Biodiversity, Survival, and Influence on Quality of Yeast Biota in Virgin Olive Oil

The microbial stability and sensory quality of extra virgin olive oil (EVOO) depend largely on its oil-borne yeast biota during storage. Virgin olive oil (VOO) harbors a low-abundance yeast biota in its aqueous microphase, whereas bacteria and molds are generally inhibited by low water activity and high phenol content. The genera Candida (6 species), Yamadazyma (5 species), Brettanomyces (2 species), Kuraishia (2 species), Nakazawaea (2 species), and Ogataea (2 species) dominate, representing 70% of reported yeast diversity. Yeast survival is strongly shaped by water content, oxygen, and phenolic concentration, with populations declining over time unless free water is available. Yeast metabolic activity can be detrimental or beneficial: lipolytic species (e.g., Candida adriatica, Yamadazyma terventina) increase free acidity and oxidative susceptibility, causing sensory defects, whereas oleuropeinolytic yeasts reduce bitterness via β-glucosidase and esterase-mediated hydrolysis of oleuropein. Since additives and starter cultures are prohibited by EU regulations, controlling process parameters (like blending and decantation) remains the only sound strategy. As demonstrated in trials with Don Carlo and Coratina cultivars, selective management of endogenous yeasts successfully mitigates bitterness while keeping quality parameters within EVOO legal limits, thus balancing sensory profile, shelf life, and commercial value.