Arthur J. Miller

Evidence of Salmonella internalization into fresh mangos during simulated postharvest insect disinfestation procedures.

A recent U.S. salmonellosis outbreak was epidemiologically associated with consumption of imported fresh mangos. Studies were conducted to simulate the commercial heat disinfestation method used to eliminate tephritid fly larvae from mangos, as well as subsequent product cooling procedures, to assess whether this process promotes internalization of Salmonella into mangos. The experimental parameters were chosen to mimic the disinfestation method used by the South American producer/packer implicated in the recent outbreak. Untreated domestically grown immature and ripened Tommy Atkins variety mangos were immersed in water at 47 degrees C for 90 min and then immersed in 21 degrees C water containing brilliant blue FD&C no. 1 dye for 10 min. After dye internalization potential was established (67%), the same experiment was performed using 21 degrees C water containing 10(7) CFU/ml Salmonella Enteritidis expressing constitutive green fluorescent protein. Fruit was then stored at 10, 20, or 30 degrees C for up to 1 week. Immature and ripened mangos were positive for Salmonella internalization at a frequency of 80 and 87%, respectively. Internalization frequency into the stem-end segment (83%) was significantly higher (P < 0.05) than internalization into the middle-side (19%) or blossom-end (9%) segments of the fruit. Salmonella was detected in the mango pulp after 1 week of incubation. The degree of fruit ripeness, posttreatment holding temperature, or duration of storage had no significant effect (P > 0.05) on internalization frequency or survival of Salmonella inside mangos. This study illustrates the high potential for pathogen internalization if heat-disinfested mangos are cooled using contaminated water.

Potential for internalization, growth, and survival of Salmonella and Escherichia coli O157:H7 in oranges

Internalization potential, survival, and growth of human pathogens within oranges were investigated in a series of laboratory experiments. Submerging oranges into dye solutions at various temperature differentials was used to assess internalization potential. Conditions in which dye internalization was observed were further studied by applying Escherichia coli O157:H7 or Salmonella onto the stem scar, subjecting the oranges to a temperature differential, juicing, and measuring numbers of pathogens in the resulting juice. Pathogens for growth and survival studies were applied to or injected into simulated peel punctures. Oranges with small peel holes of selected sizes were also placed into solutions containing these pathogens. Bacterial survival was also evaluated in orange juice at 4 and 24 degrees C. Oranges internalized pathogens at a frequency of 2.5 to 3.0%, which mirrored dye internalization frequency (3.3%). Pathogens were internalized at an uptake level of 0.1 to 0.01% of the challenge applied. Bacteria grew within oranges at 24 degrees C, but not at 4 degrees C. Thirty-one percent of oranges with 0.91-mm surface holes showed pathogen uptake, whereas 2% of oranges with 0.68-mm holes showed pathogen uptake. Pathogens added to fresh orange juice and incubated at 24 degrees C declined 1 log CFU/ml within 3 days. These results suggest that internalization, survival, and growth of human bacterial pathogens can occur within oranges intended for producing unpasteurized juice.

Antibotulinal properties of selected aromatic and aliphatic aldehydes

Aromatic and aliphatic aldehydes were tested for their effectiveness against Clostridium botulinum spores and cells. Six-tenths millimolar benzaldehyde, piperonal, phenylacetaldehyde, α-amylcinnamaldehyde, vanillin, or phenylglyoxal delayed germination in botulinal assay medium (BAM) broth after 6 h exposure at 32°C. Sporicidal activity was observed with 1.25 mM vanillin, 39 mM isobutyraldehyde, 156 mM pyruvaldehyde or valeraldehyde, 625 mM benzaldehyde, and 2,500 mM α-amylcinnamaldehyde. Twenty-five millimolars of cinnamaldehyde, phenylacetaldehyde, pyruvaldehyde, and vanillin were most active against vegetative cells at pH 7.0 in BAM broth, while 125 mM was required for benzaldehyde, acetaldehyde, piperonal, or phenylglyoxal. Three millimolars benzaldehyde, 5.0 mM phenylglyoxal, 150 mM cinnamaldehyde, 200 mM pyruvaldehyde and vanillin, and 300 mM piperonal inhibited 9 h dipicolinic acid release in BAM broth at 32°C. Spore resistance to a 20-min 80°C thermal treatment was reduced when challenged with prior exposure to 100 mM cinnamaldehyde, piperonal, pyruvaldehyde, vanillin, or phenylglyoxal. Inhibition by cinnamaldehyde, piperonal, and phenylglyoxal was retained in commercial canned chicken and in beef broths. Five millimolars of benzaldehyde, cinnamaldehyde, piperonal, pyruvaldehyde, or phenylglyoxal delayed neurotoxin production for 48 h at 32°C, while 25 mM was required for vanillin. These results indicate that certain aldehydes inhibit C. botulinum , and aromaticity improves efficacy.

