Volatilomics analysis of table olive 'Bella di Cerignola' PDO and associated brines: a case study on different fermentation styles and olive sizes

The present study provides the comprehensive volatilomic characterisation of Olea europaea L. cv. Bella di Cerignola Protected Designation of Origin (PDO) table olives and their associated brines by integrating Proton Transfer Reaction–Time-of-Flight Mass Spectrometry (PTR-ToF-MS) with Gas Chromatography–Mass Spectrometry (GC–MS). In particular, this work aimed to evaluate how fermentation style (Natural/Greek, NAT; Sivigliano/Spanish, SIV) and fruit size influence Volatile Organic Compounds (VOCs) associated with these fermented products, with particular focus on microbial metabolic markers. PTR-ToF-MS analysis detected 296 mass peaks, of which 145 significantly differed from blanks. Principal Component Analysis revealed a clear discrimination between NAT and SIV samples, with fermentation style emerging as the dominant source of variance, whereas fruit size had a negligible impact. NAT fermentation, which proceeds spontaneously through brining (10% NaCl), displayed a markedly richer and more heterogeneous volatilome than the alkali-treated SIV process (2% NaOH), including also a few volatiles potentially associated with spoilage phenomena. Among the key volatile markers majorly associated with NAT fermentation, such as ethanol, acetaldehyde, acetic acid, propionic acid, and ethyl esters, indicated active alcoholic, heterolactic, and propionic fermentations, predominantly in NAT samples. Additional compounds, such as 3-hexen-1-ol, cyclohexanol, and phenylethyl alcohol, suggested lipoxygenase-like and yeast-associated metabolic pathways. The brines were found to be much richer in volatile compounds, an aspect of potential interest also in the management of these matrices. The combined PTR-ToF-MS and GC–MS approach proved decisive for both rapid, non-invasive screening and robust compound identification, interesting also for future studies, to exploit the potential of the analytical technique for green chemical analysis, massive screenings, and real-time studies. This study presents a methodological update for volatilomic monitoring of complex plant-based fermented foods, highlighting the link between metabolic diversity, fermentative processes and sensory potential in traditional table olive production