Alkaline fermentation of Bambara groundnut (Vigna subterranean L. Verdc. ) as dawadawa-like African food condiment

Abstract

Dawadawa is an African condiment produced solely from the spontaneous alkaline fermentation of African locust beans but production from other legumes such as Bambara groundnut to produce dawadawa-type condiments has become of interest. Dawadawa is an integral part of the African diet due to its distinct aroma and flavour enhancing properties when added during cooking of soups or stews which are imparted by volatile compounds in the condiments. Bacillus species are known to dominate the alkaline fermentation of legumes in the production of dawadawa. Bacillus species isolated from spontaneously fermented dawadawa were identified using 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 GTG5 rep-PCR typing, 16S rRNA and gyrA gene sequencing. Alkaline fermentation of Bambara groundnut using B. subtilis subsp. subtilis (strain SFBA3), B. amyloliquefaciens subsp. plantarum (strain SFBA2), B. cereus (strain PALB7) and B. licheniformis (strain OALB2) starter cultures was reported. Volatile compounds were isolated from the dawadawa-like condiments using headspace solid phase microextraction (SPME) and analysed by comprehensive gas chromatography coupled to time of flight mass spectrometry (GC × GC–TOFMS). Acids, aldehydes and alcohols accounted for over 70% of the volatile compounds produced in the Bacillus fermented samples. B. subtilis subsp. subtilis SFBA3 produced the highest content of acids (5089.88 μg kg-1), while the highest content of aldehydes (2811.16 μg kg-1) and alcohols (1255.58 μg kg-1) was detected with B. cereus PALB7 and B. licheniformis OALB2, respectively. Sulphur–containing compounds concentration (84.44 μg kg-1) was highest for B. amyloliquefaciens SFBA2. The highest concentrations of 2–methyl butanoic acid and 3-methyl butanoic acid, indicative of typical dawadawa aroma, were produced by B. subtilis subsp. subtilis SFBA3. The sensory properties of dawadawa-like condiments produced using B. subtilis subsp. subtilis (strain SFBA3), B. amyloliquefaciens subsp. plantarum (strain SFBA2), B. licheniformis (strain OALB2) and B. pumilus (strain PALB2) for fermentation of Bambara groundnut were evaluated in terms of aroma, flavour, aftertaste and colour. A trained descriptive sensory panel evaluated the sensory characteristics of the uncooked paste and cooked broths using 3 appearance, 9 aroma and 18 flavour descriptors. The intensities of ammoniacal, pungent, chocolate/cocoa, rancid and dawadawa aromas differed significantly amongst the condiments made using the different Bacillus starter cultures. Strain SFBA3 had the highest intensity of pungent and dawadawa aroma, while ammoniacal aroma were more pronounced in strains SFBA2 and PALB7. Strain OALB2 had the lowest intensity of dawadawa aroma. The production of dawadawa–like African condiments using Bacillus strains starter cultures from the alkaline fermentation of Bambara groundnut was achieved. The production of affordable dawadawa–like condiments from Bambara groundnut using Bacillus starter cultures identified with polyphasic identification methods would be beneficial in terms of product quality and flavour consistency in the small to medium scale food industry in Africa.