Determination of ethyl alcohol and ethyl esters content in extra virgin olive determination of ethyl alcohol and ethyl esters content in extra virgin olive oils oils obtained from certain local olive varieties

Fatty Acid Alkyl Esters (FAAE) are among the most extensively studied topics in the olive oil sector over the past two decades, both in academic and commercial contexts. One of the most critical quality parameters required for the classification of an olive oil as extra virgin is the fatty acid ethyl ester (FAEE) content. According to national and international regulations, the maximum allowable limit for FAEE is 35 mg/kg. Moreover, fatty acid ethyl esters are currently the only valid parameter for detecting illegal blending with deodorized olive oils, a practice also known in the international literature as "soft deodorization." Fatty acid alkyl esters (FAAE) namely, fatty acid ethyl esters (FAEE) and fatty acid methyl esters (FAME) are a natural lipid family formed by the esterification of free fatty acids (FFA) with short-chain alcohols present in olive oil. Free fatty acids may be present in the olive fruit naturally or may increase as a result of triglyceride hydrolysis. Short-chain alcohols such as ethanol and methanol can be found in the fruit due to pectin degradation, improper harvesting, prolonged storage, fermentation of fruit sugars, or alcohol dehydrogenase (ADH) activity. When both these components and related enzymes coexist in the fruit or oil, FAAEs can rapidly form through esterification reactions. The more damaged the olive fruit, the higher the FAEE content in the resulting oil. The formation of FAAEs in virgin olive oil adversely affects both its chemical and sensory attributes, potentially causing its classification to be downgraded. To mask the negative sensory properties of low-quality virgin olive oils and reduce their free acidity, these oils may be subjected to low-temperature neutralization and/or mild deodorization and subsequently blended with extra virgin olive oil before being marketed. Therefore, both the ethanol content and the FAEE levels in olive oil are of great significance. In this context, it is evident that controlling the formation of fatty acids and alcohols is critical for achieving low FAAE levels. In this thesis study, the contents of FAAE, ethanol, methanol, and diglycerides were investigated in extra virgin olive oils produced from widely cultivated cultivars in Turkey such as Ayvalık, Memecik, and Gemlik, as well as from regional/local cultivars such as Domat, Beylik, Tavşan Yüreği, Sarı Ulak, Nizip Yağlık, and Saurani. No statistically significant differences (p > 0.05) were observed in FAEE levels across different geographical regions. However, it was found that climatic conditions (average temperature and rainfall) and post-harvest fruit storage duration significantly affected FAEE levels. Climatic factors were also found to have a significant impact on diglyceride (DG) content. While the ripeness index of the harvested fruit did not influence DG content, the 1,3-diglyceride levels were significantly affected by post-harvest storage duration. Furthermore, 1,3-DGs were found to vary depending on malaxation time. The effects of harvest year, region, cultivar, ripeness index, post-harvest storage duration, and malaxation time on Free Fatty Acidity (FFA), Fatty Acid Ethyl Esters (FAEE), Fatty Acid Methyl Esters (FAME), Ethanol (EtOH), Methanol (MeOH), Diglycerides (DG), and Fatty Acid Composition (FAC) of olive oils were analyzed using multivariate analysis of variance (ANOVA) and orthogonal partial least squares discriminant analysis (OPLS-DA), and classification based on harvest year was conducted.