Assessing water-assisted UV-C light and its combination with peroxyacetic acid and Pseudomonas graminis CPA-7 for the inactivation and inhibition of Listeria monocytogenes and Salmonella enterica in fresh-cut 'Iceberg' lettuce and baby spinach leaves

Effects of Slightly Acidic Electrolyzed Water on the Quality of Fresh-Cut Apple

To investigate the effects of a slightly acidic electrolyzed water (SAEW) treatment on the quality of fresh-cut apples during storage, this research used a Box-Behnken design to determine the optimal SAEW treatment conditions. Then, the fresh-cut apple was treated under the optimal condition and subjected to a 13-d storage experiment at 4 °C. For fresh-cut apple treated under the optimal SAEW treatment conditions, the total number of surface colonies was reduced by 2.82 logarithms compared to the control group and the sensory score was 8.73. For the treated fresh-cut apple during storage, the quality of the treated group was significantly greater than the non-treatment group. Thus, the SAEW treatment not only effectively controlled the number of microbes on fresh-cut apple, but also slowed quality deterioration during storage.

Evaluation of water-assisted UV-C light and its additive effect with peracetic acid for the inactivation of Listeria monocytogenes, Salmonella enterica and murine norovirus on whole and fresh-cut strawberries during shelf-life

BACKGROUND

The purpose of the present study was to examine the inactivation of Salmonella enterica (50 μL; 10⁹  CFU g^-1 ), Listeria monocytogenes (50 μL; 10⁹  CFU g^-1 ), and murine norovirus (MNV-1; 50 μL; 10⁷ 50% tissue culture infectious dose (TCID₅₀ ) mL^-1 ) on whole and fresh-cut strawberries after 2 min disinfection treatments (water (H₂ O), chlorine 200 mg L^-1 (NaClO), water-assisted ultraviolet-C (UV-C) (WUV), and the combination WUV and 40 mg L^-1 of PA (WUV + PA)) in a water tank (15 L) equipped with 4 UV-C lamps (17.2 W each), and after 7 days of cold storage (4 and 10 °C). For MNV-1, dry UV-C treatment (DUV) was also tested. For all UV-C treatments, an irradiation dose of 1.3 kJ m^-2 was used.

RESULTS

When strawberries were washed with WUV, L. monocytogenes and S. enterica were reduced by 2.8 and 2.2 log CFU g^-1 , respectively. The addition of 40 mg L^-1 of PA to WUV (WUV + PA) increased the reduction range of L. monocytogenes and S. enterica by 1.9 and 0.8 log, respectively. Regarding the wash water, no pathogens were recovered after the WUV + PA treatment (detection limit 50 CFU mL^-1 ). Depending on storage conditions (7 days at 4 or 10 °C), reductions observed were 0.5 to 2.0 log for S. enterica and 0.5 to 3.0 log for L. monocytogenes. The reductions in MNV-1 titer after disinfection treatments ranged from 1.3 to 1.7 log. No significant differences between storage conditions were observed for MNV-1: titers did not decline or were reduced up to 0.3 log after 7 days of cold storage.

CONCLUSION

The three-way action for disinfecting strawberries by UV-C irradiation and PA, plus the physical removal of the microorganisms by agitated water, are effective against foodborne pathogens on strawberries and water wash. During storage, WUV had a larger impact on the inactivation kinetics of S. enterica. Storage had little impact on MNV-1 inactivation. © 2022 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Pathogenic potential of the surviving Salmonella Enteritidis on strawberries after disinfection treatments based on ultraviolet-C light and peracetic acid

Fresh fruits, especially strawberries, are usually consumed raw without any step to ensure their food safety. Salmonella enterica is one of the most important etiologic agents for foodborne diseases throughout the world and its ability to respond to some stress responses makes it even more dangerous. In the present investigation, we study the survival of S. Enteritidis (CECT-4300) on strawberries after 2-min of various disinfection steps (NaClO (200 ppm), peracetic acid (PAA; 40 ppm), water-assisted UV-C (WUV-C), and the combination WUV-C and 40 ppm of PAA (WUV-C + PAA)) and after 5 days of cold storage (4 °C). Moreover, the pathogenic potential of the surviving bacteria, such as the ability to survive throughout the gastrointestinal tract (GI) and subsequently the capability to adhere to and invade Caco-2 cells, was tested at each sampling point. After 2-min of washing procedures, reductions of S. Enteritidis on strawberries were ≥1.2 log, with no significant differences among treatments. However, the use of WUV-C + PAA treatment achieved the highest reductions in washing water, in which S. Enteritidis was not detected (<DL). At the end of 5-day storage period, reductions of the WUV-C + PAA treated-samples were lower in comparison with PAA-treated samples (P < 0.05). The effect of the treatments used did not interfere with the survival of S. Enteritidis along the GI tract. After disinfection and subsequent GI simulation, all remaining populations demonstrated an elevated ability to adhere in Caco-2 cells (67.5-81.1%) compared with those obtained on untreated strawberries (61.4%). Concerning the ability of invasion, no significant differences could be observed. Remarkably, after 5 days at 4 °C, the adherence of S. Entertidis significantly decreased in the samples with the combined treatment meanwhile the invasion ability was not detected for any treatment. The results of the present study are essential for the quantitative microbial risk estimations.

