Combination treatments for killing Escherichia coli O157:H7 on alfalfa, radish, broccoli, and mung bean seeds.

In this study, the effectiveness of prolonged dry-heat treatment (50 degrees C) alone or in combination with chemical treatments (1% oxalic acid, 0.03% phytic acid, 50% ethanol, electrolyzed acidic water, and electrolyzed alkaline water) in eliminating Escherichia coli O157:H7 on laboratory-inoculated alfalfa, radish, broccoli, and mung bean seeds was compared with that of dry-heat treatment in combination with irradiation treatment. Dry-heat treatment for 17 or 24 h alone could reduce E. coli O157:H7 numbers to below detectable levels in radish, broccoli, and alfalfa seeds, but was unable to reduce the pathogen numbers to below the detectable level in mung bean seeds. In addition, dry-heat treatment for 17 h plus sanitizer treatments were effective in greatly reducing pathogen populations on radish, broccoli, and alfalfa seeds, without compromising the quality of the sprouts, but these treatments did not eliminate the pathogen from radish and alfalfa seeds. Seventeen hours of dry heat followed by a 1.0-kGy dose of irradiation completely eliminated E. coli O157:H7 from radish and mung bean seeds, whereas only a minimum radiation dose of 0.25 kGy was required to completely eliminate the pathogen from broccoli and alfalfa seeds. Dry heat in combination with radiation doses of up to 1.0 kGy did not negatively impact the seed germination rate or length of alfalfa, broccoli, and radish seeds or the length of alfalfa, broccoli, and radish sprouts, but did decrease the length of mung bean sprouts.

Irradiation inactivation of Listeria monocytogenes in low-fat ground pork at freezing and refrigeration temperatures.

Gamma radiation effectively controls Listeria monocytogenes in uncooked and in ready-to-eat foods. This study was conducted to determine if gamma radiation could be used to control L. monocytogenes in ground pork. Ground pork was contaminated with L. monocytogenes, kept at refrigeration (4 degrees C), chilling (0 degrees C), and freezing (-18 degrees C) temperatures overnight, exposed to gamma radiation and stored at 4 degrees C for 7 days, and at 0 and -18 degrees C for 60 days. Following irradiation, the meat was assayed for L. monocytogenes viable counts and lipid oxidation. A triangle test was performed to determine if sausage made from the irradiated and nonirradiated ground pork differed in sensory quality. It was observed that a 5-log reduction of L. monocytogenes viable counts would require a 3.0-kGy radiation dose. The results of a 60-day storage study of ground pork inoculated with 10(5) to 10(6) CFU of L. monocytogenes per gram indicated that counts for nonirradiated meat remained fairly constant at refrigeration, chilling, and freezing temperatures. However, irradiation of ground pork at 3.0 kGy could inactivate L. monocytogenes totally in ground pork subsequently held at all the temperatures used in this study. Lipid oxidation measurements, as determined by the thiobarbituric acid-reactive substance assay, ranged from 0.16 nmol/g for nonirradiated ground pork and 0.20 nmol/g for meat irradiated at 3.0 kGy. Sensory panelists could distinguish between irradiated and nonirradiated sausage but were divided on whether irradiation adversely affected the sausage quality. Our results suggest that gamma radiation could be useful to control L. monocytogenes in ground pork and improve the safety of ground pork products.

Effectiveness of irradiation treatments in inactivating Listeria monocytogenes on fresh vegetables at refrigeration temperature.

Ionizing radiation can be effective in controlling the growth of food spoilage and foodborne pathogenic bacteria. This study reports on an investigation of the effectiveness of irradiation treatment to eliminate Listeria monocytogenes on laboratory-inoculated broccoli, cabbage, tomatoes, and mung bean sprouts. Irradiation of broccoli and mung bean sprouts at 1.0 kGy resulted in reductions of approximately 4.88 and 4.57 log CFU/g, respectively, of a five-strain cocktail of L. monocytogenes. Reductions of approximately 5.25 and 4.14 log CFU/g were found with cabbage and tomato, respectively, at a similar dose. The appearance, color, texture, taste, and overall acceptability did not undergo significant changes after 7 days of postirradiation storage at 4 degrees C, in comparison with control samples. Therefore, low-dose ionizing radiation treatment could be an effective method for eliminating L. monocytogenes on fresh and fresh-cut produce.

Radiation-heat synergism for inactivation of Alicyclobacillus acidoterrestris spores in citrus juice.

