Efficacy of antimicrobial interventions in reducing Salmonella enterica, Shiga toxin-producing Escherichia coli, Campylobacter, and Escherichia coli biotype I surrogates on non-chilled and chilled, skin-on and skinless pork

Fresh pork microbiota is temporally dynamic and compositionally diverse across meat, contact surfaces, and processing lines in a pork processing facility

The goal of this study was to analyze the microbial profiles of meat and contact surfaces from two different processing lines in a pork processing plant, using a 16S rRNA gene amplicon sequencing workflow specifically designed to investigate fresh meat and environmental samples throughout a commercial production schedule. Results indicated that the microbiota differed between the meat and contact surface, both across the two processing lines and within each individual processing line. Differences in the microbiota composition were also strongly associated with both the specific processing dates and the time of day during processing. Much of this variation was associated with distinct amplicon sequence variants unique to each processing date and each processing line throughout the day. The abundance of key taxa associated with food safety and spoilage was also temporally dynamic across a production shift and was different between the meat and contact surface. Overall, the results of this study indicate significant differences in the microbial profiles of the meat and contact surfaces between two processing lines within the same plant. These differences are likely influenced by daily variation in processing and sanitation procedures, as well as differences in the design of the processing lines, which appear to affect the microbiotas of both the meat and contact surfaces.IMPORTANCEThis study provides critical knowledge that can be used as a foundation for tailored processes to improve fresh pork safety and quality, potentially customized to individual processing lines, time points within a shift, and/or production days. Additionally, this study provides a list of potential biological markers associated with food safety and quality that could be used by processors to develop and validate intervention strategies specific to different processing lines.

Differences in Salmonella Serovars Response to Lactic Acid and Peracetic Acid Treatment Applied to Pork

Pathogen control in the meat industry relies on the effectiveness of postharvest interventions in reducing microbial populations. This study investigated differences in the survival of Salmonella serovars when exposed to organic acids used as antimicrobials on raw pork meat. Seven serovars were included in this study (S. Newport, S. Kentucky, S. Typhimurium, S. Dublin, S. Heidelberg, S. Infantis, and S. Enteritidis). Multistrain serovar cocktails were prepared and tested against lactic acid (LA) and peracetic acid PAA at two concentrations, LA 2 and 4% and PAA 200 and 400 ppm. Pork samples were assigned to each serovar, inoculated with 6.0 Log CFU/cm2Salmonella (one serovar at a time), and treated with the corresponding antimicrobials. A two-way analysis of variance was conducted to examine the effects of serovar and antimicrobial concentrations on Salmonella survival. A significant main effect of serovar was identified, indicating that Salmonella concentration and reduction rate were significantly affected by serovar. Similarly, a significant main effect of antimicrobials was observed, suggesting that the treatment types impacted Salmonella concentration and reduction rate. However, the interaction effect between serovar and antimicrobial was not significant. Posthoc comparisons indicate that PAA 400 ppm is more effective at reducing Salmonella concentrations and that S. Dublin may be more susceptible than S. Newport to antimicrobial sprays. Additionally, under PAA exposure, only S. Dublin, S. Kentucky, and S. Heidelberg showed statistically significant differences (P < 0.05) compared with the control, indicating that these three serovars are more susceptible to PAA treatments than the rest. The behavior of different Salmonella serovars under stress conditions can give us an insight into how these pathogens survive processing.

Potential Application of Ovalbumin Gel Nanoparticles Loaded with Carvacrol in the Preservation of Fresh Pork

Plant essential oil has attracted much attention in delaying pork spoilage due to its safety, but its low antibacterial efficiency needs to be solved by encapsulation. Our previous research had fabricated a type of ovalbumin gel nanoparticles loaded with carvacrol (OCGn-2) using the gel-embedding method, which had a high encapsulation rate and antibacterial activity. The main purpose of this study was to further evaluate the stability and slow-release characteristics of OCGn-2 and potential quality effects of the nanoparticles on the preservation of fresh pork pieces during 4 °C storage. The particle test showed that the nanoparticles had better heat stability below 85 °C and salt stability below 90 mM. The in vitro release study indicated that the carvacrol in OCGn-2 followed a Fickian release mechanism. The pork preservation test suggested that the OCGn-2 coating treatments could remarkably restrict the quality decay of pork slices compared to free carvacrol or a physical mixture of ovalbumin and carvacrol treatment. Nano-encapsulation of ovalbumin is beneficial to the sustained release, enhanced oxidation resistance, and improved antibacterial activity of carvacrol. The study suggested that ovalbumin gel nanoparticles embedded with carvacrol could be applied as an efficient bacterial active packaging to extend the storage life of pork.

