Microbial succession in indigenous fermented cereal beverages of Lesotho
Mahlomaholo, Bokang John
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Indigenous fermented foods represent large portions of daily diets particularly within the marginalised low-income groups. Most of the fermentation processes are spontaneous and are driven by complex microbial communities which are sourced from raw materials, producer’s handling, utensils and unstandardized indigenous starter cultures. These complex microbial communities influence the organoleptic quality, nutrient availability as well as the safety of the fermented product. In order to improve the nutritional and organoleptic quality as well as safety of these fermented products, it is imperative that the processes are systematically studied and documented, the ingredients should be quantified and preparation conditions required for a successful fermentation identified. The primary objectives of this study were to document the vital indigenous knowledge of cereal based fermented foods in Lesotho and investigate the microbial loads of sesotho as well as to assess the possible stages where contamination or even pathogenic microorganisms might be introduced. The diversity of cereal based products in Lesotho ranges from non-alcoholic and alcoholic gruels to alcoholic beverages. In this study, both non-alcoholic and alcoholic gruel based beverages have been documented. Non-alcoholic gruels include motoho, ntsoana-tsike, and tsoeu-koto, these food products are consumed as weaning food for infants as well as thirst quenching beverages. Alcoholic beverages are represented by sesotho, hopose, sekumukumu and tintana. Also outlined in this study are factors that could negatively impact the quality of fermented final products and the health of ultimate consumers. These include the compromised hygiene of food handlers and equipment, unstandardized temperature for fermentation, cooking and storage and the quality of raw materials and starters used. In assessing the microbial content, a total of 25 different sesotho fermentation processes were scientifically investigated from the initial stages to the final product, including five locally different processes in each region representing the south, north, east, west and central. Five sampling points during the processing were carefully selected in order to get well-defined representative microbial patterns during the fermentation process. From following the microbial dynamics, lactic acid bacteria (LAB) and yeasts emerged as the dominant groups as the fermentation was progressing. A combination of conventional culture-dependent and high-throughput culture-independent (Next Generation Sequencing) techniques were employed to complement a comprehensive representation of the microbial content and succession of sesotho. The results revealed that dominant yeasts were those belonging to the genera of Pichia, Issatchenkia and Saccharomyces. As for dominant bacterial groups in all the processes were LAB belonging to the genera of Enterococcus, Pediococcus, Lactobacillus, Leuconostoc and Wiesella. It was interesting to observe that as the fermentations progressed, there was a decline in the enteric bacteria to undetectable levels, thus suggesting a promise of a good safety record as well as a probiotic potential for sesotho. This trend was observed in all the processes followed across Lesotho. Microbial assessments indicated that the third stage during the fermentation was critical for contamination or introduction of pathogenic microorganisms. Harbored in this stage, was mostly enteric bacteria and other bacterial groups that are usually found on human body as part of the normal microbiota. From the microbial succession patterns, there was an observable lack of antagonism between yeasts and LAB and thus suggesting a symbiotic relationship. The Scanning Electron Microscope was employed to examine the spatial arrangements of these groups of microorganisms as well as the biofilm formation on the fermentation vessel. From the micrographs obtained, there was an observable proximity between the LAB and yeasts thus strengthening the suggestion of symbiosis during the fermentation process of sesotho.