PROBIOTICS AND ANTIMICROBIAL ACTIVITIES OF LACTIC ACID BACTERIA FROM PALM WINE

PROBIOTICS AND ANTIMICROBIAL ACTIVITIES OF LACTIC ACID BACTERIA FROM PALM WINE

CHAPTER ONE

1.0       Introduction

Palm wine is a beverage obtained from the fermentation of palm sap from palm tree (Elaeis guineensis) by indigenous microbes which consist of fungi and bacteria (Ezeronye, 2004; Okereke and Okereke, 2008). Natural palm sap is clean, sweet, colourless syrup containing about 10-20% of sugar that exudes from the trunk of the various species of palm tree during tapping operations (Elijah et al., 2010). Palm wine appears as a white liquid due to the increased microbial suspension arising from growth of the fermenting organisms. The predominant LAB reported in palm wine fermentation are Lactobacillus plantarum and Leuconostoc mesenteroides (Amoa-Awua et al., 2007). These micro-organisms are responsible for the sour taste of palm wine and are responsible for pH decrease during tapping through the organic acid production (Amoa-Awua et al., 2007, Ouoba et al., 2012).

Lactic acid bacteria (LAB) is gram positive, non-spore forming, non-respiring (lack catalase), cocci or rods which produce lactic acid as the major end product during fermentation of carbohydrate. The core group of LAB includes Lactobacillus, Leuconostoc, Pedicoccus and Streptococcus. Others include Tertagencoccus and Vogococcus (Batt, 2000). Lactic acid bacteria are found in foods (dairy products, fermented meat, sour dough, fermented vegetable, silage beverage; including wine), on plant, in sewage but can also be in the genital, intestinal and respiratory tract of man and animals (Hames et al., 1991). In food industry lactic acid bacteria acts as a beneficial and spoilage organism.

The antimicrobial effect of LAB is mainly due to the lactic acid and organic acid production, causing the pH of the growth environment to decrease (Caplice and Fitzgerald 1999; Kulper et al., 2000). Low pH induces organic acid to become lipid soluble and diffuse through the cell wall and cytoplasm (Gottschalk 1998). LAB also produces acetaldehyde, hydrogen peroxide, diacetyl, carbon dioxide, polysaccharides and bacterocins (Rodriques et al., 2003) some of which acts as antimicrobials.

Probiotics are generally defined as live microorganisms that can only be seen with a microscope which, when administered in adequate amounts, confer a health benefit to the host (FAO/WHO, 2002). They are mostly bacteria that colonize the gut by maintaining a balance between beneficial and harmful bacteria thus enhancing a healthy digestive tract. Probiotics are different from other types of bacteria in that they are considered “good” bacteria or non-pathogenic in healthy people. The antimicrobial properties of probiotics may be due to the production of bacterocin such as nisin, or lowering the pH. Probiotics strains compete with other infectious bacteria for nutrients and cell surface and help get rid of them by inhibiting their colonization. The health benefit of probiotics has always been investigated with regards to the capability to sustain their availability, viability, digestibility, and rendering of health benefit without altering the safety and organoleptic property of food in which it has been incorporated(Santiago-Urbina, 2013)..

1.1       Justification

LAB found in palm wine may serve as bacterocin potentially promoting host specific health due to their probiotic nature. LAB predominate the micro flora of fermented food which produces an array of antimicrobial substances such as organic acid, diacetyl acetone, hydrogen peroxide, reuterin and bacterocin. The antimicrobial produced makes them suitable for food preservation. The study is however carried out to ascertain the full benefit of LAB found in palm wine and the best way of utilizing them in promoting human health.

1.2       Problem Statement

A large number of LAB, isolated from various fermented foods in different parts of the world, have been studied for their probiotic potential and ability to produce important substances for foods and pharmaceutical preparation (Yavuzdurmaz, 2007). LAB have become the focus of probiotic research internationally and their health benefits in the prevention of diarrhoea, reduction of the cholesterol level, relief of both irritable bowel syndrome and milk allergy in infants are well documented (Yavuzdurmaz, 2007). However, these properties cannot be extrapolated or generalised for all probiotic strains as such effects are strain-specific depends on the source of the AB. There is a dearth of information on the probiotic potential of LAB isolated from palm wine.

1.3       General Objectives

The general objective of the study is to determine the probiotic and antimicrobial activity of lactic acid bacteria from palm wine. The specific objectives included:

1. To isolate and identify lactic bacteria from palm wine.
2. To screen for the antimicrobial activities of the lactic acid bacteria against selected test organisms.
3. To determine the probiotic characteristics of lactic acid bacteria isolated from palm wine.