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This study investigated the performance of a 222 nm far-UV-C krypton-chloride excilamp for inactivation of major foodborne pathogenic and spoilage bacteria in thin liquid films (TLF, 1.2 mm thickness), on solid stainless steel surfaces (SS), and against biofilm formation on SS. Both gram-positives (Listeria monocytogenes , Staphylococcus aureus) and gram-negatives (Escherichia coli O157:H7, Pseudomonas aeruginosa) (109 CFU/mL starting concentration) were exposed to 222 nm light at cumulative doses of up to 354 mJ/cm2. Significant (P < 0.05) reductions (1.4–5.1 log CFU) were found for all bacteria, and inactivation kinetics was described well by the Weibull model (0.77 ≤ R 2 ≤ 0.95). Substrate type (i.e. , TLF vs. SS) substantially impacted treatment efficacy. No detectable resistance of L. monocytogenes was developed after repeated exposure to 222 nm in TLF. The 222 nm treatment also effectively minimized biofilm formation and growth by S. aureus and P. aeruginosa and increased the surviving cells' susceptibility to sodium hypochlorite by at least 2 fold. This work demonstrates that 222 nm krypton-chloride excilamps can be used to effectively inactivate planktonic bacteria and inhibit biofilm formation and growth. This recommends them for use as novel nonthermal light-based systems for mitigation of pathogens and biofilms in a range of applications, including food processing, food service, and clinical environments. • Inactivation of gram-positive and gram-negative bacteria ranging between 1.4 and 5.1 log CFU was achieved after a cumulative fluence of up to 354 mJ/cm2 • Exposure to 222 nm far-UV-C inhibited biofilm formation & growth by Staphylococcus aureus and Pseudomonas aeruginosa on for up to 48 h • No bacterial resistance to 222 nm light was developed for Listeria monocytogenes over five repeated exposure-growth cycles • Pre-treatment with 222 nm for up to 48 h increased the susceptibility of surviving cells to 0.02 M sodium hypochlorite [ABSTRACT FROM AUTHOR]

Thermal pasteurization can achieve the U.S. Food and Drug Administration-required 5-log reduction of pathogenic Escherichia coli O157:H7 and Cryptosporidium parvum in apple juice and cider, but it can also negatively affect the nutritional and organoleptic properties of the treated products. In addition, thermal pasteurization is only marginally effective against the acidophilic, thermophilic, and spore-forming bacteria Alicyclohacillus spp., which is known to cause off-flavors in juice products. In this study, the efficiency of a combined microfiltration (MF) and UV process as a nonthermal treatment for the reduction of pathogenic and nonpathogenic E. coli, C. parvum, and Alicyclohacillus acidoterrestris from apple cider was investigated. MF was used to physically remove suspended solids and microorganisms from apple cider, thus enhancing the effectiveness of UV and allowing a lower UV dose to be used. MF, with ceramic membranes (pore sizes, 0.8 and 1.4 µm), was performed at a temperature of 10°C and a transmembrane pressure of 155 kPa. The subsequent UV treatment was conducted using at a low UV dose of 1.75 mj/cm². The combined MF and UV achieved more than a 5-log reduction of E. coli, C. parvum, and A. acidoterrestris. MF with the 0.8-² m pore size performed better than the 1.4-²m pore size on removal of E. coli and A. acidoterrestris. The developed nonthermal hurdle treatment has the potential to significantly reduce pathogens, as well as spores, yeasts, molds, and protozoa in apple cider, and thus help juice processors improve the safety and quality of their products. [ABSTRACT FROM AUTHOR]

