Inactivation of Escherichia coli Population on Fruit Surfaces Using Ultraviolet-C Light: Influence of Fruit Surface Characteristics

Biofilm inactivation using LED systems emitting germicidal UV and antimicrobial blue light

Biofilms have been widely detected in water distribution and water storage systems posing potential risks to drinking water safety by harboring and shedding pathogens. Light-based disinfection methods, such as germicidal ultraviolet (UV) and antimicrobial blue light (aBL), could serve as non-chemical alternatives for biofilm control. This study investigated the inactivation of pure-culture Pseudomonas aeruginosa biofilms and mixed-culture biofilms using three distinct light-based disinfection methods: a low-pressure (LP) UV lamp emitting at 254 nm, a UV light emitting diode (LED) at 270 nm, and an aBL LED at 405 nm. The biofilms were developed on three commonly used materials including polycarbonate (PC), polytetrafluoroethylene (PTFE), and polyvinyl chloride (PVC), to assess the impact of surface characteristics on light-based biofilm inactivation. Our findings show that all selected devices can effectively inactivate pure-culture and mixed-culture biofilms. While both UV devices (LP UV lamp and UV LED) provided significant inactivation at lower fluences (>1 log reduction at 20 mJ/cm2), aBL LED achieved significant inactivation at higher fluences for pure culture (maximum log reduction of 3.8 ± 0.5 at > 200,000 mJ/cm2). Inactivation performance also varied with surface materials, likely attributed to different surface properties including roughness, hydrophobicity, and surface charge. This study provides important information on using light-based technologies for biofilm control and highlights the effect of surface materials on their inactivation performance.

The Attenuation of Microbial Reduction in Blueberry Fruit Following UV-LED Treatment

Ultraviolet-C (UV-C) irradiation is a well-recognized technology for improving blueberry postharvest quality, and previous literature indicates that it has the potential for dual-use as an antimicrobial intervention for this industry. However, the practicality and feasibility of deploying this technology in fresh blueberry fruit are significantly hindered by the shadowing effect occurring at the blossom-end scar of the fruit. The purpose of this study was to determine if treating the blueberry fruit within a chamber fitted with UV-Light Emitting Diodes (LEDs) emitting a peak UV-C at 275 nm could minimize this shadowing and result in improved treatment efficacy. Ten blueberry fruits were dip-inoculated with E. coli at a concentration of 10⁵ CFU/mL and irradiated within the system at doses of 0, 1.617, 3.234, 9.702, and 16.17 mJ/cm² (0, 30, 60, 180, and 300 s). Statistical analysis was performed to characterize the extent of microbial survival as well as the UV-C inactivation kinetics. A maximum of 0.91-0.95 log reduction was observed, which attenuated after 60 s of treatment. The microbial inactivation and survival were thus modeled using the Geeraerd-tail model in Microsoft Excel with the GInaFIt add-in (RMSE = 0.2862). Temperatures fluctuated between 23 ± 0.5°C and 39.5°C ± 0.5°C during treatment but did not statistically impact the treatment efficacy (P = 0.0823). The data indicate that the design of a UV-LED system may improve the antimicrobial efficacy of UV-C technology for the surface decontamination of irregularly shaped fruits, and that further optimization could facilitate its use in the industry.

Ultraviolet Applications to Control Patulin Produced by Penicillium expansum CMP-1 in Apple Products and Study of Further Patulin Degradation Products Formation and Toxicity

Patulin is a mycotoxin whose presence in apple-derived products and fruit juices is legally regulated, being its maximum limits established in the legislation of multiple countries. However, the management of contaminated batches is still an issue for producers. This investigation aims to evaluate ultraviolet light (254 nm, UV-C254nm) irradiation to find solutions that can be applied at different stages of the apple juice production chain. In this regard, 8.8 (UV-1) and 35.1 (UV-2) kJ m−2 treatments inactivated spores of Penicillium expansum CMP-1 on the surface of apples. Although the same treatments applied to wounded apples (either before the infection or after the infection, immediately or when the lesion had appeared) did not show any effect on the growth rate of P. expansum during storage (up to 14 days, at 4 or 25 °C), they reduced patulin content per lesion size in apples treated after the infection had occurred (patulin decreased from 2.24 (control) to 0.65 µg kg−1 cm−2 (UV-2 treated apples)). Additionally, the treatment of juice with patulin with ultraviolet light up to 450.6 kJ m−2 resulted in more than 98 % reduction of patulin. Degradation products of patulin after UV-C254nm treatments were tentatively identified by HPLC–MS, and toxicity and biological activities were assessed in silico, and results indicated that such products did not pose an increased risk when compared to patulin.