The objective of this study was to investigate the influence of electron-beam and gamma-ray irradiation and temperature (85 to 95 degrees C) on Alicyclobacillus acidoterrestris GD3B strain (NCIMB 13137) spores by calculating and comparing the decimal reduction dose or time (D-values). The survival rate of A. acidoterrestris spores decreased exponentially with irradiation doses of an electron beam or gamma ray. D-values determined for electron-beam and gamma-ray irradiated spores on filter paper ranged from 1.02 to 1.10 kGy. On the other hand, the thermal sterilization effect showed a single exponential decrease within 1.5-log decreases in cell numbers (D85 degrees C = 70.5 min, D90 degrees C = 16.1 min, and D95 degrees C = 5.19 min and z-value [change in temperature required to change the D-value] was 8.83 degrees C), and prolonged heating produced an increase of 10 to 13 times that of the thermal resistance. However, within all time ranges studied (5 to 360 min), a linear decrease in the D-value was observed with an increase in the temperature. A combination of two different methods, irradiation before heating, was appropriate for reducing the duration of the heat treatment required to achieve the inactivation of conidia. Moreover, a necessary radiation dosage for complete inactivation of A. acidoterrestris spores that contaminated dextrin was examined. Dextrin is often used in the juice industry as an augmentor, and it is known to be sometimes contaminated by these spores. The D-values of the spores in dextrin for electron-beam and gamma-ray irradiations were 1.72 and 1.79 kGy, respectively. The doses required for elimination of the spores could be lowered by using irradiation in combination with heat sterilization. When dextrin powder contaminated with 10(4) CFU/g of A. acidoterrestris was preirradiated at 1.0 kGy of electron beam, the citrus juice containing dextrin at a concentration of 10% (wt/vol) was completely sterilized by heating for 20 min at 95 degrees C.

Irradiation to kill Escherichia coli O157:H7 and Salmonella on ready-to-eat radish and mung bean sprouts.

A study was carried out to evaluate the effectiveness of ionizing radiation in eliminating Escherichia coli O157:H7 and Salmonella on commercial ready-to-eat radish and mung bean sprouts and to assess the chemical and physical quality of these sprouts. The use of ionizing radiation was investigated as a means of reducing or totally inactivating these pathogens, if present, on the sprouts. Treatment of mung bean and radish sprouts with a dose of 1.5 and 2.0 kGy, respectively, significantly reduced E. coli O157:H7 and Salmonella to nondetectable limits. The total vitamin C content was gradually reduced with the increase in irradiation dose (P < 0.0001). However, the effect of storage interval on the loss of vitamin C was nonsignificant for radish sprouts and significant for mung bean sprouts (P < 0.04). The color, firmness, and overall visual quality of the tested sprouts were acceptable when effective doses were applied to both radish and mung bean sprouts. Therefore, ionizing radiation could be useful in reducing the population of pathogens on sprouts and yet retain acceptable quality parameters.

Chemical and irradiation treatments for killing Escherichia coli O157:H7 on alfalfa, radish, and mung bean seeds.

In this study, the effectiveness of dry-heat treatment in combination with chemical treatments (electrolyzed oxidizing [EO] water, califresh-S, 200 ppm of active chlorinated water) with and without sonication in eliminating Escherichia coli O157:H7 on laboratory-inoculated alfalfa, radish, and mung bean seeds was compared with that of dry-heat treatment in combination with irradiation treatment. The treatment of mung bean seeds with EO water in combination with sonication followed by a rinse with sterile distilled water resulted in reductions of approximately 4.0 log10 CFU of E. coli O157:H7 per g. whereas reductions of ca. 1.52 and 2.64 log10 CFU/g were obtained for radish and alfalfa seeds. The maximum reduction (3.70 log10 CFU/g) for mung bean seeds was achieved by treatment with califresh-S and chlorinated water (200 ppm) in combination with sonication and a rinse. The combination of dry heat, hot EO water treatment, and sonication was able to eliminate pathogen populations on mung bean seeds but was unable to eliminate the pathogen on radish and alfalfa seeds. Other chemical treatments used were effective in greatly reducing pathogen populations on radish and alfalfa seeds without compromising the quality of the sprouts, but these treatments did not result in the elimination of pathogens from radish and alfalfa seeds. Moreover, a combination of dry-heat and irradiation treatments was effective in eliminating E. coli O157:H7 on laboratory-inoculated alfalfa, radish, and mung bean seeds. An irradiation dose of 2.0 kGy in combination with dry heat eliminated E. coli O157:H7 completely from alfalfa and mung bean seeds, whereas a 2.5-kGy dose of irradiation was required to eliminate the pathogen completely from radish seeds. Dry heat in combination with irradiation doses of up to 2.0 kGy did not unacceptably decrease the germination percentage for alfalfa seeds or the length of alfalfa sprouts but did decrease the lengths of radish and mung bean sprouts.

