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Electrolyzed Water and Its Application in the Food Industry

Electrolyzed water (EW) is gaining popularity as a sanitizer in the food industries of many countries. By electrolysis, a dilute sodium chloride solution dissociates into acidic electrolyzed water, AEW (Anolyte), which has a pH of 2 to 3, an oxidation reduction potential of 1,100 mV, and an active chlorine content of 10 to 90 ppm, and basic electrolyzed water, BEW (Catholyte), which has a pH of 10 to 13 and an oxidation-reduction potential of 800 to 900 mV. Vegetative cells of various bacteria in suspension were generally reduced by 6.0 log CFU/ml when AEW was used…

Cleaning and sanitizing are important elements of the hygiene practices in a food processing plant. Typical sanitizers applied in the food industry include chlorine compounds, organic acids, trisodium phosphate, iodophores, and quaternary ammonium compounds. Chlorine compounds are often the most effective, although they may be more corrosive and irritating than alternatives such as iodine and quaternary ammonium compounds. Chemical substances also are used for decontamination of certain food products.

In the United States, decontamination treatments with certain antimicrobials have been authorized for carcasses, but such treatments are not permitted at present in the European Union. Some of these procedures have been found unacceptable because of chemical residues, high cost, limited effectiveness, or discoloration of products. Currently, electrolyzed water (EW) is gaining popularity as a sanitizer in the food industry to reduce or eliminate bacterial populations on food products, food-processing surfaces, and non–food contact surfaces. In Japan, the Health, Labor and Welfare Ministry has approved EW as a food additive.

EW generators also have been approved for use in the food industry by the U.S. Environmental Protection Agency. The purpose of this review is to provide an overview of issues related to EW, its antimicrobial activity, and its application in the food industry.

CONCEPT OF EW

History. The concept of Electrolyzed water (EW) was originally developed in Russia, where it has been used for water decontamination, water regeneration, and disinfection in medical institutions. Since the 1980s, EW also has been used in Japan. One of the first applications of EW was the sterilization of medical instruments in hospitals. Later, it was utilized in various fields such as agriculture or livestock management, but the use of EW has been restricted by its short shelf life. With recent improvements in technology and the availability of better equipment, EW has gained popularity as a disinfectant in the food industry.

Generation. EW is the product of the electrolysis of a dilute NaCl or KCl-MgCl2 solution in an electrolysis cell, within which a diaphragm (septum or membrane) separates the anode and cathode. The basic approach for producing EW is shown in Figure 1. The voltage between the electrodes is generally set at 9 to 10 V (5). During electrolysis, NaCl dissolved in deionized water dissociates into negatively charged chlorine (Cl-) and positively charged sodium (Na+). At the same time, hydroxide (OH-) and hydrogen (H+) ions are formed. Negatively charged ions such as Cl- and OH- move to the anode to give up electrons and become oxygen gas (O2), chlorine gas (Cl2), hypochlorite ion (OCl-), hypochlorous acid (HOCl), and hydrochloric acid, and positively charged ions such as H+ and Na+ move to the cathode to take up electrons and become hydrogen gas (H2) and sodium hydroxide (NaOH).

 

The solution dissociates into an acidic solution from the anode, with a pH of 2 to 3, an oxidation-reduction potential (ORP) of >1,100 mV, and an active chlorine content (ACC) of 10 to 90 ppm, and a basic solution from the cathode, with a pH of 10 to 13 and an ORP of -800 to -900 mV. The solution from the anode is called acidic electrolyzed water (AEW), acid oxidizing water, or electrolyzed oxidizing water, and the cathodic solution is known as basic electrolyzed water (BEW), alkaline electrolyzed water, or electrolyzed reducing water.

Neutral electrolyzed water (NEW), with a pH of 7 to 8 and an ORP of 750 mV, is produced by mixing the anodic solution with OH- ions or by using a single-cell chamber. Various EW-producing machines are available in the market. Generally, machines can be divided into those that contain a diaphragm and produce AEW and BEW (two-cell chamber) and those that do not contain a diaphragm and therefore produce NEW (single-cell chamber).

