Effect of gamma irradiation on unsporulated and sporulated Toxoplasma gondii oocysts.

The effect of 137Cs irradiation on unsporulated and sporulated Toxoplasma gondii oocysts was investigated as a model system for sterilisation of fruit contaminated with other coccidia such as Cyclospora or Cryptosporidium. Unsporulated oocysts irradiated at > or = 0.4 to 0.8 kGy sporulated but were not infective to mice. Sporulated oocysts irradiated at > or = 0.4 kGy were able to excyst, and sporozoites were infective but not capable of inducing a viable infection in mice. Toxoplasma gondii was detected in histologic sections of mice up to 5 days but not at 7 days after feeding oocysts irradiated at 0.5 kGy. Transmission electron microscopy revealed that sporozoites from irradiated oocysts penetrated enterocytes and all cells in the lamina propria except for red blood cells. Sporozoites appeared normal ultrastructurally and formed a typical parasitophorous vacuole containing a well-developed tubulovesicular membrane network. Raspberries inoculated with sporulated T. gondii oocysts were rendered innocuous after irradiation at 0.4 kGy. Results indicate that irradiation at 0.5 kGy is effective in "killing" coccidian oocysts on fruits and vegetables.

Radiation-induced cell lethality of Salmonella typhimurium ATCC 14028: cooperative effect of hydroxyl radical and oxygen.

The lethality of gamma-radiation doses of 0.2 to 1.0 kGy for Salmonella typhimurium ATCC 14028 was measured in the presence of air, N2 and N2O and with the hydroxyl radical scavengers formate and polyethylene glycol (PEG), M(r) 8,000. Saturation of cell suspensions with either N2O or N2/N2O (1:1, v/v) gas was expected to double the number of hydroxyl radicals (OH.) and to produce an equivalent increase in lethality, but this did not occur. Adding 10% (v/v) O2 to either N2 or N2O gas produced approximately the same gamma-irradiation lethality for S. typhimurium as did air. Addition of hydroxyl radical scavengers, 40 mM formate and 1.5% (w/v) PEG, significantly reduced the lethality of gamma radiation for S. typhimurium in the presence of air but not in the presence of N2 or N2O gases. Membrane-permeable formate provided slightly better protection than nonpermeable PEG. Cells of S. typhimurium grown under anaerobic conditions were more sensitive to radiation, and were less protected by hydroxyl radical scavengers, especially formate, than when cells grown under aerobic conditions were irradiated in the presence of oxygen. Hydroxyl radical scavengers provided no further protection during irradiation in the absence of oxygen. These results indicated that the increased radiation sensitivity of cells grown under anaerobic conditions may be related to superoxide radicals which could increase intercellular damage during irradiation in the presence of oxygen. However, endogenous superoxide dismutase and catalase activities did not protect cells from the radiation-induced lethality of S. typhimurium. Cytoplasmic extracts protected bacterial DNA in vitro in either the presence or absence of oxygen, and no radiation-induced lipid peroxidation of the cellular components was identified by measuring the levels of 2-thiobarbituric acid. These results suggest that most radiation-induced cell lethality was related to the cooperative effects of extracellular OH. and O2 on the cell surface as the radiation dose increased.

Effect of reductant level in skeletal muscle and liver on the rate of loss of thiamin due to gamma-radiation.

A study was made of thiamin content of the skeletal muscles and livers of pork, chicken and beef after gamma-irradiation. gamma-Radiation from a 137Cs source was used to irradiate the samples with doses of 0, 1.5, 3, 6 and 10 kGy at 2 degrees C. Samples were also titrated with dichlorophenol-indophenol to determine the reducing capacity of the tissues. The rate of loss of thiamin upon irradiation was found to be about three time as as fast in skeletal muscle as it was in liver, and to be a function of the reducing capacity of the tissues, the loss decreasing with increasing reductant titer. For the same amount of thiamin loss, liver could be irradiated to three times the dose as could muscle.

Effect of gamma irradiation on the B vitamins of pork chops and chicken breasts.

