Raw and Dry Salted Olives
In the table olive processing, salt concentration, temperature and pH adjustments during fermentation and the use of starter culture increase the formation of lactic acid, resulting in more delicious and durable olives (Mcfeeter, 2004; Oliveira et al, 2004; Randazzo et al, 2010; Irmak, 2015).
TABLE 2 Some physikochemical properties of raw and dry salted olives
Although the pH values of raw olives were high, with the development of lactic acid, it decreased at the end of the fermentation. It reached the final values of pH-4.78 in traditional olives and pH-4.23 in culture added olives (Table 2). The final pH value reached by starter culture used indicates a successful lactic fermentation.
The effect of starter culture use on pH and titratable acidity values was found to be statistically significant (p<0.01). Titratable acidity of starter culture added olives was found to be higher than normal production. The pH values of the samples decreased below the safe pH value of 4.6 after 3 months of processing. The pH decrease in both olives during processing is mainly due to the production of lactic acid, the main LAB metabolic product, and the conversion of some phenols on acids such as the glucoside elenolic acid, which is released after hydrolysis of oleuropein (Kiai et al., 2020). It is also stated that other organic acids such as acetic, malic, citric, formic and succinic contribute to the overall pH.
Parallel to the findings of the study, Benincasa et al. (2015) and Ünal & Nergiz (2003) mentioned, similar pH values at the end of fermentation. On the contrary of Benincasa et al. (2015), in particular, since the starter culture added table olive samples showed higher pH and titratable acidity content, they did not seem to be affected by phenolics.
Differences detected in titratable acidity values according to processing methods showed that processing methods were effective on titratable acidity value. The change in titratable acidity values determined depending on the olive processing methods was found to be statistically significant at the p<0.01 level with the variance analysis applied on the titratable acidity values obtained from the olive samples.
As shown in Table 2, the acidity of raw olives was found to 0.46% (as lactic acid). The dry salting process caused an increase in the acidity of olive fruits. After fermentation, it increased to the value of 0.54% and 0.71% in normal and starter culture added samples respectively. The reason of this increase in the acidity is the lactic asid formed by lactic acid bacteria.
Parallel to our findings the highest titratable acidity, were determined at inoculated samples (Kumral and Sahin, 2009). Ünal and Nergiz (2003) found acidity in black table olives slightly lower than our research findings (0.45%).
The reducing sugar value of the raw olives was 1.92%. dry salting method reduced sugar content of olives and determined 0.45% (N) and 0.36% (K) at the end of fermentation. The change in reducing sugar values depending on the olive processing methods was found to be statistically significant at the p<0.01 level.
The initial sugar concentration in traditional olives was almost 20% higher than in starter culture added olives. This may be because, during the fermentation phase, cultured olives produce higher titratable acidity and therefore more degradation at sugar levels. It is seen in our study that the production of more titratable acidity causes the breakdown of sugars and with it, faster removal of bitterness and a lower pH development.
The total phenolic compound in the raw olive samples is 389 mgCAE/100g, the total phenolic substance values of the olive samplesobtained according to the processing methods are in the normal production and the cultured production methods 238 and 206 mgCAE/100g, respectively.
Our results showed that processing methods affected the phenolic contents and they decreased in both olive processing methods. The phenolic concentration is quite low in olives produced by the culture added method. Due to the rapid pH and titratable acidity changes during fermentation, the faster decomposition and diffusion of water-soluble phenols increases the losses. In traditional production, relatively low titratable acidity causes less degradation of phenols and may be slower to pass to the external environment as it affects the fruit peel less. Besides, we can say that the phenolics in the olive do not adversely affect the culture inoculated for a rapid fermentation.
The processing method of the final products has also a significant effect on the phenolic compound concentration. Olive fruit processing methods affect the taste and can significantly alter the health properties of the olive fruit, mostly because different processing methods can lead to different capacity of hydrolysis products (Marsilio et al., 2005; Zoidou et al., 2010; Charoenprasert & Mitchell, 2012; Salis et al., 2021). Research results showed that table olive processing techniques have a significant effect on the total phenolic content of olives and that the applied processing techniques cause a significant reduction in the total phenol content of olives (Irmak et al., 2010).
As a result, the level of phenolic compounds of olives decreased during fermentation and during storage compared to raw fruit. This is also in line with previous studies (Blekas et al., 2002; Romero et al., 2004; Irmak et al., 2010; Sahan et al., 2013; Kiai et al., 2020). On the other hand, polyphenol contents of end products of all studied treatments were decreased comparing to the traditional one (Abd El-Samie Ibraheem, 2015).
Generally the results of polyphenols were in agreement with those reported by Marsilio et al. (2006), who reported that, processing of olive resulted in a 35-40 % loss of total phenols (during 7 months), where the results indicated that they were lost more during the first 3 months of fermentation. (Abd El-Samie Ibraheem, 2015)
The differences detected in the total phenolic substance values according to the processing methods showed that the processing methods were effective on the total phenolic compound value. The change in the total phenolic matter 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 total phenolic matter values obtained from the olive samples (Table 7). Along with the differences detected in the total phenolic compound values of the processing methods, the irradiation and storage process were found statistically significant at the p<0.01 level.
According to the Durante et al. (2018) and Blekas et al. (2002) total phenol of black olives vary from 10 mg/100 g of flesh to 83.3 mg/100 g of fresh weight. These results are lower than the results obtained from our study. This may be due to the different olive cultivars and processing methods they used. Kiai and Hafidi (2014) stated a significant loss in the total amount of phenolic substances in olives during fermentation due to the diffusion of water-soluble phenolic compounds into the brine, and similar results have been reported by other researchers (Alvarez et al., 2014; Othman et al., 2009; Romero et al., 2009).