميکروبات ممرضة تسبب الأمراض للمستهلک. وقد أجريت الدراسة على مائة عينة من الزبادي (50 زبادى عادى ، 25 زبادى بالفراولة ، 25 زبادى بالعسل) جمعت من مختلف محلات بيع الالبان والسوبرمارکت بمحافظة الشرقية. ولقد تضمنت الدراسة فحص العينات فحصا ظاهريا من حيث الشکل واللون مع فحصها للجودة من خلال تحديد نسبة الحموضة اضافة الى فحصها بکتيريولوجيا لتقرير حالتها الصحية ومدى تلوثها بالميکروبات الممرضة والمسببة لتلفها مما يؤدى الى خسارة اقتصادية کبيرة. وقد اسفرت الدراسة ان النسبة المئويةللفحص الظاهرى لعينات الزبادى العادى والزبادى بالفراولة والزبادى بالعسل والتى تحقق اعلي الدرجات من 93-100% هي (44% ، 72% ، 88%)على التوالى. بلغ متوسط النسبة المئوية للحموضة فى الزبادى العادى والزبادى بالفراوله والزبادى بالعسل 0.83% ، 0.90% ، 1.06% على التوالى. تواجدت ميکروبات الکوليفورم فى عينات الزبادى العادى والزبادى بالفراوله والزبادى بالعسل بنسبة 40% ، 20% ، 8% على التوالي. وقد کان متوسط عدد تلک الميکروبات فى هذه العينات هو 4.6×⁴10 و 4.7׳10 و 4.6ײ10على التوالي.تم عزل وتصنيف عترات ستروباکتر فرينداى وانتيروباکتر اجلوميرانز وکليبسيلا اوکسى توکا من عينات الزبادى العادى والزبادى بالفراولة بنسبة (20% و 14% و 18%) و (12% و 16% و 8%) على التوالى بينما تم عزل عترات ستروباکتر فرينداى وانتيروباکتر اجلوميرانز فقط من عينات الزبادى بالعسل.بنسبة 8% ، 4% على التوالى.بلغ متوسط عدد المکورات العنقودية فى عينات الزبادى العادى والزبادى بالفراولة والزبادى بالعسل 1.7×⁴10 و 5.2ײ10و 1.6׳10  على التوالي. تم عزل ميکروب المکور العنقودى الذهبى من عينات الزبادى العادى والزبادى بالفراولة والزبادى بالعسل بنسبة 12% ، 12% ، 4% على التوالى اما ميکروب المکور العنقودى من نوع ابيدرميدس فتم عزله من نفس العينات بنسبة 6% ، 4% ، 4%. لم نتمکن من عزل ميکروب السالمونيلا من عينات الزبادى المفحوصة. بلغت النسبة المئوية لليرسينيا فى عينات الزبادى بالفراولة 16%، بينما لم يتم عزلها من عينات الزبادى العادى والزبادى بالعسل. تم عزل وتصنيفعترات اليرسينيا  سيدوتوبرکلوسس ويرسينيا انترميديا ويرسينيا کريستن سناى من عينات الزبادى بالفراولة بنسبة 8% ، 4% ، 4% على التوالى. هذا وقد تمت مناقشة أهمية الميکروبات المعزولة من کل من الناحيتين الصحية والاقتصادية بالإضافة إلى اقتراح التوصيات الواجب اتباعها لتحسين جودة الألبان الزبادى للحفاظ على صحة المستهلک من الأخطار الصحية.

 

SUMMARY

 

