Detection of irradiated lamb meat with bone: effect of chilled storage and cooking on esr signal strength

Summary The effect of gamma-irradiation doses of 1, 2, 4 and 5 kGy on ESR signal intensity in pre-packed irradiated lamb meat chunks containing bones was studied. Irradiation-induced a characteristic ESR signal in bone that was not detected in non-irradiated samples and its intensity was proportional to irradiation dose up to 5 kGy. In samples irradiated to 2.5 kGy for shelf-life enhancement, ESR signal intensity was monitored immediately after irradiation and subsequently at weekly intervals during storage at 0–3 °C and after cooking by different methods. Hind leg bones (femur) displayed a higher signal intensity than rib bones. The ESR signal intensity faded by 30 and 42% during 4 weeks at 0–3 °C in hind leg and rib bones, respectively. The magnitude of ESR signal in hind leg bone declined by a maximum of 30% upon pressure cooking (for 15 min), 10% on microwave cooking (for 5 min) and 13% after boiling (for 30 min). However, in the case of rib bones, all cooking methods reduced the ESR signal by about 40%. Storage of irradiated freeze-dried bone powder samples at ambient temperature also resulted in slight reduction in ESR signal intensity. Results point to the suitability of ESR technique for detection of irradiated lamb meat even after storage or cooking, and also in samples that had been stored and then cooked.     

Gamma Ray Processing to Destroy Staphylococcus aureus in Mechanically Deboned Chicken Meat

Gamma radiation doses of 0.26 kGy and 0.36 kGy, administered in vacuo at 0°C, destroyed 90% of log-phase and stationary-phase colony forming units (CFU) of Staphylococcus aureus ATCC 13565 (FDA 196E), respectively, in mechanically deboned chicken meat (MDCM). Samples inoculated with 10^3.9 CFU/g of S. aureus were treated with gamma radiation in vacuo at 0°C and then held for 20 hr at 35°C (abusive storage). Viable CFU were found in samples irradiated to 0.75 kGy but not in those irradiated to 1.50 kGy either before or after storage. Enterotoxin was not detected in irradiated MDCM. A predictive equation was developed for the response of S. aureus in MDCM to radiation dose and irradiation temperature.     

Microbiological Method to Identify Irradiated Meat

Beef, chicken, mutton and pork exposed to -γ-radiation doses of 0–5 kGy were inoculated with Aeromonas hydrophila initially, after 7 days and 15 days of storage at 3°C and -11°C. After 18 hr incubation at 30°C TVBN values of nonirradiated samples were found to be 210 mg% and TVA value were 205 while the corresponding irradiated samples showed 30–80 mg% and 40–80. A similar pattern was observed in stored samples. A rapid method was developed by incubating chicken meat at 37°C for 6–7 hr with bacteria followed by estimation of volatile acids (TVA) and bases (TVBN). A 40–50% reduction in TVA and TVBN in irradiated samples was observed suggesting its possible application for detecting irradiated meat samples.     

EFFECT OF GAMMA IRRADIATION ON THE LIPID PEROXIDATION IN CHICKEN, LAMB AND BUFFALO MEAT DURING CHILLED STORAGE

Chicken, lamb and buffalo meat were subjected to low-dose gamma irradiation (2.5 kGy) and stored at 0–3C. Lipid peroxidation in terms of thiobarbituric acid (TBA) number and carbonyl content were monitored during storage. While irradiated meat showed slight increase in TBA number and carbonyl content on storage as compared to nonirradiated meat, this did not affect the sensory qualities of meat. Free fatty acid content decreased markedly on irradiation. Irradiated meats were microbiologically safe and sensorily acceptable up to 4 weeks in the nonfrozen state (0–3C) while nonirradiated meat had a shelf-life of less than 2 weeks .     

Preservation of iced refrigerated sea bream (Sparus aurata) by irradiation: microbiological, chemical and sensory attributes

Quality and shelf life of non-irradiated and irradiated (2.5 and 5 kGy) sea bream in ice conditions and stored at +4 °C were investigated by measurement of microbiological, chemical and sensory analysis. Microbial counts for non-irradiated sea bream samples were higher than respective irradiated fish. Total volatile base nitrogen (TVB-N) values increased value of 38.64 mg/100 g for non-irradiated, sea bream during iced storage whereas for irradiated fish lower values of 13.48 and 12.06 mg/100 g were recorded at 2.5 and 5 kGy, respectively (day 19). Trimethylamine (TMA-N) values and thiobarbituric acid (TBA) values for irradiated samples were lower than non-irradiated samples. Acceptability scores for odour, taste and texture of cooked decreased with storage time. The sensory scores of sea bream stored in control and 2.5–5 kGy at +4 °C were 13 and 15 days, respectively. The results obtained from this study showed that the shelf life of sea bream stored in ice, as determined by overall acceptability all data, is 13 days for non-irradiated sea bream and 15 days for 2.5 kGy irradiated and 17 days for 5 kGy irradiated sea bream.     

