Identification and characterization of Saccharomyces cerevisiae strains isolated from West African sorghum beer

Abstract

The occurrence and characterization of yeasts isolated from sorghum beer produced in Ghana and Burkina Faso, West Africa, were investigated. The yeasts involved in the fermentations were found to consist of Saccharomyces spp. almost exclusively. Of the isolates investigated, 45% were identified as Saccharomyces cerevisiae, whereas more than half of the isolates (53%) had physiological properties atypical of S. cerevisiae or any other member of the complex sensu strictu, as they were able to assimilate only glucose, maltose and ethanol as carbon sources. Both ITS-PCR RFLP and PFGE strongly indicated that these isolates were related to S. cerevisiae, regardless of their phenotypic characteristics. Sequencing of the D1/D2 domain of the 26S rDNA confirmed the close relatedness to S. cerevisiae with 0.5% nucleotide differences. The MAL1 and MAL3 loci were found for all isolates as the only recognized MAL loci. Besides, for 40% of the isolates the MAL61 probe hybridized to a position of about 950 kbp, which has not formerly been described as a MAL locus. The results showed that the spontaneous fermentation of West African sorghum beer is dominated by a variety of strains of S.cerevisiae not previously described, among which starter cultures should be selected.

Expression Patterns of Genes and Enzymes Involved in Sugar Catabolism in IndustrialSaccharomyces cerevisiaeStrains Displaying Novel Fermentation Characteristics

“…The chromosomal location of many of these sequences enabled them to be identified as one of the 5 MAL loci reported to date. The MAL1, MAL3 and MAL4 loci were represented in all industrial strains in agreement with previous studies 28,29,61 . Strain NCYC 1324 also possessed sequences corresponding to the MAL2 locus.…”

“…4). In agreement with others 28,29,44,61 , the occurrence of permease genes from the MAL1, MAL3 and MAL4 loci, as deduced from their apparent chromosomal location, was observed. Whilst the absence of the wellcharacterised MAL6 locus has been reported among brewing strains 28 and Saccharomyces species isolated from natural sources 41 , the absence of MAL6 from the laboratory strains studied here is more likely an indication of the divergence of this gene sequence from the MAL31 probe used.…”

Microbiological Quality of a Locally Brewed Alcoholic Beverage (Pito) Sold in a Community within the Greater Accra Region, Ghana

“…This observation is not surprising since this fungus is known to be involved in fermentation [14,15,17] and could therefore have been implicated in the fermentation of the pito. Apart from Saccharomyces cerevisiae, the bacterial isolates from the pito samples can be considered microbial contaminants even though the quantities were within the acceptable limits.…”

“…Similar to other openly sold foods and drinks, several factors may make pito prone to microbial contaminations. Potential microbes that can contaminate pito may include bacteria such as E. coli, Salmonella species, Shigella species and Staphylococcus aureus [13], whiles fungal contaminants may include Aspergillus flavus, Aspergillus niger and Saccharomyces cerevisiae [14][15][16]. Meanwhile, Saccharomyces cerevisiae is known to be associated with fermentation [14,15,17].…”

“…Potential microbes that can contaminate pito may include bacteria such as E. coli, Salmonella species, Shigella species and Staphylococcus aureus [13], whiles fungal contaminants may include Aspergillus flavus, Aspergillus niger and Saccharomyces cerevisiae [14][15][16]. Meanwhile, Saccharomyces cerevisiae is known to be associated with fermentation [14,15,17]. A microbiological and physico-chemical analysis of a traditional sorghum beer "Ikigage", collected from the southern province of Rwanda showed the presence of microbes such as aerobic mesophilic bacteria, lactic acid bacteria, E. coli, feacal streptococci, Staphylococcus aureus, yeast, and moulds [18].…”