Slightly Acidic Electrolyzed Water
As a novel type of bactericide, SAEW has the characteristics of low pH, high redox potential, and effective chlorine, which can kill bacteria quickly and widely. In the field of food, compared with the commonly used sodium hypochlorite or alcohol fungicides, it has the characteristics of ensuring safety, reducing cost, and reducing environmental load. The germicidal effect of slightly acidic electrolytic water is affected by the available chlorine mass concentration, pH value, and redox potential.
3.1. The Impact of Slightly Acidic Electrolyzed Water on Microorganisms
SAEW is a potential alternative to antibacterial detergents and is considered an environmentally beneficial disinfection method with the advantage of reducing the impact of residual chlorine on human health and safety compared with other disinfectants. The antibacterial action of SAEW is mostly due to the ability of HClO to cause oxidative damage to biomolecules. Microorganisms in food can be significantly reduced by using SAEW in combination with other germicidal or mechanical forces in the washing process.
Liu et al. have suggested that SAEW exhibits strong antibacterial activity against tested microorganisms, which is significantly correlated with the available chlorine concentration (ACC) of SAEW. The mortality rate of S. putrefaciens and S. saprophyticus reaches 96% and 85%, respectively, at the ACC value of mildly acid electrolytic water of 60.0 mg/L. The results of scanning electron microscopy (SEM) indicated that SAEW disrupts cell morphology and structure. Furthermore, the formation of ROS is influenced by SAEW. Ultimately, the accumulation of ROS causes a cascade of physiological abnormalities within the cell, leading to bacterial death. Hao et al. studied the efficacy of SAEW and AEW against three test bacteria (e.g., Escherichia coli, Staphylococcus aureus, and Bacillus subtilis). The result of experiments has suggested that the disinfection effect on the three studied strains rapidly diminished with increasing dilution of AEW and SAEW, as indicated by the existing research. When AEW is diluted 17 times, the number of live E. coli, Staphylococcus aureus, and Bacillus subtilis fell to 7.84, 7.34, and 7.90 log10 CFU / ml, respectively. Survival rates for E. coli, S. aureus, and Bacillus subtilis decreased to 7.96, 6.45, and 7.89 log10 CFU /mL, respectively, at the dilution of 47 times. In addition, the results demonstrate that SAEW is more effective against the above strains than AEW in terms of antibacterial efficacy. However, even when SAEW is diluted more than AEW, its disinfection efficiency is the same. Xuan et al. suggested that SAEW-ice is much more beneficial to enhance squid preservation than TW-ice during storage. After SAEW ice treatment, the bacterial count decreases by 1.46 ± 0.10 log10 CFU/g, and microbial growth remains relatively slow during storage. SAEW-ice extends the shelf life of seafood and improves its safety and quality by serving as a preservative and disinfectant. Zhang et al. investigated the sporangial inactivation effect of slightly acidic electrolyzed water (SAEW) at different available chlorine concentrations (ACC, 20, 60, and 100 mg/L), as well as the spore structure changes, mutagenesis, and inner membrane (IM) properties. The findings show that SAEW treatment causes damage to the spore surface and IM, and loss of core content due to rupture. Surviving SAEW-treated spores do not produce mutants. SAEW significantly attenuates spore viability media in high salinity environments. Spores treated with SAEW were induced to germinate with L-alanine or inosine and stained with propidium iodide (PI), but lysozyme addition failed to restore them . Furthermore, SAEW treatment inhibits spore germination during germination induction. The above findings suggest that SAEW inactivates spores mainly by destroying the spore IM.
Through the above studies, it is found that microorganisms, such as Escherichia coli and Salmonella, are significantly reduced by SAEW treatment. Spores of botrytis cinerea, Botrytis cinerea, Bacillus anthracis, and Phytophthora capsicum cannot be cultured following treatment. Therefore, SAEW has strong broad-spectrum antibacterial and fungal activities.
3.2. Slightly Acidic Electrolyzed Water Mechanism
The physicochemical properties of fungicides (e.g., water solubility, to a large extent, and stability regarding biological and abiotic degradation processes) affect the actual effect of fungicides. Pure water and electrolyte are pumped into the electrolytic cell. Under the action of direct current, the negatively charged ions (chloride and hydroxide) move to the anode and lose electrons in the anode while forming oxygen (O2), chlorine gas (Cl2), hypochlorite ion (ClO), hypochlorous acid (HClO), and hydrochloric acid (HCl). Furthermore, positively charged ions (hydrogen and sodium) move to the cathode where they gain electrons to form hydrogen gas (H2) and sodium hydroxide (NaOH).-
The chemical reactions:at anode: 2NaCl→Cl2(g) + 2e− + 2Na, 2H+2O(l)→4H(aq) + O+2(g) + 4e−,Cl2 + H2O(1)→HCl + HOClat cathode: 2H2O(l) + 2e−→2OH−(aq) + H2(g),2NaCl + 2OH−→2NaOH + Cl−
Figure 3 presents a schematic for the application of SAEW. Slightly acidic electrolytic water is made by low-voltage electrolysis. In the anode, 2HCl→ H + Cl+−, which in turn reacts with OH to form hypochlorous acid (HOCI) and hydrochloric acid (HCl). Slightly acidic electrolytic water occurs after the REDOX reaction to generate water. The raw materials do not contain salt; thus, even after drying, the water will not cause harm related to the concentration and crystallization of salt.-
Figure 3. The schematic illustration for slightly acid electrolyzed water application.
