EFFECT OF RAPID COOLING ON THE GROWTH AND PENETRATION OF SALMONELLA ENTERITIDIS INTO EGG CONTENTS

Shell eggs were inoculated internally with approximately 10 cells of Salmonella enterica serovar enteritidis (S. enteritidis) and subjected to three different cooling treatments. Eggs were cooled from an initial temperature of 27C to approximately 7.2C. After cooling, eggs were stored at approximately 7.2C for 36 days, or stored at 5.7–9.5C for 30 days plus 6 days at 37C to simulate temperature abuse. Rapid cooling and subsequent storage of eggs at approximately 7.2C inhibited the growth of S. enteritidis in eggs. Slow cooling, and/or temperature abuse promoted growth of S. enteritidis in eggs. The penetration study indicated that rapid cooling and subsequent storage at 7.2C for 30 days did not affect the penetration of S. enteritidis into egg contents. The S. enteritidis isolated from the eggshell with shell membranes was significantly higher (P < 0.05) than from the internal egg contents, indicating that most of the S. enteritidis cells were trapped within the shell pores and/or shell membranes.     

EFFECTS OF TRISODIUM PHOSPHATE ON POPULATIONS OF SALMONELLA TYPHIMURIUM AND SALMONELLA ENTERITIDIS IN VITRO

This study determined the bactericidal activity of different concentrations of trisodium phosphate (TSP) against Salmonella typhimurium and Salmonella enteritidis in vitro. One milliliter of each TSP solution (0.5, 1, 1.5 and 2% w/v) was mixed with 1 mL of each bacterial culture and left to stand at room temperature (18  ±  1C) for 0, 15, 30, 45, 60 or 90 min before enumeration of the surviving pathogens.
The effects of 1.5 and 2% TSP were apparent on both bacterial species from 0 min and bacterial counts reached undetectable ( < 1.0  ×  10¹ cfu/mL) levels immediately. The 1% TSP solution effected close to 4.20–5.72 log reduction after 15 min. However, the reduction effect of 0.5% TSP was a function of treatment time, and some culturable bacteria remained even after 90 min of treatment. These results suggest that the bactericidal effect of TSP solution on these pathogens depends on its concentration and on the duration of treatment.

PRACTICAL APPLICATIONS

Poultry has been identified as one of the most important reservoirs of Salmonella typhimurium and Salmonella enteritidis in food chain. Efforts to eliminate or reduce Salmonella spp. and other pathogens attached to poultry carcasses during processing have been made for many years. In 1992, the U.S. Department of Agriculture approved the use of trisodium phosphate (TSP) as a processing aid to reduce Salmonella spp. on raw poultry carcasses. The aim of the present study was to determine the bactericidal effects of different concentrations of TSP on pure cultures of these pathogens in vitro .     

EFFECT OF GAMMA IRRADIATION ON SOME CHARACTERISTICS OF SHELL EGGS AND MAYONNAISE PREPARED FROM IRRADIATED EGGS

Shell eggs were irradiated at doses of 0.0, 0.5, 1.0 and 1.5 kGy of gamma irradiation. Immediately after irradiation, bacterial, physical and chemical analyses of eggs and sensory evaluation of the mayonnaise prepared from irradiated egg yolk were performed. Results indicated that all doses of gamma irradiation reduced the total counts of mesophilic bacteria and total coliforms of eggs. The radiation dose required to reduce the Salmonella load one log cycle (D₁₀) in eggs was 448 Gy. Eggs irradiated with 1.5 kGy may be suitable microbiologically to prepare safe mayonnaise. There were no significant differences in saturated fatty acids (C14:0; C16:0; C18:0) and thiobarbituric acidvalues between the yolk lipid extracted from irradiated eggs and that of nonirradiated ones. Gamma irradiation reduced the viscosity of egg whites. Sensory evaluation showed no significant differences between mayonnaises prepared from irradiated and nonirradiated egg yolks.     

RAPID DETECTION OF SALMONELLA ENTERITIDIS AND ESCHERICHIA COLI USING SURFACE PLASMON RESONANCE BIOSENSOR

The Biacore surface plasmon resonance (SPR)‐based biosensor was used to detect Salmonella enterica serovar Enteritidis and Escherichia coli in spiked skim milk using specific antibodies. The optical SPR biosensor registers changes in the refractive index during binding of the analyte (bacteria) to the ligand (antibody) on the gold‐coated sensor chip surface. Immobilized protein A‐captured specific antibodies were used to detect the bacteria in less than an hour. The reaction was found to be specific, and the limits of detection of the assay were found to be 25 cfu/mL for E. coli and 23 cfu/mL for Salmonella. Because the assays were shown to be sensitive, reproducible and very specific, the SPR‐based Biacore biosensor has the potential for near real‐time, yet specific, detection and presumptive identification of bacteria in food and water.     