Gamma irradiation as a means to eliminate Listeria monocytogenes from frozen chicken meat

Cells of Listeria monocytogenes ATCC 35152 were sensitive to gamma irradiation in phosphate buffer, pH 7.00 (D₁₀, dose required for 10% survival—0.15 kGy) at 0–5°C. The cells showed higher radiation survival when irradiated under frozen condition, with a D₁₀ of 0.3 kGy. The protection offered by shrimp/chicken/kheema homogenates (100 g litre^?1) was evidenced by even higher D₁₀ values (0.5 kGy) at both 0–5°C and cryogenic temperature. Boneless chicken meat samples were artificially inoculated with L monocytogenes ATCC 35152 cells at low (5 × 10³) colony-forming unit (cfu) g^?1 and high (5 × 10⁶ cfu g^?1) concentrations and irradiated at 1, 3, 4, 6 kGy doses under cryogenic conditions. The efficacy of the radiation process was evaluated by detecting L monocytogenes during storage at 2–4°C in the irradiated samples. These studies, when repeated with three other serotypes of L monocytogenes, clearly suggested the need for a dose of 3 kGy for elimination of 10³ cfu cells of L monocytogenes g^?1 from air-packed frozen chicken meat.     

Quality characteristics of pork patties irradiated and stored in different packaging and storage conditions

Patties were made from pork loin, individually vacuum- or aerobic-packaged and stored either at 4 or -40°C. Refrigerated patties were irradiated at 0, 1.5, 3.0 or 4.5 kGy absorbed dose, and frozen ones were irradiated at 0, 2.5, 5.0, or 7.5 kGy. Samples were analyzed for lipid oxidation, volatile production and odor characteristics. Refrigerated samples were analyzed at 0, 1 and 2 weeks, and frozen ones after 0, 1.5 and 3 months of storage. With vacuum packaging, the lipid oxidation (TBARS) of both refrigerated and frozen patties was not influenced by irradiation and storage time except for the patties irradiated and refrigerated at 7.5 kGy. With refrigerated storage, panelists could detect irradiation odor at day 0, but not after 1 week at 4°C. With frozen storage, however, irradiation odor was detected even after 3 months of storage. With aerobic packaging, the TBARS of refrigerated pork patties increased with storage time. The TBARS of pork patties increased as irradiation dose increased at day 0, but the effect disappeared after 1 week at 4°C. Nonirradiated patties were preferred to the irradiated ones at day 0 because of the significant irradiation odor in the irradiated ones, but the off-odor disappeared after 1 week at 4°C. With frozen storage, patties irradiated at 7.5 kGy had higher TBARS than those irradiated at lower doses. Nonirradiated patties had higher preference scores than the irradiated ones for 1.5 months in frozen storage. Sulfur-containing compounds were responsible for most of the irradiation off-odor, but these volatilized quickly during storage under aerobic conditions. Overall, vacuum packaging was better than aerobic packaging for irradiation and subsequent storage of meat because it minimized oxidative changes in patties and produced minimal amounts of volatile compounds that might be responsible for irradiation off-odor during storage.     

2‐Alkylcyclobutanones as markers for the detection of irradiated mango,papaya, Camembert cheese and salmon meat

Experimental work was carried out in order to determine the usefulness of the 2‐alkylcyclobutanones as markers for irradiated Camembert cheese, salmon meat, mango and papaya. Both 2‐dodecylcyclobutanone (2‐DCB) and 2‐tetradecylcyclobutanone (2‐TCB) were readily detected in Camembert cheese even after storage for 26 days at 10 °C. A linear relationship was observed between irradiation dose (0.5–5 kGy) and the amount of cyclobutanone produced in the cheese. 2‐DCB and 2‐TCB were both identified in salmon meat irradiated in either the chilled (4 °C) or frozen state (−40 °C), although it was noted that less 2‐DCB was measured in the frozen samples. A linear response to increasing irradiation dose was demonstrated for salmon over the experimental range of 1–10 kGy. 2‐TCB was identified as the main marker for irradiated mango and could be detected in samples following storage for 14 days at 10 °C at doses as low as 0.1 kGy. As for the other products investigated, the concentration of this cyclobutanone increased linearly with increasing dose (0.1–2 kGy). With regard to papaya, 2‐DCB was identified as the principal irradiation marker. However, the concentration of this cyclobutanone decreased significantly with time, so that by day 21 of storage at 10 °C it could only be detected at the 2 kGy dose level. 2‐Tetradecenylcyclobutanone (2‐TDCB) was also detected in irradiated mango and papaya. © 2000 Society of Chemical Industry     

