Efficacy of chlorine and peroxyacetic acid to control Listeria monocytogenes on apples in simulated dump tank water system.

Chlorine and peroxyacetic acid (PAA) are commonly applied in dump tanks and flume systems in commercial fresh apple packing lines; however, little is known about their practical efficacies in dump tank water systems. This study evaluated the efficacies of chlorine and PAA to control Listeria monocytogenes on fresh apples and cross-contamination in simulated dump tank water (SDTW). Efficacies of chlorinated water with initial free chlorine (FC) of 25-100 ppm against L. monocytogenes on apples were significantly impacted by the presence of organic matter, especially for chlorine with 25 ppm initial FC. Chlorine with initial FCs of 50-100 ppm and 2 min contact reduced L. monocytogenes on apples by ∼0.9 log10 CFU/apple in SDTW with 1000 ppm chemical oxygen demand (COD). However, 2-5 min wash of chlorine with 25 ppm initial FC only led to ∼0.3 log10 CFU/apple reduction of L. monocytogenes on apples in SDTW compared to ∼0.9 log10 CFU/apple reduction in clean water. The impacts of organic matter on the antimicrobial efficacy of PAA are concentration dependent. At 20-80 ppm and tested contact times (2-5 min), efficacies of PAA against L. monocytogenes were not influenced by organic matter presented in SDTW; 2-5 min wash with PAA 80 ppm caused 1.7-1.8 log10 CFU/apple log reduction. However, the anti-Listeria efficacy of 10 ppm PAA was significantly lower in SDTW than in clean water. Sanitizers at the tested concentrations reduced L. monocytogenes transferred from contaminated apples to uncontaminated apples and SDTW but did not eliminate it. There were 1.7-0.6 and 1.0-0.9 log10 CFU/apple of L. monocytogenes transferred to uninoculated apples in SDTW treated with 50-100 ppm FC and 60-80 ppm PAA, respectively, for 2 min, while 3.6-3.7 log10 CFU/apple of L. monocytogenes were transferred to uncontaminated apples in SDTW without any sanitizer treatments. Data indicated that sanitizer treatments in SDTW are effective but can be further improved to ensure the microbial safety of apples.

Effects of 1-methylcyclopropene and gaseous ozone on Listeria innocua survival and fruit quality of Granny Smith apples during long-term commercial cold storage.

This study evaluated the impact of 1-methylcyclopropene (1-MCP), an ethylene synthesis inhibitor, followed by long-term commercial cold storage with low-dose gaseous ozone on the microbiological safety and quality of fresh apples. Granny Smith apples were inoculated with or without Listeria innocua, treated with or without 1.0 mg/L 1-MCP for 24 h, then subjected to commercial cold storage conditions including refrigerated air (RA, 0.6 °C, control), controlled atmosphere (CA, 2% O2, 1% CO2, 0.6 °C), and CA with 51-87 µg/L ozone gas for up to 36 weeks. RA storage reduced L. innocua on apples by up to 3.6 log10 CFU/apple. CA had no advantage over RA in controlling Listeria. Continuous ozone gas application resulted in an additional ∼2.0 log10 CFU/apple reduction of L. innocua (total reduction up to 5.7 log10 CFU/apple) and suppressed native bacteria and fungi. Treatment with 1-MCP had a minor impact on survival of L. innocua or background microbiota on apples, while it significantly delayed fruit ripening and reduced the incidence of superficial scald and internal browning. In summary, 1-MCP treatment followed by CA storage with low-dose continuous ozone gas can effectively control Listeria on fresh apples and delay fruit ripening.

Effectiveness of Low-Dose Continuous Gaseous Ozone in Controlling Listeria innocua on Red Delicious Apples During 9-Month Commercial Cold Storage.

This study aimed to investigate the effects of low-dose continuous ozone gas in controlling Listeria innocua and quality attributes and disorders of Red Delicious apples during long-term commercial cold storage. Red Delicious apples were inoculated with a three-strain L. innocua cocktail at ∼6.2 log10 CFU/apple, treated with or without 1-methylcyclopropene, and then subjected to controlled atmosphere (CA) storage with or without continuous gaseous ozone in a commercial facility for 36 weeks. Uninoculated Red Delicious apples subjected to the above storage conditions were used for yeast/mold counts and quality attributes evaluation. The 36 weeks of refrigerated air (RA) or CA storage caused ∼2.2 log10 CFU/apple reduction of L. innocua. Ozone gas application caused an additional > 3 log10 CFU/apple reduction of L. innocua compared to RA and CA storage alone. During the 36-week CA storage, low-dose continuous gaseous ozone application significantly retarded the growth of yeast/mold, delayed apple firmness loss, and had no negative influence on ozone burn, lenticel decay, russet, CO2 damage, superficial scald, and soft scald of Red Delicious apples compared to CA-alone storage. In summary, the application of continuous low-dose gaseous ozone has the potential to control Listeria on Red Delicious apples without negatively influencing apple quality attributes.