Conventional and non-conventional disinfection methods to prevent microbial contamination in minimally processed fruits and vegetables

Pandemic COVID-19 warned the importance of preparing the immune system to prevent diseases. Therefore, consuming fresh fruits and vegetables is essential for a healthy and balanced diet due to their diverse compositions of vitamins, minerals, fiber, and bioactive compounds. However, these fresh products grew close to manure and irrigation water and are harvested with equipment or by hand, representing a high risk of microbial, physical, and chemical contamination. The handling of fruits and vegetables exposed them to various wet surfaces of equipment and utensils, an ideal environment for biofilm formation and a potential risk for microbial contamination and foodborne illnesses. In this sense, this review presents an overview of the main problems associated with microbial contamination and the several chemicals, physical, and biological disinfection methods concerning their ability to avoid food contamination. This work has discussed using chemical products such as chlorine compounds, peroxyacetic acid, and quaternary ammonium compounds. Moreover, newer techniques including ozone, electrolyzed water, ultraviolet light, ultrasound, high hydrostatic pressure, cold plasma technology, and microbial surfactants have also been illustrated here. Finally, future trends in disinfection with a sustainable approach such as combined methods were also described. Therefore, the fruit and vegetable industries can be informed about their main microbial risks to establish optimal and efficient procedures to ensure food safety.

Free radicals removing extracellular polymeric substances to enhance the degradation of intracellular antibiotic resistance genes in multi-resistant Pseudomonas Putida by UV/H2O2 and UV/peroxydisulfate disinfection processes

UV-based advanced oxidation processes (UV-AOPs) have been recommended to disinfect wastewater treatment plant (WWTP) effluents to control the dissemination of antibiotic resistance, but the mechanism of intracellular antibiotic resistance genes (i-ARGs) degradation by UV-AOPs is still poorly understood. Here we compared the efficacies of UV, UV/H₂O₂, and UV/PDS in degrading seven i-ARGs carried by a multi-drug resistant P. putida MX-2 isolated from sewage sludge and investigated the roles of free radicals and UV irradiation in degrading the carried i-ARGs in UV-AOPs. The results suggested that although UV/H₂O₂ and UV/PDS were only slightly superior to UV to inactivate P. putida MX-2, they significantly promoted the degradation of i-ARGs. The generated free radicals mainly reacted with the bacterial extracellular polymeric substances (EPS), increased the cell membrane permeability of bacteria, and consequently facilitated UV irradiation enter into the intracellular environment to damage the i-ARGs, thus enhancing their degradation during UV-AOPs processes. Our findings suggested that the removal of bacterial EPS by free radicals greatly contributed to the degradation of i-ARGs by UV irradiation in UV-AOPs, and more efficient approaches that are capable of removing EPS should be further developed to effectively control the dissemination of antibiotic resistance by UV treatment of wastewater effluent.

Effect of UVC Light-Emitting Diodes on Pathogenic Bacteria and Quality Attributes of Chicken Breast

ABSTRACT

This study was conducted to investigate the inactivation of foodborne pathogens and the quality characteristics of fresh chicken breasts after UVC light-emitting diode (UVC-LED) treatment. Fresh chicken breasts were separately inoculated with Salmonella Typhimurium, Escherichia coli O157:H7, and Listeria monocytogenes at initial populations of 6.01, 5.80, and 6.22 log CFU/cm2, respectively, and then treated with UVC-LED irradiation at 1,000 to 4,000 mJ/cm2. UVC-LED irradiation inactivated the test bacteria in a dose-dependent manner. After UVC-LED treatment at 4,000 mJ/cm2, the populations of Salmonella Typhimurium, E. coli O157:H7, and L. monocytogenes on chicken breasts were decreased by 1.90, 2.25, and 2.18 log CFU/cm2, respectively. No significant changes (P > 0.05) were found in color, pH, texture, and thiobarbituric acid-reactive substances of chicken breasts following UVC-LED irradiation at doses ≤4,000 mJ/cm2. These results indicate that UVC-LED radiation is a promising technology for reducing the level of microorganisms while maintaining the physicochemical characteristics of poultry meat.

HIGHLIGHTS

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.

