Olive oil analysis
Increasing evidence of significant climate change in the coming decades necessitates adaptation measures. Forecasts point to significant warming and drought trends. Already changes in olive trees have been reported for the past few decades (Fraga et al., 2021). In this study, 4 harvest year (-2 on-2 off) climate data and the oils obtained from the fruits harvested from the regions were examined. It was investigated whether there were deviations in the quality and purity criteria of olive oils.
Harvest time is very important parameter on the quality of olive oil to be obtained from olives. During the maturation of olives, which takes place in two stages, namely green and greenish/pink/black period, a series of important physical and chemical changes occur for both olive and olive oil production (Franco et al., 2014). Olives for oil extraction are generally harvested during the greenish/pink/black period, while olives to be processed into table olives are harvested at different maturity levels depending on the processing method (Emmanouilidoua et al., 2020). As seen Table 1 the lowest MI values was determined from Kilis (KY) with 0.94 in 2018, and the highest was determined from Bursa (G) with 4.15 in 2018 (p<.0001). It was determined that the MI values of the Gemlik variety olives were higher, and the Ayvalık and Memecik olive varieties were lower. Maturation time may vary depending on climatic conditions, irrigation, amount of product and variety characteristics (Beltran et al., 2004; Roshani et al., 2016). In the same garden and sometimes even on the same tree, the maturation and coloration of olives do not occur at the same time. Considering that low temperatures and high precipitation delay fruit growth and ripening (Mafrica et al., 2021), climate is very important for MI and fruit quality.
FFA is often the first parameter discussed to assess the quality of olive oil production. It is well known that FFA is affected by many factors, including fruit quality, harvest time, storage and production conditions (Piscopo et al., 2021). According to the years, the lowest FFA was found in Bursa (G) with 0.07 (in oleic acid %) in 2017, and the highest in Çanakkale (A) with 1.27 (in oleic acid %) in 2019. The FFA values of only 2 samples were exceeded the limit of 0.8 (in oleic acid %) for extra virgin olive oil. For that reason they were categorization as VOO (IOC, 2021) (Table 1). As the harvest time progresses, due to the increase in enzymatic activity in the fruit, especially with the increase of lipolytic enzymes, and also due to the sensitivity of olive fruits to pathogenic infections and mechanical damage with ripening, the FFA value increases (Yousfi et al., 2006). UV spectrophotometric indices (K232 and K270 values) of olive oils were not found to be statistically significant (Table 1).
The presence of methyl and ethyl esters in olive oil is due to the fermentation that occurs in the olive fruit. Therefore, it is the formation of methyl and ethyl alcohols esterified with FFAs. Methyl and ethyl alcohols are higher in lampant oils. These esters are an indication of the presence of lampant oil in VOO. The FAEE value is both a quality criterion and a purity criterion. The FAEE values of samples were found to be statistically significant. According to the years, the lowest FAEE value was determined in Bursa (G) in 2017 with 1.56 mg/kg, and the highest in Balıkesir (A) in 2018 with 27.32 mg/kg (Table 1). Since the FAEE values of all olive oil samples were not exceed the limit of 35 mg/kg, they were classified as extra virgin olive oil in accordance with the IOC standart (IOC, 2021). It has been determined in some studies that FAEE is 30-90 mg/kg in Spanish oils and 1-11 mg/kg in Italian oils. It is generally stated that it is higher in Spanish oils and lower in Italian oils (Garcia-Oliveira et al., 2021). Depending on the olive quality (such as the maturity level of the olive, whether it is damaged or not, the holding time and conditions after harvesting), methanol and ethanol formed by the developing fermentation process are transformed into FAEEs by trans esterification (Mariani & Bellan, 2008). The FAEE value is also often associated with fermentation processes and sensory defects such as moldy/muddy, musty/moist/earthy sediment and wine/vinegar (Di Serio et al., 2017). Addition of water at the oil extraction stage reduces the presence of ethanol, so low FAEE value may not always be an indicator of high quality. It should also be noted that the presence of FAAE at a certain concentration is not always an indicator of low quality, since ethanol is a by-product of fermentation in fruit during flavor development (Gómez-Coca et al., 2016; Garcia-Oliveira et al., 2021). Storage conditions increase the FAEE values statistically significantly, however, the filtration process does not affect the FAEE values (Köseoğlu et al., 2019). As previously investigated by Piscopo et al. (2016) and Mafrica et al. (2021) the FAEE content not affected from the climate of the growing environment or harvesting time, its linked more to processing conditions. Low temperatures and high precipitation slow down fruit growth and development and delay ripening (Mafrica et al., 2021). Therefore, low temperatures, high precipitation and maturity index are very important parameters for olive oil quality.
