Microbiological Quality and Flavor Profile of Alkaline Fermented Bambara Groundnut Made into a Dawadawa-type African Food Condiment Using Bacillus Species Starter Cultures

Introduction: Dawadawa, an African food condiment, is a soup flavoring agent and low-cost meat substitute. It is typically produced through alkaline fermentation (pH 6 to 9) of African locust bean; but, there is interest in using other substrates, such as the bambara groundnut. Production from bambara groundnut is limited, despite the legume’s high potential as a substrate due to its high carbohydrate and protein contents. Fermentation is usually spontaneous; thus, food safety and flavor consistency is a concern. The microbial diversity of alkaline fermentation of African condiments indicated several Bacillus species as the predominant genera. Therefore, controlled fermentation, utilizing specific Bacillus species as starter cultures, may improve food safety and flavor consistency.

Purpose: This study was performed to identify Bacillus species starter cultures for the controlled alkaline fermentation of bambara groundnut into Dawadawa-type condiments; determine their ability to suppress pathogenic microbial contaminants; and to determine volatile flavor compounds produced by these Bacillus species.

Methods: DNA sequencing of the 16S rRNA and gyrA genes was performed to identify Bacillus species starter cultures. Microbial growth parameters (specific growth rate, antimicrobial production) and physicochemical properties were analyzed during alkaline fermentation. Flavor compound profiles were determined using GC×GC–TOF MS.

Results: Molecular typed strains Bacillus subtilis subsp. subtilis, Bacillus amyloliquefaciens, Bacillus pumilus and Bacillus licheniformis were identified as starter cultures for fermentation with bambara groundnut. Bacillus amyloliquefaciens and B. pumilus had the highest µ_max at 0.14 and 0.13, respectively, and final pH values of 8.53 and 8.36, respectively. All strains have the ability to inhibit the growth of pathogenic microorganisms with levels of Enterobacteriaceae ≤ 7.0 × 10¹ CFU/g; molds ≤ 3.1 × 10² CFU/g. Significant differences in flavor profiles were apparent amongst starter cultures, with differing levels of acids, ketones, and pyrazines.

Significance: Bacillus strains as starter cultures for the alkaline fermentation of African condiments suppressed pathogenic microbial contaminants; thus, enhancing product food safety and flavor consistency.