Evaluation of viability of lactic acid bacteria in a Nigerian commercial yogurt and its antagonistic effects on selected strains of diarrheagenic <i>Eschericia coli</i>

Abstract

Background: Yogurt is one of the most popular fermented milk products worldwide and has gained widespread consumer acceptance as a healthy food supplements. It provides an array of nutrients in significant amount in relation to its energy, fat contents and other health benefits. The micro organism in the final product must be viable and abundant enough to confer health benefits to consumers.
Objective: The objective of this study was to determine the viability of lactic acid bacteria in selected yoghurt at refrigerated and room temperature storage conditions and antimicrobial properties of the selected yoghurt against diarrheagenic E.coli.
Methods: The viability of LAB was assessed in Quincy yogurt for one month using pour plate method at refrigerated and room temperature storage conditions. The antimicrobial activities of LAB in the yoghurt against 6 diarrheagenic E.coli strains were assessed by coculture method at lower (104 cfu/ml) and higher (2.1 x 106 to 1.64 x 108 cfu/ml) pathogen concentrations.
Results: The viable count of LAB in yoghurt decline from 5.3 log10 cfu/ml to 4.2 log10 cfu/ml and 5.3 log10 cfu/ml to 4.4 log10 cfu/ml for room temperature and refrigeration respectively. No E. coli strain survived in yoghurt samples after incubation for 24 hours at lower pathogen concentration while reductions of 2 log to total inhibition were observed at higher pathogen concentration.
Conclusion: This study reports interesting high antimicrobial properties of yoghurt against diarrheagenic E. coli strains. Storage of the tested yogurt at room temperature still retained relatively high log count of lactic acid bacteria over 1 month period, however, storage at refrigerated temperature retained higher quantities of lactic acid bacteria..

Keywords: Yogurt, Diarrhea, Probiotics, Intestinal Pathogens, Storage.