Comparison of organic acid salts for Clostridium botulinum control in an uncured turkey product.

Health concerns have led consumers toward purchasing nitrite-free, low salt meat and poultry products. Lacking these barriers to control growth of bacterial pathogens, such products carry heightened risks for botulism, especially if temperature abused. To address this threat, five organic acid salts were evaluated as potential antibotulinal agents. Ground turkey breast was formulated with 1.4% NaCl, 0.3% sodium pyrophosphate, 0-6% organic acid salts, 10% ice, and 500 spores per g of a 6-strain mixture of proteolytic Clostridium botulinum . Vacuum-packaged product (10 g) was heated in 75°C water for 20 min, cooled, and incubated for up to 18 d at 28°C. Botulinal neurotoxin was detected by mouse bioassay at 2 d in samples which lacked any of the test compounds. Samples containing 2% acid salt developed neurotoxin, which was detected at 2, 2, 4, 5, and 5 d for pyruvate, citrate, lactate, acetate, and propionate, respectively. With 6% acid salt additions, samples remained neurotoxin free until 7 d with pyruvate, 18 d with citrate, and >18 d for the remaining compounds. Monocarboxylic acid salts exhibited antibotulinal activity related to their dissociation constants (pKa) Citrate did not fit this pattern, however, suggesting a different mechanism of action. This study reveals that a variety of organic acid salts possess activity that can be used alone or possibly in combination to enhance the safety of nitrite-free turkey products.

Cold shock induction of thermal sensitivity in Listeria monocytogenes.

ABSTRACT Cold shock at 0 to 15°C for 1 to 3 h increased the thermal sensitivity of Listeria monocytogenes. In a model broth system, thermal death time at 60°C was reduced by up to 45% afterL. monocytogenes Scott A was cold shocked for 3 h. The duration of the cold shock affected thermal tolerance more than did the magnitude of the temperature downshift. The Z values were 8.8°C for controls and 7.7°C for cold-shocked cells. TheD values of cold-shocked cells did not return to control levels after incubation for 3 h at 28°C followed by heating at 60°C. Nine L. monocytogenes strains that were cold shocked for 3 h exhibited D60 values that were reduced by 13 to 37%. The D-value reduction was greatest in cold-shocked stationary-phase cells compared to cells from cultures in either the lag or exponential phases of growth. In addition, cold-shocked cells were more likely to be inactivated by a given heat treatment than nonshocked cells, which were more likely to experience sublethal injury. The D values of chloramphenicol-treated control cells and chloramphenicol-treated cold-shocked cells were no different from those of untreated cold-shocked cells, suggesting that cold shock suppresses synthesis of proteins responsible for heat protection. In related experiments, theD values of L. monocytogenes Scott A were decreased 25% on frankfurter skins and 15% in ultra-high temperature milk if the inoculated products were first cold shocked. Induction of increased thermal sensitivity in L. monocytogenes by thermal flux shows potential to become a practical and efficacious preventative control method.

Comparison of wooden and polyethylene cutting boards: potential for the attachment and removal of bacteria from ground beef

The potentials for removal of beef bacterial microflora from unscored polyethylene and hardwood cutting boards were compared. Ground beef was placed for 0 to 90 min onto cutting boards at room temperature and then removed; the surfaces were swabbed and the bacteria were enumerated. The boards were cleaned with various cleaning agents and then analyzed for bacterial removal. In addition, aqueous extracts from eight hardwoods were incubated with Escherichia coli O157:H7 for 0 to 30 h at 37°C to determine their inhibitory potential. Differences between the bacterial levels on wooden and plastic boards were not significant regardless of contact time. Washing with any cleaner, including water, removed most bacteria from either type of board. White ash extracts reduced E. coli O157:H7 levels to undetectable within 24 h; black cherry and red oak exhibited low inhibitory activity. Slight growth was observed in extracts from all other hardwoods, including hard maple, suggesting that aqueous extractable agents that are active against E. coli O157:H7 are not generally present in hardwoods. This study demonstrates the need to control cutting board sanitation regardless of composition.

