In-package inhibition of E. coli O157:H7 on bulk Romaine lettuce using cold plasma.

Dielectric barrier discharge atmospheric cold plasma (DACP) treatment was evaluated for the inactivation of Escherichia coli O157:H7, surface morphology, color, carbon dioxide generation, and weight loss of bulk Romaine lettuce in a commercial plastic clamshell container. The lettuce samples were packed in a model bulk packaging configuration (three rows with either 1, 3, 5, or 7 layers) in the container and treated by DACP (42.6 kV, 10 min). DACP treatment reduced the number of E. coli O157:H7 in the leaf samples in the 1-, 3-, and 5-layer configurations by 0.4-0.8 log CFU/g lettuce, with no significant correlation to the sample location (P > 0.05). In the largest bulk stacking with 7 layers, a greater degree of reduction (1.1 log CFU/g lettuce) was observed at the top layer, but shaking the container increased the uniformity of the inhibition. DACP did not significantly change the surface morphology, color, respiration rate, or weight loss of the samples, nor did these properties differ significantly according to their location in the bulk stack. DACP treatment inhibited E. coli O157:H7 on bulk lettuce in clamshell containers in a uniform manner, without affecting the physical and biological properties and thus holds promise as a post-packaging process for fresh and fresh-cut fruits and vegetables.

Flavisolibacter tropicus sp. nov., isolated from tropical soil.

A Gram-stain-negative, non-motile, deep yellow, rod-shaped bacterium, designated strain LCS9T, was isolated from a soil sample at the tropical zone within the Ecorium of the National Institute of Ecology in Seocheon, central-western Korea. 16S rRNA gene sequence analysis showed that strain LCS9T clustered with members of the genus Flavisolibacter of the family Chitinophagaceae, phylum Bacteroidetes. Sequence similarities between strain LCS9T and the type strains of the genus Flavisolibacter ranged from 94.6 to 94.9 %. Strain LCS9T grew at 10-37 °C (optimum, 25 °C) and at pH 6.0-10.0 (optimum, pH 7); was positive for catalase and oxidase; and negative for nitrate reduction and production of indole. Cells showed pigment absorbance peaks at 451 and 479 nm, and had 0.03 % survival following exposure to 3 kGy gamma radiation. Strain LCS9T had the following chemotaxonomic characteristics: the major quinone was menaquinone-7 (MK-7); the major fatty acids were iso-C15 : 0 and iso-C17 : 0 3-OH; polar lipids included phosphoatidylethanolamine, an unidentified aminophospholipid, unidentified aminolipidsand unidentified lipids. The DNA G+C content was 39.4 mol%. Based on polyphasic analysis, the type strain LCS9T (=KCTC 42070T=JCM 19972T) represents a novel species for which the name Flavisolibacter tropicus sp. nov. is proposed. Radiation resistance in the genus Flavisolibacter has not been reported to date, and so this is the first report of low-level radiation resistance of a member of the genus.

Inactivation of Potato Polyphenol Oxidase Using Microwave Cold Plasma Treatment.

This study was conducted to examine the effects of microwave cold plasma (CP) treatment on inactivation of polyphenol oxidase (PPO) of potato. The PPO activity and treatment variables were fit to first-order kinetics, the Weibull model, and the second-order model. The optimum CP-generation power and treatment time for inactivating PPO in the PPO extract were found to be 900 W and 40 min, respectively, which resulted in the highest inactivation of PPO (49.5%). PPO activity after CP treatment of potato slices decreased from 72.4% to 59.0% as the sample surface-to-volume ratio increased from 7.1 to 9.0. CP treatment delayed the browning of potato slices. Microwave CP treatment effectively inactivated PPO in potatoes, demonstrating the potential of CP treatment for controlling PPO activity in foods. PRACTICAL APPLICATION: This study demonstrated that microwave CP treatment, a nonthermal food processing technology, inactivates PPO activity in potatoes. The results showed that the inactivation effect of CP treatment on PPO corresponded to the surface-to-volume ratio of potato slices. Furthermore, this study proposed an enzyme inactivation model that is suitable for predicting the inactivation of PPO activity and confirmed that CP treatment delayed browning in potatoes.

