Microbial colonization of naturally black olives during fermentation and associated biochemical activities in the cover brine

AIMS: To establish the site of microbial growth on naturally black fermented table olives, and to monitor the population dynamics of yeasts and selected micro-organisms together with the changes in organic acid profile and pH in the cover brine during fermentation. METHODS AND RESULTS: During fermentation, the numbers of Enterobacteriaceae and Pseudomonas spp. in the brine decreased whilst lactic acid bacteria and yeast populations increased. Scanning electron microscopy showed that a yeast-rich biofilm developed on the epicuticular wax of the olive skin during fermentation. Yeasts also predominated in the stomatal openings, but bacteria were more numerous in intercellular spaces in the sub-stomatal flesh. Citric, malic and tartaric acids were the major organic acids accumulating in the brine during fermentation. CONCLUSIONS: Micro-organisms associated with the skin, stomata and flesh in fermenting black olives may experience different local conditions to those prevailing in the cover brine. SIGNIFICANCE AND IMPACT OF THE STUDY: These are the first observations of the micro-organisms associated with the fruit of naturally fermented black olives and of the accumulation of specific organic acids during fermentation.