INDICATOR MICROORGANISMS AS INDICES OF QUALITY FOR MILK AND SOME DAIRY PRODUCTS

Document Type : Research article

Authors

1 Food Hygiene Department, Faculty of Veterinary Medicine, Beni-Suef University, Egypt

2 Animal Health Research Institute, Egypt

Abstract

A total of 150 samples including raw cow's milk, pasteurized milk, small scale ice cream, large scale plain and flavored yoghurt (30 of each) were collected randomly from dairy shops, super markets and small scale ice cream producers in Fayoum city, Egypt and examined for sanitary and microbiological status. The result revealed that the mean value of titratable acidity % in plain and flavored yoghurt were 1.41± 0.02 and 1.67± 0.04, respectively. The mean values of total Coliforms were 7.5×105± 3.9×105, 8.25×102± 5.04×102, 8.2×104± 4.1×104, 4.83×102 ± 3.15×102 and 2.72×103± 9.5 ×102 cfu/mlorg., respectively. While the mean values of Faecal coliforms were 2.8×104± 1.5×104, 1.16×102 ± 7.11×10, 1.02×103 ±1.71×102, 2.01×10± 1.07×10 and 3.13×102± 1.30×102 cfu/mlorg., respectively. The mean values of E.coli were1.38×103± 6.89×102,1.84×10 ± 9.5, 4.87×102±1.18×102, 1.36×10± 8.4 and 4.68×10± 1.50×10 cfu/mlorg. The mean values of Enterococci were 1.12×106± 1.29×105, 2.1 ×103± 4.20×102, 1.1 ×106 ±1.87×105, 2.23×103± 6.29×102 and 7.77×103±1.67×103 cfu/mlorg., respectively. Staph. aureus was detected in the examined raw cow's milk and small scale ice cream samples, with the mean values of 1.98×105 ± 3.91×104 and 7.65×104 ± 2.41×104 cfu/mlor g., respectively, but was not detected in the other samples. Total yeasts  and moulds were detected in the examined large scale plain and flavored yoghurt samples with mean values of  1.15×10²± 3.59×10 and 4.48×10²± 8.17×10 (cfu/mlor g.), respectively.

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Assiut University web-site: www.aun.edu.eg

 

INDICATOR MICROORGANISMS AS INDICES OF QUALITY FOR MILK AND SOME DAIRY PRODUCTS

 

ADEL EL-KHOLY 1; GAMAL HASSAN 1; MOHAMED EL-SHATER 2

and AMANY BAKR 2

 

1 Food Hygiene Department, Faculty of Veterinary Medicine, Beni-Suef University, Egypt

2 Animal Health Research Institute, Egypt

 

Received: 7 June 2018;     Accepted: 25 July 2018

 

 

ABSTRACT

 

A total of 150 samples including raw cow's milk, pasteurized milk, small scale ice cream, large scale plain and flavored yoghurt (30 of each) were collected randomly from dairy shops, super markets and small scale ice cream producers in Fayoum city, Egypt and examined for sanitary and microbiological status. The result revealed that the mean value of titratable acidity % in plain and flavored yoghurt were 1.41± 0.02 and 1.67± 0.04, respectively. The mean values of total Coliforms were 7.5×105± 3.9×105, 8.25×102± 5.04×102, 8.2×104± 4.1×104, 4.83×102 ± 3.15×102 and 2.72×103± 9.5 ×102 cfu/mlorg., respectively. While the mean values of Faecal coliforms were 2.8×104± 1.5×104, 1.16×102 ± 7.11×10, 1.02×103 ±1.71×102, 2.01×10± 1.07×10 and 3.13×102± 1.30×102 cfu/mlorg., respectively. The mean values of E.coli were1.38×103± 6.89×102,1.84×10 ± 9.5, 4.87×102±1.18×102, 1.36×10± 8.4 and 4.68×10± 1.50×10 cfu/mlorg. The mean values of Enterococci were 1.12×106± 1.29×105, 2.1 ×103± 4.20×102, 1.1 ×106 ±1.87×105, 2.23×103± 6.29×102 and 7.77×103±1.67×103 cfu/mlorg., respectively. Staph. aureus was detected in the examined raw cow's milk and small scale ice cream samples, with the mean values of 1.98×105 ± 3.91×104 and 7.65×104 ± 2.41×104 cfu/mlor g., respectively, but was not detected in the other samples. Total yeasts  and moulds were detected in the examined large scale plain and flavored yoghurt samples with mean values of  1.15×10²± 3.59×10 and 4.48×10²± 8.17×10 (cfu/mlor g.), respectively.

