CHAPTER ONE

INTRODUCTION

1.1     Background to the Study

Lactic acid bacteria, primarily belonging to genera such as Lactobacillus, Leuconostoc, Pediococcus, and Streptococcus, are essential in the fermentation process. They produce lactic acid as the major metabolic end product, which lowers the pH and inhibits the growth of spoilage organisms and pathogens, thereby extending the shelf life of fermented foods. Additionally, LAB are known to produce antimicrobial substances like bacteriocins, hydrogen peroxide, and carbon dioxide, which contribute to food safety. (Papadimitriou, 2021). These properties make LAB important for both naturally fermented and processed foods, where they act as biopreservatives and help enhance food safety.

Lactic acid bacteria (LAB) are a group of Gram-positive bacteria known for their ability to convert sugars into lactic acid through fermentation. LAB are commonly found in fermented foods and play a vital role in enhancing food quality by improving taste, texture, and shelf life. These bacteria, which include genera such as Lactobacillus, Leuconostoc, Pediococcus, and Streptococcus, are known for their ability to convert sugars into lactic acid, which inhibits the growth of harmful bacteria, thereby enhancing food safety and quality (Vinderola et al., 2020). Their presence in fermented foods and snacks is of interest due to their natural preservative qualities and potential health benefits as probiotics. They are also known for their probiotic potential, contributing to gut health and boosting the immune system. LAB species such as Lactobacillus, Leuconostoc, Pediococcus, and Streptococcus are widely studied in food microbiology for their beneficial roles in various food products. AB are essential in food preservation and fermentation, where they inhibit the growth of spoilage organisms and pathogens by producing organic acids, bacteriocins, and hydrogen peroxide. In developing countries and urban areas, snacks and street food often rely on natural fermentation processes, which may involve the growth of LAB, either intentionally or unintentionally. Lactic acid bacteria (LAB) have been exploited for centuries as probiotics to promote good human and animal health. They play important role in food fermentation, primarily by causing the characteristic flavor changes and contributing a preservative effect on the fermented product. These bacteria are widely used as starter cultures in most fermented foods such as dairy products. However, some strains of LAB could be used as probiotic. LAB used for centuries by man to preserve food, produce antagonistic compounds, including lactic acid, hydrogen peroxide and bacteriocins. Bacteriocins are antimicrobial peptides that are bactericidal toward bacteria taxonomically close to the producer. The specific actions of some bacteriocins toward foodborne pathogenic bacteria and undesirable flora like Listeria spp. and Clostridium spp. have increased the interest in these compounds. LAB are safe microorganisms with abilities to produce different inhibitory compounds such as bacteriocins, organic acids, hydrogen peroxide, diacetyl and carbon dioxide. LAB can inhibit harmful microorganisms through competitive exclusion mechanism based on competition for binding sites and nutrients (ViecoSaiz et al., 2019).

LAB are essential in food preservation and fermentation, where they inhibit the growth of spoilage organisms and pathogens by producing organic acids, bacteriocins, and hydrogen peroxide. In developing countries and urban areas, snacks and street food often rely on natural fermentation processes, which may involve the growth of LAB, either intentionally or unintentionally.

The presence of harmful microorganisms in food results in spoilage, making the food product unappealing and unacceptable to consumers (Petruzzi et al., 2017). Food spoilage is a metabolic process that alters the sensory characteristics of food, making it unappealing or unacceptable for human consumption. Although spoiled food may not pose a health risk as there are no pathogens or toxins present, changes in texture, smell, taste, or appearance make it unappealing. Some researchers have suggested that the unpleasant smells produced by microbes are used to repel larger animals and keep the food source for themselves. The diverse range of foods available presents a challenge for microbiologists, engineers, and technologists to discover effective methods of preventing the entry of microorganisms, destroying those that do manage to enter, and halting the growth and activity of those that evade processing treatments. A variety of microorganisms can cause food spoilage, including aerobic psychrotrophic bacteria, gram-negative bacteria, yeasts, molds, heterofermentative lactobacilli, and spore-forming bacteria. Psychrotrophic bacteria are known to produce large amounts of extracellular enzymes that can cause recontamination of pasteurized fluid milk products, which greatly affects their shelf life. Fungal spoilage is characterized by the presence of a wide range of metabolic by-products, leading to off-odors and flavors, as well as visible changes in color or texture. Yeasts, coliforms, heterofermentative lactic acid bacteria, and spore-forming bacteria can also cause defects in cheeses. The spoilage of many foods can be slowed by reducing the pH through fermentation, adding acids or other preservatives, introducing desirable microflora, adding sugar or salt to reduce water activity, removing water, packaging to limit oxygen, and freezing. The type of spoilage microorganisms varies widely among dairy foods due to the selective effects of production, formulation, processing, packaging, storage, distribution, and handling practices (Martorell et al., 2021).

Statement of the Problem

The consumption of snacks sold by street vendors and small-scale sellers is common in many academic environments. While these snacks provide convenient and affordable food options for students and staff, they often lack proper microbial quality control due to inconsistent hygiene practices during preparation, handling, and storage. This poses a potential risk of foodborne illnesses, as these snacks may become contaminated with pathogenic microorganisms

Lactic acid bacteria (LAB) are naturally present in many fermented foods and play a vital role in improving food safety by inhibiting the growth of harmful bacteria. However, the specific types and roles of LAB in snacks sold have not been studied, leaving a gap in understanding their contribution to food safety and potential health benefits in this context. Moreover, identifying LAB with probiotic potential could offer added health benefits to consumers, but without scientific investigation, this possibility remains unexplored.

The problem, therefore, is the lack of scientific data on the presence, identification, and roles of LAB in snacks sold. Without this information, it is difficult to determine whether these snacks are microbiologically safe for consumption and whether they could provide probiotic benefits. There is a need to isolate and identify LAB strains from these snacks to assess their contribution to food safety, potential health risks, and possible probiotic properties. This study aims to address this gap by investigating the types of LAB present in snacks thereby contributing to improved food safety practices and promoting public health within the university community.