In Vitro Evaluation of Probiotic Properties of Indigenous Yeasts Isolated from Nigerian Fermented Food Products

Probiotics are living microbial food supplements which beneficially affect the host by improving the intestinal microbial balance. Before an organism can be designated as probiotic there are certain criteria that must be fulfilled. These include acid and bile tolerance, antimicrobial activity, ability to co-aggregate, hydrophobicity etc. One hundred and eighty one indigenous yeast isolates recovered from various fermented food products of Nigeria were characterized and grouped using phenotypic methods. Forty two selected yeast isolates were identified using molecular method which involved sequencing of D1 and D2 domain of the large subunit of ribosomal DNA. Then nine indigenous Saccharomyces cerevisiae were evaluated for their probiotic characteristics such as acid and bile tolerance, transit in simulated gastric and intestinal juices, autoaggregation and hydrophobicity. Saccharomyces cerevisiae SC10 was included as a positive control. The S. cerevisiae were able to grow in the presence of acidic medium with pH as low as 2 and 3. In the minimum inhibitory concentration test with 0-1% ox bile, all the S. cerevisiae tested were able to grow. The growth for 3% bile tolerance test ranged from 4.81 to 5.35 log cfu/ml. These isolates were able to survive in simulated gastro-intestinal transit. All the yeast isolates exhibited bile salt deconjugation activity against sodium glycodeoxycholate and were able to grow in the presence of all other bile salts investigated. Autoaggregation ability (an adhesive property) of the indigenous yeast isolates ranged from 89.80% for S. cerevisiae BK19 to 99.91% for S. cerevisiae OB03. The native yeast isolates also exhibited high percentage hydrophobicity, another adhesive property of probiotics. The values obtained ranged from 31.62 to 83.45% for isolates AG23A and OB 17. These observations indicate that the native yeast isolates from Nigerian fermented foods have the potential of being use as probiotics for making functional foods.