Investigating the Level of Microbial Contamination of Yoghurts Sold in Enugu Urban
CHAPTER ONE
OVERVIEW OF THE STUDY
Yoghurt is a cultural diary product produced by lactic fermentation of milk (Hui, 1992). Yoghurt is produced by the controlled fermentation of milk by two species of bacteria; Lactobacillus bulgaricus and Strptococcus thermophilus.
These two species of bacteriae have now been established as the yoghurt starters.
Any sort of milk may be used to make yoghurt, but modern production is dominated by cow milk. It is the fermentation of the milk sugar (Lactose) into lactic acid that gives yoghurt its gel-like texture and characteristics tang (Davis, 1974).
Milk is often regarded as being nature’s most complete food. It earns this reputation by providing many of the nutrients which are essential for the growth of the human body. It is an excellent source of protein, vitamins, minerals particularly calcium and also some anti-bacterial substances such as lysozyme, ladoferin (transferin) and lactoperoxidases. In addition to the major constituent, milk contains a large amount of lactose sugar, phosphate, peptone and nitrogenbase enzyme (Clurance et al., 1963). Yoghurt has practically the same food value as the basic milk product (Ruud and Bert, 2004).
Fermented milk products such as yoghurt contain bacteria from the lactobacilli group. These bacteria occur naturally in the digestive tract and have a cleansing and healing effect. Therefore, the introduction of fermented products like yoghurt into the diet can help prevent certain pathogenic bacteria, which may cause illness. Many people suffer from a condition known as “LACTOSE INTOLERANCE”. This means that they are unable to digest the milk sugar (lactose). Such people can however, tolerate milk if it is fermented to produce foods such as yoghurt. During fermentation, lactic acid producing bacteria breakdown lactose and in doing so eliminate the cause of irritation (Ruud and Bert, 2004).
CHAPTER TWO
LITERATURE REVIEW
Chemical Composition Of Milk
Milk is composed of milk fat, lactose (milk sugar), proteins, vitamins, minerals and water. The non-fat portion of milk is termed skimmed milk even when not separated from the whole milk. Normal milk also contains the immunoglobulins, which protect the young from infectious diseases. The composition of milk is influenced by several factors, which include: type of the animal, its quality/health, time between milking, animal feeds, age and season of the year (Jennes and Patton, 1999).
Chemical Composition Of Milk
Milk is composed of milk fat, lactose (milk sugar), proteins, vitamins, minerals and water. The non-fat portion of milk is termed skimmed milk even when not separated from the whole milk. Normal milk also contains the immunoglobulins, which protect the young from infectious diseases. The composition of milk is influenced by several factors, which include: type of the animal, its quality/health, time between milking, animal feeds, age and season of the year (Jennes and Patton, 1999).
History of Yoghurt
Yoghurt is traditionally believed to be an invention of the Bulgar people of Central Asia, although there is evidence of cultured milk products as far back as 2000 BC. The earliest yoghurt was probably spontaneously fermented, perhaps by wild bacteria residing inside goatskin bags used for transportation.
Yoghurt remained primarily a food of Central and Eastern Europe until the 1900s when a Russian biologist named Llyich Mechnikov theorized in 1990that heavy consumption of yoghurt was responsible for the unusually long lifespan of the Bulgar people. Believing LACTOBACILLUS to be essential for good health, Mechnikov worked to popularize yoghurt as a foodstuff throughout Europe. It fell to a Spanish entrepreneur named Isaac Carasso to industrialize the production of yoghurt. In 1919, he started a commercial yoghurt plant in Barcelona.
Traditional Method of Yoghurt Production
Vander berg (1988), indicated that the manufacture and composition of cultures used for the fermentation of milk vary from one area to the other. From skimmed milk C1-5-2.0% fat, the milk is heated to 70oC in a covered pot and held for two minutes to destroy pathogens and spoilage organisms to provide a clearer medium in which the desired microorganisms can be established. The heat denatures the proteins, which increases the viscosity of the product.
Pasteurized milk is immediately immersed in a basin of cold water to bring the milk temperature to 40oC – 47oC. This is to subject the thermoduric organisms in the milk to thermal shock resulting in autolysis and to provide convenient environment for the inoculation with starter cultures.
