Dennis G. Olson

Effect of muscle type, packaging, and irradiation on lipid oxidation, volatile production, and color in raw pork patties.

Effects of packaging and irradiation combinations on lipid oxidation, off-flavor, and color changes of raw patties prepared from three pork muscles were studied. Patties were prepared from each of the ground L. dorsi (L. thoracis and lumborum), psoas, and R. femoris muscles of pig, packaged either in oxygen permeable polyethylene bags or impermeable nylon/polyethylene bags, irradiated with an electron beam at 0 or 4.5 kGy dose, and then stored up to two weeks at 4 °C. Lipid 8 oxidation and color of the patties were determined after 0, 3, 7, and 14 days of storage, and volatiles 24 hr after irradiation. Irradiation and high fat content accelerated the lipid oxidation in raw meat during storage. Oxygen availability during storage, however, was more important than irradiation on the lipid oxidation and color values of raw patties. Irradiated meat produced more volatiles than nonirradiated patties, and the proportion of volatiles varied by the packaging-irradiation conditions of patties. Irradiation produced many unidentified volatiles that could be responsible for the off-odor in irradiated raw meat. No single volatile components but total volatiles, however, could be used to predict lipid oxidation status of raw meat.

Analysis of volatile components and the sensory characteristics of irradiated raw pork

Longissimus dorsi muscle strips, approximately 20 mm long, 40 mm wide, and 5 mm thick (4 g), of pig were randomly placed in a single layer into labeled bags (four strips per bag) and packaged either aerobically or under vacuum. Samples in the bags were irradiated at 0, 5, or 10 kGy and stored at 4°C for 5 days. Lipid oxidation, the amount and identity of volatile components and sensory characteristics of raw pork strips were determined at 0 and 5 days of storage. Irradiated muscle strips produced more 2-thiobarbituric acid reactive substances (TBARS) than nonirradiated only in aerobic packaging during storage. Irradiation had no effect on the production of volatiles related to lipid oxidation, but produced a few sulfur-containing compounds not found in nonirradiated meat. This indicates that the major contributor of off-odor in irradiated meat is not lipid oxidation, but radiolytic breakdown of sulfur-containing amino acids. Many of the irradiation-dependent volatiles reduced to 50 to 25% levels during the 5-days storage under aerobic conditions. Irradiated muscle strips produced stronger irradiation odor than nonirradiated, but no irradiation dose or storage effect was found. Irradiation had no negative effect on the acceptance of meat, and approximately 70% of sensory panels characterized irradiation odor as barbecued-corn-like odor.

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.

Elimination of pathogens of significance in food by low-dose irradiation : a review

Food irradiation is a processing technology that has been shown to be a wholesome process by many scientific studies conducted worldwide during the past 40 years. The research has been supported by the World Health Organization, the Food and Agricultural Organization, and govemmental agencies in many different countries. Industrial support also has been substantial. Some of the benefits ascribed to this technology include improved shelf life, reduced use of Chemicals as preservatives, and reduced levels of pathogens in foods. Pathogens such as Listeria monocytogenes , Yersinia enterocolitica , and Aeromonas hydrophila are capable of growing at temperatures as low as 0°C and are considered to pose a threat to the safety of refrigerated products. The number of cases of foodborne illness caused by contamination by Salmonella and Campylobacter spp. continues to increase. Researchers have been investigating ways in which food safety can be improved without sacrificing product quality and wholesomeness. The sensitivity of these pathogens to low-dose irradiation has been studied in several food products. Survival curves have been elucidated, and some studies on the effects of storage atmosphere, storage temperature, heating, and various treatments in combination with irradiation have been conducted. This review presents background information on this technology, with an emphasis on the radiation sensitivity of some pathogens of importance. Suggestions for future work in this area are also discussed.