FREQUENCY OF SALMONELLA, CAMPYLOBACTER, LISTERIA AND ENTEROBACTERIACEAE DETECTION IN COMMERCIALLY COOL WATER-WASHED SHELL EGGS

The effect of cool water washing on shell egg temperature and pathogen detection was examined. Three temperature schemes were utilized in commercial dual washer systems: (1) HH = 48.9C, 48.9C; (2) HC = 48.9C, 23.9C; and (3) CC = 23.9C, 23.9C. HH eggsmaintainedthe highest surface temperature (26.25C in‐line, 20.25C off‐line and 23.25C combined, P < 0.05). The lowest temperatures were found in the CC eggs (21.25C in‐line, 17.25C off‐line and 19.25C combined). The frequency of Enterobacteriaceae detection in shell and membrane emulsions was greatest for the CC eggs (P < 0.05 for in‐line and combined). There was no difference in Enterobacteriaceae detection for the off‐line facility. Salmonella was detected in three of 384 samples from the in‐line facility. They were found in HC (2) and CC (1) shell emulsions. Two of 384 samples were positive for Campylobacter from the in‐line facility (CC). Three wash water samples were positive for Listeria in the off‐line facility (1 HC, 2 CC). No pathogens were detected in the egg contents during this study. The results of this study indicate that warm followed by cool water washing has the potential of decreasing egg temperature while maintaining surface microbiology at an acceptable level.     

SURVIVAL OF ESCHERICHIA COLI, STAPHYLOCOCCUS AUREUS AND SALMONELLA ENTERITIDIS IN FROZEN CHICKEN HAMBURGER

The survival of food pathogens during frozen storage of chicken hamburgers was evaluated. Hamburgers were contaminated with Escherichia coli (ECHC), Staphylococcus aureus (SAFH) and Salmonella Enteritidis (SE86), separately, and stored at −18C for 28 days. Results demonstrated reductions of 0.63 log₁₀ cfu/g, 0.73 log₁₀ cfu/g and 0.27 log₁₀ most probable number/g in the populations of ECHC, SAFH and SE86, respectively. These microorganisms were also stored at −18C in 0.1% peptone water and presented significantly different reductions ( P <  0.05) when compared with frozen hamburgers, suggesting that components of chicken hamburger may exert a cryoprotective effect on microbial cells.

PRACTICAL APPLICATIONS

Even though Brazilian poultry meat industries present high levels of quality control, the presence of bacterial pathogens in hamburgers may occur. In Brazil, chicken hamburgers are frequently commercialized frozen, and it is well established that frozen temperatures are able to avoid microbial growth. However, frozen temperatures can also be able to inactivate part of the bacterial population, and the magnitude of its effect will vary according to the type of food and the process that it was submitted. This study evaluated the survival of Escherichia coli , Staphylococcus aureus , and Salmonella Enteritidis in frozen hamburgers, aiming to verify if this process could provide an additional margin of safety to this product.     

THERMAL INACTIVATION OF SALMONELLA ENTERITIDIS BY BOILING AND FRYING EGG METHODS

Salmonella enteritidis was cultivated in egg yolks and submitted to boiling and frying methods commonly used in domestic conditions in the south of Brazil. The results have demonstrated a rapid growth of the microorganism reaching counts of 9.0 log₁₀at 168 h. When contaminated shell eggs were placed in water and slowly heated, a population of approximately 7.0 log₁₀was completely inactivated after boiling for 1 min. However, in eggs placed directly in boiling water, the reduction was only 1.35 log₁₀after 1 min, and the entire population was eliminated after 3 min. A reduction of approximately 2.78 log₁₀was observed after frying for 1.5, 2.0 and 2.5 min. Even though the solidification of yolk has been pointed out as an indicator of S. enteritidis elimination in egg yolks, attention should be given to frying procedures, as considerable high levels of this microorganism could be recovered even from solidified yolks.     

EFFECT OF GAMMA RADIATION ON TOXICITY AND IMMUNOGENICITY OF SALMONELLA TYPHIMURIUM

Salmonella typhimurium H391 neurotoxin was sensitive to gamma radiation under in vivo conditions but resistant under in vitro conditions. Cells were detoxified after exposure to a radiation dose of 500 krad while isolated neurotoxin retained toxicity up to a dose of 3,000 krad. Detoxification of S. typhimurium H391 cells after exposure to 500 krad was accompanied by loss of antigenic properties which may be attributed to changes in the physico-chemical behavior of the neurotoxin moiety after in vivo radiation.     