Use of Doehlert Matrix as a Tool for High-Throughput Screening of Organic Acids and Essential Oils on Miniaturized Pork Loins, Followed by Lab-Scale Validation That Confirmed Tested Compounds Do Not Show Synergistic Effects against Salmonella Typhimurium

The many possible treatments and continuously changing consumer trends present a challenge when selecting antimicrobial interventions during pork processing. Thirty-five potential antimicrobials were screened at commercial working concentrations by individually adding them to miniaturized (69 cm3) disks of pork loin ends, followed by inoculation with Salmonella Typhimurium ATCC 19585. Two organic acids and nine essential oils significantly inhibited Salmonella counts on pork (p < 0.05). However, six compounds that represent different levels of significance (p < 0.05-p < 0.0001) were selected as independent variables to build a Response Surface Methodology model based on a Doehlert matrix (Doehlert Matrix-RSM): lactic acid 1.25%, formic acid 0.25%, cumin 0.25%, clove 0.25%, peppermint 0.5%, and spearmint 0.5%. The goal of the Doehlert Matrix-RSM was to study single and paired effects of these antimicrobials on the change in Salmonella over 24 h. The Doehlert Matrix-RSM model predicted that lactic acid, formic acid, cumin, peppermint, and spearmint significantly reduced Salmonella when added alone, while no significant interactions between these antimicrobials were found. A laboratory-scale validation was carried out on pork loin end slices, which confirmed the results predicted by the model. While this screening did not identify novel synergistic combinations, our approach to screening a variety of chemical compounds by implementing a miniaturized pork loin disk model allowed us to identify the most promising antimicrobial candidates to then formally design experiments to study potential interactions with other antimicrobials.

Efficacy of Antimicrobial Spray Treatments in Reducing Salmonella enterica Populations on Chilled Pork

Studies reporting on alternative antimicrobial interventions for pathogen control on chilled pork carcasses and cuts are limited. In this study, the antimicrobial effects of various spray treatments against Salmonella enterica inoculated on skin-on pork samples were evaluated. Chilled pork jowls were portioned (10 by 5 by 1 cm) and inoculated, on the skin side, with a mixture of six S. enterica serotype strains to target levels of 6 to 7 log CFU/cm² (high inoculation level) or 3 to 4 log CFU/cm² (low inoculation level). Samples were then left nontreated (control) or were treated (10 s) using a laboratory-scale spray cabinet with water, formic acid (1.5%), a proprietary blend of sulfuric acid and sodium sulfate (SSS, pH 1.2), peroxyacetic acid (PAA, 400 ppm), or PAA (400 ppm) that was pH-adjusted (acidified) with acetic acid (1.5%), formic acid (1.5%), or SSS (pH 1.2). Samples (n = 6) were analyzed for Salmonella populations after treatment application (0 h) and after 24 h of refrigerated (4°C) storage. Irrespective of inoculation level, all spray treatments effectively reduced (P < 0.05) Salmonella levels immediately following their application. Overall, pathogen reductions for the chemical treatments, compared to the respective high and low inoculation level nontreated controls, ranged from 1.2 to 1.9 log CFU/cm² (high inoculation level) and 1.0 to 1.7 log CFU/cm² (low inoculation level). Acidification of PAA with acetic acid, formic acid, or SSS did not (P ≥ 0.05) enhance the initial bactericidal effects of the nonacidified PAA treatment. Salmonella populations recovered from all treated samples following 24 h of storage were, in general, similar (P ≥ 0.05) or up to 0.6 log CFU/cm² lower (P < 0.05) than those recovered from samples analyzed immediately after treatment application. The results of the study may be used by processing establishments to help identify effective decontamination interventions for reducing Salmonella contamination on pork.