Use of high hydrostatic pressure and irradiation to eliminate Clostridium sporogenes spores in chicken breast

High pressure has been studied for its usefulness in reducing microbial contaminants in foods. We sought to determine whether this technology could be used in combination with irradiation to develop shelf-stable products. We first determined the optimal pressure, temperature, and time conditions that would result in maximum reduction of Clostridium sporogenes spores in fresh chicken. At ambient temperature, a pressure of 6,800 atm for up to 60 min resulted in a 5-log-unit reduction. Heating the samples during pressurization at 80°C for 20 min resulted in the lowest number of survivors compared to samples that were heated and pressurized for only 1 and 10 min. Further, irradiation at a medium dose (3.0 kGy) before and after pressurization at 6,800 atm and 80°C for 1, 10, and 20 min revealed no significant differences in spore counts between samples that were pressurized and then irradiated or vice-versa. We then examined the effect of high pressure in lowering the irradiation dose necessary to eliminate all spores. The irradiation D value of C. sporogenes spores was calculated to be 4.1 kGy. Samples were then irradiated at various doses followed by pressurization at 6,800 atm at 80°C for 20 min. The irradiation D value was lowered to approximately 2 kGy, indicating that a combination of high hydrostatic pressure and irradiation can be used to produce chicken with an extended shelf life without the use of high irradiation doses.

Irradiation and packaging of fresh meat and poultry

Extensive research on the irradiation of fresh meat and poultry has been carried out during the past 40 years; yet there is a need for consideration of combined use with other technologies such as modified atmosphere (MA) packaging. Some of the past work has focused on spoilage microorganisms and pathogens, whereas other reports emphasize the sensory quality of fresh meat and poultry. Reports published indicate that the effects of irradiation in conjunction with packaging vary depending upon the kind of meat and poultry and the atmosphere composition in the package. Irradiation may result in off-flavor and/or odor and discoloration of fresh meat and poultry in packages containing air (oxygen). One concern is that pathogens may grow and/or produce toxins in irradiated meat or poultry packaged using modified atmospheres because of a lack of competing organisms. This is of even greater concern if spoilage is suppressed and does not provide the usual warning signals. On the other hand, even though there is some evidence of the growth of pathogens in temperature-abuse conditions, most reports have indicated that spoilage preceded toxin production. Therefore, considering the sensory quality and concerns for safety, the effects of irradiation in combination with vacuum or MA packaging of fresh meat and poultry should be studied further. More complete information is needed to ensure the appropriate use of vacuum or MA packaging in combination with irradiation for the safety of fresh meat and poultry.

Impact of Irradiation on the Safety and Quality of Poultry and Meat Products: A Review

For more than 100 years research on food irradiation has demonstrated that radiation will make food safer and improve the shelf life of irradiated foods. Using the current food safety technology, we may have reached the point of diminishing returns even though recent figures from the CDC show a significant drop in the number of foodborne illnesses. However, too many people continue to get sick and die from eating contaminated food. New and under utilized technologies such as food irradiation need to be re-examined to achieve new levels of safety for the food supply. Effects of irradiation on the safety and quality of meat and poultry are discussed. Irradiation control of the principle microbial pathogens including viruses, the differences among at-risk sub-populations, factors affecting the diminished rate of improvement in food safety and published D values for irradiating raw meat and poultry are presented. Currently permitted levels of irradiation are probably not sufficient to control pathogenic viruses. Typical gram-negative spoilage organisms are very sensitive to irradiation. Their destruction leads to a significant increase in the acceptable shelf life. In addition, the destruction of these normal spoilage organisms did not provide a competitive growth advantage for irradiation injured food pathogens. Another of the main focuses of this review is a detailed compilation of the effects of most of the food additives that have been proposed to minimize the negative quality effect of irradiation. Most of the antimicrobials and antioxidants used singly or in combination produced an increased lethality of irradiation and a decrease in oxidation by-products. Combinations of dosage, temperature, dietary and direct additives, storage temperature and packaging atmosphere can produce meats that the average consumer will find indistinguishable from non-irradiated meats. A discussion of the production of unique radiological by-products is also included.

Shelf Life Extension, Safety, and Quality of Fresh Pork Loin Treated with High Hydrostatic Pressure