A study was made of the effect of low-dose gamma irradiation on the content of thiamine (B1), riboflavin (B2), niacin, pyridoxine (B6) and cobalamin (B12) in pork chops, and thiamine, riboflavin and niacin in chicken breasts. Gamma irradiation from a caesium-137 source was used to irradiate the samples in a range of 0.49 to 6.65 kGy from -20 to +20 degrees C. Over the range of dose and temperature studied it was possible to derive a mathematical expression for predicting the losses. A calculation was made of the effect of the loss of thiamine, riboflavin and niacin due to irradiation on the overall loss of these vitamins in the American diet. The losses of riboflavin and niacin were of the order of a fraction of a per cent. Pork is an important source of thiamine, but the calculated loss at 1.0 kGy of this vitamin in cooked pork was only 1.5 per cent. There were initial increases with radiation doses up to 2-4 kGy in the measured concentrations of riboflavin and niacin in both pork and chicken. The increases were highly significant, and are of concern both to the study of radiation effects and the chemical method of the determination of these two vitamins.

Fate of unirradiated Salmonella in irradiated mechanically deboned chicken meat.

Mechanically deboned chicken meat was irradiated at 0, 1.25 and 2.50 kGy (Cesium 137) and inoculated with Salmonella dublin ATCC 15480, Salmonella enteritidis ATCC 9186 or Salmonella typhimurium ATCC 14028. Samples were then stored at 5 degrees C and 10 degrees C and were subjected to microbiological analysis directly after irradiation and inoculation (time 0), and after 24, 72, 120, 168 and 216 h of storage. Samples stored at 20 degrees C were examined at time 0 and after 6, 12 and 24 h of storage. Irradiation at 1.25 and 2.50 kGy caused an average reduction in bacterial levels of 2.23 and 3.44 logs, respectively. S. dublin, S. enteritidis and S. typhimurium showed very small, insignificant changes in numbers, during storage of meat for 9 days at 5 degrees C. The final populations of S. dublin and S. typhimurium in samples irradiated before inoculation and stored at 10 degrees C or 20 degrees C were greater than the equivalent populations in samples which had not been irradiated before inoculation. Reduction of indigenous microflora in mechanically deboned chicken meat by irradiation may create better conditions for the growth of salmonellae and may thus increase the risk of salmonellosis when accidental contamination and temperature abuse occur after a radiation treatment. Therefore, irradiated mechanically deboned chicken meat should be properly refrigerated and protected against contamination.

Reduction of normal flora by irradiation and its effect on the ability of Listeria monocytogenes to multiply on ground turkey stored at 7 degrees C when packaged under a modified atmosphere.

Listeria monocytogenes did not multiply faster during storage at 7 degrees C on irradiated than on nonirradiated raw ground turkey, and there was a concentration-dependent inhibition of its multiplication by CO2. Ground turkey was gamma irradiated at 5 degrees C to 0, 1.5, and 2.5 kGy and inoculated (approximately 100 CFU/g) after irradiation with a cocktail of L. monocytogenes ATCC 7644, 15313, 49594, and 43256. The meat was then packaged in air-permeable pouches or under atmospheres containing 30 or 53% CO2, 19% O2, and 51 or 24% N2 and stored at 7 degrees C for up to 28 days. A dose of 2.5 kGy extended the time for the total plate count (TPC) to reach 10(7) CFU/g from 4 to 19 days compared to that for nonirradiated turkey in air-permeable pouches. Following a dose of 2.5 kGy at the end of the 28-day study, the TPCs were 10(6.42) and 10(4.98) under 25% and 50% CO2 atmospheres, respectively. Under air, 30% CO2, and 53% CO2 atmospheres, the populations of L. monocytogenes after 19 days incubation were 10(4.89), 10(3.60), and 10(2.67) CFU/g. The populations of lactic acid bacteria and anaerobic or facultative bacteria were also reduced by irradiation. Irradiating ground turkey did not decrease its safety when it was contaminated following processing with L. monocytogenes.

Alfalfa seed germination and yield ratio and alfalfa sprout microbial keeping quality following irradiation of seeds and sprouts.