Practical in-storage interventions to control foodborne pathogens on fresh produce

Although tremendous efforts have been made to ensure fresh produce safety, various foodborne outbreaks and recalls occur annually. Most of the current intervention strategies are evaluated within a short timeframe (less than 1 h), leaving the behavior of the remaining pathogens unknown during subsequent storages. This review summarized outbreak and recall surveillance data from 2009 to 2018 obtained from government agencies in the United States to identify major safety concerns associated with fresh produce, discussed the postharvest handling of fresh produce and the limitations of current antimicrobial interventions, and reviewed the intervention strategies that have the potential to be applied in each storage stage at the commercial scale. One long-term (up to 12 months) prepacking storage (apples, pears, citrus among others) and three short-term (up to 3 months) postpacking storages were identified. During the prepacking storage, continuous application of gaseous ozone at low doses (≤1 ppm) is a feasible option. Proper concentration, adequate circulation, as well as excess gas destruction and ventilation systems are essential to commercial application. At the postpacking storage stages, continuous inhibition can be achieved through controlled release of gaseous chlorine dioxide in packaging, antimicrobial edible coatings, and biocontrol agents. During commercialization, factors that need to be taken into consideration include physicochemical properties of antimicrobials, impacts on fresh produce quality and sensory attributes, recontamination and cross-contamination, cost, and feasibility of large-scale production. To improve fresh produce safety and quality during storage, the collaboration between researchers and the fresh produce industry needs to be improved.

Water UV-C treatment alone or in combination with peracetic acid: A technology to maintain safety and quality of strawberries

Disinfection of fruits is one of the most important steps since they are going to be eaten fresh-or minimally-processed. This step affects quality, safety, and shelf-life of the product. Despite being a common sanitizer in the fruit industry, chlorine may react with organic matter leading to the formation of toxic by-products. Alternative sustainable disinfection strategies to chlorine are under study to minimize environmental and human health impact. Water-assisted UV-C light (WUV-C) is proposed here as an alternative sanitizing method for strawberries. In this study, strawberries were washed for 1 or 5 min in a tank with 2 or 4 lamps on, each emitting UV-C light at 17.2 W/cm², or in a chlorine solution (200 ppm, pH 6.5). Moreover, trials with 4 lamps on, together with a washing solution consisting on peracetic acid at 40 or 80 ppm, were carried out. Overall, quality and nutritional parameters of strawberries after treatments were maintained. Changes in color were not noticeable and fruits did not lose firmness. No major changes were observed in antioxidant activity, organic acid, anthocyanin, vitamin C, and total phenolic content. Yeasts and molds were not affected by the WUV-C treatment, and 5 min were needed to significantly reduce total aerobic mesophylls population. However, reductions of artificially inoculated Listeria innocua and Salmonella Typhimurium after WUV-C treatments were comparable to those obtained with chlorine-wash, which were 3.0 log CFU / g. Moreover, WUV-C light was effective to minimize microorganisms remaining in washing water, avoiding cross-contamination and thus, allowing water recirculation. This effect was improved when combining the action of UV-C light with peracetic acid, showing the suitability of this combined treatment, understood as an alternative to chlorine sanitation, for sanitizing strawberries and keeping the populations of pathogenic bacteria in washing water lower than 0.6 ± 0.1 log CFU / mL.

A Review on Individual and Combination Technologies of UV-C Radiation and Ultrasound in Postharvest Handling of Fruits and Vegetables

Ultraviolet-C radiation and ultrasound technology are widely accepted and continuously being appraised as alternatives to conventional thermal techniques for decontamination of fruits and vegetables. However, studies in these areas have presented challenges related to quality, safety, limited capability, and cost of energy. This review paper presents an up-to-date summary of applications of ultraviolet-C radiation and ultrasound technology for postharvest handling of fruits and vegetables from relevant literature. The limitations associated with applications of ultraviolet-C radiation and ultrasound technology individually has prompted their combination alongside other antimicrobial strategies for enhanced bactericidal effect. The combination of ultraviolet-C radiation and ultrasound technology as a hurdle approach also provides enhanced efficiency, cost effectiveness, and reduced processing time without compromising quality. The review includes further scope of industrial-led collaboration and commercialization of ultraviolet-C radiation and ultrasound technology such as scale-up studies and process optimization.