Dietary Vitamin E Affects Lipid Oxidation and Total Volatiles of Irradiated Raw Turkey Meat

Breast and leg meat patties, prepared from turkeys fed diets containing 25, 200, 400 or 600 IU of dl-α-tocopheryl acetate (TA) per kg diet, were irradiated at 0 or 2.5 kGy with vacuum or loose packaging. The effects of dietary TA on storage stability and production of volatiles in irradiated raw turkey meat were determined. Dietary TA at > 200 IU/kg decreased lipid oxidation and reduced total volatiles of raw turkey patties after 7-days of storage. However, the antioxidant effects of dietary TA were more notable when the patties were loosely packaged than when vacuum-packaged. Irradiation increased lipid oxidation of raw turkey meats only when loosely packaged but had limited effects on formation of total volatiles after storage at 4°C for 7 days or longer.     

Gamma Irradiation Effects on Shelf Life and Gel Forming Properties of Washed Red Hake (Urophycis chuss) Fish Mince

Fresh washed red hake (Urophycis chuss) mince without cryoprotectants was irradiated at 0 (control), 0.66 and 1.31 kGy and stored aerobically at 3.3°C. The total aerobic plate counts of the control and the low and high levels irradiated samples remained less than 10⁶ CFU/ g for 4, 10, and 17 days, respectively. Gel strength decreased after irradiation of mince, and such decreases were dose-dependent. Irradiation extended sensory shelf life of unfrozen fish mince 12–18 days and microbiologically (<10⁶ CFU/g) 6–13 days longer than the unirradiated control.     

Control of Yersinia enterocolitica in raw pork and pork products by γ-irradiation

γ-Radiation response of Y. enterocolitica 5692 and 152 was studied at 0°C and at −40°C in phosphate buffer (pH 7.00) as well as in 10% raw meat/salami homogenate. The strains investigated did not differ in their response and were found to be sensitive to γ-radiation but exhibited a tailing phenomenon in the survival curve. The D₁₀ in homogenate was 0.25 kGy at 0°C. This response was not affected at −40°C. Storage studies of packs, inoculated artificially with heavy inoculum of Y. enterocolitica (10⁶ cfu/g) showed that while samples of salami and cooked ham could be decontaminated at doses of 4 and 3 kGy respectively; cells could not be eliminated from raw pork meat even at the higher dose of 6 kGy. The role of different treatments given prior to irradiation for revival of Y. enterocolitica after irradiation storage was also studied. The dose of 1 kGy at −40°C was efficient in eradicating low numbers (<10³) of naturally occuring Y. enterocolitica from raw pork meat without any revival during storage at refrigeration temperature.     

Effect of Low-Dose (100 krad) Gamma Radiation on the Microflora of Vacuum-Packaged Ground Pork With and Without Added Sodium Phosphates

Survival and growth of naturally occurring or inoculated bacteria were studied in refrigerated (5°C), vacuum-packaged ground pork irradiated at 100 krad (1kGy). Numbers of naturally occurring mesophiles, psycbrotrophs and anaerobes or facultative anaerobes were reduced (P<0.01) by irradiation, whereas lactic acid bacteria were least affected. Partial bacterial recovery during subsequent storage at 5°C suggested sublethal bacterial injury due to irradiation. Irradiation prolonged shelf-life 2.5–3.5 days (30–44%) in uninoculated and 1.0–1.5 days in inoculated (10⁵ CFU/g) meat. Added sodium acid pyrophosphate (SAPP) (0.4%) contributed two additional days to inoculated, irradiated pork shelf-life but had no effect on the naturally occurring micrbflora. Lipid oxidation did not increase (P>0.05) due to irradiation and was unaffected by phosphates.     