Verification of peroxyacetic acid treatment against L. monocytogenes on fresh apples using E. faecium NRRL B-2354 as a surrogate in commercial spray-bar operations.

Peroxyacetic acid (PAA) is a commonly used antimicrobial in apple spray bar interventions during post-harvest packing. However, limited information is available about its efficacy against foodborne pathogens on fresh apples under commercial packing conditions. In this study, the practical efficacies of PAA against Listeria monocytogenes on fresh apples during spray bar operation at ambient and elevated temperature were validated in three commercial packing facilities using Enterococcus faecium NRRL B-2354 as a surrogate strain. Apples were inoculated with E. faecium at ~6.5 Log10 CFU/apple and subjected to PAA spray bar interventions per commercial packing line practice. At each temperature and contact time intervention combination, 20-24 inoculated apples were processed together with 72-80 non-inoculated apples. Applying 80 ppm PAA at ambient temperature (17-21 °C) achieved a similar log reduction (P > 0.05) of E. faecium on Granny Smith apples (GSA) in three apple packing facilities, which caused 1.12-1.23 and 1.18-1.32 Log10 CFU/apple reductions of E. faecium on GSA for 30-sec and 60-sec intervention, respectively. Increasing the temperature of the PAA solution to 43-45 °C enhanced its bactericidal effect against E. faecium, causing 1.45, 1.86 and 2.19 Log10 CFU/apple reductions in three packing facilities for a 30-sec contact, and 1.50, 2.24, and 2.29 Log10 CFU/apple reductions for a 60-sec contact, respectively. Similar efficacies (P > 0.05) of PAA at both ambient and elevated temperature were also observed on Fuji apples. Spraying PAA on apples at ambient or elevated temperature reduced the level of E. faecium cross-contamination from inoculated apples to non-inoculated apples but could not eliminate cross-contamination. Data from this study provides valuable technical information and a reference point for the apple industry in controlling L. monocytogenes and verifying the effectiveness of their practices.

Efficacy of Ozonated Water, Chlorine, Chlorine Dioxide, Quaternary Ammonium Compounds and Peroxyacetic Acid Against Listeria monocytogenes Biofilm on Polystyrene Surfaces.

Listeria monocytogenes contaminated processing equipment and the general packing environment have been implicated in deadly foodborne listeriosis outbreaks, highlighting the significance of proper sanitization and disinfection of food contact surfaces. This study aims to comprehensively evaluate antimicrobial efficacy of commercially available, economical sanitizers at practical concentrations against L. monocytogenes biofilm formed on polystyrene surfaces under different conditions. Ozonated water 1-min treatment at 1.0, 2.0, and 4.0 ppm resulted in ∼0.9, 3.4, and 4.1 log reduction of L. monocytogenes single strain biofilm grown on polystyrene surfaces, respectively. However, its efficacy was dramatically diminished in multi-strain L. monocytogenes biofilm and was further compromised by aged biofilm and in the presence of organic matter. Quaternary ammonium compounds (QAC) at 100/400 ppm, chlorine at 100/200 ppm, chlorine dioxide at 2.5/5.0 ppm and peroxyacetic acid (PAA) at 80/160 ppm resulted in 2.4/3.6, 2.0/3.1, 2.4/3.8, and 3.6/4.8 log reduction of L. monocytogenes single strain biofilm, respectively. Antimicrobial efficacies of all tested sanitizers against 7-day-old biofilm were much lower when compared to 2-day-old biofilm, with PAA being the least influenced by the age of the biofilm. Organic matter conditioning with diluted milk or apple juice dramatically impacted the antimicrobial efficacy of all sanitizers. PAA treatment of 1 min at 160-200 ppm resulted in a 3.2-3.5 log reduction against 7-day-old biofilm in the presence of organic matter, thus showing its effectiveness in eradicating L. monocytogenes biofilm on polystyrene surface. Collectively, data highlight the importance of timely and thoroughly cleaning food contact surfaces before disinfection and provides practical information and guidance for the food industry in selecting the most effective sanitizer in their sanitizing regimes to eliminate L. monocytogenes biofilm.

