Changes of pH values during storage
The pH values of the table olive is crucial parameter from technological
and sanitary point of view, so pH values measured during storage period
(Table 3). pH values were determined between 4.64-4.83 in normal
produced olives and between 4.30-4.55 in starter culture added olives.
TABLE 3 pH values of dry salted olives during storage
Irradiation applications together with processing methods were also
statistically effected pH values of samples (p<0.01). There
was no statistical difference between irradiation doses (1, 3, 5 kGy) on
pH values. The applied irradiation doses were found to be different only
from the non-irradiated group.
pH values did not change significantly but slightly decreased during
storage and at the end of storage, all samples were found to be
appropriate according to the Turkish Food Codex (Anon., 2014). Parallel
with our research findings, Sanchez et al. (1997) reported that pH
increased during storage.
Değirmencioğlu (2011) states that the pH changes of olives stored at 4°C
and 20°C after fermentation vary between 5.05-5.25 and 4.99-5.36.
Değirmencioğlu (2011) determined that the pH values of olives stored at
4°C and 20°C ranged between 5.05-5.25 and 4.99-5.36. Panagou, (2006) and
Ramírez et al., (2013) reported pH as 5.0–5.2 for black dry-salted
olives These values are quite higher than the pH values obtained in our
study. This may be due to the differences in olive processing and
preservation methods.
Fluctuations observed in pH values durung storage. It might be due to
the the organic acids formed by the microflora
Titratable acidity changes of dry salted
olives during storage
Titratable acidity of the table olive is also crucial parameter from
technological and sanitary point of view when black olives are processed
according to the naturally dry-salted black olives, Titratable acidity
values during storage are shown in Table 4. Olive titratable acidity
change was similar to pH change in both methods during fermentation.
However, this increase was more rapid in olives using starter culture
Table 4.
TABLE 4 Titratable acidity values of samples during
storage (%)
The processing method, irridation and storage time effect on titratable
acidity were found statistically significant (p <0.01).
Preservation methods applied increased the acidity of olives. Starter
culture added and vaccum applied group were found to be the highest
(1.02%) and the group without culture were the lowest (0.68%). This
may be due to the high number of lactic acid bacteria because of the
addition of starter culture.
The highest acidity values obtained in the storage period were 0.79%
(NV0) in the 1st month of storage and as 1.02% (KV0 and KV1) in the 1st
month of storage. The lowest values were found as 0.68% and 0.83% in
the NV3 and KV5 in 8th month of storage, respectively (Table 4).
As noted by Rodriguez-Gomez et al. (2014), there were significant
decreases in titratable acidity during the storage. The highest acidity
drop was observed in KV5.
According to the LSD test applied, in terms of acidity values, 1 and 3
kGy doses of irradiation were in the same group, while the sample with 5
kGy irradiation was in a separate group from the other samples.
Reducing sugar changes during storage
Soluble sugars extracted from olive fruits into the brine are the
substrates for microbial fermentation, leading to the production of
acids responsible for the low pH, but also to the production of
secondary metabolites responsible for the organoleptic characteristics
of the final product (Kailis and Harris, 2007).
The highest values obtained at the end of the storage period were 0.46%
(NMP0) in the 1st month of storage and as 0.36% (KV0 and KV1) in the
1st month of storage. The lowest values were found as 0.37% in the NV1,
NV3, NV5 and as 0.29% KMP5 in 8th month of storage, respectively.
TABLE 5 Reducing sugar values of dry salted olives during
storage (%)
Effect of processing methods, irradiation and storage on reducing sugar
were found to be statistically significant (p<0.01). According
to the LSD test applied for the difference between irradiation
applications, the sample with non- irradiated samples was in a separate
group from the other samples but there was no difference between the 1,
3, 5 kGy irradiation doses. Data obtained by other authors also showed
that gamma irradiation, using a doses up to 10 kGy, did not induce
significant loss in water soluble components such as, sugars and
the sugar content of with and without added culture processed olives
followed a similar trend and slightly decreased during storage (Table
5). This may be due to continued microbial activation during storage.
Our results, seems to be compatible with the decrease in the amount of
sugar that stated by López-López et al. (2007) and Kiai et al. (2020)
Total phenolic compound (TPC) changes during storage
Phenolics are a major category of components with important biological
properties present in olive drupes. Apart from their contribution to
sensory and aromatic characteristics of olives, they are also regarded
as natural antioxidants due to their reducing properties as hydrogen- or
electron-donating agents (Grounta et al., 2017).
The highest values obtained at the end of the storage period were 232
mgCAE/100g in the first month of storage in NV0 and 200 mgCAE/100g in
the second month of storage in KV0. The lowest values obtained at the
end of the storage period were 144 mgCAE/100g in the eight month of
storage in NMP5 and 138 mgCAE/100g in the eight month of storage in KV5.
The total phenolic compound values of olives are shown in Table 6.
Total phenolic content of the olive samples (wet basis) range between
229.12 and 415.34 mgCAE/100g (Yıldız and Uylaşer, 2015). Total phenol
content obtained in this study were lower. Such differences may be due
to the varieties amd processing methods studied.
