Control of microbes on barley grains using peroxyacetic acid and electrolysed water as antimicrobial agents

Effect of neutral electrolyzed water on biofilm formed by meat-related Listeria monocytogenes: Intraspecies variability and influence of the growth surface material

Listeria monocytogenes raises major challenges for the food industry. Due to its capacity to form biofilms, this pathogen can persist in processing environments and contaminate the final products. Neutral electrolyzed water (NEW) may offer a promising and eco-friendly method for controlling L. monocytogenes biofilms, though current in vitro studies on its antibiofilm activity are limited and often focused on reference strains. In this study, we assessed the effect of NEW on biofilms formed by meat-related and reference L. monocytogenes strains on polystyrene and stainless steel. Forty wild-type strains isolated from meat products and processing environments were firstly screened for their biofilm-forming abilities and classified as weak (30 %; 12/40), moderate (55 %; 22/40), and strong (15 %; 6/40) biofilm producers. Twenty-two wild-type and two reference strains were selected for the eradication assays, performed by treating the biofilms with NEW for 9 minutes of total contact time. In silico functional enrichment analysis and the visualization of biofilms by scanning electron microscopy (SEM) were also performed. The NEW treatment resulted in a greater average reduction of viable cells in biofilms formed on polystyrene (4.3 ± 1.0 log10 CFU/cm2) compared to stainless steel (2.9 ± 2.0 log10 CFU/cm2), and a remarkable intraspecies variability was observed. SEM images revealed higher structural damage on biofilms formed on polystyrene. Functional enrichment analysis suggested that clustered regularly interspaced short palindromic repeats (CRISPR)-associated elements could be involved in resistance to the treatments. NEW could be a promising additional tool to mitigate L. monocytogenes biofilms in meat processing environments, although its effect varied with surface material and strain-specific characteristics.

Biologically synthesized nanoparticles: barley-mediated silver and gold nanoparticles and caged gold nanoplatform for advanced drug delivery system engineering in medicine

The integration of green synthesis methods and advanced nanostructure designs holds significant promise for the development of innovative nanomaterials with diverse biomedical applications. This commentary delves into the use of barley grains for the eco-friendly synthesis of silver and gold nanoparticles, highlighting their potential as biocompatible agents with potent antibacterial properties. The barley-mediated synthesis approach not only offers a sustainable and cost-effective method for producing these nanoparticles but also underscores their remarkable efficacy against pathogenic bacteria. The barley-mediated approach not only offers a sustainable and cost-effective method for producing biocompatible nanoparticles but also demonstrates remarkable antibacterial efficacy against pathogenic bacteria. By critically evaluating the strengths and potential gaps in this synthesis approach, this commentary emphasizes the importance of integrating green synthesis techniques with advanced nanoparticle applications. Future research directions should aim at optimizing synthesis processes, ensuring enhanced stability and biocompatibility, and exploring the full potential of biologically synthesized nanoparticles in medical treatments and environmental sustainability. This focus on sustainable synthesis and application could pave the way for the next generation of nanomaterials, offering significant advancements in both healthcare and ecological preservation. By examining the strengths, gaps, and potential synergies between these two approaches, this commentary underscores the importance of sustainable synthesis techniques and the development of multifunctional nanoparticles. This integrated approach could lead to the creation of next-generation nanomaterials, offering significant advancements in medical treatments and environmental sustainability.

Effect of pre-harvest sanitizer treatments on Listeria survival, sensory quality and bacterial community dynamics on leafy green vegetables grown under commercial conditions

