Investigating interspecific quorum sensing influence on cocoa fermentation quality through defined microbial cocktails
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The fermentation of cocoa beans is a key process to supply high quality ingredients for the chocolate industry. In spite of several attempts to obtain standardised microbial cultures for cocoa fermentation, it is still a spontaneous process. It has been suggested lactobacilli present potential for quorum sensing (QS) regulation in cocoa fermentation, and in the present research, laboratory scale fermentations were carried out to further elucidate possible QS influence on microbial shifts and fermented seeds quality. The experimental design comprised the 96 hours-fermentations designated as F0 (control), F1 (yeasts, lactic acid bacteria, and acetic acid bacteria), F2 (yeasts and acetic acid bacteria), F3 (yeasts only), with evaluation of the microbial succession by plate counting, determination of enzymatic activities by classical methods and qualitative evaluation of flavour compounds by gas-chromatography (GC-MS) with headspace sampling. Besides, QS was estimated by quantification of the expression of luxS genes by Reverse Transcriptase Real Time PCR analysis using selected primers. The results demonstrated that microbial successions were displayed in lab conditions, but no statistical difference in terms of microbial enumeration and α-diversity metrics were observed among the experimental and control fermentations. Moreover, enzymatic activities were not correlated to the total microbiota, indicating the seeds’ endogenous hydrolases protagonist enzymes secretion and activity. Regarding luxS genes measuring for the species Lactiplantibacillus plantarum and Limosilactobacillus fermentum , genes were active in fermentation in the start to the end phase and to the beginning to the middle phase of fermentation, respectively. Correlation analysis among luxS expression and volatile metabolites evidenced Lp. plantarum association with detrimental compounds for fermentation quality. This data contributes to our previous research which monitored fermentations to survey enzymatic changes and QS potential along the process and sheds light of QS-related strategies of lactobacilli dominance in cocoa fermentations.