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.