hundred random samples, fifty of natural yoghurt (plain) and 25 each of fruit yoghurt (strawberry) and flavored yoghurt (honey) were collected from different dairy shops and markets in Sharkia Governorate, Egypt. The collected samples were examined physically (sensory evaluation), sanitary (determination of titratable acidity), and bacteriologically. The obtained results revealed that the highest frequency distribution of examined yoghurt samples based on suggested score for sensory evaluation was 44% of examined natural yoghurt samples and lies within the range of 93-100%, while 72% of the examined fruit yoghurt samples and 88% of examined flavored yoghurt lie within the same range. Acidity% in natural and fruit yoghurt samples was 0.83% and 0.90%, respectively, while in case of flavored yoghurt samples was 1.06%. The mean coliform count/g in examined yoghurt samples was 4.6x10⁴ and 4.7x10³ for natural and fruit yoghurt, respectively while, coliform organisms in examined flavored yoghurt were 4.6x10²/g. The most prevalent coliform species isolated from examined natural and fruit yoghurt samples were Citrobacter freundii, Enterobacter agglomerans and K. oxytoca in percentages of (20%, 14% and 18%) and (12%, 16% and 8%), respectively, while in the examined flavored yoghurt samples the most prevalent coliform species were Citrobacter freundii and Enterobacter agglomerans in percentages of 8% and 4%, respectively. The mean staphylococci count/g in examined natural and fruit yoghurt was 1.7x10⁴ and 5.2x10², respectively but in case of flavored yoghurt it was 1.6x10³. Staphylococcus aureus and Staph. epidermidis were the predominated staphylococci isolated from the examined natural, fruit and flavored yoghurt samples in percentages of (12% and 6%), (12% and 4%) and (4% and 4%), respectively. Salmonellae failed to be detected in examined samples. Yersinia spp. could be detected in 16% out of examined fruit yoghurt samples while they couldn’t be detected in both examined natural and flavored yoghurt samples. Yersinia pseudotuberculosis, Y. intermedia and Y. kristensenii could be isolated from the fruit yoghurt samples in percentages of 8%, 4% and 4%, respectively. The sanitary and public health importance of isolated microorganisms as well as their control measures were discussed to improve the quality of yoghurt and to safe guard the consumers from infection.

 

Key words: Hygienic quality, yoghurt, coliforms, staphylococci,  yersinia spp., salmonellae.

 

INTRODUCTION

 

Milk and milk products are universally recognized as first class food stuff due to their exceptional richness in high quality animal protein, milk fat, high content of calcium, phosphorous and performed vitamin A and B2. The outstanding nutritive value of these products makes them indispensable in human nutrition. Moreover, such products are good supplement for a deficient diet at all times.

Many claims may be made for the therapeutic value of fermented milk in the diet of people. Ancient physicians prescribed sour milk for dysentery, tuberculosis, liver complaints and inflammation of intestinal tract a host of other maladies. Even though most of the claims for therapeutic value of fermented milks are grossly exaggerated, physicians today prescribe acidophilus milk in the diet of some persons affected with constipation or diarrhoea. In fact, researches have recently proved that antibiotics could be produced by organisms used in milk fermentation as acidophilin, lactocidin, lactoline, nicin and diplococcin. Such antibiotics may inhibit the growth of several food-borne pathogens(Steven, 1969; Goel et al., 1971; Shahani et al., 1974; Abou-Donia        et al., 1975).

Natural or plain yoghurt was the traditional type of fermented milks with a sharp acidic taste, while fruit yoghurt was made by the addition of fruits and sweeting agents to natural yoghurt (Potter and Hotchkiss, 1995).Fruit yoghurt usually have incorporated stabilizers to reduce whey separation during distribution and many of the stabilizers are complex carbohydrates which providing “a bulking agent “for stimulating intestinal peristalsis and avoiding some the risk of colonic malfunction. It also absorbs some of the potentially toxic chemicals that may be formed in the large intestine as a result of bacterial action. These unavailable carbohydrates are acting to further delay the diffusion of sugar to the intestinal wall that could help lactose intolerant patients and those prone to post prandial hyperglycemia. (Robinson and Khan, 1978 and Tamime and Robinson, 1985).

Contaminations of milk with coliforms with special reference to faecal coliforms give an indication of either direct or indirect faecal contamination and considered as a mirror for the degree of disregard of numerous hygienic rules during milking (ICMSF, 1986 and Varnamand Evans, 1991).Coliform also appear to be capable of colonizing in the human gut and producing potent enterotoxins in high yield. During the last few years, strains of Klebsilla, Enterobacter and Citrobacter have been isolated from stools or the intestinal tract of children and adults in several epidemiological studies of acute and chronic diarrheal diseases(Robert and Brenda, 1979).

The presence of coagulase positive, Staphylococcus aureus in a food gave an indication about its contamination from skin, mouth or handling, but inadequately cleaned utensils or equipment may be also a source of contamination. (Newsome, 1988). Staphylococcus aureus possess a public health hazard due to production of thermostable enterotoxins that was responsible for food-poisoning. (Wernozy-Rozand et al., 1996).

