Dynamic changes of bacterial community and volatile compounds during the production of adjuevan, a fermented fish of Côte d’Ivoire

Adjuevan, a fermented fish used as a condiment, is produced using two methods. This study aimed to investigate the impact of the fermentation method on the evolution of the bacterial community and volatile compounds. For this purpose, adjuevan samples were taken at different stages of production in three locations in Côte d'Ivoire. The bacterial community was then analysed using the high-throughput sequencing method and volatile compounds were determined by GC–MS. The results showed an increase in diversity indices during production, reaching a peak during secondary fermentation for both production methods. However, the number of OTUs observed in the closed method (1,814 OTUs) was higher than in the open method (1,239 OTUs), with more than 1,000 OTUs specific to the closed method. The bacterial composition changed significantly between primary and secondary fermentation. In the closed method, the proportions of Brevibacillus and Lactococcus decreased significantly, while those of Erysipelothrix, Vagococcus and Wohlfahrtiimonas increased. In the open method, the genera Ralstonia and Lactococcus were dominant at the start of fermentation, then Brevibacillus, Pseudomonas, Clostridium and Wohlfahrtiimonas became dominant. The dynamics of volatile compounds showed a decrease in aldehydes during secondary fermentation, while an increase in volatile organic acids and sulphur or nitrogen compounds was observed. Compounds with a strong sensory impact, such as nonanal, 2-octenoic acid and nonanoic acid, were detected only in the adjuevan produced using the open method, while 2-methylhexanoic acid, isopropyl 3-phenylpropanoate, ethyl isocapronate and ethyl butyrate were observed exclusively in the adjuevan produced using the closed method.