Application of Neutral Electrolyzed Water on pork chops and its impact on meat quality

Foodborne illness associated with pork products remains a significant concern due to microbial contamination, notably with Listeria monocytogenes. Conventional chemical decontaminants (e.g., organic acids, chlorine) can be effective but may affect meat quality attributes such as color, odor, and texture, and sodium hypochlorite use is restricted in several European countries. Electrolyzed Water (EW), particularly Neutral Electrolyzed Water (NEW), offers an alternative sanitizer with reported antimicrobial activity and minimal impacts on surfaces and the environment, reverting to water and ions post-use. NEW typically exhibits an ORP of 750–900 mV and is primarily composed of hypochlorous acid. The study aimed to evaluate whether spraying highly concentrated NEW onto pork chops can reduce high levels of L. monocytogenes or Salmonella Typhi contamination while preserving physicochemical quality parameters (color, pH, lactic acid, lipid oxidation) and quality indices (TVBN) during refrigerated storage.

Prior research has applied EW to various foods (lettuce, spinach, strawberries) and found it effective without significant negative effects on product quality and with low environmental impact. Studies report EW does not harm human mucosa, stainless steel (for neutral EW), or eggshell cuticles, and slightly acidic EW did not adversely affect chicken meat physicochemical and sensory characteristics. Regulations limit or ban sodium hypochlorite use in parts of Europe, motivating alternatives. Previous work with acidic or slightly acidic EW on pork demonstrated reductions in L. monocytogenes and other pathogens, with efficacy influenced by contact time and application method (dipping vs spraying). Some studies noted limited efficacy of neutral EW against certain pathogens in the presence of organic matter and improved results when samples were immersed or agitated during treatment. The literature also links meat color changes to oxidation states of myoglobin and recognizes TBARS and TVBN as indicators of lipid oxidation and freshness, respectively.

Bacterial strains: Listeria monocytogenes (ATCC 19115) and Salmonella Typhi (ATCC 9992) were used. L. monocytogenes was grown on Brain Heart Infusion agar at 37 °C for 24 h; S. Typhi on Salmonella Shigella agar. Identity confirmation employed Gram staining and the Vitek2 system. Overnight cultures in Trypticase Soy Broth (37 °C, 16 h) were prepared, serially diluted in PBS, plated on TSA, incubated 37 °C overnight, and CFU enumerated per Mexican Official Norm. Solutions: NEW was supplied commercially. NaClO was adjusted to 35 ppm (below allowed maxima) as disinfectant control; saline solution (SS) served as wash control. pH and ORP were measured (Hanna HI98121). Free chlorine was quantified with a portable photometer (HI96771) and by the iodometric method. In vitro bactericidal test: Following Mexican Norm NMX-BB-040-SCFI-1999, 99 mL of each solution was placed in sterile flasks; 1 mL of bacterial inoculum was added during shaking. After 30 s contact, 1 mL was transferred to 9 mL of 0.1% peptone water (neutralizer), serially diluted, plated on TSA, incubated 48 h at 37 °C, and surviving CFU enumerated. Pork chops: From UNAM’s CEIEPP herd (York-Pietrain × Duroc-Landrace), chops were cut to ~150 g, 90 pieces prepared, bagged, and stored at 4 °C. Artificial contamination: Two groups (n=45 each) were submerged 15 min in 10⁷ CFU/mL inocula of L. monocytogenes or S. Typhi in 0.1% peptone water, drained 5 min under biosafety cabinet conditions. Treatments: Contaminated chops were assigned to NEW, NaClO, or SS (n=15 each). Each chop was sprayed with 15 mL solution (half per side), with 60 s contact. Post-treatment, chops were massaged in 100 mL 0.1% peptone water for 1 min to recover bacteria; aliquots were plated for counts. Chops were stored at 4 °C, and bacterial recovery performed at days 1 and 8. Non-contaminated chops (n=45) were similarly treated and stored for physicochemical analyses at days 1, 3, 5, 12, and 19; total aerobic viable counts at days 1 and 8. Bacterial analyses: Most probable number methodology and CFU counts (adjusted by dilution) were used; percent reduction relative to SS was computed. Color: CIELab parameters (L, a, b) were measured with a Konica Minolta CM-600d at five random zones per chop pre- and post-treatment; ΔE was calculated and tracked at days 0, 1, 5, 12, 19. pH: Measured potentiometrically per Mexican Norm after homogenizing 10 g sample in 100 mL water at 20±0.5 °C. Lactic acid: Determined by titration per NMX-F-102-NOR-MEX-2010 using phenolphthalein indicator and 0.1 N NaOH; percent lactic acid computed. TBARS: Quantified as mg MDA/kg using TCA extraction, reaction with thiobarbituric acid, absorbance at 530 nm, and MDA standard curve. TVBN: Quantified following Chen’s method using diffusion of volatiles into boric acid/glycerin, titration with 0.01 N HCl, and expression as mg N/100 g. Statistics: Normality assessed; two-way ANOVA with Tukey’s HSD (α=0.05). Pearson correlations examined relationships among pH, lactic acid, TBARS, TVBN, and color parameters. Analyses used GraphPad Prism 7.00.

