Determining the core bacterial and fungal genera in table olive fermentations

Table olives are among the most ancient and important fermented foods of the Mediterranean basin. Their production is still strongly related to traditional practices, and the lack of thermal treatments, the reliance on natural contamination and on selective factors (NaCl, anaerobiosis, occurrence of food phenolics, etc.) determine the dynamics of the microbial community. Lactic acid bacteria (LAB) and yeasts have a pivotal role in table olive microbial communities, but several halophilic and alkalophilic microorganisms may also contribute, positively or negatively, to the quality.

We have use metataxonomic data extracted from the FoodMicrobionet database to provide quantitative insights on the structure of bacterial and fungal microbial communities of table olvies and to identify core genera in different trade preparations.

A set of bacterial genera may be representative of the dominating core microbiota in table olives, with Celerinatantimonas and Lactiplantibacillus as the most prevalent genera, followed by several LAB, halophilic and alkalophilic lactic acid bacteria (HALAB) and Gram negatives, including non-halophilic species. Similarly, 3 fungal genera (Pichia, Candida and Wickerhamomyces) were the most abundant and prevalent among those representing the core microbiota of table olives.

The distribution of both bacteria and yeasts varied significantly in different olive varieties, among olives, brines and contact surfaces or materials, and at different production stages, and no clear grouping related to the combination of ripeness and trade preparation was found, although HALAB were characteristically abundant in Spanish style green olives. Addition of starter cultures affected the composition and dynamics of microbial communities to a variable extent.

Highlights

• Data from 16 metataxonomic studies on table olives, including 833 samples, were combined

• Enhanced metadata facilitated the comparison among different studies

• Composition of the microbiota of table olives was highly variable

• Celerinatantimonas and Lactiplantibacillus dominated the core bacterial microbiota

• Pichia , Candida and Wickermahomyces were the most prevalent and abundant yeasts