Microbiological and Probiotic Assessment of Yeast Isolated from Wholegrain Millet Sourdoughs

Abstract

Background: The term probiotics have been described as live microorganisms associated with fermented foods that confer health benefit to the host. For a long time, researches into the world of probiotics have extensively and predominantly centred upon species of lactic acid bacteria and until recently Saccharomyces cerevisiae, as the only well-defined and proven probiotic yeast strain. The purpose of this study was to isolate and characterise the yeast species associated with the fermentation of wholegrain millet sourdoughs and investigate in vitro the possible probiotic potential of the isolates. Methodology: Wholegrain millet sourdoughs were prepared by spontaneous fermentation of the flours with tap water in the ratio 1:1 (w/v) for 48 h at 28 ± 2ºC through backslopping. A total of twenty five yeasts were identified based on their cultural, morphological and biochemical characteristics. The selected isolates were characterized to species level using API 20 C AUX test identification kit. Probiotic properties examined included bile salt and acid tolerance under conditions simulating the human gastrointestinal tract (GIT) and positive antagonistic activity against selected pathogens following well established procedures. Results: The selected isolates investigated were characterized to belong to species of Saccharomyces and Kluveromyces. All of the isolates were discovered to exhibit sufficient survival under acidic pH of 2.0 with values ranging from 1.0log cfu ml-1 to 7.8log cfu ml-1 and showed high resistance to bile salt with values ranging from 63-99%. They also exhibited good antimicrobial activity against enteric pathogens of E. coli, Salmonella typhimurium, Staphylococcus aureus, Klebsiella pneumonia, Streptococcus pyogenes, Proteus vulgaris and Pseudomonas sp. Conclusion: Millet sourdoughs can serve as an affordable nutritionally healthy substrate for delivery of probiotics to the gastro-intestinal tract, thereby proffering basic health functionality. This study allowed to isolate and to identify yeast species present in millet sourdoughs with technological potential for sourdough applications.