Salmonellae are world wide and universally recognized as zoonotic agents. Numerous animal reservoirs have been identified, many foods, particularly of animal origin and those subjected to sewage pollution, have been identified as vehicle for transmitting these pathogens to human being (Robert et al., 1996).

Yersinia enterocolitica is one of the human pathogenic species of Yersinia and of major importance in view of food hygiene. Raw milk and milk products have been shown to be a vector of infections in a number of Yersinia enterocolitica related food-borne outbreaks. (Moustafa et al., 1983; Odinot et al., 1995). Yersinia enterocolitica has been isolated from many animal species, with most isolates being virulent strains for humans. Exception was swine; they were principle resevior for virulent strains, which were often isolated from oral cavity (tounge and tonsils) of apparently healthy animals. (Anonymous, 1977; Tacket et al., 1984).

In recognition of public health and economic significance of these microorganisms, therefore, the present study was done to investigate the examined yoghurt samples physically, sanitary and bacteriology as well as assessment of the economic and public health significance of isolated microorganisms in relation to yoghurt.

 

MATERIALS and METHODS

 

Collection of samples:

One hundred random samples, fifty of natural yoghurt (plain) and 25 each of fruit yoghurt (strawberry) and flavored yoghurt (honey) were collected in their retail packages from different dairy shops and markets in Sharkia Governorate. Collected samples were transferred directly to the laboratory in an insulated ice-box at 4°C with a minimum of delay to be examined physically, sanitary and bacteriologically.

 

Preparation of the Samples:

On arrival to the laboratory each sample was perfectly mixed and examined physically (sensory evaluation) before being divided into two parts. The first one used for sanitary examination (determination of titratable acidity), while the second one was examined bacteriologically.

 

A- Physical examination:

Sensory evaluation (Sangwan, 2008):Yoghurt samples were examined for physical properties then graded according to the scores.

 

Attribute	Maximum score
Flavor Body and Texture Appearance Sediment Container	45 30 10 10 5
Total	100

Table 1: Sensory evaluation of yoghurt samples.

 

Table 2: Suggested scores for a defective yoghurt samples.

Attribute	Defect	Degree of defect
		Slight	Moderate	Pronounced
Flavor             Body and Texture           Sediment Appearance Container	Bitter Cheesy Flat Low-acid High-acid Yeasty Foreign Curdy Gassly Lumpy Ropy Thin Wheyed off Chalky,dull Unsighty, Soiled	38-40 38-40 40-42 40-42 40-42 38-40 38-40 26-27 26-27 27-28 27-28 27-28 27-27 9 9 4	35-37 35-37 37-39 37-39 37-39 35-37 35-37 23-26 23-26 24-26 24-26 24-26 24-26 7 8 3	32-34 32-34 34-36 34-36 34-36 32-34 32-34 21-22 21-22 21-22 22-23 22-23 22-23 5 7 2

 

B-Sanitary examination:

Determination of titratable acidity percentage by using standard method (A.P.H.A., 1992).

C-Bacteriological examination:

1- Preparation of serial dilutions (A.P.H.A., 1992).

2- Enumeration and isolation of coliforms(MPN/gm); (A.P.H.A., 1992).

      Identification of the isolated coliform organisms (Krieg and Holt, 1984).

3- Enumeration and isolation of staphylococci(A.P.H.A., 1992).

    Identification of the isolated Staphylococcus organisms (Cowan and Steel, 1974).

4- Isolation of Salmonella spp.(A.P.H.A., 1992).

5- Isolation of Yersinia spp. (A.P.H.A., 1992).

   Identification of the isolated Yersinia spp.(FDA, 1998).

 

Results

 

Table 3: Frequency distribution of the examined yoghurt samples based on their sensory evaluation.

   n: means the number of examined samples

 

Table 4: Statistical analytical results of titratable acidity % in the examined yoghurt samples.

 

Table 5: Frequency distribution of the examined yoghurt samples based on their titratable acidity %.

Table 6: Statistical analytical results of coliform count/g. in the examined yoghurt samples (MPN/g).

 

 

Table 7: Frequency distribution of the examined yoghurt samples based on their coliform count/g.

 

 

Table 8: Incidence of isolated coliforms in the examined yoghurt samples.