As seen at Table 1, total beta-sitosterol values were ranged from 93.79% (2020) to 96.68% (2018), delta-7-stigmastenol values were ranged from 0.16% (2019) to 1.14% (2017), campesterol values were ranged from 1.59% (2020) to 3.75% (2017), stigmasterol values were ranged from 0.26% (2017) to 2.22% (2019) and cholesterol values were ranged from 0.00% (2019 and 2020) to 1.77% (2017). All the results were within the limits of IOC (2021) except for delta-7-stigmastenol. The delta-7-stigmastenol value varied between 0.50 and 1.14% in 21 olive oil samples according to years. The other 18 samples were determined below the value of ≤0.5%. Deviations occurred in 5 samples in 2017, 5 samples in 2018, 2 samples in 2019 and 9 samples in 2020. Results are in accordance with Yorulmaz & Bozdogan Konuskan (2017), İlyasoğlu (2009), Ben Temime et al. (2008), Hannachi et al. (2013), Fernández-Cuesta et al. (2013). Most compounds in the sterol composition of olive oil are affected not only by geographical origin but also by environmental conditions (Ben Temime et al., 2008). In some research, it seen that total β-sitosterol concentration values in olive oil increased in the colder region (Piravi-Vanak et al., 2012).
TABLE 1 MI of olives, FFA (oleic acid %), K232and K270, sterol composition (%) and FAEE (mg/kg) values of olive oils by years
As seen Table 2, according to the years, the oleic acid, linoleic acid, linolenic acid values ranged between 63.39% (2018) and 75.79% (2017), ranged between 4.47% (2020) and 15.56% (2018), ranged between 0.43% (2019) and 0.91% (2019), respectively (Table 2). Results are in accordance with researchers of Yorulmaz & Bozdogan Konuskan (2017), Köseoğlu et al. (2016), Aparacio & Luna (2002), Mafrica et al. (2021) and Rodrigues et al. (2021). Both the olive variety and the harvest year have significant effects on the FAME of olive oils. In addition, environmental conditions mainly affect oleic acid and linoleic acid content (Rodrigues et al., 2021). Rodrigues et al. (2021), was definitely confirmed that the fatty acid composition changes depending on the olive variety, and it was stated that the climate had an effect on the changes in the fatty acid composition. İlyasoğlu (2009) stated that the chemical composition of Ayvalık and Memecik olive oils varies according to the harvest season, and these changes may be due to changes in climatic conditions (temperature and precipitation amount). It is stated that the irrigation regime positively affects the % oil content and fatty acid composition of olive oil, and the fruit structure in the irrigated regions is better for table olive production and olive oil extraction. In addition, in recent studies, it has been reported that there are differences in the sensory and chemical characteristics of olive oil obtained from trees that are irrigated and grown depending on precipitation (Solinas, 1990; Aparicio & Luna, 2002; Patumi et al., 2002).
TABLE 2 FAME values of olive oils by years (%)
The chemical composition and sensory properties of extra virgin olive oil are affected by many different variables such as environmental factors, cultivation and farming techniques, genetic factors (variety), degree of maturity of the fruit, harvest-transport and storage systems of olives, production techniques, storage and packaging conditions of the oil (Angerosa et al., 2004; Kalua et al., 2007). High temperatures cause losses in some sensory properties and total phenol content of virgin olive oil (Servili et al., 2002). According to the sensory analysis results of fruitness, bitterness and puncency were found to be statistically significant (Table 3). The lowest fruity was determined in Gaziantep (NY) olive oil with 3.68 in 2020 and the highest in Bursa (G) olive oil with 5.33 in 2017. It has been determined that samples are in the “Medium Fruity” group (3.0< median ≤ 6) according to the IOC (2021) (Table 3). The bitterness of olive oils by years were not determined statistically significant. The bitterness ranged between 2.10 and 4.20. The lowest pungency in 2019 was obtained from Hatay (G) olive oil with 2.57, and the highest from Gaziantep (NY) olive oil with 4.53. The samples were in the “Medium Bitter” and “Medium Pungent” group (3.0< median ≤ 6) and “Light Bitter” and group “Light Pungent” (median ≤ 3) in terms of bitterness and puncency according to the IOC (2021). Origin, variety and fruit maturity have a great influence on sensory characteristics of olive oils (Delgado & Guinard, 2011). Results are in accordince with Büyükgök & Gümüşkesen (2015).
TABLE 3 Sensory analysis values of olive oils by years (intensity)