Revealing microbial succession and its association with volatilome evolution along the spontaneous fermentation of Spanish-style and natural cv. Chalkidiki green olives at industrial scale.

In this study, a multi-omics approach combining metataxonomic and volatilomic analysis was employed to investigate microbial community dynamics, volatilome evolution and microbiota-volatilome associations during the spontaneous fermentation of cv. Chalkidiki green olives, processed at industrial scale according to the Spanish-style (Treatments SS and RS) and natural processing methods (Treatment NF). Notable differences in bacterial composition were observed across treatments. Secundilactobacillus and Lactiplantibacillus dominated SS brines (8% NaCl), Lactiplantibacillus prevailed in the exploratory RS brines (4% NaCl, 3% KCl, 1% CaCl2), whereas NF brines (5.5% NaCl, 0.25% CaCl2) exhibited greater diversity, including also Oenococcus, Loigolactibacillus and Pediococcus. However, fungal communities were consistently dominated by the genus Pichia. Volatilomic analysis identified more than 95 volatile organic compounds (VOCs), including acids, alcohols, carbonyls, esters, hydrocarbons, phenols, terpenoids and miscellaneous compounds. These differences were also reflected in distinct correlation profiles. In SS brines, Lactiplantibacillus was positively correlated with 2,3-butanediol, whereas Secundilactobacillus was positively correlated with ethyl heptanoate, while Pichia spp. showed associations with acetic acid and ethyl lactate. In NF brines, Lactiplantibacillus was positively correlated with benzaldehyde, while Oenococcus kitaharae exhibited correlations with 2-ethyl-1-butanol, methyl salicylate, linalool and α-terpineol. Additionally, Pichia membranifaciens displayed positive correlations with 2-heptanol and (E)-2-hexen-1-ol. Among fungal taxa, Pichia spp. and T. delbrueckii showed frequent associations with VOCs shared between brines and olives. Overall, these findings provide a useful framework for monitoring microbial succession and volatilome evolution in industrial-scale table olive fermentation systems.