Antagonistic activity of synbiotics: Response surface modeling of various factors

Synbiotic compositions have a great potential for curing microbial intestinal infections. Novel targeted synbiotics are a promising field of the modern functional food industry. The present research assessed the effect of various fructan fractions, initial probiotic counts, and test strains on the antagonistic properties of synbiotics. The research involved powdered roots of Arctium lappa L. and strains of Bifidobacterium bifidum, Bacillus cereus, and Salmonella enterica. The experiment was based on the central composite rotatable design. A water extract of A. lappa roots was purified and concentrated. Fructan fractions were precipitated at various concentrations of ethanol, dried, and sub jected to carbon-13 nuclear magnetic resonance (13C-NMR) spectrometry. The bifidobacteria and the test strains were co-cultivated in the same medium that contained one of the fractions. Co-cultivation lasted during 10 h under the same conditions. The acid concentrations were determined by high-performance liquid chromatography to define the synbiotic factor. The obtained fructans were closer to commercial oligofructose in terms of the number and location of NMR peaks. However, they were between oligofructose and inulin in terms of signal intensity. The response surface analysis for bacilli showed that the minimal synbiotic factor value corresponded to the initial probiotic count of 7.69 log(CFU/mL) and the fructan fraction precipitated by 20% ethanol. The metabolites produced by the bacilli also affected their growth. The synbiotic factor response surface for the experiments with Salmonella transformed from parabolic to saddle shape as the initial test strain count increased. The minimal synbiotic factor value corresponded to the lowest precipitant concentration and the highest probiotic count. The research established a quantitative relationship between the fractional composition of fructans and the antagonistic activity of the synbiotic composition with bifidobacteria. It also revealed how the ratio of probiotic and pathogen counts affects the antagonism. The proposed approach can be extrapolated on other prebiotics and microbial strains in vivo.

Salmonella spp. Response to Lytic Bacteriophage and Lactic Acid on Marinated and Tenderized Raw Pork Loins

Bacterial food poisoning cases due to Salmonella have been linked with a variety of pork products. This study evaluated the effects of a Salmonella-specific lytic bacteriophage and lactic acid (LA) on Salmonella Enteritidis, Salmonella Montevideo, and Salmonella Heidelberg growth on raw pork loins. Pork loins were cut into approximately 4 cm thick slices. Pork slices were randomly assigned to five treatment groups (control, DI water, LA 2.5%, phage 5%, and LA 2.5% + phage 5%) with six slices per group per replication. Pork loins were inoculated with 106 CFU/mL of Salmonella spp. and stored at 4 °C for 30 min. After 1 h of treatment application and marination, phage 5% significantly (p < 0.05) reduced the surface bacterial population by 2.30 logs when compared with the control group. Moreover, the combined treatment of LA 2.5% + phage 5% significantly (p < 0.05) reduced the surface bacterial population by more than 2.36 logs after 1 h of marination. In the post-tenderization surface samples, the combination of both phage and LA showed a significant reduction (p < 0.05) when compared with the control group. However, the treatments had no effect (p > 0.05) when analyzing the translocation of pathogens on pork loins.

Differences in biofilm formation of Salmonella serovars on two surfaces under two temperature conditions

AIMS

Salmonella is extremely diverse, with >2500 serovars that are genetically and phenotypically diverse. The aim of this study was to build a collection of Salmonella isolates that are genetically diverse and to evaluate their ability to form biofilm under different conditions relevant to a processing environment.

METHODS AND RESULTS

Twenty Salmonella isolates representative of 10 serovars were subtyped using Clustered regularly interspaced short palindromic repeats (CRISPR)-typing to assess the genetic diversity between isolates of each serovar. Biofilm formation of the isolates on both plastic and stainless-steel surfaces at 25 and 15°C was assessed. At 25°C, 8/20 isolates each produced strong and moderate biofilm on plastic surface compared to stainless-steel (3/20 and 13/20 respectively). At 15°C, 5/20 produced strong biofilm on plastic surface and none on stainless-steel. Several isolates produced weak biofilm on plastic (11/20) and stainless-steel (16/20) surfaces. Serovar Schwarzengrund consistently produced strong biofilm while serovars Heidelberg and Newport produced weak biofilm.

CONCLUSION

These results suggest that Salmonellae differ in their attachment depending on the surface and temperature conditions encountered, which may influence persistence in the processing environment.

SIGNIFICANCE AND IMPACT OF STUDY

These differences in biofilm formation could provide useful information for mitigation of Salmonella in processing environments.