Effects of the treatment parameters on the efficacy of the inactivation of Salmonella contaminating boiled chicken breast by in-package atmospheric cold plasma treatment.

The effects of surface coating, microbial loading, surface-to-volume ratio, sample stacking, mixing of samples with romaine lettuce, and shaking of the samples on the inactivation of Salmonella contaminating boiled chicken breast (BCB) cubes using in-package atmospheric dielectric barrier discharge cold plasma (ADCP) treatment at 38.7 kV were investigated. Whey protein coating increased the ADCP treatment efficacy in inactivating Salmonella on BCB cubes; the D-value increased from 0.2 to 1.3 min when the initial inoculum concentration increased from 3.8 to 5.7 log CFU/sample. ADCP decontaminated stacked BCB samples uniformly, and shaking during the treatment increased the inactivation rate. The concentrations of chicken protein isolate, water, and soybean oil in a chicken breast model food that resulted in the highest Salmonella reduction (1.7 log CFU/sample) were 20.5%, 68.9%, and 10.6%, respectively. ADCP treatment did not affect the color and tenderness of the model food, irrespective of its composition. The present study indicated that ADCP is a feasible technology to decontaminate prepackaged ready-to-eat meat cube products.

In-package atmospheric cold plasma treatment of bulk grape tomatoes for microbiological safety and preservation.

Effects of dielectric barrier discharge atmospheric cold plasma (DACP) treatment on the inactivation of Salmonella and the storability of grape tomato were investigated. Grape tomatoes, with or without inoculation with Salmonella, were packaged in a polyethylene terephthalate (PET) commercial clamshell container and cold plasma-treated at 35 kV at 1.1 A for 3 min using a DACP system equipped with a pin-type high-voltage electrode. DACP treatment inactivated Salmonella (p < 0.05) without altering the color or firmness of the grape tomatoes (p > 0.05). DACP treatment inactivated Salmonella uniformly in both layers of the double-layer configuration of the grape tomatoes regardless of the position of the tomatoes in each layer. Salmonella was most efficiently inactivated when the headspace to tomato volume ratio of the container was highest. Integration of rolling of tomatoes during treatment significantly increased the Salmonella reduction rates from 0.9 ±â€¯0.2 log CFU/tomato to 3.3 ±â€¯0.5 log CFU/tomato in the double-layer configuration of the tomato samples. Rolling-integrated DACP also initially reduced the number of total mesophilic aerobic bacteria and yeast and molds in the double-layer configuration of tomato samples by 1.3 ±â€¯0.3 and 1.5 ±â€¯0.2 log CFU/tomato, respectively. DACP treatment effectively reduced the growth of Salmonella and indigenous microorganisms at 10 and 25 °C, and did not influence the surface color, firmness, weight loss, lycopene concentration and residual ascorbic acid of grape tomatoes during storage at 10 and 25 °C. DACP treatment holds promise as a post-packaging process for improving microbial safety against Salmonella and storability of fresh grape tomatoes.

Inactivation of Escherichia coli O157:H7 and Aerobic Microorganisms in Romaine Lettuce Packaged in a Commercial Polyethylene Terephthalate Container Using Atmospheric Cold Plasma.

The effects of dielectric barrier discharge atmospheric cold plasma (DACP) treatment on the inactivation of Escherichia coli O157:H7 and aerobic microorganisms in romaine lettuce packaged in a conventional commercial plastic container were evaluated during storage at 4°C for 7 days. Effects investigated included the color, carbon dioxide (CO2) generation, weight loss, and surface morphology of the lettuce during storage. Romaine lettuce pieces, with or without inoculation with a cocktail of three strains of E. coli O157:H7 (~6 log CFU/g of lettuce), were packaged in a polyethylene terephthalate commercial clamshell container and treated at 34.8 kV at 1.1 kHz for 5 min by using a DACP treatment system equipped with a pin-type high-voltage electrode. Romaine lettuce samples were analyzed for inactivation of E. coli O157:H7, total mesophilic aerobes, and yeasts and molds, color, CO2 generation, weight loss, and surface morphology during storage at 4°C for 7 days. The DACP treatment reduced the initial counts of E. coli O157:H7 and total aerobic microorganisms by ~1 log CFU/g, with negligible temperature change from 24.5 ± 1.4°C to 26.6 ± 1.7°C. The reductions in the numbers of E. coli O157:H7, total mesophilic aerobes, and yeasts and molds during storage were 0.8 to 1.5, 0.7 to 1.9, and 0.9 to 1.7 log CFU/g, respectively. DACP treatment, however, did not significantly affect the color, CO2 generation, weight, and surface morphology of lettuce during storage (P > 0.05). Some mesophilic aerobic bacteria were sublethally injured by DACP treatment. The results from this study demonstrate the potential of applying DACP as a postpackaging treatment to decontaminate lettuce contained in conventional plastic packages without altering color and leaf respiration during posttreatment cold storage.