Solution characteristics: NEW pH 6.92±0.06, ORP 820±9.3 mV, free chlorine 58.0±2.0 ppm; NaClO pH 7.36±0.28, ORP 790±20.19 mV, free chlorine 35.0±0.59 ppm; SS pH 5.71±0.30, ORP 371±14.76 mV, no detectable chlorine. In vitro bactericidal activity: For L. monocytogenes, SS control showed 7.93±0.024 log CFU/mL; both NEW and NaClO reduced detectable counts to <3 log CFU/mL (>4.9 log reduction; P<0.0001 vs SS). For S. Typhi, SS 9.3±0.03 log CFU/mL; NEW and NaClO reduced to <3 log CFU/mL (>6.3 log reduction; P<0.0001 vs SS). In situ on contaminated pork (spray, 60 s): - L. monocytogenes at 24 h: SS 5.52±0.035 log CFU/g; NEW 4.883±0.085 (−0.637 log vs SS); NaClO 4.899±0.064 (−0.621 log vs SS). NEW and NaClO both significantly lower than SS (P<0.0001), not different from each other. - L. monocytogenes at 8 days: SS 7.945±0.03; NEW 6.885±0.06 (−1.06 log); NaClO 6.777±0.112 (−1.168 log). Both treatments significantly lower than SS (P<0.0001); greater reductions at day 8 than day 1 (P<0.0001). - S. Typhi at 24 h: SS 5.12±0.21; NEW 4.65±0.27 (−0.47 log); NaClO 4.82±0.27 (−0.30 log). No significant differences versus SS. - S. Typhi at 8 days: SS 5.29±0.33; NEW 5.51±0.14; NaClO 5.09±0.34. No significant reductions observed across groups. Total aerobic viable counts (non-contaminated pork): 24 h SS 6.00±0.11; NEW 5.74±0.12; NaClO 5.67±0.08 (small decreases vs SS). At 8 days: SS 7.26±0.05; NEW 7.19±0.11; NaClO 7.32±0.09 (no meaningful advantage). Color (CIELab): NEW caused minimal color change. ΔE values were lowest for NEW and NaClO from days 5–19 compared with SS, indicating reduced overall color change under refrigeration. L, a, b parameter trends showed NEW often maintaining higher a (redness) values without significant time-related deterioration compared with controls. pH and lactic acid: pH remained relatively stable across treatments from day 1 to 19. Lactic acid increased over time in all groups, but SS exhibited significantly higher lactic acid from day 5 onward; NEW and NaClO limited lactic acid accumulation (P<0.01 vs SS). TBARS (lipid oxidation): TBARS rose up to day 5 then stabilized for all treatments. NEW and NaClO showed higher TBARS than SS early, consistent with higher ORP, but all remained below the off-flavor threshold of 0.5 mg MDA/kg and far below the 2 mg MDA/kg consumption limit. TVBN (freshness indicator): TVBN increased with storage time, but NEW consistently yielded lower or slower increases, with significant differences emerging from day 3 onward and the lowest values at day 19 among treatments, indicating slowed decomposition. Overall: NEW’s antimicrobial efficacy on pork was strong against L. monocytogenes but limited against Salmonella Typhi under the tested spray application and organic load. NEW preserved color better than SS, restrained lactic acid and TVBN increases, and modestly increased lipid oxidation without exceeding quality thresholds.

The study addressed whether Neutral Electrolyzed Water can effectively decontaminate pork while preserving quality. NEW exhibited potent in vitro bactericidal activity and achieved significant in situ reductions of L. monocytogenes on pork at both 24 h and 8 days compared with a saline wash, aligning with prior reports of EW efficacy against gram-positive organisms. However, reductions against Salmonella Typhi were minimal or non-significant, particularly over storage, suggesting that organic matter on meat surfaces and the spray application method reduced efficacy against this gram-negative pathogen. Despite this limitation, NEW did not negatively affect pH or cause undesirable color changes; in fact, NEW and NaClO reduced overall color change (lower ΔE) compared with SS during refrigerated storage. NEW also mitigated lactic acid accumulation and TVBN formation, indicating slower microbial spoilage and protein degradation, beneficial for shelf-life and product quality. While TBARS increased slightly with NEW and NaClO, values remained well below sensory and safety thresholds, indicating no practical deterioration in lipid stability. Collectively, NEW can serve as an alternative sanitizer comparable to NaClO in antimicrobial performance against L. monocytogenes, with additional benefits for maintaining pork quality during storage, though method of application and organic load are critical determinants of performance against diverse pathogens.

NEW demonstrated high antibacterial activity against L. monocytogenes in vitro and on highly contaminated pork chops, with performance comparable to sodium hypochlorite. Under refrigerated storage (4 °C), NEW helped preserve meat quality by limiting overall color change, restraining lactic acid and TVBN increases, and maintaining pH, while only slightly increasing lipid oxidation, remaining below sensory and safety thresholds. Organic matter presence appeared to compromise NEW’s activity, especially against Salmonella Typhi. NEW shows promise as an effective alternative for decontaminating pork, carcasses, and processing environments. Future work should evaluate different application modes (spray versus dip), contact times, broader pathogen panels, and real-world contamination scenarios to optimize efficacy.

- Efficacy against Salmonella Typhi was limited under the tested spray application and in the presence of organic matter on pork surfaces. - Only spray application with fixed contact time (60 s) was evaluated; dipping or extended contact may yield different results. - High artificial inoculum levels were used, which may not reflect typical industry contamination loads. - The study focused on specific strains and on pork chops; generalizability to other meats, cuts, and broader microbial communities was not assessed. - Physicochemical quality was measured, but comprehensive sensory evaluations were not reported.