Efeitos da radiação UV-C em alface e maçã minimamente processadas: uma revisão

Resumo A alta procura por alimentos nutritivos e de fácil consumo tem impulsionado o mercado de frutas e hortaliças minimamente processadas (MP). No entanto, estes alimentos têm uma curta vida de prateleira, são marcados pela rápida deterioração. A radiação ultravioleta-C (UV-C) é uma técnica não térmica, limpa e de baixo custo que pode servir como alternativa aos sanitizantes comuns. Porém, a sua baixa penetração em alimentos tem limitado sua aplicação neste ramo da indústria. Objetivou-se revisar o efeito germicida da radiação UV-C em alface e maçã minimamente processados e os possíveis danos às características físicas e sensoriais, além de realizar uma avaliação dos fatores envolvidos nesta técnica. Uma redução de 1 a 2 log UFC/g da microflora natural destes vegetais é facilmente atingida com doses moderadas, para diversos grupos de microrganismos deteriorantes. Uma maior redução nos níveis de patogênicos inoculados, acima de 4 log UFC/g, foi verificada quando doses maiores foram utilizadas. Para a alface MP, a superfície irregular é considerada um limitante, por reduzir o contato entre a radiação e os microrganismos. Essa limitação pode ser superada alterando parâmetros do processo, como distância da fonte emissora e exposição de ambos os lados do vegetal. A cor das folhas foi melhor preservada com emprego de radiação UV-C em doses moderadas. Na maçã MP, alterações indesejáveis, como a intensa perda de massa e o escurecimento pronunciado, estão associadas a um severo dano celular em doses mais elevadas. Tais efeitos puderam ser evitados expondo a fruta por um menor tempo. Em geral, verificou-se boa aceitabilidade de alface e maçã MP tratadas com radiação UV-C. O tipo de fruta ou hortaliça utilizado e a sua topografia exercem grande influência na eficiência da técnica. Não foi possível sugerir uma dosagem adequada para a alface ou a maçã MP, visto que os poucos estudos disponíveis diferem quanto à variedade de alface ou maçã estudada, na forma como os tratamentos foram conduzidos e na dose exposta.

Inactivation of Escherichia Coli and Salmonella Using 365 and 395 nm High Intensity Pulsed Light Emitting Diodes

High intensity pulsed light emitting diode (LED) treatment is a novel approach to inactivate foodborne pathogens. The objective of this study was to evaluate the antibacterial potential of high intensity 365 (UV-A) and 395 nm (NUV-Vis) LED treatments against Escherichia coli and Salmonella enterica at high and low water activity (a_w) conditions, and to understand the influence of different process parameters on their antibacterial efficacy. Bacteria at high (in phosphate buffer saline, PBS) and low a_w (a_w = 0.75) conditions were treated with both the LEDs with specific doses at a fixed distance from the LEDs. The 365 nm LED showed more effectiveness in reducing the dried bacteria compared to 395 nm LED. The dry E. coli showed more resistance to LED treatments compared to Salmonella. The 365 and 395 nm LED treatments with ~658 J/cm² dose resulted in reductions of 0.79 and 1.76 log CFU/g of Salmonella, respectively, on 0.75 a_w pet foods. The LED treatments increased the surface temperature, resulting in water loss in the treated samples. This study showed that the dose, duration of light exposure, bacterial strain, and a_w played a major role in the antibacterial efficacy of the 365 and 395 nm LEDs.

Bactericidal effect of intense pulsed light on seeds without loss of viability

This study investigated the microbial inactivation effects of intense pulsed light (IPL) treatment as an alternative to chemical treatment for decontaminating the radish and pak choi seeds. The f R values (which indicate the resistance to IPL treatment) for radish and pak choi seeds were 24.50, 20.81 J/cm2, respectively. This resistance exhibited by seeds to IPL treatment is related to their surface roughness. Their Rq (the root-mean-square roughness), average surface roughness (Ra), and 10-point height roughness (Rz) values indicate that each crevice on a rough surface could shelter microorganisms from IPL. Viability tests of seeds exposed to IPL treatment indicated that the average germination rates of treated seeds exceeded 85% on day 3 of germination, which is considered as an acceptable criterion for germination. Also, on day 5 of germination the average shoot lengths of sprouts exposed to IPL did not differ significantly from those of untreated seeds.