The physical properties and chemical composition of EW vary depending on the concentration of NaCl, amperage level, time of electrolysis, or water flow rate. Based on their control systems, machines allow the users to select (i) the brine flow rate, (ii) the amperages and/or voltages, or (iii) a preset chlorine concentration.

General application. AEW has strong antimicrobial activity against a variety of microorganisms. It may have a wide range of applications such as medicine (e.g., treatment of wounds or disinfection of medical equipment and surfaces), dentistry, agriculture, livestock management, aquaculture, and food industries.

BEW is mostly used as cleanser and degreaser before treatment with disinfecting agents. BEW also has a strong reducing potential that is responsible for the reduction of free radicals. In some applications, pretreatment with BEW followed by treatment with AEW was more effective than AEW treatment only. Pretreatment with BEW seems to sensitize bacterial cell surfaces to the disinfecting agent…..

Antimicrobial activity of AEW. It is not clear whether pH, chlorine compounds, ORP, or combinations of these factors are responsible for the antimicrobial activity of AEW. The presence of chlorine and a high ORP seem to be the main contributors to the antimicrobial activity of AEW. The low pH of AEW is believed to reduce bacterial growth and make the bacterial cells more sensitive to active chlorine by sensitizing their outer membrane to the entry of HOCl.

Active chlorine compounds can destroy the membranes of microorganisms, but other modes of chlorine action (e.g., decarboxylation of amino acids, reactions with nucleic acids, and unbalanced metabolism after the destruction of key enzymes) also have been proposed. Studies suggest that HOCl is the most active of the chlorine compounds. HOCl penetrates cell membranes and produces hydroxyl radicals, which exert their antimicrobial activity through the oxidation of key metabolic systems.

The relative fractions of chlorine compounds (Cl2, HOCl, and OCl-) are pH dependent and affect the bactericidal activity of AEW. The highest proportion of HOCl and maximal efficiency of AEW for inactivating bacteria was found at a pH of about 4.0 to 5.0. More Cl2 was present at lower pH values, and more OCl- was present at higher pH values. The bactericidal activity of AEW and ORP increase with active chlorine concentrations, indicating that chlorine is a strong oxidizing agent.

Complete inactivation of Escherichia coli O157:H7 and Listeria monocytogenes was reported at ACCs of 2 ppm or higher, regardless of pH. Some authors have suggested that the high ORP is the determining factor for the antimicrobial activity of AEW. Al-Haq et al. reported that inactivation of E. coli was primarily dependent on ORP and not on residual chlorine. The ORP of a solution is an indicator of its ability to oxidize or reduce, with higher ORP values corresponding to greater oxidizing strength. The high ORP of AEW may be due to the oxygen released by the rupture of the weak and unstable bond between the hydroxy and chloric radicals.

The high ORP probably changes the electron flow in the cells. Oxidation due to the high ORP of AEW may damage cell membranes, cause the oxidation of sulfhydryl compounds on cell surfaces, and create disruption in cell metabolic processes, leading to the inactivation of bacterial cells. Basically, the high ORP and low pH of AEW seem to act synergistically with HOCl to inactivate microorganisms. Besides, complete loss of bactericidal activity was observed when ORP decreased to less than 848 mV.