Abstract: Pulsed light (PL) technology is able to effectively destroy a wide variety of food spoilage and pathogenic microorganisms. However, the effectiveness of PL treatment depends on direct exposure of the target microorganisms to the short, high energy pulses of light. The complex physical and chemical properties of foods affect the way light propagates through a given food substrate, and thus there is a real potential for insufficiently or non-uniformly treated products. The objective of this work was to develop a method for predicting levels and spatial distribution of microbial inactivation in PL treatment of liquid substrates, and to validate the predictions with experimental data. Three liquids with different composition and optical properties (BPB, TSB, apple juice) were inoculated with either Escherichia coli ATCC 25922 or Listeria innocua FSL C2-008 and treated with PL, in two different geometries. The Weibull model was used to describe the microbial inactivation kinetics for each organism. The kinetic equations were coupled with previously determined equations describing either the total fluence (F total) or UV fluence (F UV) distribution in each of the liquids, for either cylindrical or rectangular prismatic geometries. COMSOL simulation software was used to generate maps of spatial distribution of microbial inactivation and to predict the average volumetric inactivation for each substrate. The model that used F total provided gross over-estimations for microbial inactivation, while using F UV as the treatment dose yielded reasonably good predictions of microbial inactivation, especially for the more opaque and turbid substrates. This approach can help processors determine which substrates would be suitable for PL treatment, and to design highly effective and uniform PL treatments. [Copyright &y& Elsevier]

The main objective of this work was to evaluate the effectiveness of pulsed light (PL) treatment for the inactivation of Escherichia coli in liquids with different levels of clarity. Nonpathogenic E. coli ATCC 25922 and pathogenic E. coli O157: H7 were used as challenge organisms. Butterfield's phosphate buffer (BPB), tryptic soy broth (TSB), apple juice, and apple cider were used as substrates. The inoculated liquids were placed in a thin layer (1.3 mm) into glass chambers (23 by 53 by 11 mm) and exposed to PL doses of up to 13.1 J/cm². PL treatments were performed in a Xenon RS-3000C PL unit, both static mode and under turbulence. Survivors were determined by standard plate counting or the most-probable-number technique. For static treatments, reduction levels exceeding 8.5 log were obtained in BPB for all strains and reduction levels of about 3.5 log were obtained in TSB. For apple juice, inactivation levels of 2.66 ± 0.10 log were obtained for E. coli ATCC 25922 and 2.52 ± 0.19 log for E. coli O157:H7. In cider, inactivation levels of 2.32 ± 0.16 log and 3.22 ± 0.29 log obtained for the nonpathogenic and pathogenic strains, respectively. Inactivation kinetics was characterized using the Weibull model. Turbulent treatments resulted in 5.76 ± 0.06 log reduction in cider and 7.15 ± 0.22 log reduction in juice, which satisfies the U.S. Food and Drug Administration requirement of 5-log reduction of E. coli. These results show promise for the use of PL for the effective reduction of E. coli in apple juice and cider. [ABSTRACT FROM AUTHOR]

Pulsed light (PL) treatment is an alternative to traditional thermal treatment that has the potential to achieve several log-cycle reductions in the concentration of microorganisms. One issue that is still debated is related to what specifically causes cell death after PL treatments. The main objective of this work was to elucidate which portions of the PL range are responsible for bacterial inactivation. Stainless steel coupons with controlled surface properties were inoculated with a known concentration of Listeria innocua in the stationary growth phase and treated with 1 to 12 pulses of light at a pulse rate of 3 pulses per s and a pulse width of 360 µs. The effects of the full-spectrum (λ = 180 to 1,100 nm) were compared with the effects obtained when only certain regions of UV, visible, and near-infrared light were used. The effectiveness of the treatments was determined in parallel by the standard plate count and most-probable-number techniques. At a fluence of about 6 J/cm², the full-spectrum PL treatment resulted in a 4.08-log reduction of L. innocua on a Mill finish surface, the removal of λ < 200 nm diminished the reduction to only 1.64 log, and total elimination of UV light resulted in no lethal effects on L. innocua. Overwhelmingly, the portions of the PL spectrum responsible for bacterial death are the UV-B and UV-C spectral ranges (λ < 300 nm), with some death taking place during exposure to UV-A radiation (300 < λ < 400 nm) and no observable death upon exposure to visible and near-infrared light (λ > 400 nm). This work provides additional supporting evidence that cell death in PL treatment is due to exposure to UV light. Additionally, it was shown that even a minor modification of the light path or the UV light spectrum in PL treatments can have a significant negative impact on the treatment intensity and effectiveness. [ABSTRACT FROM AUTHOR]