 

 

Table 9: Statistical analytical results of staphylococci count/g. in the examined yoghurt samples.

 

 

Table 10: Coagulase production of the isolated staphylococci strain in examined yoghurt samples.

 

 

 +++ means strong positive coagulase

 ++ means positive coagulase

 + means weekly positive coagulase

 

Table 11: Incidence of the isolated staphylococci in the examined yoghurt samples.

 

 

Table 12: Incidence of Yersinia spp. in the examined yoghurt samples.

 

 

 

Table 13: Incidence of different types of Yersinia spp. in the examined fruit yoghurt samples.

 

Table 14: Correlation between titratable acidity, coliforms, staphylococci and Yersinia spp. in the examined yoghurt samples.

 

Type of samples	Organisms	Pearson correlation between isolated M.Os and acidity	Sig.   (2-tailed)	Sig.
Natural yoghurt (plain) (n=50)	Coliforms	0.240-	0.094	N.S.
	Staphylococci	0.155-	0.284	N.S.
Fruit yoghurt (Straw berry) (n=25)	Coliforms	0.330	0.107	N.S.
	Staphylococci	0.161	0.441	N.S.
	Yersinia spp	0.102	0.074	N.S.
Flavored yoghurt (Honey) n=25))	Coliforms	0.570	0.003	**H.S.
	Staphylococci	0.080	0.702	N.S.

 

  **H.S.: Highly significant (P < 0.01)

  N.S.: Non significant

 

DISCUSSION

 

Table 3 revealed that the highest frequency distribution of examined yoghurt samples based on their suggested score for sensory evaluation was 44% in examined natural yoghurt samples and lies within the range of 93-100%, while it was 72% for examined fruit yoghurt samples and 88% for examined flavored yoghurt which lies within the previously mentioned range. Sensory criteria are essential parameters that constitute the “eating quality” of dairy products which cann’t be easily measured either chemically or physically. All primary classic senses: sight, smell, taste, touch and sound should be used in the sensory evaluation of yoghurt. Sight is used for evaluation of many factors as style, cleanliness of package, exterior attractiveness of finished product, package closure, body and texture, color and overall appearance and quality defects. The flavor sense of yoghurt samples detects the normal and impact (defective) flavor. Quality of yoghurt samples can be described as a value related to flavor, color and texture. It also includes imperceptible traits such as aesthetic value and safety, evaluation of raw material and final products standards, the design of dairy plant, process line layout and the design storage and distribution of yoghurt. It also concerned with packaging, storage and distribution of yoghurt samples (Al-Ashmawy et al., 1991).

The results summarized in Table 4 showed that the titratable acidity % in examined natural yoghurt samples was ranged from 0.66 to 1.12% with an average of0.83, while in examined fruit yoghurt samples it was ranged from 0.73-1.24% with a mean value of 0.90 ± 0.021 and 0.99 to 1.32% with a mean value of 1.06 ± 0.017 for examined flavored yoghurt samples. The highest frequency distribution of examined natural yoghurt samples based on their titratable acidity % was 36.0% which lies within the range of 0.71-0.80, while in case of fruit yoghurt samples was 52.0% and lies within the range of 0.81-0.90 but in case of examined flavored yoghurt samples it was 72.0% and lies within the range of     0.91-1.0 (Table 5).

Nearly similar data were obtained by Ayoub (1986); Moustafa     et al. (1988); Al-Ashmawy et al. (1991); Abd El-Fatah (2007), while higher values were reported byEl-Shinawy (1987); Ayoub (1991)

Titratable acidity% of yoghurt samples has a greater importance where it is used for assessing the keeping quality. Higher acidity of yoghurt samples may be attributed to contamination either by lactic acid producing microorganisms or pathogenic microorganisms which ferment lactose and elevate the acidity. It is rendering the yoghurt samples unmarketable due to off-taste and unfit for human consumption due to pathogens (A.P.H.A., 1992).

The therapeutic value of yoghurt is due to it^’s acidity which lead to inhibiting or inactivating the most pathogens such as Salmonella spp. and coliforms. The inhibition of potential pathogens is reinforced by the production of antibiotic substances produced by lactic acid-producing bacteria (Rubin 1985; Prakash and Kulkarni, 1986).

