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This study delved into the evolution of fungal population during the fermentation of Spanish-style green table olives (Manzanilla cultivar), determining the influence of different factors such as fermentation matrix (brine or fruit) or the use of a lactic acid bacteria inoculum, on its distribution. The samples (n = 24) were directly obtained from industrial fermentation vessels with approximately 10.000 kg of fruits and 6.000 L of brines. Our findings showcased a synchronized uptick in lactic acid bacteria counts alongside fungi proliferation. Metataxonomic analysis of the Internal Transcribed Spacer (ITS) region unearthed noteworthy disparities across different fermentation time points (0, 24, and 83 days). Statistical analysis pinpointed two Amplicon Sequence Variants (ASV), Candida and Aureobasidium, as accountable for the observed variances among the different fermentation time samples. Notably, Candida exhibited a marked increase during 83 days of fermentation, opposite to Aureobasidium , which demonstrated a decline. Fungal biodiversity was slightly higher in brines than in fruits, whilst no effect of inoculation was noticed. At the onset of fermentation, prominently detected genera were also Mycosphaerella (19.82 %) and Apohysomyces (16.31 %), hitherto unreported in the context of table olive processing. However, their prevalence dwindled to nearly negligible levels from 24th day fermentation onwards (<2 %). On the contrary, they were replaced by the fermentative yeasts Saccharomyces and Isstachenkia. Results obtained in this work will be useful for designing new strategies for better control of table olive fermentations. • Metataxonomic analysis of ITS region was applied in Spanish-style olive fermentations. • Variances in yeast population were detected at 0, 24, and 83 days of fermentation. • Candida and Aureobasidium were the responsible genera for the statistical differences • No significant differences were observed in fermentation matrix or inoculation process. [ABSTRACT FROM AUTHOR]

In this work, metataxonomic-compositional data analysis was applied to study the influence of inoculation, type of ecosystem (brine or fruit), and time of fermentation (0, 24, and 83 days) on the bacterial composition dynamic during industrial Manzanilla Spanish-style green table olive fermentations. Differences in the physicochemical and microbiological characteristics between inoculated and spontaneous fermentations were scarce, except for the high lactic acid bacteria population (>10 million CFU/g) in the inoculated olive biofilms. The metataxonomic analysis showed eight relevant taxa (Lactiplantibacillus, Vibrio, Halolactibacillus, Aerococcus, Catenococcus, Salinivibrio, Alkalibacterium, and Marinilactibacillus) and absence of pathogens, but the microbiota composition markedly changed throughout fermentation. At the process onset, the main genera were Vibrio, Halolactibacillus, Marinilactibacillus, and Alkalibacterium, while Lactiplantibacillus was almost absent. Regardless of inoculation, Lactiplantibacillus became the predominant genus as the fermentation progressed, albeit Vibrio, Marinilactibacillus, Alkalibacterium, and Halolactibacillus also persisted until the end of the process (but did not cause spoilage). Ferrimonas genus was detected for the first time in table olives, being found in 71% of the samples. Besides, there was more bacterial biodiversity in the brine ecosystem than olive biofilms. Overall, inoculation led to more homogenous and equilibrated bacterial populations at the end of the process. This study expands the knowledge on the bacterial population changes occurring during industrial table olive fermentation, the differences between populations in brines and biofilms, and the beneficial effects of inoculation for using table olives as a carrier of beneficial microorganisms. • Compositional analysis provided new insights of food metataxonomic data. • Low number of bacterial genera typifies green Spanish-style table olive processing. • Lactiplantibacillus became the predominant genera as the fermentation progressed. • Inoculation led to more homogenous bacterial populations at the end of the process. [ABSTRACT FROM AUTHOR]