Diversity and functionality of bacillus species associated with alkaline fermentation of bambara groundnut (Vigna subterranean L. Verdc) into dawadawa-type African condiment

The aim of this study was to investigate the diversity of Bacillus species in dawadawa; aiding potential starter cultures selection for alkaline fermentation of bambara groundnut into dawadawa-type condiments based on their genotypic and volatile compound profiles. Bacillus species (n = 71) isolated from spontaneously fermented dawadawa were identified using matrix assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF MS) as B. cereus (35%), B. licheniformis (30%), B. pumilus (21%), B. subtilis (10%) and B. amyloliquefaciens (4%). Further molecular typing was performed using GTG(5) rep-PCR typing, 16S rRNA and gyrA gene sequencing. The gyrA gene sequence analysis exhibited the highest species discriminatory power with B. subtilis subsp. subtilis, B. amyloliquefaciens subsp. plantarum, B. pumilus and B. licheniformis as the distinct clusters. Representative strains from each cluster were then used as starter cultures for the production of dawadawa from bambara groundnut. Volatile compounds analysis using headspace solid phase microextraction (SPME) and comprehensive gas chromatography coupled to time of flight mass spectrometry (GC x GC-TOF MS) identified distinct chemical profiles produced by each of the four strains. Volatile compounds produced by B. subtilis subsp. subtilis (strain SFBA3) were categorized by dimethyl disulfide, methanethiol and nonanal while B. amyloliquefaciens subsp. plantarum (strain SFBA2) produced acetic acid and hexadecanoic acid. B. cereus (strain PALB7) produced 2,5-dimethyl pyrazine and 2-butanone which were not detected in the other condiments. Hexanal was the main compound produced by B. licheniformis (strain OALB7).