ANTIMICROBIAL ACTIVITY OF EW AGAINST MICROORGANISMS IN SUSPENSION
The antimicrobial activity of AEW and NEW against various microorganisms is shown in Table 1. Generally, reductions of 6.0 log CFU/ml were reported for a variety of bacteria. The effectiveness of EW for reducing microorganisms is influenced by several factors such as type of EW, ACC, exposure time, treatment temperature, pH, and amperage or voltage…

ANTIMICROBIAL ACTIVITY OF EW AGAINST MICROORGANISMS ON SURFACES AND UTENSILS

Cutting boards. Venkitanarayanan et al. examined the efficiency of AEW at different temperatures and ACCs for inactivating E. coli O157:H7 and L. monocytogenes on plastic cutting boards. The highest reductions were obtained for E. coli O157:H7 at 35C for 20 min, 45C for 10 min, or 55C for 5 min and for L. monocytogenes at 35C for 10 min. Vibrio parahaemolyticus was reduced from 5.8 to less than 1.0 log CFU/cm2 after 1 min of exposure to AEW. By rinsing plastic cutting boards with NEW, E. coli, S. aureus, P. aeruginosa, and L. monocytogenes were reduced by about 5 orders of magnitude. Wooden cutting boards are considered more difficult to sanitize than plastic boards. Because of its physical structure, wood is able to absorb moisture and protect bacteria from disinfecting agents. However, certain wood species have endogenous antibacterial properties, resulting in the desiccation of bacteria as a result of hygroscopic characteristics. Rinsing wooden cutting boards with NEW for 1 min reduced populations of E. coli, S. aureus, P. aeruginosa, and L. monocytogenes by less than 3 orders of magnitude magnitude. Extending the exposure time to 5 min yielded reductions of about 4 orders of magnitude…

Processing gloves. Liu and Su analyzed the effects of AEW on reusable and disposable gloves (natural rubber latex, natural latex, and nitrile) and on clean and soiled gloves. L. monocytogenes was completely inactivated on each glove type after 5 min of treatment…

Stainless steel, tiles, glass, and vitreous china. On stainless steel, application of AEW for 5 min yielded reductions of 1.8 to 3.7 orders of magnitude. Populations of V. parahaemolyticus were reduced by more than 5.0 log CFU/cm2 within only 0.5 min. In the presence of organic matter (crab meat residues), L. monocytogenes was reduced by 2.3 orders of magnitude. On tiles, application of AEW for 5 min yielded reductions of 1.8 to 4.2 orders of magnitude. Populations of V. parahaemolyticus were reduced by more than 5.0 log CFU/cm2 within less than 1 min. In the presence of organic matter, L. monocytogenes was reduced by
1.5 to 2.3 orders of magnitude. Results from vitreous china were comparable with those from stainless steel, tiles, or glass. With agitation, Enterobacter aerogenes and S. aureus were reduced to nondetectable levels (3.0 log CFU/cm2) on vitreous china.

Biofilms. Biofilms are a structured community of bacterial cells enclosed in a self-producing polymer matrix (glycocalyx), which is a protected mode of growth on surfaces and allows survival in hostile environments. The higher resistance of bacteria in biofilms to sanitizers has been attributed to various factors such as protection by the matrix, neutralization of the sanitizer, genetic modification
of the cell wall, and slow uptake of antimicrobial agents. Only limited data exist on the efficiency of EW for inactivating bacteria in biofilms. Kim et al. found that AEW reduced L. monocytogenes in biofilms on stainless steel to nondetectable levels within 5 min. The highest inactivation rate was reported within the first seconds of treatment…

Abattoirs. Bach et al. (9) compared the effectiveness of AEW and a common sanitizer (Mikrolene) for the use in abattoirs. After standard precleaning, AEW was more effective for inactivating bacteria in various slaughterhouse areas. During the slaughter of cattle, the contamination risk associated with the hide is of special concern. Both saprophytes and pathogens such as E. coli O157:H7 can be transferred to the carcass during dehiding (6, 70, 73, 89). In addition to the maintenance and optimization of slaughter hygiene practices, decontamination treatments for hides have been established (10, 49, 96). Bosilevac et al. (15) used a high-pressure spray treatment of BEW (52C for 10 s at pH 11.2) and AEW (60C for 10 s at pH 2.4 and an ACC of 70 ppm) on cattle hides. The results were comparable to those obtained with other hide treatments; total microbial counts and Enterobacteriaceae counts were reduced by 3.5 and 4.3 log CFU/100 cm2, respectively…

