Thesis Abstract

Abstract
Yoghurt is a popular fermented dairy product consumed worldwide due to its nutritional benefits and unique taste. However, the presence of microbial contamination in yoghurts poses a significant concern for public health. This study aimed to investigate the level of microbial contamination in different types of yoghurts available in the market. A total of 100 samples of yoghurts, including plain, flavored, and Greek varieties, were collected from various supermarkets and local stores. The samples were analyzed for microbial contamination, including total viable count (TVC), coliforms, yeast, and molds. The results revealed varying levels of microbial contamination among the different types of yoghurts tested. The TVC ranged from 2.5 x 10^3 to 1.2 x 10^6 colony-forming units per gram (CFU/g) across all yoghurt samples. Coliforms were detected in 40% of the samples, with counts ranging from 0 to 140 CFU/g. Yeast and mold counts ranged from 0 to 380 CFU/g and 0 to 250 CFU/g, respectively. Interestingly, the plain yoghurts showed lower levels of microbial contamination compared to flavored and Greek yoghurts. Further analysis revealed that the storage conditions of yoghurts significantly influenced the microbial contamination levels. Yoghurts stored at refrigeration temperatures had lower microbial counts compared to those stored at room temperature. Additionally, the presence of preservatives in flavored yoghurts was found to impact the microbial growth, with higher counts observed in samples containing artificial additives. The identification of specific microbial contaminants in yoghurts was conducted using molecular techniques, including polymerase chain reaction (PCR) and sequencing. The results indicated the presence of various bacterial and fungal species, some of which have the potential to cause foodborne illnesses if consumed in large quantities. Overall, this study highlights the importance of monitoring and controlling microbial contamination in yoghurts to ensure product safety and quality. Proper storage practices and the use of natural preservatives can help mitigate the risk of microbial growth in yoghurts. Continued surveillance and adherence to good manufacturing practices are essential to safeguard consumer health and maintain the integrity of yoghurt products on the market.

Thesis Overview

 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). Diary 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.