Lipolytic yeasts distribution in commercial extra virgin olive oil.

The olive oil lipase-producing yeasts can lower the quality of the product through the hydrolysis of the triacylglycerols. In this research the olive oil total yeasts were divided into five chromogenic groups, for each group the amount of the lipase-producing yeasts was evaluated and the more active isolates were classed. The trials showed the prevalence of more than three chromogenic yeast groups in the commercial poly-varieties of extra virgin olive oil mixture, whereas in the mono-varieties one, no more than one chromogenic yeast group prevailed according to the olive variety. The ratio of the lipase-producing yeast varied from 33% in the smooth brown chromogenic group to 83% in the wrinkly bluish one. The physiological and genetic analyses of the more active lipase-producing yeast belonging to each chromogenic group allowed us to classify the wrinkly red 1892 strain and the wrinkly bluish 1890 strain as Candida parapsilosis, whereas the smooth white 1885 strain was classed as Candida wickerhamii. The ribosomal (26S) D1/D2 region sequencing results of the wrinkly white 1886 strain and the smooth brown 1887 strain are not identical to that of any known yeast species. They showed 8 substitution and 11 substitution plus 2 indels, respectively, different from Pichia mexicana and Pichia minuta. This is the first report where the human pathogen C. parapsilosis species was found in commercial extra virgin olive oil. The chromogenic group evaluation permitted the rapid preliminary identification of technological and human health important olive oil yeasts.