A SURVEY ON INSTITUTIONAL USERS OF SHELL EGGS AND EGG PRODUCTS IN FLANDERS

A survey assessed the handling of shell eggs and processed eggs from purchase until serving to potentially vulnerable people in care homes, acute hospitals, handicapped institutions, and crèches (i.e. nurseries). In 94% of the institutions shell eggs are consumed at a weekly average of 1.1 ± 0.3 eggs for each person. In 52% of the institutions egg products are used. The shell eggs are held on average at 6.4C for 1–2 weeks. The questionnaire listed a series of egg dishes, which were classified afterwards in three risk categories. Of the high-risk dishes, shell eggs are particularly used for addition to mashed potatoes, for preparing soft-boiled eggs and eggs sunny-side-up and for inclusion in hot sauces. Of the medium-risk dishes, shell eggs are used for preparing scrambled eggs and omelets. When egg products are bought next to shell eggs, relatively less high-risk dishes and more low-risk dishes on the total dishes were made from shell eggs. Thus, egg products are purchased on a rational base. The distribution of storage temperature, storage time and preparation frequency of high-risk meals were combined using a Monte Carlo resampling technique, which indicated that the majority of the samples (98.5%) fell into a low-hazard category.     

EFFECT OF EVAPORATIVE COOLING STORAGE ON RIPENING AND QUALITY OF TOMATO

Tomatoes (Lycopersicon esculentum Mill cv. Rupali) ripened in evaporative cooling (EC) storage conditions (20°C–25°C, 92–95% RH) were compared with control fruits stored under room conditions (28°C–33°C, 45–65% RH) during summer in Mysore. EC ripened tomatoes on the 15th day reached 100% ripening index (RI) with a value of 2.48 for the ratio of redness to yellowishness (a/b) and hue angle (θ) of 22.1° whereas the control tomatoes on the same day reached a maximum 83.3% RI with a/b ratio of 1.59 and a hue angle of 32.9°. Higher development of chroma and total color difference were exhibited by EC stored tomatoes than control samples. The lycopene content of EC ripened fruits double that of the control. EC stored fruits showed lower values for rupture and shear stresses. The rate of moisture loss for control fruits was 6.5 times as great as for EC stored tomatoes.     

ACID AND THERMAL RESISTANCE OF A SALMONELLA ENTERITIDIS STRAIN INVOLVED IN SEVERAL FOODBORNE OUTBREAKS

Acid and thermal resistances of a Salmonella enteritidis strain involved in several foodborne outbreaks in southern Brazil were compared with other two Salmonella serovars. Strains were cultivated in Nutrient Broth supplemented with 1% glucose for acid adaptation, and then cells were exposed to different pH and temperatures. Survivors were enumerated and cellular proteins were analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). S. enteritidis presented better acid adaptation than S. typhimurium and S. bredeney after exposure to pH 3.5 and 4.0, but all serovars demonstrated a similar behavior at pH 4.5. At 52C, nonadapted and acid-adapted S. bredeney presented enhanced survivor rates when compared to the other serovars, although acid adaptation protected S. enteritidis. At 56C and 60C, nonadapted and acid-adapted S. enteritidis was more thermally resistant than other serovars. Differences in protein profiles of nonadapted and acid-adapted cells of all serovars were observed by SDS-PAGE. S. enteritidis demonstrated greater acid adaptation and thermal resistance after acid adaptation than other serovars.

PRACTICAL APPLICATIONS

These results could be related to the frequent involvement of this strain with salmonellosis in southern Brazil. Information on the thermal resistance of pathogenic microorganisms is an important step toward the optimization of the thermal processing of foods. Underestimation of thermal resistance increases the risk that a sufficient portion of an initial pathogen population may persist after thermal treatments, which could result in a foodborne outbreak.     

EFFECT OF STORAGE AND PROCESSING CONDITIONS ON SORGHUM KERNEL STRENGTH

Compressive strength of sorghum kernels was measured to determine the effect of storage conditions on processing for animal feed. Ensiling grain affected a larger decrease in kernel compressive strength than did storage at a high moisture level. Results similar to the above were noted for tests conducted on kernels obtained from animal feces. Microscopic examination of kernels from each treatment revealed greater removal of kernel structure for those of lower compressive strength.     

LISTERIA MONOCYTOGENES SURVIVAL ON SHELL EGGS AND RESISTANCE TO SODIUM HYPOCHLORITE1

The survival of a mixture of five strains of Listeria monocytogenes inoculated onto the surface of chicken eggs and stored at 10C for up to 14 days was studied. The numbers of survivors which were loosely bound to the shell decreased steadily from day 1 to 7, with no detectable Listeria after 11 days. The Listeria cells which were judged to be tightly bound to the shell did not decrease significantly after 11 days, with less than a 2-log reduction at 14 days. Application of sodium hypochlorite solutions (50 ppm and 100 ppm available chlorine) to inoculated eggs completely eliminated the loosely bound cells after the shortest exposure time used (30 s), while little or no decrease was observed for the cells which were more strongly attached, even after 5 min. No Listeria were recovered from the egg contents (meat) of any of the inoculated eggs used in this study.