Fungal Gene Mutation Analysis Elucidating Photoselective Enhancement of UV-C Disinfection Efficiency Toward Spoilage Agents on Fruit Surface

Short-wave ultraviolet (UV-C) treatment represents a potent, clean and safe substitute to chemical sanitizers for fresh fruit preservation. However, the dosage requirement for microbial disinfection may have negative effects on fruit quality. In this study, UV-C was found to be more efficient in killing spores of Botrytis cinerea in dark and red light conditions when compared to white and blue light. Loss of the blue light receptor gene Bcwcl1, a homolog of wc-1 in Neurospora crassa, led to hypersensitivity to UV-C in all light conditions tested. The expression of Bcuve1 and Bcphr1, which encode UV-damage endonuclease and photolyase, respectively, were strongly induced by white and blue light in a Bcwcl1-dependent manner. Gene mutation analyses of Bcuve1 and Bcphr1 indicated that they synergistically contribute to survival after UV-C treatment. In vivo assays showed that UV-C (1.0 kJ/m²) abolished decay in drop-inoculated fruit only if the UV-C treatment was followed by a dark period or red light, while in contrast, typical decay appeared on UV-C irradiated fruits exposed to white or blue light. In summary, blue light enhances UV-C resistance in B. cinerea by inducing expression of the UV damage repair-related enzymes, while the efficiency of UV-C application for fruit surface disinfection can be enhanced in dark or red light conditions; these principles seem to be well conserved among postharvest fungal pathogens.

UV-C inactivation of foodborne bacterial and viral pathogens and surrogates on fresh and frozen berries

Outbreaks of foodborne illness associated with berries often involve contamination with hepatitis A virus (HAV) and norovirus but also bacteria such as Escherichia coli O157:H7 and parasites such as Cyclospora caytanensis. We evaluated the applicability of UV-C to the inactivation of pathogens on strawberries, raspberries and blueberries. Our three-step approach consisted of assessing the chemical safety of UV-C-irradiated berries, evaluating the sensory quality after UV-C treatment and finally studying the inactivation of the target microorganisms. Treatments lasting up to 9 min (4000 mJ cm^-2) did not produce detectable levels of furan (<5 μg/kg), a known photolysis product of fructose with genotoxic activity and thus were assessed to be toxicologically safe. No effect on taste or appearance was observed, unless treatment was excessively long. 20 s of treatment (an average fluence of ~ 212 mJ cm^-2) reduced active HAV titer by >1 log₁₀ unit in 95% of cases except on frozen raspberries, while 120 s were required to inactivate murine norovirus to this extent on fresh blueberries. The mean inactivation of HAV and MNV was greater on blueberries (2-3 log₁₀) than on strawberries and raspberries (<2 log₁₀). MNV was more sensitive on fresh than on frozen berries, unlike HAV. Inactivation of Salmonella, E. coli O157:H7 and Listeria monocytogenes was poor on all three berries, no treatment reducing viable counts by >1 log₁₀ unit. In most matrices, prolonging the treatment did not improve the result to any significant degree. The effect was near its plateau after 20 s of treatment. These results provide insight into the effectiveness of UV-C irradiation for inactivating bacterial and viral pathogens and surrogates on fresh and frozen berries having different surface types, under different physical conditions and at different levels of contamination. Overall they show that UV-C as single processing step is unsuitable to inactivate significant numbers of foodborne pathogens on berries.

Selection of Surrogate Bacteria for Use in Food Safety Challenge Studies: A Review

Nonpathogenic surrogate bacteria are prevalently used in a variety of food challenge studies in place of foodborne pathogens such as Listeria monocytogenes, Salmonella, Escherichia coli O157:H7, and Clostridium botulinum because of safety and sanitary concerns. Surrogate bacteria should have growth characteristics and/or inactivation kinetics similar to those of target pathogens under given conditions in challenge studies. It is of great importance to carefully select and validate potential surrogate bacteria when verifying microbial inactivation processes. A validated surrogate responds similar to the targeted pathogen when tested for inactivation kinetics, growth parameters, or survivability under given conditions in agreement with appropriate statistical analyses. However, a considerable number of food studies involving putative surrogate bacteria lack convincing validation sources or adequate validation processes. Most of the validation information for surrogates in these studies is anecdotal and has been collected from previous publications but may not be sufficient for given conditions in the study at hand. This review is limited to an overview of select studies and discussion of the general criteria and approaches for selecting potential surrogate bacteria under given conditions. The review also includes a list of documented bacterial pathogen surrogates and their corresponding food products and treatments to provide guidance for future studies.