The result tabulated in Table 6 showed that the total coliform count (MPN/g.) of examined natural yoghurt was ranged from 3.0x 10² to 7.0x 10⁵ with an average of 4.6x 10⁴, while in those of fruit type it ranged from 8.0x 10² to 6.0x 10⁴ with a mean value of 4.7x 10³ but it ranged from 2.0x10² to 9.0x 10³ with a mean of 4.6x10² in case ofexamined flavored yoghurt samples. These finding were inagreement with those reported by Aboul-Khire et al. (1985); Saad et al. (1987); Moustafa et al. (1988);    Al-Hadethi et al. (1992); El-Barbary (1999); Mansour et al. (1999);     Abd El-Fatah (2007), while higher results were obtained by Ayoub (1986); Farid et al. (1992); El-Badry (1998). But lower results were recorded by Saudi et al. (1988); Al-Ashmawy et al. (1991).

The results listed in Table 7 revealed that the highest frequency distribution of examined yoghurt based on their coliform counts was 65% in examined natural yoghurt and lies within the range of 10²-10³, while it was 80% and 50% in examined fruit and flavored yoghurt samples, respectively which lies within the same range.

The result reported in Table 8 showed that Citrobacter freundii, Enterobacter agglomerans and Klebsiella oxytoca could be isolated from the examined natural yoghurt samples in percentages of 20%, 14% and 18%, respectively, while in examined fruit yoghurt samples were 12%, 16% and 8%, respectively. Only Citrobacter freundii and Enterobacter agglomerans were isolated from examined flavored yoghurt samples in percentages of 8% and 4%.

Slightly higher findings were reported by Ayoub (1986). The result obtained by Pintor et al. (1989); El-Badry (1998); Abd El-Fatah (2007) showed that E. coli failed to be detected in examined plain and fruit yoghurt samples, but it could be isolated by Brazal Garcia et al. (1986); Ahmed (1989); Bahout and El-Shawaf (1999).

It^’s evident from the last few years that some strains of Klebsiella, Enterobacter and Citrobacter had been isolated from stools and the intestinal content of both children and adults in several epidemiological studies of acute and chronic disturbances (Twedt and Boutin, 1979).

Certain numbers of Citrobacter had been suspected to cause enteric infection (Cruickshank et al., 1975), while Citrobacter freundii had been found among urinary and other pyogenic infections in humans (Mackie and MacCarteny, 1962).

The results tabulated in Table 9 revealed that (18%) of examined natural yoghurt samples were contaminated by staphylococci, the level of contamination was ranged from 2.0x10² to 4.0x10⁵ with a mean value of 1.7x 10⁴, while (16%) out of examined fruit yoghurt samples were ranged from 4.0x 10² to 7.0x 10³ with a mean value of 5.2x10². Only (8.0%) of examined flavored yoghurt samples were contaminated by staphylococci, as the level of contamination was ranged from 2.0x 10² to 3.0x 10³ with an average of 1.6x 10³.

Relatively similar results were obtained by El-Shinawy (1987), Al-Ashmawy et al. (1991); Ali et al. (2004), while higher values were reported by El-Badry (1998).

The results presented in Table 10 showed coagulase production of isolated staphylococci strains in examined yoghurt samples 12% of natural yoghurt samples were strongly coagulase positive and 4% were positive coagulase and 2% were weakly positive coagulase, while in examined fruit yoghurt samples 12% and 4% were strongly positive and positive coagulase, respectively, but in case of flavored yoghurt samples 4 % were strongly coagulase positive and the same percentages were weakly positive coagulase.

According to identification of isolated staphylococci Table 11 showed that Staphylococcus aureus was detected in 6(12%) out of examined natural yoghurt samples, while (6%) out of them were contaminated by Staphylococcus epidermidis, while in case of fruit and flavored yoghurt samples (12% and 4%) and (4% and 4%) were contaminated by Staphylococcus aureus and Staphylococcus epidermidis, respectively.

These findings were inagreement with that reported by Saleem     et al. (1989) and coincided with those obtained by El-Bessery (2001) who found that all examined yoghurt samples were free fromStaphylococcus aureus.

