Antibacterial Activity of Probiotic Yoghurt and Soy-Yoghurt against Escherichia coli and Staphylococcus aureus

Abd El Gawad Ia ,El Sayed Em

doi:10.4172/2155-9600.1000303

Abstract

Introduction: Biopreservation systems in food are becoming increasingly interesting for the industry and consumer. Methods: Yoghurt milk and soymilk samples were inoculated separately with E.coli or S. aureus immediately after adding the starter (bifidobacteria and/or yoghurt culture) to investigate the antimicrobial activity of probiotic yoghurt and soy-yoghurt. Results: Probiotic yoghurt containing Bifidobacterium lactis (Bb-12) and Bifidobacterium longum (Bb-46) exhibited a slight pH drop compared with plain yoghurt (without bifidobacteria) during the refrigerated storage period. Plain yoghurt and probiotic yoghurt containing Bb-12 and Bb-46 inoculated with or without test organisms showed a significant (P<0.05) increase in lactic and acetic acids than the probiotic soy-yoghurt containing Bb-12 and Bb-46 which produces not only lactic and acetic acids but also formic acid. From the initial count of E.coli, % decreases were 96.00, 99.43, 99.14, 97.14 and 98.43%, for the plain yoghurt, probiotic yoghurt containing Bb-12 & Bb-46 and soy-yoghurt containing Bb-12 and Bb-46, respectively. E. coli counts were disappeared in probiotic yoghurt, soy- yoghurt and plain yoghurt after 2, 3 and 5 days of storage, respectively .The decrease percentage for the plain yoghurt, probiotic yoghurt containing Bb-12 and Bb-46 and soy-yoghurt containing Bb-12 & Bb-46 were 85.62, 93.36, 95.58, 93.36 and 95.58 from the initial inoculum level, respectively. The growth of S.aureus was not detected in the probiotic yoghurt containing Bb- l 2 and Bb-46 after the 10th day of storage. Low numbers of S.aureus survived in the plain yoghurt and probiotic soy-yoghurt Bb- 12 and Bb-46, after 15 days of cold storage. Conclusion: According to this data probiotic yoghurt, Soy-yoghurt and their antibacterial metabolites can be used to control pathogenic microorganisms

Highlights

Biopreservation systems in food are becoming increasingly interesting for the industry and consumer
Bifidobacterial population in the probiotic yoghurt containing Bb-12 & Bb-46 and probiotic soy-yoghurt made with Bb-12 and Bb-46, decreased by 98.56, 92.00, 96.43 and 98.86%, without inoculation with test organisms at the end of refrigerated storage period, respectively
In case of the treatments inoculated with E. coil the corresponding decrease ratios were 74.22, 99.36, 48.13 and 62.72%, respectively, whereas for the treatments inoculated with S.aureus the population of bifidobacteria decrease by 82.50, 97.96, 84.19 and 99.00%, respectively

Summary

Introduction

Biopreservation systems in food are becoming increasingly interesting for the industry and consumer. The food industry has unique opportunities to develop products that are nutritional in the traditional sense, but which have additional activity that can lead to an improved state of health and well-being and/or reduction in risk disease «functional foods» Probiotics have been defined as «live microbial feed supplements that have beneficial effects on the host by improving its intestinal microbial balance» [1]. Bifidobacteria are known to exhibit inhibitory effects on many pathogenic organisms both in vivo and in vitro, including Salmonella, Shigella, Colstridium, Bacillus cereus, Staphylococcus aureus, Candida albicans, Listeria monocytogenes, Escherichia coli and Campylobacter Jejuni [2,3,4]. Because bifidobacteria has been associated with health-promoting effects, there has been an increasing in incorporating this microbial group into dairy and dairy like foods or supplementing dairy foods with these organisms. The ultimate intent of this strategy is to provide the gastrointestinal tract of humans with viable populations of bifidobacteria

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Conclusion