Inactivation of Salmonella, Listeria monocytogenes, Aspergillus and Penicillium on lemons using advanced oxidation process optimized through response surface methodology

Sequential Pulsed Light and Ultrasound Treatments for the Inactivation of Saccharomyces cerevisiae and PPO and the Retention of Bioactive Compounds in Sweet Lime Juice

Designing a pasteurization con dition for sweet lime juice while ensuring microbial safety, enzymatic stability, and high nutritional quality is crucial for satisfying stakeholder demands. The present research investigates the effects of matrix pH, ultrasound treatments, and sequential pulsed light on the microbial population, enzyme activity, and bioactive chemicals in sweet lime juice. The sequential pulsed light (PL: 0.6-0.84 J/cm2) and ultrasound (US: 0.2-0.4 W/cm3) treatments for sweet lime juice were optimized using response surface methodology (RSM). A three-factor full factorial design was used for this purpose. The independent variables encompassed pH (X1), PL effective fluence (X2, J/cm2), and US intensity (X3, W/cm3). The responses assessed included the inactivation of Saccharomyces cerevisiae (Y1, log cfu/mL) and polyphenol oxidase (PPO: Y2 in %) and the retention of vitamin C (Y3, %). The polynomial models were optimized using numerical optimization to attain the maximum desirability value (0.89). The optimized PL + US sample (0.8 J/cm2 + 0.4 W/cm3, respectively) at pH 3.5 resulted in a 5-log cycle reduction in S. cerevisiae count and a 90% inactivation in PPO activity and retained 95% of its vitamin C content. This optimized sample underwent further analysis, including phenolic profiling, assessment of microbial cell morphology, and examination of enzyme conformational changes. After sequential pulsed-light (0.8 J/cm2) and ultrasound (0.4 W/cm3) treatments, yeast cells showed unusual structural changes, indicating additional targets besides membranes. Following PL + US treatment, the PPO composition changed to 2.7 ± 0.1% α-helix, 33.9 ± 0.3% β-sheet, 1.4 ± 0.2% β-turn, and 62 ± 0.7% random coil. Impressively, the optimized PL + US sample maintained a sensory acceptance level similar to that of the untreated sample.

Surface disinfection of wheat kernels using gas phase hydroxyl-radical processes: Effect on germination characteristics, microbial load, and functional properties

Wheat kernels harbor a diverse microflora that can negatively affect the suitability of the grains for further processing. To reduce surface microflora, a kernel disinfection method is required that does not affect grain functionality. Three different versions of gas phase hydroxyl-radical processes were compared with the common method for grain disinfection, that is, a bleach treatment. The gas phase hydroxyl-radicals are generated by the UV-C mediated degradation of hydrogen peroxide and/or ozone in a near water-free process. It was found that treating kernels with a bleach solution could reduce total aerobic count (TAC) and fungal count to below the level of enumeration. In comparison, the gas phase hydroxyl-radical treatment, that is, H2 O2 -UV-ozone treatment, could support a 1.3 log count reduction (LCR) in TAC and a 1.1 LCR in fungal count. The microbial load reduction for the wholemeal samples was less pronounced as endophytic microorganisms were less affected by all treatments, hinting at a limited penetration depth of the treatments. Despite reducing the microbial load on the kernel surface through the bleach and H2 O2 -UV-ozone treatments, none of these treatments resulted in a reduced microbial count on grains that underwent sprouting after the treatments. No negative effect on germination power or development of the seedling was observed for any of the treatments. The gluten aggregation behavior and xylanase activity of the wholemeal also remained unchanged after the gas phase hydroxyl-radical treatments. Our findings suggest that UV-H2 O2 -ozone treatment shows promise for dry-kernel disinfection, but further optimization of the processing parameters is required.