TABLE 6 The TPC values of dry salted olives during
storage
Processing method, irridation and srorage were significantly effect the
TCP of olives (p<0.01)
TABLE 7 Applications with significant statistical
differences in the TPC values
Gamma irradiation provoked significant changes in TPC of olives.
According to the LSD test applied to determine the differences between
applications,. the unirradiated group differed from the 3 and 5 kGy
irradiated groups. A seen in the Table 6, irradiation slightly decreased
the total amount of phenol of table olives and continued to decrease
during the storage period. Similarly De Toledo et al., (2007) observed
that gamma irradiation decreased phenolics. Contrary to our findings
Stajner et al. (2007) and Harrison and Were, (2007) found significant
increase in total phenolic by applied doses of γ-irradiation in soybeans
and almond skin, respectively. This increase in phenolics may be partly
due to the higher extractability of these materials after irradiation
Antioxidant activity changes during storage
The DPPH• RSA amount was determined as 67.28 µmolTE/100g oil in oils
obtained from raw olive samples. The amount of DPPH• RSA at the end of
the fermentation period was 54.47 µmolTE/100g oil in the normal
production group of the turned olives obtained according to different
processing methods, and the DPPH• RSA amount was 51.54 µmolTE/100g oil
in the group produced by adding culture (Table 8).
During the post-packaging storage period, DPPH• RSA values were
determined in olive samples in the 4th and 8th months of storage. In the
normal production N group, the highest DPPH• RSA value was determined as
57.35 µmol TE/100g oil in the irradiated NV3 coded sample, and the
lowest was 47.14 µmolTE/100g oil in the 5 kGy irradiated vacuum sample
in the NV group. In the K group produced with culture addition, the
highest value was 60.94 µmol TE/100g oil in the KMP3 coded sample at the
4th month, and the lowest was 49.97 µmolTE/100g oil in the KV0 coded
sample.
The differences detected in the DPPH• RSA values according to the
processing methods showed that the processing methods were effective on
the antioxidant activity values. The change in the antioxidant activity
values determined depending on the olive processing methods was found
statistically significant at the p<0.01 level with the
analysis of variance applied on the antioxidant activity values obtained
from the olive samples. Along with the differences detected in DPPH• RSA
values according to processing methods, packaging, irradiation and
storage were statistically significant (p <0.01 level).
TABLE 8 The DPPH• RSA values of olive oils obtained
from dry salted olives
In the DPPH• RSA values determined in the olive oil samples that
obtained from dry salted olives during the research, the applications
that are found to be statistically significant and their significance
levels are presented in Table 9.
TABLE 9 Applications with significant statistical
differences in the TPC values
It was observed that at higher dose of irridation decreased the free
radical activity of oils as compared to raw fruit oils. However 3 and 5
kGy doses significantly increased the antioxidant activity of oils
obrained from table olive after processing. The enhanced antioxidant
capacity/activity of a plant after irradiation is mainly attributed
either to increased enzyme activity (e.g., phenylalanine ammonialyase
and peroxidase activity) or to the increased extractability from the
tissues (Althoman et al. 2009). Similar to the findings of the study,
Latreche et al., (2018) reported that the irradiation at 10 kGy
increases antioxidant activity.
According to several authors, there is a linear correlation between the
total polyphenol content in table olives and their antioxidant activity
( Othman et al., 2009; Romero et al., 2004; Sousa et al., 2014). The
study of Irmak et al. (2017) showed that processing style of olives had
significant effects on quality parameters of olive oils obtained from
raw and fermented olives. Kiai et al. (2020) states that during the
fermentation, there is a decrease of approximately 43% in total
phenolic components. For this reason, it is stated that phenol losses
during fermentation reduce the antioxidant activity of olives. They also
report that changes in processing methods change the profile and level
of phenolic compounds and thus affect the antioxidant activity of the
final product.
Contrary to our study findings some studies showed that gamma
irradiation did not change the radical scavenging activities of some
medicinal plants (Jeong et al., 2009, Brandstetter et al., 2009), dried
spices (Nagy et al., 2011) and olive leaves (Aouidi et al., 2011).
Others reported that low or mild gamma irradiation could increase or
slightly increase the antioxidant activities of seeds of soybean and
cumin (Dixit et al., 2010; Kim et al., 2009) and peach fruit (Hussain et
al., 2010).
Aşık & Özkan (2011) stated that tocopherol, carotene, chlorophyll and
especially phenolic compounds characterize the antioxidant activity in
extra virgin olive oils, and that these natural antioxidants protect the
activity by decomposing peroxides and preventing the formation of free
radicals. In our research, it is observed that storage affects the
antioxidant activity values. It has been determined that the decrease in
the total amount of phenolic substances during storage also determines
the decrease in antioxidant activity. Besides, it is one of the results
obtained in our study that MAP packaging has a preventive effect on the
decrease of antioxidant activity.
According to several authors, there is a linear correlation between the
total polyphenol content in table olives and their antioxidant activity
(Othman et al., 2009; Romero et al., 2004; Sousa et al., 2014). They
found a positive corelation between the TPC and DPPH. The study of Irmak
et al. (2017) showed that harvest year, process type and salt content of
olives had significant effects on quality parameters of olive oils of
raw olives and fermented olives.