AN INVESTIGATION OF THE MICROBIAL CONTAMINATION OF YOGURT
ABSTRACT
Ten authorized Yogurt products purchased within Ota metropolis, Ogun State of Nigeria were subjected to pH, Total Bacterial Count (TBC) and Total Fungal Count (TFC) analysis. pH values were in the range of 4.05 to 5.50, the TBC and TFC values ranged between 1.0 x 103 – 5.0 x 105 cfu/ml and 1.0 x 103 – 5.0 x 105 cfu/ml respectively. Eleven bacterial isolates were detected in the yogurt samples. Lactobacillus spp. and Bacillus spp. constituted 16% of the total microbial load, Corynebacterium spp., Klebsiela spp., Staphylococcus spp., and Pseudomonas spp. constituted 8% while Proteus spp., Micrococcus spp., Shigella spp., Listeria spp., and Streptococcus spp. constituted 4%. Fungal isolates obtained were Mucor spp. (22%), Geotrichum spp. (17%), Montospora spp. (11%), while Aspergillus spp., Rhizopus spp., and Fusanrium spp. constituted 6%.The antimicrobial susceptibility test showed that the isolates exhibited susceptible to Ciprofloxacin and Ofloxacin and resisted Nitrofurantoin, Augumentin, Cefixime, Ceufuroxime, Gentamicin and Ceftazidime. The isolates were plasmid encoded, with size range of 20,000- 40,000 Kilo base pairs. Result show no significant difference within the bacteria isolates (P> 0.05), while the fungi isolates showed significant difference (P<0.05). Significant difference also occurred between the bacteria and the fungi isolate (P>< 0.05).
CHAPTER ONE
INTRODUCTION
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).
In countries where food borne illness are investigated and documented, the relative importance of pathogens like Staphylococcu aureus and Escherichia coli in yoghurt borne infection is well known (Obende, 1999). Dairy foods are frequently contaminated with staphylococci and cases of staphylococcal contamination of milk and milk products like yoghurt have been recorded (Umoh et al., 1985). More than 50% of the strains of S. aureus are able to produce enterotoxin associated with food poisoning. The most important source of contamination by S. aureus is the human. (Payre and Wood, 1974).
The coli forms bacteria are also reported to be contaminants of yoghurt. The study of Obende, (1999) shows that 60% of yoghurt samples analyzed in Enugu Urban are contaminated with coli forms. The source of contamination of coli forms bacteria is through water used or through the workers or utensil used in processing (Gillies and Bodds, 1973). Interestingly, most of the yoghurts are produced in little less than the cottage industries at homestead level under different brand names and are found in stalls, or more commonly hawked along the streets, motor parks and in the market. In view of this, the objective of this study was to investigate the level of microbial contamination of yoghurts sold in Enugu Urban.
