Abstract
Hausa koko is an indigenous porridge processed from millet in Ghana. The process involves fermentation stages, giving the characteristic organoleptic properties of the product that is produced largely at a small-scale household level and sold as a street food. Like many other indigenous foods, quality control is problematic and depends on the skills of the processor. In order to improve the quality of the product and standardize the process for large-scale production, we need a deeper understanding of the microbial processes. The aim of this study is to investigate the microbial community involved in the production of this traditional millet porridge and the metabolites produced during processing. High-throughput amplicon sequencing was used to identify the bacterial (16S rRNA V4 hypervariable region) and fungal [Intergenic Transcribed Spacer (ITS)] communities associated with the fermentation, while nuclear magnetic resonance (NMR) was used for metabolite profiling. The bacterial community diversity was reduced during the fermentation processes with an increase and predominance of lactobacilli. Other dominant bacteria in the fermentation included Pediococcus, Weissella, Lactococcus, Streptococcus, Leuconostoc, and Acetobacter. The species Limosilactobacillus fermentum and Ligilactobacillus salivarius accounted for some of the diversities within and between fermentation time points and processors. The fungal community was dominated by the genus Saccharomyces. Other genera such as Pichia, Candida, Kluyveromyces, Nakaseomyces, Torulaspora, and Cyberlindnera were also classified. The species Saccharomyces cerevisiae, Stachybotrys sansevieriae, Malassezia restricta, Cyberlindnera fabianii, and Kluyveromyces marxianus accounted for some of the diversities within some fermentation time points. The species S. sansevieria and M. restricta may have been reported for the first time in cereal fermentation. This is the most diverse microbial community reported in Hausa koko. In this study, we could identify and quantify 33 key different metabolites produced by the interactions of the microbial communities with the millet, composed of organic compounds, sugars, amino acids and intermediary compounds, and other key fermentation compounds. An increase in the concentration of organic acids in parallel with the reduction of sugars occurred during the fermentation process while an initial increase of amino acids followed by a decrease in later fermentation steps was observed.
Highlights
Porridges produced from fermented cereals such as maize, millet, and sorghum are essential diets in many parts of Africa, where they are used mostly as staple, weaning, or complementary foods, providing necessary nutrients (Omemu et al, 2007; Omemu and Omeike, 2010; Owusu-Kwarteng et al, 2010b)
Significant differences were detected between the observed operational taxonomic unit (OTU) at the various time points (p-value = 0.026), a reduction in the observed OTUs was detected between the grain samples and the 12-h fermentation, and the lower diversity was maintained during the production stages (Figure 2B)
Significant differences were observed in bacterial diversity at the different time points of Hausa koko production across the six regions
Summary
Porridges produced from fermented cereals such as maize, millet, and sorghum are essential diets in many parts of Africa, where they are used mostly as staple, weaning, or complementary foods, providing necessary nutrients (Omemu et al, 2007; Omemu and Omeike, 2010; Owusu-Kwarteng et al, 2010b). To prepare Hausa koko, most processors boil four volumes of water, and while stirring the fermented slurry (the supernatant and sediment together representing one volume), slowly pour in the hot boiled water to obtain the smooth gel-like porridge. Significant differences were detected between the observed OTUs at the various time points (p-value = 0.026), a reduction in the observed OTUs was detected between the grain samples and the 12-h fermentation, and the lower diversity was maintained during the production stages (pvalues: vs 12 h = 0.003; vs milled = 0.004; vs supernatant = 0.004; vs sediment = 0.001; vs koko = 0.012) (Figure 2B). Significant differences in the alpha diversity were found between grain samples and other fermentation stages when using Faith’s phylogeny diversity index (Figure 2C) (p-value = 0.030 for all groups, p-values of grain vs.: 12 h = 0.005; 24 h = 0.033; milled = 0.021; supernatant = 0.002; sediment = 0.005; koko = 0.036). No statistical differences were observed when evenness and Shannon indexes were used
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