The cooled milk is inoculated with mixed cultures of Streptococcus thermophilus and Lactobacillus bulgaricus of 1 – 2% to produce desired fermentation and to flavour the product. This can be achieved by inoculating with a freshly prepared yoghurt purchased from a reliable store.
Yoghurt is usually classified into two types; The set and stirred yoghurt. Set yoghurt is the yoghurt packed immediately after inoculation with starter cultures and incubated in the container whereas the “stirred yoghurt” is packed after inoculation and incubation also, the coagulum is broken and cooled before packaging (Alfa – Lawal, 1984).
CHAPTER THREE
MATERIALS AND METHODS
The media used in this work include nutrient agar, Macconkey agar, Eosine methyleneblue agar (EMB), peptone water. The composition of the media, their method of production and the list of other equipment and reagents used in this work are presented in the appendix.
SAMPLE COLLECTION
Six different brands of bottle packaged yoghurt were brought from hawkers and beverage stores in Enugu Urban. The two samples of each brand were used and the brands were designated A, B, C, D, E, F, giving a total of 12 yoghut samples.
The samples were brought to the laboratory and analysed within 6 hours of collection.
ANALYSIS OF SAMPLE
Each sample was serially diluted using sterile distilled water as diluents (Prescolt et al 2002) and Iml of 10-3 sample was plated in duplicate using the pour plate method on MacConkey agar and nutrient agar media the plates were incubated at 370C for the 24hrs. After incubation, pink colonies that developed in MacConkey plates were counted and used to estimate the coliform count (cfu/ml) of the yoghurt samples. The colonies that develop on the nutrient agar plates were counted and used to determine the total bacterial count of the yoghurt samples (cfu/ml) the representative colonies on the plates were sub-cultured on fresh nutrient agar to obtain pure cultures of the isolates. The pure cultures were then transformed into nutrient agar slants for biochemical identification.
CHAPTER FOUR
The heterotrophic bacterial and coliform counts (cfulml) of the yoghurt samiles are shown is table 1. The mean bacterial counts of the six brands of yoghurt is 2.35 x 03 while the means coliform count is 0.14×03.
The physiochemical properties of bacteria isolated from the yoghurt samples are shown in table 2 while bacteria isolated from different brands of the yoghurt examined are presented in table 3. bacteria isolated from the yoghurt samples include. Klebsiella sp. Streptococcus species escherichia coli, bacillus sp. Staphylococcus aureus, psendomonas sp. Enterobacter sp, lactobacillus bulgarisius and Protons sp. Escherichia coli were isolated from 3 of the six brands of yoghurt examined.
CHAPTER FIVE
DISCUSSION
The result obtained from the microbiological analysis showed that product were contaminated by microorganisms of public health concern the high heterotrophic bacterial and coliform counts may be a consequence of low level of hygiere maintained during the processing by some of the producers of the product.
The detection of escherichia coli, enterobacter sp, klebsiella sp, and Proteus sp is an indication of possible faecal contamination of the product by potentially pathogenic organisms even though they were isolated from less than three of the six brands examined.
It is not surprising that lactosacillus and streptococcus were isolated from virtually all the sample examined because they are the organisms used as starter cultures for the production of yoghurt.
Similar microorganisms were isolated from yoghurt a similar product by Uzeh et al (2006).
The isolation of staphylococcus aureus is also of public health importance because of its ability to cause a wide range of infections especially food –borne intoxication some of these organisms were also isolated by Olasupo et al (2002) from kanunzaki, a cereal based, non-alcoholic beverage Engel et al (1980), Olpala and Jideani(2006) noted that some of the sources of microorganisms that contaminate yoghurt are problem of plant sanitation, the filling operation or the container and also the workers.
Conclusion
The conclusion drawn from this research work is that yoghurt if produced under a good hygienic condition, the microbial load could be reduced to be within acceptable limits of standard organization.
It is evident from this study that most of the samples of yoghurt analysed met the requirements compared to standard. However, yoghurt samples containing relatively low counts of Staphylococcus aureus and Escherichia coli may constitute a health hazard to consumers if mishandled.
Recommendations
Yoghurt should be prepared in a good hygienic condition so as to reduce the microbial load. Also care should be taken during processing and storage of the yoghurt samples to prevent contamination with unwanted materials and microorganisms such as staphylococcus species, (e.g. staphylococcus aureus) and coliforms (e.g. Escherichia coli).
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