Leafy green vegetables (LGVs) have large surface areas and can be colonized by various microorganisms including pathogens. In this study, we investigated the effect of pre-harvest sanitizer treatments on the survival of inoculated proxy pathogen Listeria innocua ATCC 33090 and the natural microbial community of mizuna, rocket (arugula), red chard and spinach grown under commercial conditions. Electrolyzed water (e-water), peracetic acid (PAA), and 1-bromo-3-chloro-5-dimethylhydantoin (BCDMH) were tested against water controls. We also observed the subsequent sensorial changes of harvested, bagged LGV leaves over a period of 12 days within chill storage alongside the growth, diversity and structure of bacterial populations determined using 16S rRNA gene amplicon sequencing and total viable counts (TVC). Treatment with PAA resulted in the highest reductions of L. innocua (2.4-5.5 log units) compared to the other treatments (0.25-2.5 log units). On day 0 (24 h after sanitizer application), the TVC on sanitizer treated LGVs were significantly reduced compared to water controls, except for rocket. During storage at 4.5 (±0.5)°C sanitisers only hindered microbial growth on LGVs initially and did not influence final bacterial population levels, growth rates or changes in LGV sample colour, decay, odour and texture compared to water controls. Shelf-life was not extended nor was it reduced. The community structure on LGV types differed though a core set of bacterial amplicon sequence variants (ASV) were present across all samples. No significant differences were observed in bacterial diversity between sanitizer treatments, however sanitizer treated LGV samples had initially reduced diversity compared to water treated samples. The bacterial compositions observed at the end point of storage considerably differed from what was observed at initial point owing to the increase in abundance of specific bacterial taxa, mainly Pseudomonas spp., the abundance and growth responses differing between LGV types studied. This study provides a better understanding on the microbiology and sensory impact of pre-harvest applied sanitiser treatments on different LGVs destined for commercial food use.

Strategies for Microbial Decontamination of Fresh Blueberries and Derived Products

Increasing consumption of blueberries is associated with appreciation of their organoleptic properties together with their multiple health benefits. The increasing number of outbreaks caused by pathogenic microorganisms associated with their consumption in the fresh state and the rapid spoilage of this product which is mainly caused by moulds, has led to the development and evaluation of alternatives that help mitigate this problem. This article presents different strategies ranging from chemical, physical and biological technologies to combined methods applied for microbial decontamination of fresh blueberries and derived products. Sanitizers such as peracetic acid (PAA), ozone (O3), and electrolyzed water (EOW), and physical technologies such as pulsed light (PL) and cold plasma (CP) are potential alternatives to the use of traditional chlorine. Likewise, high hydrostatic pressure (HHP) or pulsed electrical fields (PEF) successfully achieve microbial reductions in derivative products. A combination of methods at moderate intensities or levels is a promising strategy to increase microbial decontamination with a minimal impact on product quality.

Effect of Storage Conditions on Shelf Stability of Undiluted Neutral Electrolyzed Water

ABSTRACT

Neutral electrolyzed water (NEW) is an oxidizing sanitizer that can be made locally on-site; it is often stored in a ready-to-use format to accumulate the large volumes required for periodic or seasonal use. The shelf stability of NEW sanitizer was, therefore, assessed under various storage conditions to guide the development of protocols for its industrial application. To that end, fresh NEW with an available chlorine concentration (ACC) of 480 mg/L, pH 6.96, and oxidation reduction potential (ORP) of 916 mV was stored under different conditions. These were open or sealed polypropylene bottles, three different surface area-to-volume (SA:V) ratios (0.9, 1.7, and 8.7), and two temperatures (4 and 25°C). NEW stored at 4°C was significantly more stable than NEW stored at 25°C; ACC and pH decreased by 137 mg/L and 0.7, respectively, whereas ORP increased by 23 mV, after 101 days of storage. At 25°C, ACC decreased to <0.01 mg/L after 52 days in bottles with a SA:V ratio of 8.7, with a similar decrease after 101 days in bottles with a SA:V ratio of 1.7. However, pH decreased by up to 3.7 pH units, and ORP increased by up to 208 mV. The antimicrobial efficacy of "aged" electrolyzed oxidizing (EO) water with different ACC and ORP, but the same pH (i.e., 3.4 ± 0.2), was evaluated against Escherichia coli and Listeria innocua to determine any differences in residual antimicrobial activity. EO water with an ACC of ≥7 mg/L and an ORP of 1,094 mV caused a reduction of at least 4.7 log, whereas EO water with nondetectable ACC and considerably high ORP (716 mV) had little antimicrobial effect (<1-log reduction). Results from this study indicate that the efficacy of NEW as a sanitizer for large-scale applications such as horticulture can be maintained for at least 3 months when it is stored in closed containers with low SA:V ratio at low temperatures.

