Abstract
The present study aimed to evaluate the effect of selected Lactiplantibacillus plantarum strains on both microbiota composition and volatile organic compound profile of Sicilian table olives. Two mixed cultures, named O1 and O2, were set up for pilot-plan scale fermentations at 5% of NaCl. Uninoculated table olives at 5 and 8% (C5 and C8) of salt were used as control. The fermentation process was monitored until 80 days through a dual approach, which included both classical microbiological and 16S amplicon-based sequencing and volatilomics analyses. Compared with control samples (C5 and C8), experimental samples, inoculated with starter cultures (O1 and O2), exhibited a faster acidification with a more pronounced drop in pH. Metagenetics data revealed significant differences of microbiota composition among samples, highlighting the dominance of lactobacilli in both experimental samples; a high occurrence of Enterobacter genus only in control samples with 5% of NaCl; and the presence of Bacteroides, Faecalibacterium, Klebsiella, and Raoultella genera only in control samples with 8% of NaCl. Furthermore, microbiota composition dynamics, through the fermentation process, significantly affected the volatile organic compounds of the final products, whereas no compounds involved in off-odors metabolites were detected in all samples investigated. In conclusion, the addition of the proposed starter cultures and the use of low concentrations of sodium chloride positively affected the microbiota and volatile organic compounds, ensuring the microbiological safety and the pleasant flavors of the final product.
Highlights
Among fermented foods, table olives are one of the most well-known and produced fermented vegetables, especially in the Mediterranean area, with a large consumption worldwide (Vaccalluzzo et al, 2020a)
Our results revealed that inoculated table olives exhibited a more pronounced drop in pH, reaching values ≤ 4.5 starting from the 15th day, indicating a faster brine acidification in respect to control samples
Enterobacter often found in fresh fruits and associated with Spanish-style and with spontaneous fermentation table olives (Cocolin et al, 2013; De Angelis et al, 2015) was drastically reduced in inoculated samples, whereas it persisted mainly in control samples processed at lower salt content
Summary
Table olives are one of the most well-known and produced fermented vegetables, especially in the Mediterranean area, with a large consumption worldwide (Vaccalluzzo et al, 2020a). It is already well established that in table olives a complex and variable microbial consortium, mainly composed of lactic acid bacteria (LAB) and yeasts, is present (Ashaolu and Reale, 2020; Vaccalluzzo et al, 2020a). Ampliconbased metagenomics analysis targeting either 16S rRNA gene or internal transcribed spacers (ITSs) DNA region is the most widely used technique to reveal the complexity of microbial consortium of LAB and yeasts/fungal communities, respectively, in food matrices, as well as in table olives (De Filippis et al, 2017; Ferrocino and Cocolin, 2017; Vaccalluzzo et al, 2020a). De Castro et al (2019) found a correlation between metagenetics and volatilomics, identifying microbial species positively correlated with off-odors of table olives
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