Abstract
Amahewu is a traditionally fermented non-alcoholic drink widely consumed in Southern
Africa. This beverage is produced from maize, an extensively consumed grain that is
prioritised for its affordability. The literature available on amahewu is limited, as it only
highlights the raw materials in a narrow spectrum, and the final product in a broader
spectrum, without exploring each production step and possible modifications that occur
during each stage.
A detailed understanding and characterisation of the physicochemical, biochemical and
health promoting properties, nutritional components, microbial communities and
metabolites present before, during and after amahewu production is lacking. To this
researcher’s knowledge, no scholarly work that applies comprehensive methodologies for
profiling a diverse set of factors involving production has been reported in the literature.
This study aimed to fully investigate some of these factors. The study thus provides insight
into deciphering genetic information from each production step using white and yellow
maize with malted sorghum as an inoculum. Changes in the bacterial populations, and
overall features of the microbial community were monitored. Targeted metabolomics was
applied using supervised and unsupervised methods which classified and identified the
clustering of metabolites, with discrimination applied to explain significant metabolites,
and to investigate the degree of similarity or dissimilarity between production stages.
Metabolic pathway analysis was also used to annotate the significant metabolic pathways
responsible for producing amahewu.
The physicochemical properties analysis of this study showed a strong correlation
between a decrease in pH with a sharp drop in pH of the final product, and a decrease in
Total Soluble Sugars (TSS) and Total titratable acids (TTA), as expected with the
fermentation of a product. The drop in pH inhibits certain microorganisms which cannot
survive in acidic environments. An abundance of Enterobacteriaceae and Lactococcus
lactis, which can survive acidic conditions were showed in the results. pH changes during
fermentation are primarily caused by the microbial formation of organic acids. These
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biochemical properties were quantified using HPLC, with results showing a prevalence of
shikimic acid in both productions.
The fermentation showed increase-decrease fluctuations in the composition of phenolics,
quantified using HPLC and mineral composition using ICP-MS. Essential minerals
potassium, phosphorus and magnesium were the most abundant in all production stages,
while ferulic acid was the phenolic compound present throughout all the production
stages. Quantitative changes to amino acids and phenolics were measured, with an
increase of significant metabolites in white maize production and a decrease in yellow
maize production.
This study highlighted the fact that fermentation is a cause-and-effect process. The
changes involved in the production of amahewu can be useful for optimizing the
production process and enhancing the nutritional, biochemical and health promoting
properties, by manipulating the presence of microorganisms which will lead to desired
metabolic pathways.
Keywords: amahewu, fermentation, metabolomics, metabolic pathways.