Inactivation of Listeria monocytogenes on Frozen Red Raspberries by Using UV-C Light

In this study, the efficacy of UV-C treatment was determined on the reduction of foodborne pathogens on artificially contaminated frozen food surfaces. At first, the UV-C inactivation rates on 100 μl of the respective cocktails of Escherichia coli O157:H7, Salmonella , and Listeria monocytogenes covered underneath 0.5-cm-thick ice were examined. Simultaneously, the energy percentage of UV-C transmitted through the ice was determined. The experiments showed that more than 65% of the UV-C light energy passed through the ice and that UV-C susceptibility was in the descending order of E. coli O157:H7, Salmonella , and L. monocytogenes . L. monocytogenes , the most UV-C-resistant strain, was then selected to test on frozen raspberries. The UV-C inactivation kinetic data of L. monocytogenes were well described using the Weibull equation. During 720 s of UV-C exposure, with a total dose of 7.8 × 10² mJ/cm², a 1.5-log CFU/g reduction of L. monocytogenes population on the surface of frozen red raspberries was noted. No significant differences in total anthocyanins, total phenolics, and total antioxidant activity were observed between UV-C-treated and untreated frozen berries immediately after treatment. At the end of 9 months of storage at -35°C, UV-C-treated berries had statistically lower total phenolics, higher total anthocyanins, and similar total antioxidant activity compared with untreated berries. This study shows that UV-C light can be used to reduce the L. monocytogenes population on frozen raspberries.

Chemical, physical and morphological properties of bacterial biofilms affect survival of encased Campylobacter jejuni F38011 under aerobic stress

Campylobacter jejuni is a microaerophilic pathogen and leading cause of human gastroenteritis. The presence of C. jejuni encased in biofilms found in meat and poultry processing facilities may be the major strategy for its survival and dissemination in aerobic environment. In this study, Staphylococcus aureus, Salmonella enterica, or Pseudomonas aeruginosa was mixed with C. jejuni F38011 as a culture to form dual-species biofilms. After 4days' exposure to aerobic stress, no viable C. jejuni cells could be detected from mono-species C. jejuni biofilm. In contrast, at least 4.7logCFU/cm² of viable C. jejuni cells existed in some dual-species biofilms. To elucidate the mechanism of protection mode, chemical, physical and morphological features of biofilms were characterized. Dual-species biofilms contained a higher level of extracellular polymeric substances with a more diversified chemical composition, especially for polysaccharides and proteins, than mono-species C. jejuni biofilm. Structure of dual-species biofilms was more compact and their surface was >8 times smoother than mono-species C. jejuni biofilm, as indicated by atomic force microscopy. Under desiccation stress, water content of dual-species biofilms decreased slowly and remained at higher levels for a longer time than mono-species C. jejuni biofilm. The surface of all biofilms was hydrophilic, but total surface energy of dual-species biofilms (ranging from 52.5 to 56.2mJ/m²) was lower than that of mono-species C. jejuni biofilm, leading to more resistance to wetting by polar liquids. This knowledge can aid in developing intervention strategies to decrease the survival and dispersal of C. jejuni into foods or environment.

Efficacy of Slightly Acidic Electrolyzed Water and UV-Ozonated Water Combination for Inactivating Escherichia Coli O157:H7 on Romaine and Iceberg Lettuce during Spray Washing Process

Spray washing is a common sanitizing method for the fresh produce industry. The purpose of this research was to investigate the antimicrobial effect of spraying slightly acidic electrolyzed water (SAEW) and a combination of ozonated water with ultraviolet (UV) in reducing Escherichia coli O157:H7 on romaine and iceberg lettuces. Both romaine and iceberg lettuces were spot inoculated with 100 μL of a 3 strain mixture of E. coli O157:H7 to achieve an inoculum of 6 log CFU/g on lettuce. A strong antimicrobial effect was observed for the UV-ozonated water combination, which reduced the population of E. coli by 5 log CFU/g of E. coli O157:H7 on both lettuces. SAEW achieved about 5 log CFU/g reductions in the bacterial counts on romaine lettuce. However, less than 2.5 log CFU/g in the population of E. coli O157:H7 was reduced on iceberg lettuce. The difference may be due to bacteria aggregation near and within stomata for iceberg lettuce but not for romaine lettuce. The UV light treatment may stimulate the opening of the stomata for the UV-ozonated water treatment and hence achieve better bacterial inactivation than the SAEW treatment for iceberg lettuce. Our results demonstrated that the combined treatment of SAEW and UV-ozonated water in the spray washing process could more effectively reduce E. coli O157:H7 on lettuce, which in turn may help reduce incidences of E. coli O157:H7 outbreaks.