Quality of Gamma Irradiated California Valencia Oranges

California Valencia oranges were irradiated at 0.30, 0.50, 0.75 and 1.0 kGy for quality evaluation and potential use of gamma-radiation as an alternative quarantine treatment and for fresh market life extension. Fruits were ocean-freighted to Honolulu, irradiated at the Hawaii Research irradiator 8 days after harvest, then stored for 7 wk at 7°C or 4 wk at 7°C and 2 wk at 21°C (6 wk total). Treatments of 0.75 kGy maintained fruit qualities at low storage temperature (7°C) up to 7 wk while 0.50 kGy retained qualities when fruits were stored at 21°C. Gamma irradiation of Valencia oranges at 0.26–0.30 kGy can achieve fruit fly disinfestation at probit 9 security level while preserving market qualities including organoleptic qualities, ascorbic acid, total acids, and total soluble solids.     

Radiation preservation of vacuum-packaged sliced corned beef

Luncheon meats are cooked meat products which are commonly sold sliced and vacuum-packaged. They are recontaminated during slicing and packing and as a result may have a starting count as high as 10⁴–10⁵ bacteria per g. Since the surface-to-volume ratio is comparatively high, bacterial spoilage may occur after only 2–3 weeks at 5° C. Treatment of vacuum-packaged sliced corned beef with radiation doses of about 1, 2 and 4 kGy reduced the initial microbial count by about 1, 2.5 and 5 log₁₀ units respectively. The treatments caused changes in the aroma and flavour of the meat and these were evaluated using a trained taste panel. Changes in aroma and flavour caused by doses of 2 and 4 kGy were significant but were rated by the panel as only slight and slight-moderate respectively. Meat treated with a dose of 2 kGy had a storage life of about 5 weeks at 5° C. Treatment with a 4 kGy dose further delayed the onset of spoilage caused by bacterial growth, Irradiation caused a change in the nature of the microbial flora present at spoilage. The normal Gram-positive flora of non-irradiated meat was replaced by a mixed flora of Gram-negative and Gram-positive bacteria following a dose of 2 kGy. Slow-growing Gram-negative rods were dominant after a dose of 4 kGy.     

Sensory Analysis and Consumer Acceptance of Irradiated Boneless Pork Chops

Flavor, texture, and aroma were determined for chilled (3 ± 2°C) and frozen (–17 ± 3°C) boneless pork chops packaged in vacuum or air and exposed to an absorbed dose of 0, 1.5, or 2.5 kGy (chilled) or 0, 2.5, or 3.85 kGy (frozen) of electron beam and cobalt⁶⁰ irradiation. Irradiation (< 3.85 kGy) had minimal effects on aroma, flavor, and textural attributes in chilled and frozen boneless pork chops. Irradiation source had limited effects and packaging type had the greatest influence. Consumers reported no difference (P>0.05) between irradiated (2.5 kGy cobalt⁶⁰ irradiated, chilled, vacuum-packaged, boneless, pork chops) and control samples for overall acceptance, meatiness, freshness, tenderness and juiciness.     

Effect of radiation processing on the quality of chilled meat products

Effect of radiation processing on the shelf-life and safety of some ethnic Indian meat products like chicken chilly, mutton shammi kababs and pork salami during chilled storage was investigated. Radiation processing resulted in dose dependent reduction in microbial counts. A dose of 3 kGy was found to be optimal for the shelf-life extension. In all the three irradiated (3 kGy) meat products the shelf-life was extended by more than 2 weeks at 0-3 °C compared to the corresponding non-irradiated samples. Staphylococcus spp. were completely eliminated by irradiation at a dose of 2 kGy. Some increase in lipid peroxidation on irradiation was observed as measured by TBA assay but it did not affect the sensory attributes of the product.     

Shelf life extension of minimally processed cabbage and cucumber through gamma irradiation

The influence of irradiation of minimally processed cabbage and cucumber on microbial safety, texture, and sensory quality was investigated. Minimally processed, polyethylene-packed, and irradiated cabbage and cucumber were stored at refrigeration temperature (5 degrees C) for 2 weeks. The firmness values ranged from 3.23 kg (control) to 2.82 kg (3.0-kGy irradiated samples) for cucumbers, with a gradual decrease in firmness with increasing radiation dose (0 to 3 kGy). Cucumbers softened just after irradiation with a dose of 3.0 kGy and after 14 days storage, whereas the texture remained within acceptable limits up to a radiation dose of 2.5 kGy. The radiation treatment had no effect on the appearance scores of cabbage; however, scores decreased from 7.0 to 6.7 during storage. The appearance and flavor scores of cucumbers decreased with increasing radiation dose, and overall acceptability was better after radiation doses of 2.5 and 3.0 kGy. The aerobic plate counts per gram for cabbage increased from 3 to 5 log CFU (control), from 1.85 to 2.93 log CFU (2.5 kGy), and from a few colonies to 2.6 log CFU (3.0 kGy) after 14 days of storage at 5 degrees C. A similar trend was noted for cucumber samples. No coliform bacteria were detected at radiation doses greater than 2.0 kGy in either cabbage or cucumber samples. Total fungal counts per gram of sample were within acceptable limits for cucumbers irradiated at 3.0 kGy, and for cabbage no fungi were detected after 2.0-kGy irradiation. The D-values for Escherichia coli in cucumber and cabbage were 0.19 and 0.17 kGy, and those for Salmonella Paratyphi A were 0.25 and 0.29 kGy for cucumber and cabbage, respectively.     

