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MICROBIAL POPULATION LOAD AND ENZYME PRODUCTION OF INDIGENOUSLY ISOLATED YEAST

MUHAMMAD TANWEER KHAN¹, MUSHTAQ HUSSAIN¹, ABDUL WAJID² AND SHEIKH AJAZ RASOOL^1*

Abstract: Traditionally, yoghurt is in use for centuries because of its beneficial effects on human health.  People and health practitioners have long been considering it as prophylactic and therapeutic agent for many gastrointestinal ailments primarily because of its microbial flora. Hence, the health benefits warrant the need to study microbial flora/natural contaminants of indigenously prepared yoghurt. In the present study, 75 yoghurt samples were collected from the retail outlets from all 18 towns of Karachi. Total yeast counts in terms of colony forming units (CFU) per gram were determined using selective media. Yeast load was also compared with bacterial load, particularly coliforms and enterococci in the samples under study. Several isolated yeast strains were screened for enzyme production that in future can be exploited in various industrial/health applications for instance amylase, beta-galactosidase, protease and lipase. Observations thus obtained were subjected to rigorous statistical analysis. The total yeast population in yoghurt samples was in between 45-2.5 x 10⁷ CFU having population mean of 5 x 10⁶ CFU compared to total bacterial counts (1.3 x 10⁴ -7 x 10⁷ CFU) with an average of 1.0 x 10⁷ CFU. The estimated coefficients of variance (CV) exhibited by total bacterial and yeast counts were 160% and 45% respectively.  Enzymatic screening results showed that 32% of yeasts were protease producer followed by lipase (8%) and β-galactosidase (7%). Interestingly no amylase activity was detected in yeast isolates. Laconically, data thus obtained showed more prevalence of bacteria in yoghurt compared to yeast. Beside useful microorganisms like Lactobacillus sp., yeast etc; some pathogenic organisms were also detected during sampling, which indicates malpractice in the preparation of yoghurt. Implication of enzymatic profile studies of the isolated yeast strains suggests that yoghurt yeast could be exploited as a source of industrially and therapeutically important metabolites

¹Laboratory of Molecular Genetics (LMG), Department of Microbiology, University of Karachi, Karachi 75270, Pakistan.

²HEJ Research Institute of Chemistry,  Int. Centre for Chem. & Biological Sciences, University of Karachi

^*Correspondence author E-mail: rasoolajaz@yahoo.com