# Volatile Composition of Industrially Fermented Table Olives from Greece
## 1 Introduction  
Table olives are currently the most popular fermented vegetable product in Western countries and constitute, along with olive oil, an important ingredient of the Mediterranean diet. Worldwide production for the 2019/2020 season was around 3.06 million tons, of which 25.1% was produced in the European Union, predominantly in Spain (458,000 t), Greece (222,000 t) and Italy (60,000 t) [1]. The three most economically important cultivars (cv.) grown in Greece for table olive processing are Conservolea, Kalamata and Halkidiki, which are found as finished products under the brand names Conservolea (or Amfissis) and Kalamata (or Kalamon) natural black olives as well as Halkidiki green olives [2, 3]. The cv. Conservolea is primarily grown in central Greece (including the prefectures of Fhiotida, Magneisa and Evia) and can be processed using either the Spanish-style or Greek-style method, although the latter is preferred. Likewise, natural black olives are produced from cv. Kalamata, which is cultivated mainly in western Greece (prefecture of Aitoloakarmania) and southern Peloponnese (Messinia, Lakonia) [2]. During Greek-style processing, the olives are harvested when they are fully ripe or just before full ripeness, immersed directly in a NaCl solution (6-10% \(m/v\)) and subjected to spontaneous fermentation for 8-12 months, mainly promoted by indigenous yeasts and lactic acid bacteria (LAB) [4]. The cv. Halkidiki is grown in northern Greece, primarily in the prefecture of Halkidiki as well as in Kavala. After harvesting, the green olives are processed using the Spanish-style method by treating the fruit with a lye solution (NaOH 2-3% \(m/v\)) to hydrolyzethe bitter glucoside dejuropein. After a washing step to remove the excess alkali, a NaCl solution (8-12% \(m/v\)) is added, and fermentation takes place promoted mainly by LAB, which lasts for 3-7 months [5]. The primary purpose of table olive fermentation is to achieve a preservation effect and enhance the organoleptic properties of the final product [6]. The pleasant fruity flavor of table olives, a highly appreciated characteristic from consumers, is closely associated with the composition of volatile compounds, which depends on various factors, including olive cultivar, fruit ripening degree, climatic and processing conditions [7]. Earlier works were carried out to examine mostly the major volatiles in the brines of industrially fermented green olives of Spanish cultivars [8], to screen for potent odorants in Moroccan green olives [9], to compare the inoculated versus the spontaneous fermentation of Conservolea cv. green [6] and black olives [10], Halkidiki green olives [11], Moresca and Kalamata cv. Greek-style olives [12], and to compare the volatile compounds in Spanish-style, Greek-style and Castelvetrano-style green olives of Nocellara del Belice cv. [13]. During the last decade, the powerful technique of solid-phase microextraction (SPME) in combination with gas chromatography-mass spectrometry (GC-MS) has been applied by several researchers to study in more depth the volatile composition of table olives. A total of 42 compounds were identified in _alcaparras_ stoneed table olives produced from Portuguese olive cultivars (cv. Cobrancosa, Madural, Negrinha de Freixo, Santulhana and Verdeal Transmontana). Aldehydes were the major chemical class in all cultivars studied, with the main contributors being hexanal, phenylacetaldehyde and (E,E)-2,4-heptadienal. By using principal component analysis (PCA) the olive cultivars were distinguished based on their volatile profile [14]. In a similar manner, [PERSON] et al. [15] demonstrated that the volatile profile of green Sicilian table olives was dependent on the cultivar as well as the storage period in brine. As regards black-ripe (or Californian-style) table olives, the effects of olive cultivar (Manzanilla, Hoijblanca), growing area and storage period on the volatile composition have been recently disclosed [16; 17; 18].