Foods can be treated with gamma radiation, a nonthermal food process, to inactivate foodborne pathogens and fungi, to kill insects on or in fruits and vegetables, and to increase shelf life. Gamma irradiation is especially well suited for these treatments because of its ability to penetrate commercial pallets of foods. Irradiated fruits, vegetables, poultry, and hamburger have been received favorably by the public and are now available in supermarkets. The use of irradiation on fresh alfalfa sprouts was studied to determine its effect on keeping quality as related to aerobic microbial load. After an irradiation dose of 2 kGy, the total aerobic count decreased from 10(5-8) to 10(3-5) CFU/g, and the total coliform counts decreased from 10(5-8) to 10(3-0) CFU/g. The results showed that the sprouts maintained their structure after irradiation, and the keeping quality was extended to 21 days, which is an increase of 10 days from the usual shelf life. The effect of various doses of irradiation on alfalfa seeds as measured by percent germination and yield ratio (wt/wt) of sprouts was determined. There was little effect on the percent germination, but as the dose increased, the yield ratio of alfalfa sprouts decreased. As the length of growing time increased, so did the yield ratio of the lower dose irradiated seeds (1 to 2 kGy). The irradiation process can be used to increase the shelf life of alfalfa sprouts, and irradiating alfalfa seeds at doses up to 2 kGy does not unacceptably decrease the yield ratio for production of alfalfa sprouts.

Quality of irradiated alfalfa sproutst.

Alfalfa (Medicago sativa L.) sprouts were irradiated with gamma rays at doses of 0, 0.85, 1.71, and 2.57 kGy at 5 degrees C. then stored at 6 degrees C for 14 days. Antioxidant power, total ascorbic acid (TAA) (ascorbic acid plus dehydroascorbic acid), carotenoid, chlorophyll, and color were measured at 1, 7, and 14 days of storage. Antioxidant power increased linearly with radiation dose at both 1 and 7 days of storage. Irradiation had minimal effect on TAA content when compared with the decrease in TAA content during storage. Carotenoid content of sprouts irradiated at 1.71 and 2.57 kGy was higher than that of control at 7 days of storage. Irradiation did not have a consistent effect on chlorophyll content or color.

Effect of irradiation temperature on inactivation of Escherichia coli O157:H7 and Staphylococcus aureus.

The resistance of Escherichia coli O157:H7 and Staphylococcus aureus in ground beef to gamma radiation was significantly (P < 0.05) higher at subfreezing temperatures than above freezing. Ground beef was inoculated (ca. 2 x 10(8) CFU/g) with five isolates of either E. coli O157:H7 or S. aureus and subdivided into 25-g samples, vacuum packaged in barrier pouches, and tempered to 20, 12, 4, 0, -4, -12, -20, -30, -40, or -76 degrees C before gamma irradiation. The studies were repeated twice. The D10-values for both of these pathogens increased significantly at subfreezing temperatures, reaching maxima at approximately -20 degrees C. The D10-values for E. coli O157:H7 at 4 and -20 degrees C were 0.39 +/- 0.04 and 0.98 +/- 0.23 kGy, respectively. The D10-values for S. aureus at 0 and -20 degrees C were 0.51 degrees 0.02 and 0.88 +/- 0.05 kGy, respectively.

Reduction of Salmonella spp. and strains of Escherichia coli O157:H7 by gamma radiation of inoculated sprouts.

There have been several recent outbreaks of salmonellosis and infections with Escherichia coli O157:H7 linked to the consumption of raw sprouts. Use of ionizing radiation was investigated as a means to reduce or to totally inactivate these pathogens, if present, on the sprouts. The radiation D value, which is the amount of irradiation in kilograys for a 1-log reduction in cell numbers, for these pathogens was established using a minimum of five doses at 19 +/- 1 degrees C. Before inoculation, the sprouts were irradiated to 6 kGy to remove the background microflora. The sprouts were inoculated either with Salmonella spp. cocktails made with either meat or vegetable isolates or with E. coli O157:H7 cocktails made with either meat or vegetable isolates. The radiation D values for the Salmonella spp. cocktails on sprouts were 0.54 and 0.46 kGy, respectively, for the meat and vegetable isolates. The radiation D values for the E. coli O157:H7 cocktails on sprouts were 0.34 and 0.30 kGy, respectively, for the meat and vegetable isolates. Salmonella was not detected by enrichment culture on sprouts grown from alfalfa seeds naturally contaminated with Salmonella after the sprouts were irradiated to a dose of 0.5 kGy or greater. Ionizing radiation is a process that can be used to reduce the population of pathogens on sprouts.

Irradiation and modified atmosphere packaging for the control of Listeria monocytogenes on turkey meat.

