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

The aprD-mutated strain modulates the development of Pseudomonas fragi population but has limited effects on the spoilage profiles of native residents

Extracellular enzymes produced by predominant bacteria exert important roles in inducing and accelerating spoilage, with their secretion regulated by specific genes. In Pseudomonas fragi, the aprD gene is a recognized regulator for secreting an alkaline extracellular protease. However, limited studies have focused on this gene in P. fragi population and its impact on meat microbial community structure and function. This study addressed this gap by monitoring the changes in biological properties of P. fragi populations and analyzing the discrepancies in spoilage phenotypes and microbial community structures of chilled chicken among groups differentiated by the initial prevalence of aprD-positive strains. The results showed that aprD-positive strains were disseminated in P. fragi populations, and its prevalence was associated with significant increases in swimming motility and biofilm formation capacities in specific groups. In situ contamination experiments revealed varying spoilage characteristics and community compositions among groups by day 3 of storage. Correlation analysis demonstrated a strong association between spoilage phenotypes and certain bacterial genera, such as Pseudomonadaceae_Pseudomonas and Carnobacterium. However, the microbial community structure and spoilage characteristics of samples from each group were not significantly different on the 5th day of storage. These findings suggest that even a small number of aprD mutants can significantly affect the assembly of the chilled meat microbial community. Nonetheless, the regulatory effect of aprD on spoilage at the strain and population levels of P. fragi is negligible in the context of complex natural microbiota. This work underscores the complex interactions between specific bacterial genes and the broader microbial ecology in refrigerated meat environments, providing deeper insights into the meat spoilage mechanisms.

Control of meat spoilage with ozone nano-bubbles: Insights from laboratory model systems and commercial scale treatments

Ozone nanobubbles represent an environmentally friendly sanitation agent. In this study, we compared the bactericidal effect of ozone nanobubbles on pork muscle and adipose tissue to peracetic acid treatments. Pork samples were surface-inoculated with a cocktail of common meat-spoilage-associated microorganisms composed of Brochothrix thermosphacta, Latilactobacillus sakei, Leuconostoc gelidum, Carnobacterium maltaromaticum, Hafnia paralvei and Yersinia rohdei at a viable cell count of 102 CFU/cm2 or 104 CFU/cm2. Both freshly inoculated and stored pork samples were treated with the two sanitation agents, followed by differential enumeration of viable bacteria. Ozone nanobubbles were comparable to peracetic acid solution, achieving a reduction between 1 and 2 log (CFU/cm2), regardless of the initial inoculum concentration and sample type. The efficacy of ozone nanobubble increased with increased solution volume and flow rate. Moreover, the sanitizing agents differentially impacted the members of the microbiota and shifted the composition of tested strains during storage. Gram-negative Y. rohdei and H. paralvei were more sensitive to peracetic acid than Gram-positive strains. Microbial profiling using 16S rRNA gene amplicon analysis of samples that were treated at a commercial processing scale revealed that Serratia, Carnobacterium, Yersinia, Vagococcus, Morganella, Dellaglioa were the dominant taxa (relative abundance >1 %) on stored pork samples. The use of ozone nanobubbles significantly reduced the relative abundance of Vagococcus and Clostridium when compared to control samples. In summary, ozone nanobubbles are an effective tool to reduce bacterial counts on meat and show promise to extend the shelf life of fresh meat.

High-throughput analysis of microbiomes in a meat processing facility: are food processing facilities an establishment niche for persisting bacterial communities?

BACKGROUND

Microbial spoilage in meat impedes the development of sustainable food systems. However, our understanding of the origin of spoilage microbes is limited. Here, we describe a detailed longitudinal study that assesses the microbial dynamics in a meat processing facility using high-throughput culture-dependent and culture-independent approaches to reveal the diversity, dispersal, persistence, and biofilm formation of spoilage-associated microbes.

RESULTS

Culture-dependent and culture-independent approaches revealed a large diversity of microbes within the meat facility, including 74 undescribed bacterial taxa and multiple spoilage-associated microbes. Ten out of 10 reconstituted microbial communities formed biofilms, and the biofilm biomass was generally higher at 4 °C than at 25 °C. Isolates obtained at different sampling times or from different sampling sites that differed in fewer than 10 genome-wide single-nucleotide polymorphisms were considered the same (persistent) strains. Strains of Carnobacterium maltaromaticum and Rahnella rivi persisted over a period of 6 months across sampling sites and time, stemming from floor drains in the cooler room. Meat isolates of Carnobacterium divergens, Rahnella inusitata, and Serratia proteamaculans originated from food contact and non-food contact environments of the packaging area.

CONCLUSIONS

Culture-dependent isolation, complemented by culture-independent analyses, is essential to fully uncover the microbial diversity in food processing facilities. Microbial populations permanently resided within the meat processing facility, serving as a source of transmission of spoilage microbes. The ability of these microbes to coexist and form biofilms facilitates their persistence. Our data together with prior data on persistence of Listeria monocytogenes indicates that microbial persistence in food processing facilities is the rule rather than an exception. Video Abstract.

