Τhe aim of this study was to investigate the microbiological and physicochemical changes
of pitted green olives (cvs. Conservolea and Halkidiki) elaborated in the Spanish
style method and packaged in two types of multi-layered pouches under nitrogen atmosphere
(100% N2) for a period of 12 months. Moreover, the evolution of microbial consortia
at the beginning (0 days), middle (180 days) and final (360 days) time points of storage
was elucidated by plating, genotyped and identified through RAPD-PCR and ITS region
amplicon sequencing, respectively, and subsequently metataxonomic analysis (for fungal
communities only). Results showed that no enterobacteria could be detected on olive
drupes, whereas the dominant microbiota from the onset of storage in both pouches
consisted of LAB in populations ranging between ca. 4.2-6.6 log CFU/g. Although yeasts
were initially enumerated at ca. 5.5 log CFU/g, they declined rapidly and could not
be detected by plate counting after 30 days. The pH values increased from 4.11 to
4.24 and 4.03 to 4.12 at the beginning and end of storage for cvs. Halkidiki and Conservolea
green olives, respectively. The total color difference index (ΔΕ*) presented a perceivable
change in visual color (ΔΕ* > 2.0) only in cv. Conservolea olives during storage.
Finally, molecular fingerprinting RAPD-PCR and 16S amplicon based identification revealed
the dominance of five LAB species, namely Pediococcus ethanolidurans, Lactiplantibacillus
pentosus, Lentilactobacillus rapi, Lentilactobacillus parafarraginis and Lentilactobacillus
buchneri. Regarding the identification of yeasts, the metagenetic amplicon sequencing
approach revealed fungal complexity in the olive samples. Pichia manshurica and Pichia
membranifaciens prevailed during the first and middle stages of storage, whereas at
the final stage higher complexity was noticeable.