Competitive and/or Cooperative Interactions of Listeria monocytogenes With Bacillus cereus in Dual-Species Biofilm Formation

Microorganisms in dairy industries can form monospecies, dual-species, or multispecies biofilms, showing cooperative or competitive behaviors, which might contribute to the reduction of efficiency of cleaning and sanitization processes and eventually turn into a potential source of contamination. This study proposes to evaluate the behavior of Listeria monocytogenes in monospecies biofilms, cocultured with Bacillus cereus. The isolates were of dairy origin, and the selection occurred after studies of competition among species. The biofilm formations on AISI 304 stainless steel at 25°C in a stationary culture were analyzed to observe the cooperative or competitive interactions among species, as well as the effect of pre-adhered cells. Biofilm formation assays were performed in four experiments: Experiment 1: in the presence of strains of antagonistic substance producer B. cereus (+); Experiment 2: extract of the antagonistic substance of B. cereus; Experiment 3: pre-adhered cells of B. cereus; and Experiment 4: pre-adhered cells of L. monocytogenes. Subsequently, cooperative behavior was observed by scanning electron microscopy. The L. monocytogenes monospecies biofilm counts of greater than 5 log colony-forming units (CFU)/cm² were also observed in dual-species biofilms in the presence of B. cereus (non-producers of antagonist substance), showing cooperative behavior between species. However, in the presence of antagonistic substance produced by B. cereus, the counts were lower, 1.39 and 1.70 log CFU/cm² (p > 0.05), indicating that the antagonistic substance contributes to competitive interactions. These data are relevant for the development of new studies to control L. monocytogenes in the dairy industry.

Biopreservation approaches to reduce Listeria monocytogenes in fresh vegetables

Two biopreservation approaches for fresh lettuce, rocket salad, parsley and spinach were studied. The potential of Pediococcus pentosaceus DT016, as a protective culture, to suppress Listeria monocytogenes in vegetables during storage was evaluated. The pathogen numbers in the vegetables inoculated with P. pentosaceus DT016 were significantly (p < 0.01) lower throughout the storage period and, at the last storage day, a minimum difference of 1.4 log CFU/g was reported when compared with the vegetables without the protective culture. Moreover, by using two levels of L. monocytogenes (about 6 and 4 log CFU/g), it was observed that the antagonist effect of P. pentosaceus was higher for the lower pathogen numbers. The second approach evaluated a pediocin DT016 solution to inactivate and control L. monocytogenes proliferation. The pathogen load was studied after washing with: water, chlorine and the pediocin solution and along storage at 4  °C. Comparing the various washing solutions, the vegetables washed with pediocin presented significantly (p < 0.01) lower pathogen numbers throughout storage, by a minimum of 3.2 and 2.7 log CFU/g, than in vegetables washed with water and chlorine, respectively. The proposed methodologies are promising alternatives to maintain the safety of fresh vegetables during extended storage at refrigeration temperature.

Evaluating a Combined Method of UV and Washing for Sanitizing Blueberries, Tomatoes, Strawberries, Baby Spinach, and Lettuce

We assessed a fresh produce decontamination system using a combined method of UV and washing (water-assisted UV [WUV]) in different scales. The system used tap water to wash fresh produce while exposing it to UV light. First, the reduction of Salmonella in tap water under UV treatment (1 to 1,740 mJ/cm2) was determined. Increasing the UV dose significantly (P < 0.05) increased the Salmonella reduction in wash water, and UV intensity of more than 2 mW/cm2 could reduce Salmonella in tap water to below 1 CFU/mL given enough processing time (more than 1 min; UV dose of 120 mJ/cm2). Then, the decontamination effectiveness of a small WUV system was tested on blueberries (50 g). Blueberries were spot or dip inoculated with a Salmonella cocktail and treated by the small WUV system (200 mL of water). In general, WUV treatments achieved significantly better Salmonella inactivation than tap water wash; tap water wash (10 min) and 2 mW/cm2 WUV treatment (with a UV dose of 1,200 mJ/cm2) reduced populations of spot-inoculated Salmonella on blueberries by 2.44 and 5.45 log, respectively. Compared with spot-inoculated Salmonella on blueberries, dip-inoculated Salmonella was more difficult to be inactivated by WUV treatments. Then, the decontamination effectiveness of WUV treatments was tested on blueberries (170 g), tomatoes (290 g), strawberries (170 g), baby spinach (60 g), and lettuce (60 g) using a larger WUV system. In general, 10 min of 29 mW/cm2 WUV treatment (a high UV dose of 17,400 mJ/cm2) resulted in significantly better Salmonella inactivation than tap water wash (for 10 min) regardless the inoculation method, agreeing with the results of the small-scale study. For both spot- and dip-inoculated lettuce, no significant difference (P > 0.05) in Salmonella inactivation by WUV treatments was observed when the quantity of lettuce increased from 50 to 100 g.