Profiling of phenol content and microbial community dynamics during pâté olive cake fermentation.

In this study, different microbial strains, as single and mixed-cultures, were used to ferment the pâté olive cake (POC), a by-product of olive oil processing. In particular, strains belonging to Candida boidinii,Wickerhamomyces anomalus and Lactiplantibacillusplantarum were used. The fermentation was carried out on diluted (3:2) POC without and with glucose (2% w/v) addition. Furthermore, phenolic compounds were monitored during fermentation in POC added with glucose differetly inoculated and the microbial community, at the end of fermentation, was evaluated by Next Generation Sequencing (NGS) techniques. Data highlighted that inoculated samples showed an hydroxytyrosol content higher than the un-inoculated controls. In particular, during fermentation the sample inoculated with C. boidinii, both in single and in mixed culture together with L. plantarum, increased the hydroxytyrosol content by 275 and 261 mg/L, respectively, after 8 days, to reach the highest content at the end of fermentation. Metagenomic analysis revealed a low abundance of 16S ribosomal RNA genes and fungal ITS in all samples at any sampling times. Furthermore, at the end of fermentation, all samples exhibited a different bacterial community with a decrease in acetic acid bacteria and an increase in Lactobacillaceae biodiversity. Finally, no effect was detected in any samples on fungal metagenomic profile, where Dipodascus geotrichum was found dominant both at initial and final fermentation. In conclusion, the present study confirmed that selected cultures can drive the fermentation and have an impact on the phenolic profile.