Volatile Dynamics and Their Associations with Microbial Genera in Spanish-Style Table Olives Processed in Interconnected Under-Vacuum and Fiberglass Independent Vessels

This study compared the volatile organic compound (VOC) profiles and their relationships with microbial genera in Spanish-style table olives fermented in an interconnected under-vacuum stainless-steel system (F) and in traditional independent fiberglass vessels (G). VOCs were analyzed by HS-SPME-GC-MS, and microbial communities were characterized by metataxonomic analysis. A total of 97 VOCs were identified, mainly alcohols (29), esters (21), carbonyls (20), hydrocarbons (5), phenols (4), and terpenes (6). Among the most abundant compounds were 4-ethylphenol, ethanol, (Z)-3-hexen-1-ol, phenylethyl alcohol, ethyl acetate, and isobutanol. Only five VOCs—decanal, methyl ethyl ether, linalool, 2-methylbutanoic acid, and ethyl lactate—showed no significant variation with fermentation system or time, suggesting formation during debittering or early fermentation. The fermentation system strongly influenced volatile development, with 16 VOCs unique to F, 15 unique to G, and 66 shared. Among shared compounds, 48 differed significantly between systems, and 43 changed during fermentation. The F system was associated with a more restricted VOC profile, whereas G generated a more diverse volatile profile. Microbial–VOC relationships also differed: Leuconostoc, Lactiplantibacillus, Candida, and Dekkera were mainly associated with F-system VOCs, whereas less common bacterial genera and fewer fungi characterized G. Overall, the interconnected under-vacuum system is suitable for standardized production, while the traditional system favors greater microbial and volatile complexity.