 

Key words: Raw cow's milk, pasteurized milk, ice cream, plain yoghurt, flavored yoghurt, coliforms, E.coli, enterococci, Staph.aureus, yeasts, moulds, titratable acidity

 

 


INTRODUCTION

 

Milk is considered the most prevalent food stuff among consumers. Where it supply the body with the nutritional needs from protein, fat, carbohydrates, minerals, fat and water soluble vitamins which are necessary for growth and building body tissue. Ice cream is a nutritionally enrichedcongealed dairy product consumed by all ages especially children during summer (El-Sharef et al., 2006).Yoghurt is the best popular cultured dairy products all over the world. Its consumption is associated with several types of human health benefits, including its effect against development of colon tumors (Wollowski et al., 2001). Milk and dairy products are subjected to spoilage or contamination with pathogens during production,   handling,   processing   and   distribution

 

 

 


Corresponding author: Dr. AMANY BAKR

E-mail address: a_mb87@yahoo.com

Present address: Animal Health Research Institute, Egypt

 

(Fernandes, 2009). Therefore the microbial content of milk and dairy products are a major feature in determining their quality (Queslati et al., 2011). Several routine examinations such as coliform count, enterococcus count, Staph.aureus count and yeasts & moulds count are generally accepted to test the quality of milk and dairy products. Results of these examinations are used to correct unhygienic production and processing and to serve as a guide to improve the quality of milk and dairy products.

 

Therefore, this study was planned to throw light on quality condition of milk and some dairy products by applying some chemical and microbiological examinations.

 

MATERIALS AND METHODS

 

1- Collection of samples

A total of one hundred and fifty samples including raw cow's milk, pasteurized milk, small scale ice cream, large scale plain and flavored yoghurt (30 of each) were collected randomly from dairy shops, super markets and small scale ice cream producers.

 

The samples were delivered to the laboratory in an insulated ice box and examined at the same day.

 

2. Determination of acidity % in yoghurt samples was done according to the technique detected by (Ling, 1963).

 

3. Microbiological examination:

 

3-1- Preparation of samples (APHA, 1992a).

11 ml/g. of well mixed raw cow's milk, pasteurized milk and yoghurt samples were added to 99 ml of sterile peptone water 0.1% to make a dilution of 1/10 from which 10-fold serial dilutions were made up.

 

3-2- Preparation of Ice cream samples.

11 g. of well mixed ice cream samples after melting at room temperature (25°C) were added separately to 99 ml of sterile peptone water 0.1% and well mixed to prepare a dilution of 1:10; from which ten –fold serial dilutions were made.

 

3-3- Total coliform count (MPN) using lauryl sulphate tryptose (LST) broth and Brilliant-green Lactose Bile 2% broth (APHA, 1992a).

 

3-4- Faecal coliform count by using EC broth (APHA, 1992a).

 

3-5- E. coli count by using Eosine Methylene Blue agar (EMB) (APHA, 1992a).

 

3-6- Enumeration and isolation of enterococci by using Kanamycin Aesculin Azide agar plates (Mossel et al., 1978).

 

3-7- Identification of enterococci (Facklam and Collins, 1989).

 

3-8- Enumeration, isolation and identification of Staph.aureus by using Baired parker's agar (APHA 1992b).

 

3-9- Total yeasts and moulds count by using Sabouraud Dextrose agar (APHA, 1985).


  

RESULTS

 

Table 1: Statistical analytical results of titratable acidity % in examined yoghurt samples (plain and flavored)

 

Samples

No. of samples

Min.

Max.

Mean

±SEM

Plain yoghurt

30

1.21

1.59

1.41

0.02

Flavored yoghurt

30

1.32

1.99

1.67

0.04

 

Table 2: Statistical analytical results of total coliform count (cfu/ml or g.) in the examined samples.     

 

Samples

No. of

samples

Positive samples

Min.

Max.

Mean

±SEM

No.

%

Raw milk

30

30

100

1.5×103

9.3×106

7.5×105

3.9×105

Pasteurized  milk 

30

14

46.67

< 3

1.5×104

8.25×102

5.04×102

Ice-cream

(small scale) 

30

30

100

2.1×102

7.5×105

8.2×104

4.1×104

Plain yoghurt

30

10

33.33

< 3

9.3×103

4.83×102

3.15×102

Flavored yoghurt

30

18

60

< 3

1.5×104

2.72×103

9.5 ×102

 

Table 3: Statistical analytical results of faecal coliform (cfu/ml or g.) in the examinedsamples.                     

 

Samples

No. of

samples

Positive samples

Min.

Max.

Mean

±SEM

No.

%

Raw milk

30

28

93.33

< 3

4.3×105

2.8×104

1.5×104

Pasteurized  milk 

30

10

33.33

< 3

2.1×103

1.16×102

7.11×10

Ice-cream

(small scale)

30

25

83.33

< 3

2.1×103

1.02×103

1.71×102

Plain yoghurt

30

6

20

< 3

2. 1×102

2.01×10

1.07×10

Flavored yoghurt

30

13

43.33

< 3

2.1×103

3.13×102

1.30×102

 

 

Table 4: Statistical analytical results of E.coli true faecal type count (cfu/mlor g.) in the examined samples.   