ANTIMICROBIAL ACTIVITY OF EW AGAINST MICROORGANISMS IN PROCESSING WATER
Water washing is widely used for produce and minimally processed vegetables, and accumulation of microorganisms
in the processing water must be prevented. Ongeng et al. investigated the effect of the electrolysis procedure on water used for the washing of vegetables, and the antimicrobial activity against Pseudomonas fluorescens, Pantoea agglomerans, and Rahnella aquatilis was tested. Industrial processing water, which had a higher microbial load (8.0 log CFU/ml) and organic load than did tap water, had a microbial load of 6.0 log CFU/ml after electrolysis with the attainable amperage of 0.7 A (ACC of 1.1 ppm). When salt was added to the water (5 ml of 20% NaCl per 10 liters), the tested bacteria were reduced by about 4 orders of magnitude. By raising the amperage to 1.3 A, which generated ACCs above 2 ppm, complete inactivation was achieved. AEW produced with tap water had stronger antimicrobial activity than did AEW produced with processing water…

ANTIMICROBIAL ACTIVITY OF EW AGAINST MICROORGANISMS ON FOOD PRODUCTS

Vegetables and fruits. On strawberries, AEW treatment for 10 min achieved a reduction of naturally present aerobic bacteria, coliforms, and fungi by 1.6, 2.4, and 1.6 log CFU per strawberry, respectively, to nondetectable levels. Similar reductions also were obtained on cucumbers. The combined treatment with BEW and AEW yielded higher reductions for cucumbers but not for strawberries. The results for strawberries are in agreement with those of other studies. Longer exposure times were required for sanitizers to infiltrate the strawberry surface, probably because of the complex surface structure. On tomatoes, AEW reduced E. coli O157: H7, L. monocytogenes, and Salmonella Enteritidis by about 7.5 log CFU per tomato.

After application to lettuce of AEW containing only 3.6 ppm of active chlorine, Ongeng et al. observed 2.6-, 1.9-, and 3.3-log reductions of Enterobacteriaceae, lactic acid bacteria, and psychrotrophs, respectively. Park et al. reported similar reductions of E. coli O157:H7 (2.8 log CFU per leaf) and L. monocytogenes (2.4 log CFU per leaf) after AEW treatment. AEW was as effective as chlorine for reducing E. coli O157:H7, Salmonella, and L. monocytogenes on leafy greens. Thus, AEW may be used as a suitable alternative to chlorine for the treatment of leafy greens.

In another study, the effects of temperature and BEW pretreatment on the efficiency of AEW against E. coli O157:H7 and Salmonella on lettuce were examined. Higher temperature (50°C) and/or exposure time (5 min) yielded greater reductions. BEW pretreatment at room temperature for 5 min increased the reductions by about 0.5 order of magnitude.

The greatest reductions were obtained at a pretreatment temperature of 50°C regardless of the duration or temperature of the AEW treatment. Yang et al. examined the effects of BEW and AEW (30°C for 5 min at pH 9 or 4, an ORP of -750 or 1,150 mV, and an ACC of 22 to 198 ppm) on biofilms attached to lettuce leaves. E. coli O157: H7, L. monocytogenes, and Salmonella Typhimurium were reduced by about 2 orders of magnitude…

Fish and seafood. On carp skin treated for 15 min with AEW, total microbial counts were reduced by 2.8 log CFU/ cm2. On tilapia skin immersed in AEW, greater reductions were obtained for V. parahaemolyticus than for E. coli O157:H7. On carp filets treated for 15 min with AEW, total microbial counts were reduced by 2.0 log CFU/g. AEW treatment of tuna filets yielded reductions of the natural microflora by about 1 order of magnitude.

Ozer and Demirci reported reductions of E. coli O157:H7 and L. monocytogenes on salmon filets ranging from 0.4 to 1.1 log CFU/g, depending on exposure time and temperature. To investigate the antimicrobial effect of AEW on oysters, inoculated oysters were placed into tanks containing AEW (ACC of 30 ppm), and the AEW salt concentration was set at 1%.

