Bacteriological Quality Of Pasteurized Liquid Milk Samples Sold At Different Shops (A Case Study Of Students Market Located At Imo State University Front Gate)

Project and Seminar Material for Biochemistry

Bacteriological Quality Of Pasteurized Liquid Milk Samples Sold At Different Shops (A Case Study Of Students Market Located At Imo State University Front Gate)


The present study was carried out to determine the bacteriological quality of pasteurized liquid milk samples sold at different shops in students market located at Imo state University front gate. A total of four samples were collected. The samples were examined to determine the total heterophilic bacterial count and total coliform count. Results revealed that two of the samples (1 and 2) yielded no growth on both Nutrient agar and MacConkey agar hence, were tagged satisfactory. Sample 2 and 3 yielded growth that ranges from 7.0X104 – 9.0 X104, 1.3 X105 – 1.3 X105 respectively. Further identification test carried out showed the presence of Escherichia coli and Enterobacter spp. in sample 3 and 4 hence they were tagged unsatisfactory. The presence of coliform bacteria shows the possibility of pathogenic bacteria and could cause disease.

Chapter One

1.0 Introduction / Literature Review

1.1 Introduction

Milk is an important food of diet of vast population on earth, due to its high nutritional value for human beings. Milk is an excellent growth medium of microorganism when suitable temperature exists. If it is produced unhygenically and handled carelessly, it gets contaminated very easily leading to its early spoilage (Oliver et al., 2005). Many milk-borne epidemics of human diseases have been spread by contamination of milk by spoiled hands of dairy workers, unsanitary utensils, flies and polluted water supplies. The same thing can be said for improper handling of foods in the home, restaurants, hospitals and other institutions.

The quality of milk is determined by aspects of composition and hygiene. Due to its complex biochemical composition and high water activity milk serves as an excellent culture medium for the growth and multiplication of many kinds of microorganisms.

The contamination of milk and milk products is largely due to human factor and unhygienic conditions. Usually milk gets contaminated with different kinds of microorganisms at milk collecting places. Milk is a major part of human food and plays a prominent role in the diet. Approximately 50% of the milk produced is consumed as fresh or boiled, one sixth as yoghurt or curd and remaining is utilized for manufacturing of indigenous varieties of milk products such as Ice cream, Butter, Khoa, Paneer, Rabri, Kheer, Burfi and Gulabjaman. The manufacture of these products is based on traditional method without any regard to the quality of raw material used and/or the hygienic quality of the products. Under such conditions many microorganisms can find access to the milk products.
Coliforms are considered as normal flora of intestinal tract of human and animals. They have been used as indicator organisms for bacteriological quality of milk and its products (Chatterjee et al., 2006).

Coliform count is always being taken as a definite index of fecal contamination of milk and its products, that besides the possible presence of enteric pathogens which may constitute health hazards to the consumers. The most important index of microbiological quality is total bacterial count, coliforms, yeast and moulds count and detection of specific pathogens and their toxins (Szita et al., 2008).

Among all micro-organisms Escherichia coli is frequently contaminating organism in food and is reliable indicator of fecal contamination and generally present due to insanitary conditions of water, food, milk and other dairy products (Jayarao and Henning, 2001). Recovery of E. coli from food is an indicative of possible presence of enteropathogenic or toxigenic micro-organism which could constitute a public health hazard. Enteropathogenic E. coli (EEC) can cause severe diarrhea and vomiting in infants and young children. Coliforms particularly Escherichia coli are frequently used in the microbiological analysis of food as an indicator of poor hygienic condition.
Microbiological examination of milk is essential to find the degree of contamination and enumeration of indicator organisms. The coliform bacteria are able to grow well in a variety of substrates and to utilize a number of carbohydrates and some other organic compounds as food for energy and a number of fairly simple nitrogenous compounds as a source of nitrogen. The coliform group of bacteria is defined as the indicator (faecal coliform) of suitability of milk for drinking (Wells et al., 1991). The present study has been designed to assess the milk quality of different milch animals with special reference to coliforms.

1.2 Aims and Objectives

The aims of this study is to determine the microbial quality of liquid milk sold in Owerri metropolis in Imo State..


The objectives of this study is as follows;

  1. Determination of the microbial load on the milk sample
  2. To isolate organisms associated with liquid milk contamination
  3. Identification of organism associated with liquid milk.

Chapter One Continues in the Complete Material…

Chapter Four

4.0 Discussion and Conclusion

4.1 Discussion

All four samples of pasteurized tin liquid milk were registered with NAFDAC and had expiry date. Microbial analysis was carried out to determine the quality of the liquid milk. From the microbial analysis, sample 1 (peak milk) and sample 2 (three crown) had no growth on both Nutrient agar and MacConkey agar plates hence, where free from microbial contamination. Sample 3 (Luna milk) and sample 4 (Nunu milk) yielded growth THBC and TCFC indicating the possibility of contamination as shown in table.

Table 2. shows the morphological appearance of colonial growth on both NA and Mac agar. The heterophilic bacterial growth showed creamy colour. The colonial growth on MacConkey agar, showed coliforms possessing red colouration.

Further identification (bacterial and biochemical test) carried out on identification of isolated organisms are shown in table 3 above. Organisms isolated reacted either positively or negatively to chemicals or reagent used in various test. Organism isolated belongs to the family of Enterobactericeae which are Escherichia coli (50%) and Enterobacter spp. (50%).

4.2 Conclusion

Higher levels of index organisms often do not, but may correlate with a greater probability of enteric pathogen(s) pollution and the absence of the index organism does not always mean that enteric pathogens are absent from the food (Grag and Usha Mandokt, 1997). However, index organisms such as E. coli are still being utilized as indicators for the overall quality of food and hygienic conditions present during food processing. The counts obtained are used as an assessment of the adequacy of pasteurization of milk. The presence of E. coli in sample 3 and 4 may be due to inadequate pasteurization, poor hygienic processing conditions and/or post processing contamination of the milk because proper pasteurization inactivates levels of E. coli anticipated in raw milk (Evancho GM. et al., 2001).

E. coli and other Enterobacteriaceae are common in food manufacturing environments and may become part of the resident microflora of the facility especially when sanitation is insufficient. It is also possible for E. coli to grow on some foods under refrigeration (Downes and Ito, 2001). This makes it important for the pasteurization process to adequately elimination of any existing E. coli and other organisms from milk. The low infectious dose of E. coli makes a serious health risk, as a small amount of E. coli consumed in milk can cause serious gastrointestinal complications. Even slight contamination of surfaces or work areas may cause serious infection (McClure P., 2002).

In this way, there are implications for a wide range of food handling and production industries including abattoirs, dairies, chilled food counters in supermarkets, salads and chilled food preparation factories. With such a significant coliform count and the characteristic low infectious dose of E. coli. The presence of E. coli in sample 3 and 4 could be the culprit of gastrointestinal illnesses if consumed. Strains of E. coli capable of causing gastroenteritis include enterotoxigenic (ETEC), enteroinvasive (EIEC), enteropathogenic (EPEC), enterohemmorrhagic (EHEC) and enteroaggregative (EAggEC) (Meng J. et al., 2005). No further tests were however employed to identify individual strains, since E. coli is a pathogenic coliform capable of producing gastrointestinal illness regardless of the strain.

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