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)