After 4 h of exposure, V. parahaemolyticus and Vibrio vulnificus were reduced by about 1 order of magnitude. Further exposure did not increase the reductions. Probably because of the unfavourable growth environment, oysters eventually stopped filtering water, thereby hampering the entry of AEW.

Carcasses, raw meat, and ready-to-eat meat. Fabrizio et al. compared the effect of AEW solutions for immersion and spray washing of chicken carcasses. Immersion of carcasses in AEW (4°C for 45 min) reduced aerobic bacteria, total coliforms, E. coli, and Salmonella Typhimurium by 0.8 to 1.3 log CFU/ml of carcass rinsate. Reductions obtained by spray washing (15 s) with AEW or distilled water did not differ significantly. Spray washing with BEW followed by immersion in AEW yielded greater reductions of 1.5 to 2.4 log CFU/ ml.

Spray treatment with BEW was as effective for removing fecal material as was the commonly used treatment with trisodium phosphate. Moreover, the results of Hinton et al. suggested that AEW treatment extended the shelf life of refrigerated poultry. Kim et al. investigated the effectiveness of AEW for reducing C. jejuni on chicken carcasses. Reductions of 2.3 log CFU/g were obtained by immersion, but additional prespraying did not improve the efficiency. Spray treatment alone reduced C. jejuni by 1.1 log CFU/g. However…

On fresh chicken wings, AEW reduced C. jejuni by about 3 orders of magnitude and was therefore as effective as chlorine water. Gellynck et al. analyzed the economics of reducing Campylobacter to different levels within the poultry meat chain (farm, processing plant, and consumer) and found that the decontamination of carcasses with AEW in the processing plant was the most efficient (cost-benefit ratio) of the evaluated measures.

Fabrizio and Cutter investigated the effectiveness of AEW spray treatment on pork bellies for reducing total microbial counts and Campylobacter coli, coliform, E. coli, L. monocytogenes, and Salmonella Typhimurium counts. Only the effect of AEW against Campylobacter differed significantly from that obtained with distilled water (1.8 log CFU/cm2)…

Eggs. Electrostatic spraying of shell eggs with AEW (hourly for 24 h) reduced E. coli, S. aureus, and Salmonella Typhimurium by 3 to 6 orders of magnitude (Table 5), whereas L. monocytogenes was reduced by 1.0 to 4.0 log CFU per egg (92). In another study, immersion of eggs in AEW for 5 min with agitation (100 rpm) reduced L. monocytogenes and Salmonella Enteritidis by 3.7 and 2.3 log CFU per egg, respectively (85). Prewash with BEW yielded reductions of 3.0 log CFU per egg after shorter exposure times (Table 6).

Application of AEW as ice. AEW may be applied as solution or ice. Frozen AEW was tested on lettuce and pacific saury. The main antimicrobial effect of frozen AEW was attributed to the emitted Cl2. Cl2 emission in frozen AEW was proportional to the ACC before freezing…

On iceberg lettuce placed into containers with frozen AEW (pH 2.6), 1.5-log reductions of L. monocytogenes were observed, and no significant differences were found at ACCs of 40 and 70 ppm…

The best results were obtained after an exposure time of 120 min. Longer exposure did not lead to further reductions. Frozen AEW may serve simultaneously for refrigeration and control of pathogens.

In another study, frozen AEW (pH 5.1 and ACC of 47 ppm) was used on pacific saury to extend shelf life, suppress lipid oxidation and the formation of volatile basic nitrogen, and retard the accumulation of alkaline compounds. In this study, the storage of saury in frozen tap water and frozen AEW were compared. The growth of aerobic bacteria and psychrotrophs was slower and growth of coliforms did not occur when saury was stored with frozen AEW…

Cit. (D. HRICOVA, R. STEPHAN,* AND C. ZWEIFEL)