## 4 Discussion
Interestingly, EEP at all concentrations for both fermentation periods showed a statistically significant difference as compared with 2.5% NaOCl, showing higher superiority of the solution in terms of cell viability over NaOCl. Our findings were consistent with the outcome reported by [PERSON] et al. [49]. In their study, the authors demonstrated the cytotoxicity of 2.5% NaOCl towards the human fibroblast cell lines using an MTT assay. Further, NaOCl has been found to be cytotoxic even at a lower concentrations, as described by [PERSON] et al. [50] and [PERSON] et al. [51], using NaOCl at 0.005% and 0.08%, respectively. Both of the authors were in agreement and added that the cytotoxic effects exerted by NaOCl are both concentration- and time-dependent. Our observation through the Live and Dead Cell assay supports the previously discussed cytotoxic outcome of NaOCl, where exposure to 2.5% NaOCl showed an abundance amount of red fluorescent cells, indicating the non-viability of the cells. One of the glaring comparisons was the presentation and appearance of the cells in samples exposed to 2.5% NaOCl and 100% EEP. Although both were cytotoxic, the latter showed red cells with more intense fluorescence, bigger cell sizes and more compact cell distribution, in contrast to the former, which presented with multiple loosely-bound small-size cells in an ununiform cell orientation, suggestive of cellular fragmentation, and the formation of cell corpses. The presence of cellular fragmentation and cell corpses is classified as type III cell death or necrosis, the most severe form of cellular damage [48; 52]. The pH of NaOCl is thought to be responsible for these findings, as it promotes tissue penetration and interrupts the cellular membrane integrity, causing damage and fragmentation to the cells' organelles and DNA [50; 53]. In addition, we were unable to perform TEM analysis for the cells exposed to 2.5% NaOCl due to excessive cell damage and fragmentation, which resulted in the absence of a cell pellet available for analysis. This is highly suggestive that NaOCl is more toxic to the cells as compared with EEP. In a study by [PERSON] et al. [50], the authors reported extreme cell lysis following exposure to 0.5 mg/mL NaOCl for 2 h, leaving almost no cell structures as observed through a scanning electron microscope. We believe that the extent of cell lysis in the current study was more profound since the concentrations of NaOCl used were higher and the duration of exposure was longer. We postulated that the presence of the active component within EEP is the main reason for the cytotoxic effects exerted by the solution at a concentration beyond 6.25%. Even though the main constituents of EEP used in the present study are still under investigation, various studies in the literature have identified and described the active component of EEP. Organic acids, mainly acetic acids, have been consistently reported as the main constituents of EEP by [PERSON] et al. [28], [PERSON] et al. [54] and [PERSON] et al. [55], regardless of the type of fruit used. In addition, the presence of naringenin and naringin, a flavonoid compound, has been reported in citrus fruit peel-based EEP [27; 56; 57]. Acetic acid can induce cell death via two mechanisms: the disruption of cellular homeostasis and the induction of oxidative stress in cells, as proposed by [PERSON] et al. [58]. The former action is induced as the acid penetrates the cell membrane through simple diffusion and dissociates into acetate and hydrogen ions. The pKa of acetic acid is 4.76, which is lower than the intracellular pH value. At high concentrations, the accumulation of hydrogen ions creates an acidic cellular environment and a drop in the intracellular pH value. This leads to the disruption of normal cellular protein folding and other enzymatic activity, contributing to cell death. In our previous study, [PERSON] [31] reported an initial pH of EEP at 4.14 and raised up to 7.38 as the concentration of EEP diluted to 6.25% and below.