The optimal conditions of pressure, time, and processing temperature required to eliminate Listeria monocytogenes Scott A and Salmonella typhimurium ATCC 13311 in fresh pork loin and the effect of these optimal conditions on quality and shelf life were determined. Twenty-five grams of fresh pork loin were inoculated with either of the two organisms and were subjected to pressures between 414 and 827 MPa at either 2 or 25 degrees C for 30 min. The D414MPa(25 degrees C) was determined to be 2.17 min for L. monocytogenes and the D414 MPa (2 degrees C) was determined to be 1.48 min for S. typhimurium. Samples subjected to a 6D process were evaluated by sensory and objective tests as well as for shelf life. These samples were found to be different (P < 0.05) from controls when evaluated after cooking by a triangle test of difference, but only when the pressure was applied at 2 degrees C and not at 25 degrees C. The descriptive analysis test showed that cooked samples treated at 25 degrees C were not different (P > 0.05) from controls in flavor, juiciness, and firmness. Color, peak load, water-holding capacity, and moisture were not found to be different (P > 0.05) between samples treated at 25 degrees C and controls when both were cooked. However, in the raw state, differences were found in the values for color parameters L and b. The level of psychrotrophs was 5.7 log CFU/g for samples treated at 25 degrees C after 33 days of storage at 4 degrees C, as compared with 7.0 log CFU/g for controls. The color and peak load (texture) did not change over the storage period (P > 0.05) in any of the samples. All samples spoiled in 5 days when stored at 25 degrees C.

Survival and injury of Listeria monocytogenes, Listeria innocua and Listeria ivanovii in ground pork following electron beam irradiation

The sensitivity of five strains of Listeria to electron beam irradiation in ground pork as well as the extent of sublethal radiation injury exhibited by each were investigated. Ground pork was inoculated with one of five strains of Listeria and irradiated with from 0 to 1.25 kGy at 0.25 kGy intervals. Listeria innocua NADC 2841 was more radiation-resistant (D10 = 0.638 kGy) than L. monocytogenes NADC 2045 Scott A (D10 = 0.447 kGy), L. monocytogenes NADC 2783 (a hamburger isolate) (D10 = 0.424 kGy), L. monocytogenes ATCC 15313 (D10 = 0.445 kGy), and L. ivanovii NADC 3518 (D10 = 0.372 kGy), when recovered on tryptic soy agar supplemented with 0.6% yeast extract. D10 values for L. innocua , L. ivanovii , and L. monocytogenes ATCC 15313 were lower when cells were recovered on modified Oxford medium. These three strains were susceptible to radiation-induced sublethal injury, with the numbers of injured organisms increasing with irradiation dose. The two pathogenic strains of L. monocytogenes were not injured significantly at the dose levels used. The results show that the dose range currently being considered by the Food and Drug Administration for the irradiation of beef and pork (1.5 to 4.5 kGy) is adequate for the elimination of L. monocytogenes from pork.

Antibacterial Mechanism of Long-Chain Polyphosphates in Staphylococcus aureus

The results of previous studies indicated that the antibacterial effects of long-chain polyphosphates (sodium polyphosphate glassy [SPG] and sodium ultraphosphate [UP]) to Staphylococcus aureus ISP40 8325 could be attributed to damage to the cell envelope (cell wall or cell membrane). Also, Ca2+ (0.01 M) or Mg2+ (0.01 M) reversed the bactericidal and bacteriolytic effects of polyphosphates in S. aureus . In the present study, 0.4 M sodium chloride (NaCl) protected the cells from leakage caused by SPG and 0.6 M NaCl protected the cells from leakage by UP. Polymyxin, a peptide antibiotic that causes cell membrane damage, induced leakage even in the presence of 0.6 M NaCl. In the presence of 0.4 M NaCl, bacterial leakage was significantly reduced by disodium ethylenediamine tetraacetate (EDTA), a metal chelator that causes cell wall damage. Bacterial leakage by polyphosphates was significantly greater at pH 8 than at pH 6, which suggested that metal-ion chelation was involved in the antibacterial mechanism. A dialysis membrane (MWCO 100) was used to separate free metal and polyphosphate-bound metal. Levels of free Ca2+ and Mg2+ in polyphosphate-treated cells were significantly lower than those of the cells without polyphosphate. This free-metal dialysis study provided Chemical evidence to show that long-chain polyphosphates interacted with S. aureus cell walls by a metal-ion chelation mechanism. In addition, long-chain polyphosphates were shown to bind to the cell wall, chelate metals, and remain bound without releasing metal ions from the cell wall into the suspending medium. A hypothesis is proposed in which the antibacterial mechanism of long-chain polyphosphates is caused by binding of long-chain polyphosphates to the cell wall of early-exponential phase cells of S. aureus ISP40 8325. The polyphosphates chelate structurally essential metals (Ca2+ and Mg2+) of the cell wall, resulting in bactericidal and bacteriolytic effects. The structurally essential metals probably form cross bridges between the teichoic acid chains in the cell walls of gram-positive bacteria.