A new method to embed branched 3D microvascular fluidic networks inside plastic substrates by harnessing electrostatic discharge phenomena is introduced. This nearly instantaneous process reproducibly generates highly branched tree‐like microchannel architectures that bear remarkable similarity to naturally occurring vasculature. This method can be applied to a variety of polymers, and may help enable production of organ‐sized tissue scaffolds containing embedded vasculature.
The effect of electron beam irradiation on microbiological quality and safety of fresh-cut tomatoes was studied. Fresh tomatoes were obtained from a local supplier and then cut into cubes that were separated from the stem scars. Both cubes and stem scars were inoculated with a rifampin-resistant strain of either Salmonella Montevideo or Salmonella Agona, separated into treatment groups, and treated by electron beam irradiation at 0.0 (control), 0.7, or 0.95 kGy. The effect of electron beam irradiation on Salmonella, lactic acid bacteria, yeast, and mold counts and pH of tomato cubes and stem scars was determined over a 15-day storage period at 4 degrees C. Results indicated that although irradiation treatment significantly reduced most microbial populations on tomato samples, there were no differences in the reduction of microbial populations between treatments of 0.7 and 0.95 kGy. Irradiation at either dose resulted in a significant reduction in Salmonella when compared with the control (P < 0.05). Lactic acid bacteria, yeasts, and molds were more resistant to irradiation than were Salmonella. No differences were detected between the two Salmonella serotypes in response to irradiation treatment. These results indicate that irradiation at doses of at least 0.7 kGy can be used for pathogen reduction in fresh-cut tomatoes. If the use of doses greater than 1 kGy were approved, this technology might be very effective for use in fresh-cut tomatoes to eliminate significant populations of pathogens and to ensure the microbial quality of the product.
Electron beam irradiated sliced cantaloupe was tested for 21 d of storage for total aerobic microbial counts, texture, color, and different sensorial parameters as a function of irradiation doses 0, 0.7, and 1.4 kGy and the wash treatments, 1 and 200 ppm chlorine applied to the melons before cutting. Irradiation resulted in a reduction in the total aerobic microbial counts with increasing doses. Melons washed only with water before cutting had total aerobic bacterial counts of 4.0, 2.0, and 0.8 log colony-forming units (CFU)/g on day 0 at irradiation doses of 0, 0.7, and 1.4 kGy, respectively. Across all doses of irradiation, counts were consistently lower for cantaloupe pieces obtained from melons that had been subjected to chlorine rinse in comparison with those washed with water without chlorine. Melons washed with chlorine before cutting had total aerobic bacterial counts of 2.7, 0.7, and 0.5 log CFU/g on day 0 at irradiation doses of 0, 0.7, and 1.4 kGy, respectively. Objective color analysis indicated no significant effect of irradiation on the color of cantaloupe. Texture measured as compression force was lower only for cantaloupe irradiated at 1.4 kGy. Irradiation did not affect descriptive attribute flavor and texture sensory attributes of cantaloupe pieces. Decontamination of whole cantaloupes before cutting using chlorine wash may be combined with low-dose irradiation for shelf-life extension of sliced cantaloupe.
The effect of low-dose electron beam (e-beam) radiation on the reduction of Escherichia coli O157:H7 and Salmonella in spinach was studied. Fresh baby spinach (Spinacia oleracea) was inoculated with a bacterial cocktail containing multiple strains of rifampin-resistant E. coli O157:H7 and rifampin-resistant Salmonella. Inoculated samples were exposed to e-beam radiation from a linear accelerator and tested for counts of both E. coli O157:H7 and Salmonella. Irradiated spinach was also stored for 8 days at 4 degrees C, and counts were made at 2-day intervals to determine if there was any effect of radiation on the survival trend of both pathogens. When no pathogens were detected on plates, additional enrichment plating was conducted to verify total destruction. Respiration rates were measured on spinach samples exposed to e-beam radiation. Each dose of e-beam radiation significantly reduced the numbers of E. coli O157:H7 and Salmonella from initial levels of 7 log CFU/g. Treatment by e-beam radiation at a dose of 0.40 kGy resulted in a reduction in populations of E. coli O157:H7 and Salmonella of 3.7 and 3.4 log cycles, respectively. At 0.70 kGy, both pathogens were reduced by 4 log. All doses above 1.07 kGy showed reductions greater than 6 log and decreased to undetectable levels when stored for 8 days. The respiration rate of spinach showed no changes after irradiation up to 2.1 kGy. These results suggest that low-dose e-beam radiation may be a viable tool for reducing microbial populations or eliminating E. coli O157:H7 and Salmonella from spinach without product damage.
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