In a membraneless chamber, electrolyzing 2–6% dilute hydrochloric acid produces somewhat acidic electrolyzed water with a pH of 5.0–6.5. There are three forms of chlorine in SAEW: chlorine gas (Cl2), hypochlorite ion (−OCl), and hypochlorous acid (HClO). The strongest effect, the bactericidal ability of HClO, is about 80 times that of −OCl. It is an aqueous solution with hypochlorous acid as the main component with bactericidal effect. Because of its minimal running expenses and excellent antibacterial action, it has been frequently used to sterilize goods (e.g., fruits, vegetables, and meat). When electrolytic water is used, microorganisms (e.g., Escherichia coli, Staphylococcus aureus, Salmonella, vibrio parahaemolyticus and Bacillus cereus) all exhibit the effects of considerable antibacterial activity. SAEW exhibits bactericidal properties by attacking multiple targets of microbial cells (e.g., cell walls, extracellular membranes, and intracellular components). The surface shape of the microbial cells changes from smooth, continuous, and bright to rough, shrunken, and decomposed after the cells are treated with SAEW. The antibacterial activity of SAEW is primarily due to the potential of hypochlorous acid in causing oxidative damage to biomolecules. Microorganisms in foods can be significantly reduced using slightly acidic electrolytic water during the washing process in combination with additional disinfectant or mechanical forces.
4. Synergistic Treatment of Ultrasonic Waves Combined with Slightly Acidic Electrolyzed Water
Sonication alone (at room temperature and ambient pressure) has been shown to be inefficient for inactivating several bacterial species. High power and extended processing durations should achieve significant microbial reduction, leading to increased energy expenditures. Over the past few years, researchers have been looking into combining ultrasound with disinfectants (e.g., chlorine, ozone, and hydrogen peroxide) to lower the cost of microbial inactivation and ultrasound technologies. Existing research has suggested that ultrasonic waves combined with SAEW are capable of effectively reducing microorganisms. At present, the combined sterilization treatment of ultrasonic waves and SAEW has been mainly used in aquatic products. Based on the bactericidal effect of electrolyzed water and ultrasound on bacteria, the combined treatment of AEW combined with ultrasound is beneficial to accelerate cell death and minimize early damage to bacteria, and it is considered as a more environment-friendly novel sterilization technology for minimizing energy consumption, avoiding the use of carbon-intensive chemicals, and reducing toxic release. Thus, this environment-friendly sterilization method has taken on a rising significance.
4.1. Synergistic Mechanism of Ultrasonic Waves Combined with Slightly Acidic Electrolyzed Water
Existing research has reported the combined use of ultrasound (US) and slightly acidic electrolyzed water (SAEW) to reduce targeted pathogens over the past few years. Under the mechanical, cavitation, and chemical effects of ultrasonic waves, micro-cracks can be generated in the cell membrane of microorganisms, and the cell membrane permeability can be changed. Cell necrosis or apoptosis is efficiently induced when SAEW is capable of easily reaching the inside of microorganism cells, thus resulting in the increased release of intracellular chemicals. In other words, since ultrasonic bubbles produce high pressures and temperatures, ultrasonication is capable of facilitating the penetration of chemical oxidants into cell membranes, thus increasing the efficacy of disinfectants. The antibacterial effect of ultrasonic waves and SAEW is enhanced, such that SAEW may serve as a liquid culture medium for ultrasonic waves. The cavitation generated by the ultrasonic wave destroys the cell wall of the bacteria in a short period while increasing the contact surface between the SAEW and the bacteria.
The sterilization mechanism of ultrasonic waves combined with SAEW treatment can be preliminarily studied by comparing sterilization effects, determining sterilization targets, observing bacterial morphological changes under a scanning electron microscope, and observing bacterial biological characteristics through flow cytometry. The results indicate that, unlike single sterilization treatments, combined sterilization treatments can affect the number and quality of bacterial colonies, and simultaneous or continuous exposure to ultrasonic and electrolyzed water pressures may show complementary inactivation mechanisms. In the combination of acidic electrolyzed water and ultrasonic sterilization, the lethality rate is higher than that of ultrasonic waves or acidic electrolyzed water alone. Ultrasound may enhance the microbial sterilization mechanism of acidic electrolyzed water, thus adding convenience for acidic electrolyzed water to penetrate and kill microorganisms during ultrasonication.
In brief, the lethality rate is higher than that of ultrasonic or acidic electrolyzed water alone in the combination of acidic electrolyzed water with ultrasonic sterilization. Ultrasound may enhance the microbial sterilization mechanism of acidic electrolyzed water, thus making it easier for acidic electrolyzed water to penetrate and kill bacteria during ultrasonication. The schematic diagram is shown in Figure 4.