Nanostructured copper-organic frameworks for the generation of sulphate radicals: application in wastewater disinfection

In recent years, the presence of pathogens in the environment has become an issue of widespread concern in society. Thus, new research lines have been developed regarding the removal of pathogens and persistent pollutants in water. In this research, the efficacy of nanostructure copper-organic framework, HKUST-1, has been evaluated for its ability to eliminate Escherichia coli and generate sulphate radicals as catalyst for the treatment of effluents with a high microbiological load via peroxymonosulphate (PMS) activation. The disinfection process has been optimized, achieving complete elimination of Escherichia coli growth after 30 min of testing using a concentration of 60.5 mg/L HKUST-1 and 0.1 mM of PMS. To overcome the operational limitations of this system and facilitate its handling and reutilization in a flow disinfection process, HKUST-1 has been efficiently encapsulated on polyacrylonitrile as a novel development that could be scaled up to achieve continuous treatment.

Mild heat treatment achieved better inactivation of Salmonella and preservation of almond quality than ultraviolet light and chemical sanitizers

This study was conducted to compare the effects of ultraviolet light (UV), chemical sanitizers, and heat treatments on Salmonella inactivation and preservation of almond quality. Whole, skinless, and sliced almonds, representing different shape and surface topography, were inoculated with a Salmonella cocktail consisting of S. Montevideo, S. Newport, S. Typhimurium, S. Heidelberg, and S. Enteritidis. Inoculated almonds (50 g) were treated by UV (30 mW/cm², 30 or 60 min), 75 °C heat (up to 150 min), and chemical sanitizers (3 % hydrogen peroxide (H₂O₂) and 1 % cetylpyridinium chloride (CPC), 30 or 60 min) alone or in combinations. Uninoculated almonds were similarly treated for analyzing color, visual appearance, and weight changes. In general, UV treatment alone was ineffective in inactivating Salmonella; the 30- and 60-min UV treatments reduced Salmonella by 1.3 (± 0.1) and 1.7 (± 0.1), 2.7 (± 0.2) and 3.3 (± 0.1), and 1.3 (± 0.1) and 1.7 (± 0.1) log CFU/g on whole, skinless, and sliced almonds, respectively. Prior wetting of almonds with water and chemical solutions in a few cases significantly (P < 0.05) increased the UV inactivation of Salmonella. The most pronounced Salmonella killing effect achieved by the combined treatments were: 1-min H₂O₂ dipping followed by 60-min UV treatment for whole (3.0 logs) and skinless almonds (3.8 logs) and 1-min CPC dipping followed by 60-min UV treatment for sliced almonds (3.0 logs). However, none of those achieved >4 log reductions of Salmonella as required by FDA. The 30-min UV treatment produced discolored but overall acceptable almonds, whereas the 60-min UV treatment led to deteriorated almonds including a dark color, oil extraction, and shrunk kernel size. Prior wetting reduced the sample weight loss but caused local burning and kernel cracking. A sequential approach of a 60-min 75 °C heat treatment and two 30-min wet UV treatments successfully reduced Salmonella by >4 logs, but more severe kernel cracking occurred. In contrast, a single heat treatment of vacuum packaged whole almonds at 75 °C for 150 min was capable of achieving >5 log reductions of Salmonella while preserving almond color and visual qualities and minimizing weight loss. These results clearly demonstrated that the heat treatment was a much better processing technology than UV and sanitizers for raw almond pasteurization.

Ozone based inactivation and disinfection in the pandemic time and beyond: Taking forward what has been learned and best practice

The large-scale global COVID-19 has a profound impact on human society. Timely and effectively blocking the virus spread is the key to controlling the pandemic growth. Ozone-based inactivation and disinfection techniques have been shown to effectively kill SARS-CoV-2 in water, aerosols and on solid surface. However, the lack of an unified information and discussion on ozone-based inactivation and disinfection in current and previous pandemics and the absence of consensus on the main mechanisms by which ozone-based inactivation of pandemic causing viruses have hindered the possibility of establishing a common basis for identifying best practices in the utilization of ozone technology. This article reviews the research status of ozone (O3) disinfection on pandemic viruses (especially SARS-CoV-2). Taking sterilization kinetics as the starting point while followed by distinguishing the pandemic viruses by enveloped and non-enveloped viruses, this review focuses on analyzing the scope of application of the sterilization model and the influencing factors from the experimental studies and data induction. It is expected that the review could provide an useful reference for the safe and effective O3 utilization of SARS-CoV-2 inactivation in the post-pandemic era.