Driving forces shaping the microbial ecology in meat packing plants

Meat production is a complex system, continually receiving animals, water, air, and workers, all of which serve as carriers of bacteria. Selective pressures involved in different meat processing stages such as antimicrobial interventions and low temperatures, may promote the accumulation of certain residential microbiota in meat cutting facilities. Bacteria including human pathogens from all these sources can contaminate meat surfaces. While significant advancements have been made in enhancing hygienic standards and pathogen control measures in meat plants, resulting in a notable reduction in STEC recalls and clinical cases, STEC still stands as a predominant contributor to foodborne illnesses associated with beef and occasionally with pork. The second-and third-generation sequencing technology has become popular in microbiota related studies and provided a better image of the microbial community in the meat processing environments. In this article, we reviewed the potential factors influencing the microbial ecology in commercial meat processing facilities and conducted a meta-analysis on the microbiota data published in the last 10 years. In addition, the mechanisms by which bacteria persist in meat production environments have been discussed with a focus on the significant human pathogen E. coli O157:H7 and generic E. coli, an indicator often used for the hygienic condition in food production.

Efficacy of commercial peroxyacetic acid on Vibrio parahaemolyticus planktonic cells and biofilms on stainless steel and Greenshell™ mussel (Perna canaliculus) surfaces

The potential of using commercial peroxyacetic acid (PAA) for Vibrio parahaemolyticus sanitization was evaluated. Commercial PAA of 0.005 % (v/v, PAA: 2.24 mg/L, hydrogen peroxide: 11.79 mg/L) resulted in a planktonic cell reduction of >7.00 log10 CFU/mL when initial V. parahaemolyticus cells averaged 7.64 log10 CFU/mL. For cells on stainless steel coupons, treatment of 0.02 % PAA (v/v, PAA: 8.96 mg/L, hydrogen peroxide: 47.16 mg/L) achieved >5.00 log10 CFU/cm2 reductions in biofilm cells for eight strains but not for the two strongest biofilm formers. PAA of 0.05 % (v/v, PAA: 22.39 mg/L, hydrogen peroxide: 117.91 mg/L) was required to inactivate >5.00 log10 CFU/cm2 biofilm cells from mussel shell surfaces. The detection of PAA residues after biofilm treatment demonstrated that higher biofilm production resulted in higher PAA residues (p < 0.05), suggesting biofilm is acting as a barrier interfering with PAA diffusing into the matrices. Based on the comparative analysis of genomes, robust biofilm formation and metabolic heterogeneity within niches might have contributed to the variations in PAA resistance of V. parahaemolyticus biofilms.

Slight Temperature Deviation during a 56-Day Storage Period Does Not Affect the Microbiota of Fresh Vacuum-Packed Pork Loins

It is profitable to export fresh meat overseas, where it is often regarded as a premium commodity. Meeting this demand for fresh meat, however, necessitates long export times, during which uncontrolled temperature increases can affect the microbiological quality of the meat and thereby, reduce shelf life or compromise food safety. To study the impact of temperature deviations on microbial community composition and diversity, we used 16S rRNA gene sequencing for Listeria monocytogenes and Salmonella spp. detection to describe the surface microbiota of eight batches of vacuum-packed loins stored at -1.5 °C (control) for 56 days and subjected to a 2 °C or 10 °C temperature deviation for a few hours (mimicking problems regularly encountered in the industry) at day 15 or 29. The presence of pathogens was negligible. The applied temperature deviations were not associated with different microbiota. Sequencing analysis showed the presence of Yersinia, an unexpected pathogen, and relative abundance increased in the groups subjected to temperature deviations. Over time, Lactobacillales_unclassified genus became the main constituent of the microbiota of vacuum-packed pork loins. Although the microbiota of the eight batches appeared similar at the beginning of storage, differences were revealed after 56 days, suggesting unequal aging of the microbiota.

Microbiological Changes during Long-Storage of Beef Meat under Different Temperature and Vacuum-Packaging Conditions

We evaluated a combination of two temperatures and two packaging materials for long-term storage of vacuum-packaged (VP) beef striploins. Microbial populations and microbiome composition were monitored during refrigerated storage (120 days between 0-1.5 °C) and refrigerated-then-frozen storage (28 days between 0-1.5 °C then 92 days at -20 °C) under low-O₂ permeability VP and high-O₂ permeability VP with an antimicrobial (VPAM). Pseudomonas (PSE) and Enterobacteriaceae (EB) counts in VPAM samples were significantly higher (p < 0.05) than in VP samples at 28, 45, 90, and 120 days of storage. Microbiome data showed that bacteria of the genera Serratia and Brochothrix were more abundant in VPAM samples at 120 days, while lactic acid bacteria (LAB) dominated in VP samples. Frozen temperatures inhibited microbial growth and maintained a relatively stable microbiome. Refrigerated and frozen VPAM samples showed the greatest difference in the predicted metabolic functions at the end of storage driven by the microbiome composition, dominated by PSE and LAB, respectively. Although no signs of visible meat deterioration were observed in any sample, this study suggests that VP meat refrigerated and then frozen achieved better microbiological indicators at the end of the storage period.

Effect of the combination of superchilling and super-chilled storage on shelf-life and bacterial community dynamics of beef during long-term storage

This study investigated the effect of superchilling (-30 °C until the core temperature achieved -3 °C, and - 1 °C until 24 h, SC) on shelf-life and bacterial community dynamics of beef loins, with a typical very fast chilling (-30 °C until the core temperature achieved 0 °C, and - 1 °C until 24 h, VFC) and conventional chilling (0- 4 °C for 24 h, CC) as controls. The super-chilled storage (-1 °C) was adopted after each chilling procedure, and physicochemical traits and microbiological quality were evaluated during a long-term storage. No remarkable adverse impact on meat color and lipid oxidation were observed in SC treatment. The bacterial composition results showed that Carnobacterium spp. were the main bacteria in SC treatment in the late storage period (63- 84 days). The loss of Lactobacillus spp., due to the "ultra-low temperature" during the superchilling, might be the reason that the SC did not result in a longer shelf-life compared with CC samples.