Ultraviolet-C Light Sanitization of English Cucumber (Cucumis sativus) Packaged in Polyethylene Film

Food safety is becoming an increasing concern in the United States. This study investigated the effects of ultraviolet-C (UV-C) light as a postpackaging bactericidal treatment on the quality of English cucumber packaged in polyethylene (PE) film. Escherichia coli k-12 was used as a surrogate microbe. The microbial growth and physical properties of packaged cucumbers were analyzed during a 28-d storage period at 5 °C. Inoculating packaged cucumbers treated at 23 °C for 6 min with UV-C (560 mJ/cm(2) ) resulted in a 1.60 log CFU/g reduction. However, this treatment had no significant effect (P > 0.05) on the water vapor transmission rate or oxygen transmission rate of the PE film. Results show that UV-C light treatment delayed the loss of firmness and yellowing of English cucumber up to 28 d at 5 °C. In addition, UV-C light treatment extended the shelf life of treated cucumber 1 wk longer compared to untreated cucumbers. Electron microscopy images indicate that UV-C light treatment influences the morphology of the E. coli k-12 cells. Findings demonstrate that treating cucumbers with UV-C light following packaging in PE film can reduce bacterial populations significantly and delay quality loss. This technology may also be effective for other similarly packaged fresh fruits and vegetables.

Efficacy of three light technologies for reducing microbial populations in liquid suspensions

The aim of the current study was to evaluate the effectiveness of three nonthermal light technologies (NUV-Vis, continuous UV, and HILP) on their ability to inactivate Escherichia coli K12 and Listeria innocua.  E. coli K12 was selected as a representative microorganism for the enterohaemorrhagic foodborne pathogen E. coli O157:H7 and L. innocua as a surrogate microorganism for the common foodborne pathogen Listeria monocytogenes, respectively. The liquid matrix used for the disinfection experiments was a liquid matrix (MRD solution). The results of the present study show that the HILP treatment inactivated both E. coli and L. innocua more rapidly and effectively than either continuous UV-C or NUV-vis treatment. With HILP at 2.5 cm from the lamp, E. coli and L. innocua populations were reduced by 3.07 and 3.77 log10 CFU/mL, respectively, after a 5 sec treatment time, and were shown to be below the limit of detection (<0.22 log10 CFU/mL) following 30 sec exposure to HILP (106.2 J/cm(2)). These studies demonstrate the bactericidal efficacy of alternative nonthermal light technologies and their potential as decontamination strategies in the food industry.

Ultraviolet light and ultrasound as non-thermal treatments for the inactivation of microorganisms in fresh ready-to-eat foods

The effects of two non thermal disinfection processes, Ultraviolet light (UV 254 nm) and Ultrasound (US) on the inactivation of bacteria and color in two freshly cut produces (lettuce and strawberry) were investigated. The main scope of this work was to study the efficacy of UV and US on the decontamination of inoculated lettuce and strawberries with a cocktail of four bacteria, Escherichia coli, Listeria innocua, Salmonella Enteritidis and Staphylococcus aureus. Treatment of lettuce with UV reduced significantly the population of E. coli, L. innocua, S. Enteritidis and S. aureus by 1.75, 1.27, 1.39 and 1.21 log CFU/g, respectively. Furthermore, more than a 2-log CFU/g reduction of E. coli and S. Enteritidis was achieved with US. In strawberries, UV treatment reduced bacteria only by 1-1.4 log CFU/g. The maximum reductions of microorganisms, observed in strawberries after treatment with US, were 3.04, 2.41, 5.52 and 6.12 log CFU/g for E. coli, S. aureus, S. Enteritidis and L. innocua, respectively. Treatment with UV and US, for time periods (up to 45 min) did not significantly (p>0.05) change the color of lettuce or strawberry. Treatment with UV and US reduced the numbers of selected inoculated bacteria on lettuce and strawberries, which could be good alternatives to other traditional and commonly used technologies such as chlorine and hydrogen peroxide solutions for fresh produce industry. These results suggest that UV and US might be promising, non-thermal and environmental friendly disinfection technologies for freshly cut produce.