by CHAPTER ONE
BACKGROUND OF THE STUDY
Yoghurt is a fermented dairy product produced by the lactic acid fermentation of milk. Early descriptions consider yoghurt as a cultured dairy product produced by lactic acid bacteria. Traditionally, yoghurt is produced when two bacterial species — Lactobacillus bulgaricus and Streptococcus thermophilus — act in symbiosis to ferment milk sugar (lactose) into lactic acid, giving the product its characteristic gel-like texture and tangy flavor (Davis, 1974). More recent literature confirms that these two species (or their modern counterparts) remain the core starters in commercial yoghurt manufacture. While a variety of milks may be used (goat, sheep, camel, etc), cow’s milk currently dominates global commercial production of yoghurt because of its widespread availability and suitable composition (Hui, 1992).
Milk itself is often regarded as “nature’s most complete food” because it provides many essential nutrients required for human growth and development, including high-quality protein, vitamins and minerals (especially calcium). When this highly nutritive matrix is fermented to yield yoghurt, it adds additional functional and sensory attributes that have made yoghurt one of the most consumed fermented dairy products worldwide.
Despite its many benefits, yoghurt is not immune to microbial safety risks. Fermentation is, at its heart, a microbiological process, and the microbial ecology of yoghurt (both during production and storage) plays a critical role in final product quality, shelf life, safety, and consumer health. Recent studies have highlighted that although the lactic acid bacteria (LAB) responsible for yoghurt fermentation are beneficial, many other microbial populations — including pathogenic or spoilage organisms — can contaminate yoghurt via raw materials, processing equipment, storage conditions, handling practices and packaging. For example, a 2024 study in Port Harcourt, Nigeria, of 20 yoghurt brands found total viable bacterial counts (TVC) of 1.1×10² to 8.0×10⁵ CFU/mL and the presence of Escherichia coli in many samples. A 2024 study of yoghurts in Addis Ababa, Ethiopia, also found TVC values that significantly exceeded standard limits, and elevated coliform counts indicative of poor hygiene or post-pasteurization contamination. These findings underline that yoghurt, while generally safe when produced under proper conditions, may become a vector for microbial contamination when standards are not maintained.
In the Nigerian context (and broadly in West Africa), rapid growth in yoghurt consumption, increasing availability of locally produced brands, informal and street-vended yoghurt products, and constraints in regulatory oversight, infrastructure, cold-chain maintenance, equipment sanitation and raw‐milk quality all contribute to elevated risks of contamination. Moreover, the high nutritional value of yoghurt (which makes it appealing to consumers) also makes it a potentially attractive medium for microbial growth if good manufacturing and storage practices are not followed.
It is therefore necessary to investigate the level of microbial contamination of yoghurts sold in Nigerian markets (whether branded, unbranded, informal or street-vended) — and to assess whether these products meet acceptable safety and quality standards; to identify the sources and potential pathways of contamination; and to propose measures toward improved production, handling, storage and regulation. Such studies not only contribute to food safety and public-health protection, but also to improving consumer confidence, strengthening local dairy markets, and guiding regulatory and industry interventions.
Hence, this research aims to examine the microbial quality of yoghurt sold in Nigeria, to determine the prevalence and levels of contamination, and to relate the findings to manufacturing, handling and storage practices. The outcome will provide empirical evidence for policymakers, industry players and public-health agencies to make informed decisions regarding yoghurt safety and quality assurance.
