Deciphering Microbial Community Dynamics and Biochemical Changes During Nyons Black Olive Natural Fermentations

Area of Science:

• Food Microbiology
• Fermentation Science
• Applied Microbiology

Background:

• French PDO Nyons black table olives rely on spontaneous brine fermentation and autochthonous microbiota for unique characteristics.
• Understanding the microbial dynamics is crucial for controlling and optimizing the fermentation process and final product quality.

Purpose of the Study:

• To unravel the microbial communities and dynamics during a 1.5-year spontaneous fermentation of Nyons olives.
• To identify key microbial drivers and link specific species to important metabolites influencing olive flavor.
• To distinguish distinct fermentation phases based on microbial succession and biochemical changes.

Main Methods:

• Culture-dependent and metabarcoding (ITS2 for fungi, V3-V4 for bacteria) approaches were used to analyze microbial communities.
• Fermentations were monitored over 1.5 years for two harvests and two olive types (organic and conventional).
• Volatiles, organic acids, and phenolic compounds were analyzed to correlate with microbial shifts.

Main Results:

• Yeast dominated the fermentation, with species like *Citeromyces nyonsensis* and *Wickerhamomyces anomalus* being prominent.
• Bacterial communities were primarily driven by the *Celerinatantimonas* genus; lactic acid bacteria were scarce.
• Four distinct fermentation phases were identified, correlating microbial succession with changes in pH, organic acids, esters, and alcohols.

Conclusions:

• The study provides an in-depth understanding of microbial species succession during Nyons olive fermentation.
• Specific microbial species, particularly yeasts like *Pichia membranifaciens* and *Candida boidinii*, were linked to the development of fruity esters and alcohols.
• This research is a foundational step towards identifying key microbial drivers that shape the distinct sensory properties of Nyons olives.