HIGHLIGHTS

Effect of physio-chemical seed treatments on opium poppy downy mildews caused by Peronospora meconopsidis and P. somniferi

Downy mildew of opium poppy is the single biggest disease constraint afflicting the Australian poppy industry. Within the pathosystem, the transmission of infections via infested seed is of major concern. Both downy mildew pathogens of poppy; Peronospora meconopsidis and P. somniferi, are known contaminants of commercial seed stocks. Using seed naturally infested with these pathogens, the effect of physio-chemical seed treatments on seedling health and disease transmission were evaluated. Individual seed treatments were tested to determine optimal treatment parameters for each; including incubation time, temperature and treatment concentration. Optimised physiochemical treatments were then compared. The most effective treatment methods were seed washes in acidified electrolytic water (400 ppm hypochlorous acid for 5 min) and hypochlorite solution (2% NaOCI for 5 min). In seed to seedling transmission assays, these two treatments reduced transmission of P. somniferi by 88.8% and 74.61%, and P. meconopsidis by 93.3% and 100%, respectively. These methods are recommended for seed treatment of commercial opium poppy seed to assist in the control of the downy mildew diseases.

Hurdle enhancement of acidic electrolyzed water antimicrobial efficacy on Bacillus cereus spores using ultrasonication

This study evaluated the inactivation effect of ultrasonic treatment combined with acidic electrolyzed water (AEW) on Bacillus cereus spores. AEW treatment reduced the spores by 1.05-1.37 log CFU/mL while the sporicidal effect of ultrasound was minor. More strikingly, simultaneous ultrasonic and AEW treatments for 30 min led to 2.29 log CFU/mL reduction and thus, considered a synergistic effect. Flow cytometry combined with SYTO/PI staining analysis revealed that ultrasound hydrolyzed the cortex while the AEW partially damaged the integrity of the inner membrane. Scanning and transmission electron microscopies were used to characterize the ultrastructural changes. The detachment of the exosporium induced by ultrasound was the most apparent difference compared with the control group, and the electron density of spores appeared to be heterogeneous after treatment with AEW. These results indicated that combining ultrasound with AEW is a promising decontamination technology with potential uses in the food industry and environmental remediation.

Exploring the Efficacy and Mechanisms of a Crop Sterilant for Reducing Infestation by Spotted-Wing Drosophila (Diptera: Drosophilidae)

Vinegar flies (Diptera: Drosophilidae) are well known to be associated with yeasts, which provide important nutrients and emit attractive semiochemicals. Drosophila suzukii (Matsumura) has become a major pest of berries and cherries around the world, requiring intensive management to maintain fruit quality. Although insecticides remain a dominant control approach, disruption of fly-yeast-host interactions remains a promising avenue for reducing the economic impact of this pest. We conducted field and laboratory experiments to explore whether a crop sterilant (peroxyacetic acid and hydrogen peroxide) developed for disease control can affect D. suzukii. In 2 yr of field tests in highbush blueberries, we found significantly lower infestation by D. suzukii in plots treated with the crop sterilant, both alone and in a rotation program with zeta-cypermethrin. When shoots from treated plots were tested in no-choice bioassays, crop sterilant treatments did not affect adult mortality or oviposition, but they reduced infestation. To explore the mechanisms in the laboratory, we found that the crop sterilant did not affect adult mortality, nor oviposition on treated fruit under no-choice settings, but adult flies settled and oviposited less on treated fruit in choice settings. When the crop sterilant was applied to colonies of Hanseniaspora uvarum (Niehaus) (Saccharomycetales: Saccharomycodaceae) and Issatchenkia terricola (Van der Walt) (Saccharomycetales: Saccharomycetacea) yeasts that are attractive and provide nutrition to D. suzukii, there was a dose-dependent inhibition of their growth. We highlight the potential for microbial management as a component of integrated pest management programs and prioritize research needs to incorporate this approach into control programs.