Gaseous nitrogen and bacterial responses to raw and digested dairy manure applications in incubated soil.

A study was conducted under laboratory conditions to compare rates of nitrous oxide (N(2)O) and ammonia (NH(3)) emissions when soil was amended with anaerobically digested dairy manure slurry containing <30% food byproducts, raw dairy manure slurry, or urea. Slurries were applied via surface and subsurface methods. A second objective was to correlate genes regulating nitrification and denitrification with rates of N(2)O production, slurry treatment, and application method. Ammonia volatilization from incubated soil ranged from 140 g kg(-1) of total N applied in digested slurry to 230 g kg(-1) in urea. Subsurface application of raw dairy manure slurry decreased ammonia volatilization compared with surface application. Anaerobic digestion increased N(2)O production. Cumulative N(2)O loss averaged 27 g kg(-1) of total N applied for digested slurry, compared with 5 g kg(-1) for raw dairy slurry. Genes of interest included a 16S rRNA gene selective for ß-subgroup proteobacterial ammonia-oxidizers, amoA, narG, and nosZ quantified with quantitative polymerase chain reaction (qPCR) and real-time polymerase chain reaction (RT-PCR). Application of anaerobically digested slurry increased nitrifier and denitrifier gene copies that correlated with N(2)O production. Expression of all genes measured via mRNA levels was affected by N applications to soil. This study provides new information linking genetic markers in denitrifier and nitrifier populations to N(2)O production.

Sterilization of biological pathogens using supercritical fluid carbon dioxide containing water and hydrogen peroxide.

Novel noninvasive techniques for the removal of biological contaminants to generate clean or sterile materials are in demand by the medical, pharmaceutical and food industries. The sterilization method described here uses supercritical fluid carbon dioxide (SF-CO(2)) containing 3.3% water and 0.1% hydrogen peroxide (v/v/v) to achieve from four to eight log viability reduction of all tested microbial species, including vegetative cells, spores and biofilms. The sterilization method employs moderate pressure and temperature (80 atm, 50°C) and a short (30-minute) treatment time. The procedure kills various opportunistic pathogens that often persist in biofilm structures, fungal spores commonly associated with nosocomial infections, and Bacillus pumilus SAFR-032 endospores that are notoriously hard to eradicate by conventional sterilization techniques.

Proteomic and targeted qPCR analyses of subsurface microbial communities for presence of methane monooxygenase.

The Test Area North (TAN) site at the Idaho National Laboratory near Idaho Falls, ID, USA, sits over a trichloroethylene (TCE) contaminant plume in the Snake River Plain fractured basalt aquifer. Past observations have provided evidence that TCE at TAN is being transformed by biological natural attenuation that may be primarily due to co-metabolism in aerobic portions of the plume by methanotrophs. TCE co-metabolism by methanotrophs is the result of the broad substrate specificity of microbial methane monooxygenase which permits non-specific oxidation of TCE in addition to the primary substrate, methane. Arrays of experimental approaches have been utilized to understand the biogeochemical processes driving intrinsic TCE co-metabolism at TAN. In this study, aerobic methanotrophs were enumerated by qPCR using primers targeting conserved regions of the genes pmoA and mmoX encoding subunits of the particulate MMO (pMMO) and soluble MMO (sMMO) enzymes, respectively, as well as the gene mxa encoding the downstream enzyme methanol dehydrogenase. Identification of proteins in planktonic and biofilm samples from TAN was determined using reverse phase ultra-performance liquid chromatography (UPLC) coupled with a quadrupole-time-of-flight (QToF) mass spectrometer to separate and sequence peptides from trypsin digests of the protein extracts. Detection of MMO in unenriched water samples from TAN provides direct evidence of intrinsic methane oxidation and TCE co-metabolic potential of the indigenous microbial population. Mass spectrometry is also well suited for distinguishing which form of MMO is expressed in situ either soluble or particulate. Using this method, pMMO proteins were found to be abundant in samples collected from wells within and adjacent to the TCE plume at TAN.