Screening and characterization of in-vitro probiotic criteria of Saccharomyces and Kluyveromyces strains

Background and Objectives: Probiotics are defined as live micro-organisms conferring a health benefit on the host. Although most probiotics are bacteria, some yeasts such as Saccharomyces and Kluyveromyces, has been found to have effective probiotic properties. The objective of this study was to isolate and identify indigenous Saccharomyces and Kluyveromyces yeast strains and to compare some probiotic characteristics between these two strains in vitro. Materials and Methods: Strains were isolated on yeast glucose chloramphenicol agar medium from 205 samples and identified by morphological, physiological and biochemical assays. The effects of different conditions such as pH and temperature on the survival and growth of the isolates were studied. In addition, resistance to acidic pH (1.5, 2, 3 and 5), pepsin and different concentrations of bile salts (1%, 3% and 5%), as well as proteolytic, lipolytic and hemolytic activity of selected isolates were assessed. Finally, the best isolates were selected for investigation of their viability in samples of dairy products. Results: 126 isolates were identified using biochemical and molecular techniques as yeast strains. Five isolates were found to have effective probiotic properties, belonging to Kluyveromyces marxianus (S97, S101 and S106) and Saccharomyces cerevisiae (S28, S34). These isolates were able to grow at 37°C, pH=1.5, withstand to concentration of 5% oxbile and pepsin and exhibit the proteolytic activity. The isolates of K. marxianus showed better viability in dairy (yogurt). Conclusion: In the in-vitro comparative experiments, the isolates of K. marxianus showed better probiotic potentials.