Dielectric barrier discharge atmospheric cold plasma inhibits Escherichia coli O157:H7, Salmonella, Listeria monocytogenes, and Tulane virus in Romaine lettuce.

The present study investigated the effects of dielectric barrier discharge atmospheric cold plasma (DACP) treatment on the inactivation of Escherichia coli O157:H7, Salmonella, Listeria monocytogenes, and Tulane virus (TV) on Romaine lettuce, assessing the influences of moisture vaporization, modified atmospheric packaging (MAP), and post-treatment storage on the inactivation of these pathogens. Romaine lettuce was inoculated with E. coli O157:H7, Salmonella, L. monocytogenes (~6logCFU/g lettuce), or TV (~2logPFU/g lettuce) and packaged in either a Petri dish (diameter: 150mm, height: 15mm) or a Nylon/polyethylene pouch (152×254mm) with and without moisture vaporization. Additionally, a subset of pouch-packaged leaves was flushed with O2 at 5% or 10% (balance N2). All of the packaged lettuce samples were treated with DACP at 34.8kV for 5min and then analyzed either immediately or following post-treatment storage for 24h at 4°C to assess the inhibition of microorganisms. DACP treatment inhibited E. coli O157:H7, Salmonella, L. monocytogenes, and TV by 1.1±0.4, 0.4±0.3, 1.0±0.5logCFU/g, and 1.3±0.1logPFU/g, respectively, without environmental modifications of moisture or gas in the packages. The inhibition of the bacteria was not significantly affected by packaging type or moisture vaporization (p>0.05) but a reduced-oxygen MAP gas composition attenuated the inhibition rates of E. coli O157:H7 and TV. L. monocytogenes continued to decline by an additional 0.6logCFU/g in post-treatment cold storage for 24h. Additionally, both rigid and flexible conventional plastic packages appear to be suitable for the in-package decontamination of lettuce with DACP.

Cold Oxygen Plasma Treatments for the Improvement of the Physicochemical and Biodegradable Properties of Polylactic Acid Films for Food Packaging.

The effects of cold plasma (CP) treatment on the physicochemical and biodegradable properties of polylactic acid (PLA) films were studied. The PLA films were exposed to CP for 40 min at 900 W and 667 Pa using oxygen as the plasma-forming gas. The tensile, optical, and dynamic mechanical thermal properties, surface morphology, printability, water contact angle, chemical structure, weight change, and biodegradability properties of the films were evaluated during storage for up to 56 d. The tensile and optical properties of the PLA films were not significantly affected by CP treatment (CPT; P > 0.05). The surface roughness and water contact angle of PLA films increased by CPT and further increased during storage for 56 d. The printability of the PLA films increased following CPT and remained stable throughout the storage period. CP-induced hydrophilicity was also sustained during the storage period. The PLA films lost 1.9% of their weight after CPT, but recovered 99.5% of this loss after 14 d in storage. Photodegradation, thermal, and microbial biodegradable properties of the films were significantly improved by CPT (P < 0.05). Accelerated biodegradation of CP-treated PLA sachets with and without cheese was observed in compost. These results demonstrate the potential of CPT for modifying the stiffness, water contact angle, and chemical structure of PLA films and improving the printability and biodegradability of the films for food packaging.