Disinfection through Advance Oxidation Processes: Optimization and Application on Real Wastewater Matrices

Disinfection is an essential and significant process for water treatment to protect the environment and human beings from pathogenic infections. In this study, disinfection through the generation of hydroxyl (Fenton process (FP)) and sulfate (Fenton-like process (FLP)) radicals was validated and optimized. The optimization was carried out in synthetic water through an experimental design methodology using the bacteria Escherichia coli as a model microorganism. Different variables were evaluated in both processes: precursor concentration (peroxymonosulfate (PMS) and H₂O₂), catalyst concentration (Fe⁺²), and pH in the Fenton process. After that, the optimized conditions (FP: 132.36 mM H₂O₂, 0.56 mM Fe⁺² and 3.26 pH; FLP: 3.82 mM PMS and 0.40 mM Fe⁺²) were applied to real matrices from wastewater treatment plants. The obtained results suggest that both processes are promising for disinfection due to the high oxidant power of hydroxyl and sulfate radicals.

Vapor-Phase Hydroxyl or Chlorine Radical Treatment for Inactivating Listeria monocytogenes on Mushrooms (Agaricus bisporus) without Negatively Affecting Quality or Shelf Life

ABSTRACT

Processes based on generating vapor-phase hydroxyl radicals or chlorine radicals were developed for inactivating Listeria monocytogenes on mushrooms without negatively affecting quality. Antimicrobial radicals were generated from the UV-C degradation of hydrogen peroxide or hypochlorite and ozone gas. Response surface modeling was used to identify the interaction among the operating parameters for the hydroxyl radical process: UV-C254nm intensity, hydrogen peroxide concentration, and ozone delivered. There was an inverse relationship between hydrogen peroxide concentration and UV-C intensity in terms of the log reduction of L. monocytogenes. The independent parameters for the chlorine radical process were hypochlorite concentration, pH, and UV-C intensity. From predictive models, the optimal hydroxyl radical treatment was found to be 5% (v/v) H2O2, 2.86 mW/cm2 UV-C intensity (total UV-C dose 144 mJ/cm2), and 16.5 mg of ozone. The optimal parameters for the chlorine radical process were 10 ppm of hypochlorite (pH 3.0), 11.0 mg of ozone, and 4.60 mW/cm2 UV-C intensity. When inoculated mushrooms were treated with the optimal hydroxyl radical and chlorine radical processes, the reduction of L. monocytogenes was found to be 2.42 ± 0.42 and 2.61 ± 0.30 log CFU, respectively, without any negative effects on mushroom quality (weight loss and Browning index during 14 days of storage at 4°C). These reductions were significantly greater than those from application of the individual elements of the radical processes and those in the control process, which used a 90-s dip in 1% (v/v) hydrogen peroxide. The study has demonstrated that hydroxyl radical and chlorine radical vapor-phase treatments are equally effective at inactivating L. monocytogenes on mushrooms and can be considered as a preventative control step.

HIGHLIGHTS

Decontamination of N95 and surgical masks using a treatment based on a continuous gas phase-Advanced Oxidation Process

A gas-phase Advanced Oxidation Process (gAOP) was evaluated for decontaminating N95 and surgical masks. The continuous process was based on the generation of hydroxyl-radicals via the UV-C (254 nm) photo-degradation of hydrogen peroxide and ozone. The decontamination efficacy of the gAOP was dependent on the orientation of the N95 mask passing through the gAOP unit with those positioned horizontally enabling greater exposure to hydroxyl-radicals compared to when arranged vertically. The lethality of gAOP was independent of the applied hydrogen peroxide concentration (2-6% v/v) but was significantly (P<0.05) higher when H2O2 was introduced into the unit at 40 ml/min compared to 20 ml/min. A suitable treatment for N95 masks was identified as 3% v/v hydrogen peroxide delivered into the gAOP reactor at 40 ml/min with continuous introduction of ozone gas and a UV-C dose of 113 mJ/cm2 (30 s processing time). The treatment supported >6 log CFU decrease in Geobacillus stearothermophilus endospores, > 8 log reduction of human coronavirus 229E, and no detection of Escherichia coli K12 on the interior and exterior of masks. There was no negative effect on the N95 mask fitting or particulate efficacy after 20 passes through the gAOP system. No visual changes or hydrogen peroxide residues were detected (<1 ppm) in gAOP treated masks. The optimized gAOP treatment could also support >6 log CFU reduction of endospores inoculated on the interior or exterior of surgical masks. G. stearothermophilus Apex spore strips could be applied as a biological indicator to verify the performance of gAOP treatment. Also, a chemical indicator based on the oxidative polymerization of pyrrole was found suitable for reporting the generation of hydroxyl-radicals. In conclusion, gAOP is a verifiable treatment that can be applied to decontaminate N95 and surgical masks without any negative effects on functionality.

