Survival of Listeria monocytogenes, Yersinia enterocolitica and Escherichia coli O157:H7 and Quality Changes After Irradiation of Beef Steaks and Ground Beef

Beef steaks and ground beef were inoculated with Listeria monocytogenes, Yersinia enterocolitica, or Escherichia coli O157:H7. Samples were packaged in air or under vacuum and irradiated at low (0.60 to 0.80 kGy) or medium (1.5 to 2.0 kGy) doses, with each dose delivered at either a low (2.8 M/min conveyor speed) or high (6.9 M/min) dose rate. Medium-dose irradiation accompanied by 7°C storage resulted in no Y. enterocolitica or E. coli O157:H7 survivors being detected. There was no effect on survival of the pathogens by dose rate or storage atmosphere. No difference (P>0.05) was observed in meat pH or color, but TBA values increased after 7 days storage.     

Dielectric Properties of Ceramics in the System (Sr0.50Pb0.25Ca0.25)TiO3-Bi2O3·3TiO2 and Their Applications in a High-Voltage Capacitor

The dielectric behavior of (1- x )(Sr_0.5Pb_0.25Ca_0.25) TiO₃-x(Bi₂O₃·3TiO₂) was studied using x=O to 8.25 mol%. Around the point at which x equals 1.56 mol%, the following phenomena were observed: (1) At −;22°C, the weak field permittivity increased substantially with a dc bias field, becoming more than twice the zero bias value at a field of 3 kV/mm; (2) the permittivity peak shifted markedly toward a high temperature under a dc bias field; (3) relaxation behavior was evident; and (4) there are large hysteresis loops at low temperatures and double hysteresis loops, which seem to be related to a field-enforced ferroelectric phase, in a wide temperature range. We used dielectrics with an optimized composition of x =4.30 mol% in a small, highly reliable, 15-kV high-voltage ceramic capacitor.     

Microbial and Quality Characteristics of Pork Cuts from Carcasses Treated with Sanitizing Sprays

Pork carcasses were sprayed with 1.5% acetic, citric, or lactic acid. Loins were vacuum packed and stored at 0–2°, chops were cut periodically from loins and stored at 2–4°. Acetic and citric acids decreased (P<0.05) aerobic plate counts (APC) and total coliforms in loins for 14 days. Species of Salmonella, Yersinia, and Campylobacter were found on 0, 6, and 5% of samples. Lisreria spp were detected on 69% of loins and on 33% of chops. The sanitizing treatments were of relatively limited effectiveness for long term storage. No pH, TBA or sensory quality differences were observed.     

Heating and Storage Conditions Affect Survival and Recovery of Listeria monocytogenes in Ground Pork

The effect of heating rate, heating atmosphere, and meat age on survival of Listeria monocytogenes was examined in ground pork, as well as the ability of injured cells to recover during storage under air and vacuum packaging at 4 and 30°C. Significantly more survivors were observed when samples were heated at 1.3°C/min than at 8.0°C/ min. Cells inoculated into 3-month-old pork were more sensitive to heating than cells inoculated into fresh ground pork (D_62°C= 5.2 min and 7.7 min, respectively). More survivors were detected when the meat was heated aerobically than anaerobically. However, storage under vacuum at 4 or 30°C resulted in faster recovery compared with cells packaged in air. Thus, heating and packaging conditions affected ability of this pathogen to survive and recover after a heat process in pork.     

EFFECT OF HEAT SHOCK ON PRODUCTION OF LISTERIOLYSIN O BY LISTERIA MONOCYTOGENES1

A Listeria monocytogenes serotype 1 strain was examined to determine the effect of heat shock on production of listeriolysin O (LLO) and the ability of injured cells to resume production of LLO after heat treatment at 62C for 10 min. Listeria cells were heat-shocked at 48C for 2 h, and hemolytic activity quantified by hemolysis of red blood cell (RBC). Heat shocking of Listeria cells resulted in almost total reduction in LLO activity. However, within 4 h of incubation of 37C, heat-shocked cells resumed production of LLO, achieving an activity level 40–times higher than that immediately after heat shock. In comparison, in the same time period there was an increase of only 2–fold in the hemolytic activity of nonheat-shocked controls. These results provide additional evidence, besides increased thermotolerance, of how heat-shock of pathogenic organisms could affect the safety of foods.     