When radiation-sterilized ground turkey meat was inoculated with Listeria monocytogenes, packaged under mixtures of nitrogen and carbon dioxide, and irradiated with gamma-radiation doses of 0 to 3.0 kGy, there was a statistically significant (P < 0.05), but probably not a biologically significant, lower (0.39 log) predicted bacterial survival in the presence of 100% carbon dioxide than in the presence of 100% nitrogen. Possibly because all atmospheres contained oxygen and because a response surface design was used, gamma-radiation resistance was not significantly (P < 0.05) different in air than in modified atmosphere packaging (MAP) mixtures containing 5% O2 or containing 20, 40, 60, and 80% CO2 and balance N2. The antilisterial effects of MAP mixtures containing 17.2, 40.5, and 64% CO2 and balance N2 were compared to those associated with air and vacuum packaging on turkey inoculated with approximately 5 x 10(3) CFU/g. Samples were irradiated to doses of 0, 0.5, 1.0, 1.5, 2.0, and 2.5 kGy and were stored at 7 degrees C for up to 28 days. Irradiation treatments were significantly more lethal in the presence of air packaging than in either vacuum packaging or MAP, and in those samples that received >1.0 kGy, there was a concentration-dependent CO2 inhibition of L. monocytogenes multiplication and/or recovery.

Thiamin, riboflavin, and alpha-tocopherol content of exotic meats and loss due to gamma radiation.

Changes in thiamin, riboflavin, and alpha-tocopherol concentrations due to gamma irradiation were followed in alligator, caiman, bison, and ostrich (exotic) meats. The proximate composition showed that the exotic meats generally had lower fat content than domestic animal meats and that the thiamin content of the reptiles was lower. The changes in the vitamins due to irradiation were similar to those previously observed for domestic species. The results indicate that the loss of vitamins in these species is negligible insofar as the American diet is concerned, and that the concept of "chemiclearance" is applicable to exotic meats.

Fate of gamma-irradiated Listeria monocytogenes during refrigerated storage on raw or cooked turkey breast meat.

The radiation resistance and ability of Listeria monocytogenes ATCC 7644, 15313, 43256, and 49594 to multiply on irradiated, air-packed, refrigerated raw or cooked turkey breast meat nuggets (ca. 25 g) and ground turkey breast meat was investigated. Gamma-radiation D values for L. monocytogenes were significantly different on raw and cooked nuggets, 0.56 +/- 0.03 kGy and 0.69 +/- 0.03 kGy, respectively; but they were not significantly different (P < or = 0.05) on raw and cooked ground turkey meat. High populations (approximately 10(9) CFU/g) of L. monocytogenes declined during 14 days of storage at 4 degrees C in both irradiated and nonirradiated samples of raw but not of cooked ground turkey breast meat. A moderate inoculum (approximately 10(3) CFU/g) did not survive a radiation dose of 3 kGy. The population increased in cooked but not in raw samples of irradiated ground turkey meat stored at either 2 or 7 degrees C for 21 days. The D value changed significantly from 0.70 +/- 0.04 to 0.60 +/- 0.02 kGy when the product was cooked to an internal temperature of 80 degrees C before irradiation. Growth on either raw or cooked turkey meat did not alter the radiation resistance of L. monocytogenes. Analyses were performed for pH, aw, moisture, and reducing potential of raw and cooked turkey meat and for pH, amino acid profile, thiamine, and riboflavin contents of aqueous extracts of raw and cooked turkey meats without identifying the factor or factors involved in differences in the survival and multiplication of L. monocytogenes on raw and cooked meat.

Killing of different strains of Toxoplasma gondii tissue cysts by irradiation under defined conditions.

To study the effect of gamma-irradiation on the viability of Toxoplasma gondii tissue cysts, brains of mice inoculated with 95 newly isolated strains of T. gondii from pigs and 10 other laboratory isolates were pooled, flattened, packed in vacuum, and irradiated to absorbed doses of 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, and 0.9 kGy at 5 C (+/- 0.5 C) with a 137Cs gamma-radiation source. Treated samples were bioassayed for viable T. gondii in mice, cats, or both. Tissue cysts of all strains were rendered nonviable at 0.4 kGy. To study the effect of temperature on inactivation by irradiation, tissue cysts were irradiated at -4, 0, 4, 8, 12, and 16 C (+/- 0.5 C) at 0.25 kGy. Temperature during irradiation had no marked effect on the viability of tissue cysts.