Human being normally harbours Staphylococcus aureus as the main reservoir is the nasal cavity and from this source, organisms find their way to skin and into wounds either directly or indirectly. In addition, Staphylococcus aureus may be found in eyes, throat and intestinal tract. Therefore, nasal carriers and individuals whose hands and arms were infected with boils and carbuncles are dangerous sources of food-poisoning (Jay, 1992).

Staphylococcus aureus is by far the most important human pathogen among the staphylococci. Under certain circumstances, Staph.aureus may cause a variety of infectious diseases, ranging from relatively benign skin infectious diseases to life threating systemic illness.

Enterotoxins producing staphylococci are the leading cause of food borne illness throughout the world. Staph. aureus posses a public health hazard due to production of thermostable enterotoxins that is responsible for food-poisoning. The growth of Staphylococcus aureus in food is a potential public health hazard, since many strains of Staphylococcus aureus produce enterotoxins which cause food-poisoning if ingested (Pazakova et al., 1997).

Although Staph. aureus, the coagulase positive is the most dangerous, but nowadays coagulase negative staphylococci have been recognized as important agents of human disease which include nasocomital and community-acquired urinary infections, bacteremia in compromised hosts, osteomyleitis and post-surgical infections.

Salmonella failed to be detected in all examined samples. The findings substantiated what had been reported by Aboul-khier et al. (1985); Amer et al. (1985); Rodriguez et al. (1990); Mufandaedza et al. (2006); Abd El-Fatah (2007). On the contrary Wang et al. (2004) could detect Salmonella in (3%) out of examined yoghurt samples. These results may be attributed to that yoghurt culture had an inhibitory effect on salmonellae within the range of (92.5-99.8%) (Lukasova et al., 1990).

The results recorded in Table 12 revealed that yersinia failed to be isolated from all examined natural and flavored yoghurt samples while 4(16%) out of 25 examined fruit yoghurt samples were contaminated with yersinia.

Table 13 showed that the isolated strains of Yersinia spp. were Yersinia pseudotuberculosis, Y. intermedia and Y. kristensenii in percentages of 8%, 4% and 4% of examined fruit yoghurt samples respectively. Yersinia enterocolitica failed to be detected in all examined natural, flavored and fruit yoghurt samples. Y. enterocolitica could be isolated by El-Prince and Sabreen (1998); El-Barbary (1999), but it failed to be detected by El-Kholy (1992). Umoh et al. (1984) could detect         Y. enterocolitica in 2% out of examined yoghurt samples. This bacterium could contaminate yoghurt through raw milk used without sufficient heating or through contaminated equipment used for its production.

Y. enterocolitica has the distinction of surviving and multiplying in food held at refrigeration temperature, therefore milk and its products contaminated initially with even low level of this bacterium may serve not only as a vehicle, but also as a medium for its proliferation (Stern et al.,1980). Milk and its products had been incriminated in several outbreaks of yersiniosis due to the psychrotrophic nature of Y. enterocolitica which was accompanied by increasing use of refrigeration in food preservation. A highly publicized food associated outbreak of yersiniosis among school children occurred in Oneida, New York, due to consumption of contaminated chocolate milk (Black et al., 1978).

Table 14 showed that the relation between acidity and isolated microorganisms. PH of the yoghurt prevents growth of coliform and act as inhibitor factors of the isolated microorganisms. These findings substantiated what had been reported by Mohammed and Younis (1990); Pesic (1991); Altaf et al. (1995); Hsin and Chou (2001); Mufandaedza     et al. (2006).

From the previously mentioned date, we observed that efficient heat-treatment of milk used in manufacture of yoghurt caused a pronounced reduction in the bacterial load of yoghurt and in turn, keeping quality were usually improved and the shelf-life may be expanded to twenty one days of storage periods (Dagher and Ali, 1985;  Mohanan et al., 1985). Although, plastic cups were not satisfactory and may be responsible for poor quality of yoghurt and its post-pasteurization contamination (Saudi et al., 1989).

 

conclusion

 

            The assessment of the results obtained allow to conclude that most of fermented milk in Sharkia Governorate don’t satisfy the consumer’s demand in obtaining such products in good sanitary condition and retaining as far as possible their nutritive value. Information given by the results of bacteriological examination reported here-in points out that the sanitary measures adopted during production and handling of this product is neglected in most cases as coliforms existed in some samples of yoghurt which are supposed to be heat treated before being manufactured.

 

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