Ozone Treatments for Preserving Fresh Vegetables Quality: A Critical Review

Ozone is recognized as an antimicrobial agent for vegetables storage, washing, and processing. This strong disinfectant is now being used in the food industry. In this review, the chemical and physical properties of ozone, its generation, and factors affecting ozone processing efficiency were explained as well as recent regulatory developments in the food industry. By then selecting three vegetables, we show that ozone avoids and controls biological growth on vegetables, keeping their attractive appearance and sensorial qualities, assuring nutritional characteristics' retention and maintaining and increasing the shelf-life. In liquid solution, ozone can be used to disinfect processing water and vegetables, and in gaseous form, ozone helps to sanitize and preserve vegetables during storage. The multifunctionality of ozone makes it a promising food processing agent. However, if ozone is improperly used, it causes some deleterious effects on products, such as losses in their sensory quality. For an effective and a safe use of ozone, specific treatment conditions should be determined for all kinds of vegetables. In a last step, we propose highlighting the different essential characteristics of ozone treatment in order to internationally harmonize the data relating to the treatments carried-out.

Validation of a vapor-phase advanced oxidation process for inactivating Listeria monocytogenes, its surrogate Lactobacillus fructivorans, and spoilage molds associated with green or red table grapes

A method based on vapor-phase advanced oxidation process (AOP) for decontaminating red or green grapes was validated for inactivating Listeria monocytogenes and spoilage molds. A Central Composite Design (CCD) and Response Surface Methodology (RSM) were applied to determine the contribution of UV-C (254 nm) dose, hydrogen peroxide, and ozone concentration on the lethality toward Aspergillus niger spores (biodensiometer) and changes to the grape quality (firmness and color over 14-day post-treatment storage at 4 °C). A high UV-C dose (>129 mJ/cm² ) or >4.0 % v/v hydrogen peroxide induced-blistering and darkening of grapes at the end of the storage period. Yet, an optimized AOP treatment (with regards to preserving grape quality) was derived to be 1.3% v/v hydrogen peroxide (5 mL/10 berries) with 9-mg ozone gas and a UV-C dose of 123 mJ/cm² (10 s at UV-C intensity of 12 mW/cm² ). A predictive model was constructed and verified based on the log reduction of A. niger spores and changes in quality characteristics of red grapes. The optimal AOP treatment supported a 1.6-log CFU/g reduction of Aspergillus spores and decreased L. monocytogenes counts by 3.92 ± 0.17 and 4.77 ± 0.30 log CFU/g on green and red grapes, respectively, that were not significantly different to the surrogate, Lactobacillus fructivorans. There was no significant difference in the reduction of L. monocytogenes with grapes arranged in a single or double layer. Botrytis cinerea counts were reduced by 1.08 to 1.35 log CFU/g using the optimized AOP treatment with no change in grape color or firmness during storage. A sensory panel could not differentiate AOP-treated grapes from nontreated controls although 3 of 15 panelists did note subtle flavor notes. PRACTICAL APPLICATION: Postharvest washing of fresh produce has limited efficacy in removing foodborne pathogens and spoilage microbes. This is especially relevant to berries, such as grapes, that are susceptible to spoilage following washing. The vapor-phase AOP treatment provides a supplemental or alternative approach for produce decontamination. However, the operating parameters need to be optimized to ensure that decontamination of grapes is not at the expense of quality. In the current study, this was achieved by ensuring a balance between hydrogen peroxide, ozone, and UV-C dose that form the elements of an AOP treatment.