Influence of dietary conjugated linoleic acid on volatile profiles, color and lipid oxidation of irradiated raw chicken meat

Forty-eight, 27-week-old White Leghorn hens were fed a diet containing 0, 1.25, 2.5 or 5.0% conjugated linoleic acid (CLA) for 12 weeks. At the end of the 12-week feeding trial, hens were slaughtered, and boneless, skinless breast and leg meats were separated from carcasses. Meats were ground through 9 and 3-mm plates, and patties were prepared. Patties prepared from each dietary treatment were divided into two groups and either vacuum- or aerobic-packaged. Patties were irradiated at 0 or 3.0 kGy using a linear accelerator and stored at 4°C. Samples were analyzed for thiobarbituric acid reactive substances, volatile profiles, color and odor characteristics at 0 and 7 days of storage. Dietary CLA reduced the degree of lipid oxidation in raw chicken meat during storage. The content of hexanal and pentanal in raw chicken meat significantly decreased as dietary CLA level increased. Irradiation accelerated lipid oxidation in meat with aerobic packaging, but irradiation effect was not as significant as that of the packaging. Dietary CLA treatment improved the color stability of chicken patties. Color a*-value of irradiated raw chicken meat was higher than that of the nonirradiated meat. Dietary CLA decreased the content of polyunsaturated fatty acid and increased CLA in chicken muscles, which improved lipid and color stability and reduced volatile production in irradiated and nonirradiated raw chicken meat during storage.     

Color and Oxidative Rancidity of Gamma and Electron Beam-Irradiated Boneless Pork Chops

Color and oxidative rancidity were determined for chilled (3 ± 2°C) and frozen (?17 ± 3°C) boneless pork chops packaged in vacuum or air and irradiated to an absorbed dose of 0, 1.5 or 2.5 kGy (chilled) or 0, 2.5 or 3.85 kGy (frozen) of electron beam or cobalt⁶⁰ irradiation. Irradiation of vacuum-packaged chops produced redder, more stable (color and rancidity) product. More pronounced oxidative rancidity and less stable display color were noted for samples irradiated in aerobic packaging. Irradiation source had varying but limited effects on color and rancidity. Optimum packaging conditions can control color and rancidity changes in boneless chops, thereby enabling irradiation to be a useful intervention technology.     

Reduction and survival of Listeria monocytogenes in ready-to-eat meats after irradiation

A five-strain Listeria monocytogenes culture was inoculated onto six different types of ready-to-eat (RTE) meats (frankfurters, ham, roast beef, bologna, smoked turkey with lactate, and smoked turkey without lactate). The meats were vacuum packed and stored at 4 degrees C for 24 h prior to irradiation. Populations of L. monocytogenes were recovered by surface plating on nonselective and selective media. The margins of safety studied include 3-log (3D) and 5-log (5D) reduction of pathogenic bacteria to achieve an optimal level of reduction while retaining organoleptic qualities of the meats. A 3-log reduction of L. monocytogenes was obtained at 1.5 kGy when nonselective plating medium was used. The dosages for 3-log reduction were 1.5 kGy for bologna, roast beef, and both types of turkey and 2.0 kGy for frankfurters and ham on the basis of use of selective medium. The D10-values ranged from 0.42 to 0.44 kGy. A 5-log reduction of L. monocytogenes was obtained at 2.5 kGy with nonselective medium. With selective medium, the dosages were 2.5 kGy for bologna, roast beef, and both types of turkey and 3.0 kGy for frankfurters and ham. Survival of L. monocytogenes in the same RTE meat types after irradiation was also studied. Meats were inoculated with 5 log L. monocytogenes per g and irradiated at doses of 2.0 and 4.0 kGy. Recovery of the surviving organisms was observed during storage at temperatures of 4 and 10 degrees C for 12 weeks. Preliminary results showed no growth in meats irradiated at 4.0 kGy. Survivors were observed for irradiated meats at 2.0 kGy stored at 10 degrees C after the second week. No growth was observed in samples irradiated at 2.0 kGy stored at 4 degrees C until the fifth week.