OPTIMIZATION OF LISTERIOLYSIN O PRODUCTION BY LISTERIA MONOCYTOGENES1

Listeria monocytogenes serotype 1 and Scott A strains were examined to determine the effect of culture conditions onproduction of listeriolysin O (LLO). The hemolytic activity was assayed by hemolysis of sheep red blood cells. The optimum pH range for LLO production in serotype 1 and Scott A were pH 6.2–6.0 and pH 5.8–6.0, respectively. Production of LLO by serotype 1 was 20–fold higher than by Scott A. Addition of more than 1.0% glucose significantly reduced production of LLO by the cells, while favoring growth. By adding 0.5% glucose after stationary phase and adjusting pH to 5.5–7.0, maximum LLO was produced after 2 h incubation at 37C by both strains.     

GENERAL MICROBIAL PROFILE OF LOW-FAT FRANKFURTERS FORMULATED WITH SODIUM LACTATE AND A TEXTURE MODIFIER1

Frankfurters formulated with starch-isolated soy protein (starch-ISP) alone, or with starch-ISP and sodium lactate were compared with controls for purge and microbial quality during storage. No significant difference was detected in purge or in initial moisture content between frankfurters containing the additives. However, there was a significant difference between these samples and controls, with the former retaining more water. Samples containing lactate had significantly lower numbers of lactic acid bacteria than samples containing starch-ISP or controls. All samples showed an increase during storage followed by a decrease, but frankfurters containing lactate decreased 7 days earlier. There was significant inhibition of psychrotrophs in samples containing the additives, with controls showing 10⁴ cells/g within 14 days compared with no counts in the treated samples. Frankfurters containing starch-ISP eventually showed growth after 42 days, while samples containing lactate showed no counts at any time during storage.     

USE of HYDROSTATIC PRESSIJRE to PRODUCE HIGH QUALITY and SAFE FRESH PORK SAUSAGE

The effects of high hydrostatic pressure (HHP) on the survival of microor ganisms and quality changes of fresh pork sausages were investigated. Pork sausage inoculated with Listeria monocytogenes at 1O⁷ CFU/gram was prepared and subjected to HHP at 414 and 552 MPa, at treatment temperatures of 25 and SOC. for various time intervals to examine pressure effects on inactivation of bacteria. At a pressure of 414 MPa and SOC for 2 min, the microorganisms in fresh pork sausages were completely inactivated. Partial discoloration of meat was observed after 10 min of pressurization above 414 MPa at either temperature.
The effect of HHP treatment on the physical and rheological properties of sausage was also studied. the sausages increased infirinness with an increase in the pressure applied. the pressure-treated sausages were generally lighter in color as compared with the heat-treated sausages.
The optimal pressure/temperature/time conditions that resulted in minimum quality changes with microbiologically safe fresh pork sausages was 414 MPa and SOC for 2 min.     

Survival of Listeria monocytogenes and Salmonella typhimurium and Quality Attributes of Cooked Pork Chops and Cured Ham after Irradiation

Cooked pork chops (pumped with salt/polyphosphate brine or untreated) and cured hams were inoculated with Listeria monocytogenes and Salmonella typhimurium. The samples were irradiated at low (0.75 to 0.90 kGy) or medium doses (1.8 to 2.0 kGy), and each dose was delivered at either a low (2.5 M/min conveyor speed) or high (5.4 M/min) dose rate. Low-dose irradiation reduced L. monocytogenes by more than 2 log and S. typhimurium by 1 to 3 log. Pathogen populations and total plate counts (TPC) were reduced to undetectable levels by medium doses. No meat quality attributes were affected, and no dose rate effect was observed. Nitrite reduced (P < 0.05) both pathogens and TPC during 7°C storage in ham, especially when combined with low-dose irradiation.     

SENSORY EVALUATION OF GROUND BEEF PATTIES IRRADIATED BY GAMMA RAYS VERSUS ELECTRON BEAM UNDER VARIOUS PACKAGING CONDITIONS

Ground beef patties were packaged in air with: nylon/polyethylene, Saran/polyester/polyethylene, or Saran film overwrap plus a styrofoam tray. Samples were irradiated at 2 kGy by either gamma rays or electron beam, and evaluated for 7 flavor, 3 mouthfeel, and 7 taste attributes by a trained sensory panel. The only difference observed between irradiated and unirradiated samples was that the latter had a more pronounced beef/brothy flavor than irradiated patties. No differences were detected according to packaging material used. Comparing the two sources of irradiation, patties irradiated by gamma rays had more intense cardboardy and soured flavors, and salty and sour tastes than patties irradiated by electron beam.