Characterization of yeast flora of “hurma” olives using molecular methods and mid-IR spectroscopy

Abstract

Among the olive varieties in Turkey, Erkence olives, grown in nearby area around Karaburun Peninsula of Izmir, go through a natural debittering phase on the tree during its ripening. As a result of this phase, the olives lose their bitter taste while still on the tree and have a dark brownish color in the inside and a wrinkled outer layer which are their differentiating appearance characteristics from olives that do not undergo this process. This naturally debittered olive type is known by the name of Hurma (Aktas et al., 2014). According to an old study performed in Greece with a similar type of olive, the debittering process was attributed to the action of a fungus, Phoma olea,which hydrolyses oleuropein, a bitter phenolic compound of olives (Kalogeras, 1932). There is no study in the literature related to the characterization of yeasts on this unique type of olive, Hurma. Until present, the characterization of yeasts associated with table olives has been made through biochemical and morphological methods, using the taxonomic keys (Kurztman and Fell, 1998). More recently, molecular methods and FTIR spectroscopy using chemometric techniques have been used for the identification of yeasts due to being rapid, easy and more precise methods for yeast identification. In order to understand the role of yeasts in maturation and debittering process of natural Hurma olives, characterization of olive yeasts from two olive types, Hurma and Gemlik, an olive variety which is commonly consumed as table olive, was aimed using molecular methods and mid-IR spectroscopy in comparison with cultural methods.