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Characterization of Mahewu, a Traditional Fermented Cereal Beverage from Zimbabwe, as a Source of Functional Lactobacilli
- Author / Creator
- Pswarayi, Felicitas
Mahewu is a non-alcoholic fermented maize and finger millet malt beverage produced in Zimbabwe. Africa has a rich tradition of cereal fermentations to produce diverse products including baked goods, non-alcoholic and alcoholic beverages with live microbiota and the widespread use of fermented porridges based on maize, millets or sorghum. The overview on the diversity of African fermented cereal foods suggests that the composition of fermentation microbiota and thus the impact of fermentation on product quality is determined by the choice of fermentation conditions. Despite the rich diversity of traditional fermented foods in Africa, there is a paucity of information on fully characterized and documented fermentation microbiota, and starter cultures developed from African traditional fermented cereal foods are scarcely available, if at all. Therefore, the aim of this research program was to characterize lactic acid bacteria isolated from mahewu and to determine their potential as functional lactobacilli in fermented cereal foods to counteract the poor sanitation endemic in rural communities in sub-Saharan Africa.
The composition and origin of mahewu microbiota were elucidated. The microbiota of mahewu samples consisted of 3 to 7 dominant strains of lactobacilli and 2 strains of yeasts. Enterobacteriaceae were not detected. Finger millet malt contained 8 to 19 strains of Enterobacteriaceae, lactobacilli, bacilli, and very few yeasts. Strain-specific quantitative PCR assays provided a direct assessment of the identity of strains from finger millet malt and mahewu. Lm. fermentum FUA3588 and FUA3589 were detected in finger millet malt, demonstrating that finger millet malt is a main source of mahewu microbiota. Model mahewu fermentations conducted with a 5-strain inoculum consisting of lactobacilli, Klebsiella pneumoniae, and Cronobacter sakazakii demonstrated that lactobacilli outcompete Enterobacteriaceae, which sharply decreased in the first 24 h.
Comparative genomic analyses indicated that mahewu isolates harbor multiple multidrug resistance (MDR) proteins of the multidrug and toxin extrusion (MATE) family and the major facilitator superfamily (MFS). Strains of Lactiplantibacillus plantarum and Limosilactobacillus fermentum encoded for the same gene, termed mahewu phenolics resistance gene mprA, with more than 99% nucleotide identity, suggesting horizontal gene transfer. Strains of Lp. plantarum were more resistant than strains of Lm. fermentum to phenolic acids, other antimicrobials and antibiotics but the origins of strains were not related to resistance. The resistance of several strains exceeded EFSA thresholds for several antibiotics. Analysis of gene expression in one strain each of Lp. plantarum and Lm. fermentum revealed that at least one MDR gene in each strain was over-expressed during growth in wheat, sorghum and millet relative to growth in MRS5 broth. In addition, both strains over-expressed a phenolic acid reductase. The results suggest that diverse lactobacilli in mahewu share MDR transporters acquired by lateral gene transfer, and that these transporters mediate resistance to secondary plant metabolites and antibiotics.
The findings presented in this thesis provide comprehensive knowledge of the microbiotas of mahewu and finger millet malt and a better understanding of spontaneous cereal fermentations. This can lead to the selection and development of functional and probiotic starter cultures that may be used to mitigate the risks associated with uncontrolled cereal fermentation processes. What is demonstrated for mahewu is likely also true for other African fermented cereal foods that are produced in a comparable way.
- Graduation date
- Spring 2022
- Type of Item
- Doctor of Philosophy
- This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.