Validation of post-harvest antimicrobial interventions to control Shiga toxin-producing Escherichia coli (STEC) on market hog carcass surfaces

Although swine are less associated with STEC foodborne disease outbreaks, the potential for swine to serve as a source of STEC infections in human beings cannot be disregarded. This study compared eight USDA-approved antimicrobial intervention technologies to quantify their ability to reduce STEC contamination on market hog carcasses. Hogs were harvested to provide skin-on carcass sides, and eight sides (per three replications) were inoculated with a 7-strain STEC cocktail (ca. 5 log CFU/cm² across all external and body cavity surfaces). Each side was randomly assigned to a final pre-chill wash treatment administered in a commercial Chad carcass cabinet using a low-volume spray [3% lactic acid (lLA; 130 °F), 400 ppm peracetic acid (lPAA), or acidified 400 ppm peracetic acid (laPAA)] or a high-volume wash [ambient water (hAW), 400 ppm PAA (hPAA), 400 or 600 ppm hypobromous acid (hDBDMH), or 71 °C water (hHW)] treatment according to a randomized complete block study design. Post-treatment (after a 10-min hanging drip) and post-chilling (18 h at 2 °C) STEC reductions were compared for external skin-on surfaces and internal body cavity lean surface tissue. Post-treatment color changes were determined for lean, adipose, and skin carcass surfaces before and after chilling. When applied to the external, skin-on surface, the hHW, hPAA, and hDBDMH₆₀₀ deluge washes were significantly (P ≤ 0.05) more effective than the other intervention technologies, achieving STEC reductions of 3.8, 3.4, and 3.2 log CFU/cm², respectively. In comparison, the hAW control reduced STEC by 1.7-log CFU/cm² on the external, skin-on surface. The carcass interventions were less effective at reducing STEC populations attached to interior body cavity (diaphragm region), with post-chill populations reduced by 0.9-2.2 log cycles, while the hAW control wash achieved a 0.6-log reduction. None of the treatments negatively impacted instrumental carcass color. While all market hog carcass interventions reduced STEC populations, larger reductions were observed when applied to the external, skin-on surface, with the largest reductions achieved by the hHW, hPAA, and hDBDMH₆₀₀ deluge washes. These data equip pork processors with the information necessary to support decision-making when selecting an intervention technology.

Effects of Peroxyacetic Acid Spray and Storage Temperature on the Microbiota and Sensory Properties of Vacuum-Packed Subprimal Cuts of Meat

We investigated the impact of peroxyacetic acid (PAA; 200 ppm) spray on the microbiota and shelf life of commercial, vacuum-packed beef stored at chiller temperatures. Ribeye cuts (n = 147) were collected from a local beef plant on the day of production for two consecutive days, with one set collected at the start of work with the PAA spray nozzles turned off (control) and during routine production with the PAA spray nozzles turned on (PAA) each day. Packs were stored at 4, 2, and -1°C for up to 34, 104, and 180 days and sampled at appropriate intervals for sensory assessment, microbial enumeration, and microbial profiling by 16S rRNA gene amplicon analysis. Treatment with PAA did not affect the initial meat pH, the initial numbers of total aerobes, lactic acid bacteria, or Enterobacteriaceae (P > 0.05) before storage; however, it delayed the onset of spoilage by 7, 21, and 54 days at 4, 2, and -1°C, respectively. Square-root models of the variation of growth rate with temperature indicated lactic acid bacteria grew faster and Enterobacteriaceae grew slower on PAA-treated than on untreated meat. Negative associations between pH and deterioration of meat during storage were observed for PAA-treated meat. During storage, the microbiota were primarily dominated by Carnobacterium and Lactobacillus/Lactococcus on control meat but by Leuconostoc on PAA-treated meat. Serratia, Yersinia, and Clostridium were identified by linear discriminant effect size analysis as biomarkers for control meat; Clostridium was found in high abundance in samples that had the highest spoilage scores.IMPORTANCE The findings of this study show that PAA solutions applied at low concentrations under commercial settings positively modulated the meat microbiota. It did not have bactericidal effects for beef subprimals with very low microbial loads. However, it differentially impacted the members of the microbiota, which resulted in delayed onset of spoilage of vacuum-packed beef subprimal stored at all three temperatures (4, 2, and -1°C). This differential impact could be through one or a combination of the following factors: favoring the growth of lactic acid bacteria, which may in turn exert a competitive exclusion that might be due to production of antimicrobial compounds such as organic acids and bacteriocins; exerting synergistic antimicrobial effects with low temperatures against members of Enterobacteriaceae; and direct or indirect inhibitory effects against members of the clostridia. These findings not only advance our understanding of the microbial ecology of vacuum-packed meat stored at chiller temperatures but also suggest that bacteriostatic concentrations of antimicrobial interventions can be explored for shelf-life extension.