INTRODUCTION
The olive tree (Olea europaea L) is largely grown in Mediterranean
countries and is one of the most important crops grown in this region.
In Turkey, olive cultivation is carried out in five regions, namely
Aegean, Marmara, Mediterranean, Southeastern Anatolia and Black Sea
Regions. Olive varieties in Turkey are distributed as 48.71% Gemlik,
20.66% Ayvalık, 19.11% Memecik, 7.56% Domat and 3.73% other
varieties. (Özaltaş et al., 2016). As of 2021, there are a total of 100
registered cultivars, 2 of which are hybrids and 1 of which are clones.
It is known that one of the most important factors affecting the spread
of the olive tree is temperature. Generally, it is desired that the
annual average temperature is between 15-20°C in olive growing regions.
When the maximum temperature rises to 40°C and/or when the minimum
temperature is lower than -7°C, olive trees may be damaged. One of the
important factors in olive cultivation is precipitation. Although the
olive tree is said to be drought resistant, the annual precipitation
demand is 600-800 mm. In order for the olive fruit to be larger and of
higher quality, water is needed for the development of the kernel
hardening in the summer months. Other precipitation types, namely hail
and snow, are undesirable precipitation for olive cultivation (Ozturk et
al., 2021; Özaltaş et al., 2016). According to the World Meteorological
Organization, the hottest days were recorded in 2010-2020.
Unfortunately, these changes in climate cannot be stopped and the
temperature is expected to increase by 3.4°C by 2095. More extreme
weather-related events are expected to increase, accompanied by greater
climatic variability and adverse weather events (Maurya et al., 2022).
Unfortunately, the increase in drought conditions in Southern Europe in
recent years (especially the extreme changes observed in temperature and
precipitation in spring and summer) has had negative consequences for
olive yield. Even the most optimistic future scenarios show that there
may be a decrease in fruit production in most olive growing areas
(Orlandi et al., 2020). North African countries are particularly exposed
to Mediterranean and Saharan climate changes and weather variability,
these countries, which are highly vulnerable to the effects of climate
change, should be seriously addressed with appropriate action plans so
that olive growers are not affected by these negative effects of climate
change (Ben Zaied & Zouabi, 2016). Future climate forecasts point to
significant warming and drought trends, and especially the Mediterranean
Basin is considered a ”hot spot” in terms of climate change (Fraga et
al., 2021). Until 2050, there will be a temperature increase of
0.8–2.3°C and a decrease in precipitation in the Mediterranean
(Rodriguez Sousa et al., 2020). Future climate changes are of great
importance for the agricultural sector as a whole and the olive tree
sector in particular (Fraga et al., 2021). The increase in drought
conditions observed in some parts of Italy in summer will pose a
significant risk in terms of reduced olive production. Increasing
temperatures from year to year in Italy are now a testament to climate
change, causing olive groves to move inland from the high-temperature
coastal plains. Risks to olive production will also increase
significantly as more severe changes in temperature or precipitation
occur (Orlandi et al., 2020). Global warming will threaten olive groves
so that insect and pest populations will increase, in parallel with
climate change, olive harvest time will need to be redefined to achieve
a balance between high yield and quality of the final product (Algataa,
2020). The predicted changes in terms of annual temperature increases
and precipitation decreases will have an impact on many parameters such
as the potential distribution area and phenological cycle of olive
cultivation (Rodriguez Sousa et al., 2020).
The quality of olive oil is affected by many factors such as
agricultural techniques, seasonal conditions, hygienic conditions of
fruits, maturity level, harvest time, transportation method and
processing technologies (Fontanazza, 1988). The quality of olive oil in
National and International Standards; it is evaluated on the basis of
FFA, peroxide value, UV specific absorbance values (K232and K270), FAEE and sensory properties. Chemical
composition of olive oil consists of triacylglycerol
(~99%) and FFAs, mono and diacylglycerols, and lipids
(Sevim et al., 2019). The fatty acid composition of olive oil varies
according to variety, altitude, climate and maturity level of the fruit
(Kayahan & Tekin 2006). For this reason, the limits given in both
International and National Standards are quite wide. Olive oil contains
higher oleic acid, less linoleic and linolenic acid than other vegetable
oils. With this feature, it is more resistant to oxidation than other
vegetable oils (Papadimitriou et al., 2006). It has been reported that
high temperatures change the fatty acid composition and decrease the oil
quality by causing a decrease in oleic acid (Nissim et al., 2020). The
most important part of the unsaponifiable matter of olive oil is
sterols. The composition and content of sterols, which are the
predominant components of the unsaponifiable part of olive oil, vary
depending on the agronomic and climatic conditions, the quality of the
fruit, the extraction and refining technique applied, and the storage
conditions. The main sterols of olive oil are; β-sitosterol,
delta-5-avenasterol and campesterol. In addition to these, there are low
amounts of stigmasterol, cholesterol, 24-methylene-cholesterol,
delta-7-campesterol, delta-5,23-stigmastadienol and delta-7-avenasterol
(İlyasoğlu, 2009). High level of stigmasterol is associated with high
acidity and low organoleptic olive oil quality (Hmida et al., 2022).
Esters of fatty acids and short-chain alcohols in olive oil have been
known for more than 30 years. On April 1, 2011, the EU commission made a
regulation 61/2011 and established the limits for FAEE parameters for
the evaluation of the quality of virgin olive oil. In this way, it is
aimed to detect the mixture of natural extra virgin olive oil and low
quality oils such as lampant or some deodorized oils. These esters are
an indicator of the presence of lampant oil in virgin olive oil (Mariani
& Bellan, 2008). FAEE and sensory data are complementary criteria in
the classification of olive oil (Gomez-Coca et al. (2012).
During the development of the olive fruit, there are chemical, physical
and physiological changes in the olive fruit, and these changes directly
affect the table olive and oil quality of the olives. On olive oil
quality; variety characteristics, cultural processes, climatic
conditions (precipitation, temperature) affect it significantly. It has
been important to investigate the effects of changes in climatic events
in recent years on the chemical properties of olive oil, especially on
purity criteria. So far, no study has been found on the effect of
climatic changes on the quality and purity criteria of olive oils in
Turkey. In this research, the effect of climate changes on the quality
and purity criteria of olive oil was investigated. For this purpose,
olive samples from the Marmara Region, Aegean Region, Mediterranean
Region and Southeastern Anatolia Region were collected from 39 orchards
in the 2017/18-2020/21 harvest years. Olive oils were obtained at the
Directorate of Izmir Olive Research Institute. MI of olive fruits, FFA,
K232 and K270, sterol composition, FAME
and FAEE analysis of obtained olive oils were performed.