Gamma-radiation induces leaf trichome formation in Arabidopsis.

We observed induction of additional trichome formation on the adaxial surface of mature leaves of Arabidopsis after massive doses (1-3 kilograys) of gamma-radiation from cobalt-60. A typical increase in trichome number was observed in the seventh leaf when the full expansion of the fifth leaf was irradiated. Under normal growth conditions, trichome numbers on the adaxial surface of seventh leaf of the Arabidopsis ecotypes Columbia (Col) and Landsberg erecta (Ler) were 122.5 +/- 22.7 and 57.5 +/- 14.5, respectively. However, gamma-radiation induced additional trichome formation and the numbers rose to 207.9 +/- 43.7 and 95.0 +/- 27.1 in Col and Ler, respectively. In Col the shape of new trichomes was intact and their formation was spatially maintained at equal distances from other trichomes. In Ler trichome morphology was aberrant and the formation was relatively random. Treatment with antioxidants before gamma-irradiation suppressed the increase in trichome number, and treatment with methyl viologen and light induced small trichomes. These results suggest that gamma-radiation-induced trichome formation is mediated by active oxygen species generated by water radiolysis. gamma-Radiation-induced trichome formation was blocked in the trichome mutants ttg-1, gl1-1, and gl2-1. These results suggest that gamma-radiation-induced trichome formation is mediated by the normal trichome developmental pathway.

Rheological properties and lipid oxidation of rice decontaminated with low-energy electrons.

Microbial load and quality of rice grains which were exposed to electrons at different acceleration voltages of 170 to 200 kV were examined to evaluate the efficacy of decontaminating rice with low-energy electrons. Electrons at any acceleration voltage between 170 and 200 kV reduced microbial loads of brown rice grains to levels lower than 10 colony-forming units (CFU)/g. Higher acceleration voltages resulted in a lower viscosity and a higher thiobarbituric acid value (TBA). Milling at a yield of 90 or 88% after electron treatment made the viscosity and TBA of rice treated with electrons at 170 kV almost the same as untreated rice. Low and high compression analyses of rice grains which were exposed to electrons at 170 to 180 kV and milled at a yield of 90% followed by cooking showed almost the same hardness and stickiness as untreated grains which were milled at 90%. The results indicate that milling at a yield of 90% or lower removes the portion of rice exposed to electrons at 170 kV and that treatment of brown rice with low-energy electrons enables the preparation of milled rice with extremely low levels of microbial load and little quality deterioration.

Role of Sucrose in Gamma-irradiated Chrysanthemum Cut Flowers.

Vase solution containing 2% sucrose prevented the deterioration of chrysanthemum (Dendranthema grandiflorum Kitamura) cut flowers induced by gamma-rays at 750 Gy. Glucose, fructose, and sucrose in florets and leaves of irradiated chrysanthemums decreased more rapidly than those of unirradiated ones, when the cut chrysanthemums were held in a vase solution without sucrose. The sugar contents of florets and leaves and the respiratory rate of irradiated chrysanthemums held with sucrose remained at higher levels than those of unirradiated ones. Incorporation of (14)C from [(14)C]sucrose into CO2 was increased by irradiation. Incorporation of [α-(32)P]dTTP into trichloroacetic acid (TCA) insoluble substances in florets was increased by irradiation and by exogenous sucrose supply. These results suggest that sucrose in a vase solution was used as a respiratory substrate and facilitated the repair of radiation-induced damage, resulting in the extension of longevity of irradiated chrysanthemums.

Comparative effects of gamma rays and electron beams on spores of Bacillus pumilus.

The effects of gamma rays and electron beams on the germination, outgrowth and the synthesis of protein and RNA of Bacillus pumilus spores were investigated to clarify the difference in the effects of the two types of radiations on bacterial spores. Gamma irradiation facilitated the germination to a slightly larger degree than electron irradiation. The outgrowth, growth and the synthesis of protein and RNA were inhibited by gamma irradiation to a greater extent than electron irradiation, when the spores were irradiated at the same dose. However, the effects of the two types of radiations were the same when the spores were irradiated with electron beams at a dose 30% higher than gamma rays. The results indicate that the effects of electron beams on bacterial spores and those of gamma rays are qualitatively the same but quantitatively different.