 

Samples

No. of

samples

Positive samples

Min.

Max.

Mean

±SEM

No.

%

Raw milk

30

25

83.33

< 3

2.1×104

1.38×103

6.89×102

Pasteurized  milk 

30

7

23.33

< 3

2.1×102

1.84×10

9.5

Ice-cream

(small scale) 

30

24

80

< 3

2.1×103

4.87×102

1.18×102

Plain yoghurt

30

6

20

< 3

2.1×102

1.36×10

8.4

Flavored yoghurt

30

12

40

< 3

2.1×102

4.68×10

1.50×10

 

Table 5: Statistical analytical results of Entercocci count (cfu/mlorg.) in the examined samples.

 

Samples

No. of

samples

Positive samples

Min.

Max.

Mean

±SEM

No.

%

Raw milk

30

30

100

6×104

2.5×106

1.12×106

1.29×105

Pasteurized  milk 

30

15

50

< 102

6 ×103

2.1 ×103

4.20×102

Ice-cream

(small scale) 

30

25

83.33

< 102

3×106

1.1 ×106

1.87×105

Plain yoghurt

30

12

40

< 102

1×104

2.23×103

6.29×102

Flavored yoghurt

30

15

50

< 102

2.5×104

7.77×103

1.67×103

 

Table 6: Incidence of the isolated Enterococcus species from the examined samples

 

The examined samples

No. of the  examined samples

 

Enterococcus faecalis

Enterococcus

faecium

Enterococcus

durans

No.

%

No.

%

No.

%

Raw milk

30

14

46.67

12

40

4

13.33

Pasteurized milk

30

10

33.33

5

16.67

0

0

Ice-cream

(small scale) 

30

16

53.33

9

30

0

0

Plain yoghurt

30

8

26.67

4

13.33

0

0

Flavored yoghurt

30

10

33.33

5

16.67

0

0

Total

150

58

36.67

35

23.33

4

2.67

 

Table 7: Statistical analytical results of staph.aureus count (cfu/mlorg.) in examined samples

 

Samples

No. of

samples

Positive samples

Min.

Max.

Mean

±SEM

No.

%

Raw milk

30

20

66.67

<102

6×105

1.98×105

3.91×104

Ice-cream (Small scale)

30

10

33.33

<102

4×105

7.65×104

2.41×104
                 

 

Table 8: Statistical analytical results of total yeasts and moulds count (cfu/g.) in the examined yoghurt samples/g

 

Samples

No. of

samples

Positive samples

Min.

Max.

Mean

±SEM

No.

%

Plain yoghurt

30

10

33.33

<10

6×10²

1.15×10²

3.59×10

Flavored yoghurt

30

18

60

<10

1.2×103

4.48×10²

8.17×10

 

 


DISCUSSION

 

1. Sanitary examination (The titratable acidity % of yoghurt):-

Inspection of Table 1 showed that the titratable acidity % of examined plain yoghurt samples ranged from 1.21 to 1.59 with a mean value of 1.41 ± 0.02. Lower results of titratable acidity % were reported byAbou El-Makarem (2013) while similar results were obtained by El- Kasas (2004) andEl-Asuoty (2011). The titratable acidity % of examined flavored yoghurt samples ranged from 1.32 to 1.99 with a mean value of 1.67 ± 0.04 Lower results of titratable acidity % were detected by El- Le boudy et al. (2017), while similar results were demonstrated byKüçüköner and Tarakçi (2003), while, higher results were shown byEl- Kasas (2004).

 

There is a variation in percentage of titratable acididty may be due to the percentage of the inoculum starter, incubation time and temperature of yoghurt storage (Walstra et al., 1999).

 

2. Micobiological examination:-

2.1- Total coliforms:

It is evident from Table 2 that total coliforms were detected in 30(100%), 14(46.67%), 30(100%), 10(33.33%) and 18(60%) of  the examined raw cow's milk, pasteurized milk, small scale ice cream and large scale plain and flavored yoghurt samples, respectively with mean values of 7.5×105± 3.9×105, 8.25×102± 5.04×102, 8.2×104± 4.1×104, 4.83×102 ± 3.15×102 and 2.72×103± 9.5 ×102 cfu/ml or g.

 

Higher results of total coliforms in raw cow's milk were reported by El-Zubeir and Ahmed (2007), while lower results were reported by El-Kholy et al. (2015). Higher results of total coliforms in pasteurized milk were obtained by Stanescu et al. (1992), while lower results were noticed bySiva et al. (1993). Higher results of total coliforms in ice-cream were reported byÇinar (2010), while lower results were revealed byEl-Kholy et al. (2015).

 

Lower results of total coliforms inplainyoghurt were detected byMoustafa (2004) and Sadik (2009), while higher results were reported by Ibrah

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