Figure 4. Reaction principle of ultrasonic and slightly acidic electrolyzed water.
4.2. The Impact of Ultrasonic-Assisted Slightly Acidic Electrolyzed Water on Microorganisms
Gram-negative bacteria, particularly Pseudomonas and Shewanella, are the most common spoilage germs in marine fish (mainly H2S-producing bacteria). Lan et al. discovered that the populations of H2S-producing bacteria and Pseudomonas increased during cold storage, following a similar growth pattern to TVC. The quantity of microorganisms grows as storage duration increases. On day 10, the Pseudomonas levels in the distilled water group had 7.0 log10 CFU/g, whereas the ultrasound, SAEW, and ultrasound + SAEW groups had 6.43, 5.49, and 4.89 log10 CFU/g, respectively. Park et al. found that compared with ultrasonic waves or SAEW alone, the synergistic treatment of ultrasonic waves and SAEW could significantly reduce the number of Escherichia coli and Vibrio parahaemolyticus in fresh-cut herring fillets, but did not affect their sensory quality. The synergistic effect exhibited by the combined treatment of ultrasonic waves and SAEW helps to ensure its sterilization and preservation effect on food, and helps to expand its application range in food sterilization and preservation.
In brief, the synergistic treatment of ultrasonic waves and SAEW and the independent action of the two cause more serious damage to microorganisms, so as to achieve a better sterilization effect.
4.3. Application of Ultrasonic-Assisted Slightly Acidic Electrolyzed Water in Aquatic Product Sterilization and Refrigeration
From the above content, it can be seen that both ultrasonic waves and SAEW have a sterilization effect.
Li et al. researched the synergistic effect and bactericidal mechanism of ultrasonic wave (US, 200 W, and 30 kHz) and SAEW (60 mg/L, and pH 6.2) treatments, as well as the correlation of mirror carp in cold storage (277.15 K). The study found that using ultrasound in conjunction with SAEW reduced water loss, lipid oxidation, and protein degradation in fresh fish during cold storage. The US + SAEW treatment significantly inhibited microbial growth and endogenous enzyme activity in refrigerated fish, as seen by changes in Pseudomonas properties. A study by Lan et al. introduced that US (20 kHz, 600 W, 600 s) + SAEW (30.0 ± 1.54 mg/L, pH:6.35 ± 0.04) treatment can keep refrigerated seabass fresh. Compared with SAEW or US treatment alone, US + SAEW therapy on sea bass inhibited protein degradation and microbial development, resulting in improved texture and sensory ratings. This combination treatment may extend the shelf life of sea bass by at least 4 days. The findings reveal that the US treatment enhances the ability of SAEW to decontaminate, prevents quality deterioration, and achieves a higher sensory score.
Accordingly, combined ultrasonic and SAEW treatment has a powerful and efficient bactericidal impact on microorganisms, and the findings support the therapy’s antibacterial mechanism, ability to keep fish fresh, and prolong the shelf life of food.
5. Conclusions
Ultrasonic treatment technology is capable of fully retaining the nutrients of aquatic products, and it shows the advantages of high efficiency and low energy consumption, consistent with consumers’ pursuit of a pollution-free, high-quality food consumption concept. SAEW is one of the most promising microbial control fungicides in the food industry, with strong broad-spectrum antibacterial and fungal activity. The synergistic treatment of ultrasonic waves and SAEW can exert a stronger sterilization effect than either treatment alone. Thus, this technology has promising prospects for development in the field of aquatic product processing.
However, the ultrasonic sterilization technology is not mature at present, and faces numerous challenges in terms of large-scale promotion and application. There is a lack of relevant standards and technical parameters for ultrasonic treatment of different aquatic products. When low-intensity ultrasound is employed alone, the killing effect on microorganisms is limited. Moreover, slightly acid electrolyzed water, as a broad-spectrum and efficient bactericide, has been extensively employed to sterilize and disinfect of aquatic products. However, the bactericidal effect of SAEW is correlated with a wide variety of factors (e.g., the mass concentration of available chlorine and treatment time. Relevant parameters should be determined in accordance with the characteristics of different types of aquatic products.
The combination of ultrasonic waves and SAEW with other physical, chemical, and biological technologies will be the future development trend of food sterilization and refrigeration technology to achieve rapid and effective sterilization, environmental protection, food quality improvement, and other purposes. Studying how to optimize the combination of sterilization and refrigeration technologies for different aquatic products and building the sterilization effect data can be beneficial to ensuring food safety and preventing adverse effects on aquatic product quality, while accelerating its industrialization and application.
Chlory's hypochlorous acid generator utilizes ultrasonic-assisted micro-acidic electrolysis technology to provide efficient sterilization solutions for the aquatic product processing industries in India, Malaysia, Vietnam, and Brazil. This ensures safety while significantly reducing energy consumption. Its innovative design perfectly meets the large-scale production needs of countries such as India, Malaysia, Vietnam, and Brazil, and helps customers enhance their international competitiveness with stable and reliable performance.
Contact
+86 15786688998
info@chlory.com