Killing of Toxoplasma gondii oocysts by irradiation and protective immunity induced by vaccination with irradiated oocysts.

Toxoplasma gondii oocysts are highly resistant to environmental influences. To study the effect of alpha-irradiation on the viability of T. gondii oocysts, 1 million sporulated oocysts of the VEG strain were irradiated to absorbed doses of 0.10, 0.15, 0.20, 0.25, 0.30, 0.40, or 0.50 kGy at 5 C with a 137Cs gamma-irradiation source. Treated oocysts were bioassayed for viable T. gondii in mice. Viable T. gondii was not found in brains of mice 2 mo after oral inoculation with oocysts irradiated at levels > or = 0.25 kGy. Therefore, alpha-irradiation is an effective means of killing T. gondii oocysts. Mice inoculated orally with oocysts irradiated at 0.20 and 0.40 kGy were partially protected when challenged orally with lethal doses of nonirradiated oocysts.

Radical oxidation of riboflavin.

Riboflavin, lumiflavin and lumichrome were produced by light catalysis and gamma irradiation. Their formation under various conditions was determined, and a number of intermediates identified. Fluorescence excitation and emission spectra were determined for the compounds and compared with the absorbency spectra. While lumiflavin predominated in alkali and lumichrome in neutral solutions in the light-catalyzed reaction, all products were produced to some extent under all conditions. Gamma radiation resulted only in the formation of lumichrome, with no observable intermediates.

Effect of ionizing radiation on unesterified tocopherols in fresh chicken breast muscle.

The effect of ionizing radiation on free tocopherols in chicken was determined Raw chicken breast muscle with skin and adipose tissue removed was subjected to gamma radiation from a (137)Cs source at 1, 2·25, 5·0, and 10·0 kGy. The chicken was packaged aerobically, and irradiated at 4°C. Free tocopherols were extracted directly from the meat without a saponification step. The tocopherols were resolved using normal phase, high performance liquid chromatography by spectrophotofluorometric detection. Irradiation resulted in a significant linear decrease in alpha and gamma tocopherol with increasing dose levels. At 3 kGy, the maximum level approved by the FDA for poultry, a 15% reduction of free gamma tocopherol and a 30% reduction for free alpha tocopherol were observed.

Effect of gamma radiation on total tocopherols in fresh chicken breast muscle.

Chicken breasts were irradiated in air with a (137)Cs source at 0.0., 1.0, 3.0, 5.6 and 10.0 kGy at 0-2°C. The fresh muscle tissue was saponified and the total tocopherols were isolated and quantitated using normal phase high performance liquid chromatography with a fluorescence detector. Gamma irradiation of the chicken resulted in a decrease in alpha tocopherol with increasing dose. At 3 kGy and 2°C, the radiation level approved by the FDA to process poultry, there was a 6% reduction in the alpha tocopherol level. No significant changes were observed for gamma tocopherol.

Effect of low dose gamma radiation on lipids in five different meats.

Five types of meats were irradiated by gamma radiation up to a dose of 10 kGy. The m. longissimus dorsi from pork, lamb and beef was irradiated as well as turkey leg and turkey breast muscle. After irradiation, the lipids were extracted from the muscles to ascertain the effect of irradiation. Peroxide and iodine values along with malonaldehyde concentration were used to assess any damage made to the lipids, and to note any significant differences in these compounds due to the type of muscle tissue. Peroxide and iodine values showed that at low irradiation dose, <10 kGy, there was no significant change in any of the meat lipids. Malonaldehyde concentration changed significantly at the micromolar level due to irradiation dose, but only in turkey breast muscle.

Effect of gamma radiation on levels of α-tocopherol in red meats and turkey.

The effect of low dose ionizing radiation on free α-tocopherol levels in beef, pork and lamb longissimus dorsi muscle and on turkey leg and breast muscle were determined. The samples were irradiated in air with a (137)Cs source at eight dose levels between 0 and 9.4 kGy at 5 °C. Irradiation resulted in a significant decrease in α-tocopherol levels in all of the meats studied. There were no statistically significant differences in the rate of loss of tocopherol due to species, with the exception of turkey breast. The rate of loss of tocopherol in turkey breast tissue was greater than the other meats. The information obtained in this study may be of use for 'chemiclearance' purposes since the relative effects due to species variation were examined.