Abstract
The olive oil is an unfavorable substrate for microbial survival and growth. Only few microorganisms use olive oil fatty acids as carbon and energy sources, and survive in the presence of olive oil anti-microbial components. In this study, we have evaluated the occurrence of microorganisms in 1-year-stored extra-virgin olive oil samples. We detected the presence of bacterial and yeast species with a recurrence of the bacterium Stenotrophomonas rhizophila and yeast Sporobolomyces roseus. We then assayed the ability of all isolates to grow in a mineral medium supplemented with a commercial extra-virgin olive oil as a sole carbon and energy source, and analyzed the utilization of olive oil fatty acids during their growth. We finally focused on two bacterial isolates belonging to the species Pantoea septica. Both these isolates produce carotenoids, and one of them synthesizes bioemulsifiers enabling the bacteria to better survive/growth in this unfavorable substrate. Analyses point to a mixture of glycolipids with glucose, galactose and xylose as carbohydrate moieties whereas the lipid domain was constituted by C6–C10 β-hydroxy carboxylic acids.
Highlights
The olive oil is an unfavorable substrate for microbial survival and growth (Ciafardini and Zullo 2002a, b; Brenes et al 2007)
A total of three bacterial and one yeast taxa were represented in the analyzed olive oil samples including two strains belonging to Enterobacteriaceae (OOWS-10, OOYS-10), two to Xanthomonadaceae (OOOWS-2, OOOWS-9), two to Pseudomonadaceae (OOBS-2, OOYW-9), two to the genus Sporobolomyces (OOPS-1, OOPS-10)
In this study we have characterized eight microbial strains from 1-year-stored extra-virgin olive oils, which were isolated under aerobic conditions
Summary
The olive oil is an unfavorable substrate for microbial survival and growth (Ciafardini and Zullo 2002a, b; Brenes et al 2007). In particular virgin and extra-virgin oils, contain small amounts of water in the form of mini-drops, and high content of various single and complex phenolic and glutaraldehyde-like compounds which are released during the malaxation phase of the olive oil extraction process, and possess strong antimicrobial activity (Brenes et al 2007; Juven and Henis 1970; Fleming et al 1973; Gourama et al 1989) In this substrate microorganisms are often below the limit of detection with standard culture methods, and only few. Some of these species are considered opportunistic pathogens of humans (Koidis et al 2008; Zullo and Ciafardini 2008; Zullo et al 2010)
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