Thermal resistance of nonproteolytic type B and type E Clostridium botulinum spores in phosphate buffer and turkey slurry.

The heat resistance of nonproteolytic type B and type E Clostridium botulinum spores in phosphate buffer and turkey slurry was determined from 70 to 90°C. Thermal-death times were determined in vials heated using a water bath. Recovery of heat-injured spores was on reinforced clostridial medium (RCM) and tryptic soy agar (TSA) with and without added lysozyme (10 μg/ml). Decimal-reduction times (D-values) were determined by fitting a survival model to the data using a curve-fitting program. The apparent or measured heat resistance was maximum with RCM supplemented with lysozyme. The D-values at 80°C for type E spores in buffer ranged from 1.03 min for strain Whitefish to 4.51 min for strain Saratoga. The D-value for the most heat-resistant nonproteolytic type B strain KAP B5 in buffer was 4.31 min at 80°C. The z-values in buffer for all strains were very similar, ranging from 8.35 to 10.08°C.Turkey slurry offered protection to the spores with a concomitant increase in heat resistance. The D-values in turkey slurry ranged from 51.89 min at 70°C to 1.18min at 85°C for type E strain Alaska (z = 9.90°C) and from 32.53 min at 75°C to 0.80 min at 90°C for nonproteolytic type B strain KAP B5 (z = 9.43°C). Thermal-death-time values from this study will assist food processors to design thermal processes that ensure safety against nonproteolytic C. botulinum in cook/chill foods.

Growth and sporulation potential of Clostridium perfringens in aerobic and vacuum-packaged cooked beef

Growth of Clostridium perfringens in aerobic-and anaerobic-(vacuum) packaged cooked ground beef was investigated. Autoclaved ground beef was inoculated with ~3.0-log10 CFU/g of C. perfringens , packaged and stored at various temperatures. Vegetative cells and heat-resistant spores were enumerated by plating unheated and heated (75°C for 20 min) meat samples on tryptose-sulfite-cycloserine agar. Clostridium perfringens grew to >7 logs within 12 h at 28, 37 and 42°C under anaerobic atmosphere and at 37 and 42°C under aerobic conditions. At 28°C under aerobic conditions, growth was relatively slow and total viable count increased to >6 logs within 36 h. Similarly, growth at 15°C in air was both slower and less than under vacuum. Regardless of packaging, the organism either declined or did not grow at 4, 8 and 12°C. Spores were not found at <12°C. Spores were detected as early as 8 h at 42°C under anaerobic conditions, but in general, the type of atmosphere had little influence on sporulation at ≥28°C. Temperature abuse (28°C storage) of refrigerated products for 6 h will not permit C. perfringens growth. However, cyclic and static temperature abuse of such products for relatively long periods may lead to high and dangerous numbers of organisms. Reheating such products to an internal temperature of 65°C before consumption would prevent food poisoning since the vegetative cells were killed.

Current approaches for reconditioning process water and its use in food manufacturing operations

Water is perhaps the most critical component in the processing of most food products. Supplies of water that is suitable for use in food processing operations are becoming limited. Three aspects of water as they relate to food processing will be discussed: water as a vehicle for various foodborne disease agents (bacterial, viral and parasitic); an overview of wastewater treatment processes, including the agents used in the final phase to disinfect water; and approaches to reconditioning food plant processing water for reuse within the food processing plant and in other areas of food production. Although the potential for the use of reconditioned water is vast, actual applications are currently very few.

Influence of Fruit Variety, Harvest Technique, Quality Sorting, and Storage on the Native Microflora of Unpasteurized Apple Cider

Apple variety, harvest, quality sorting, and storage practices were assessed to determine their impact on the microflora of unpasteurized cider. Seven apple varieties were harvested from the tree or the ground. The apples were used fresh or were stored at 0 to 4 degrees C for < or = 5 months and were pressed with or without quality selection. Cider yield, pH, Brix value, and titratable acidity were measured. Apples, postpressing apple pomace, and cider samples were analyzed for aerobic bacteria, yeasts, and molds. Aerobic bacterial plate counts (APCs) of ciders from fresh ground-picked apples (4.89 log CFU/ml) were higher than those of ciders made from fresh, tree-picked apples (3.45 log CFU/ml). Quality sorting further reduced the average APC to 2.88 log CFU/ml. Differences among all three treatment groups were significant (P < 0.0001). Apple and pomace microbial concentrations revealed harvest and postharvest treatment-dependent differences similar to those found in cider. There were significant differences in APC among apple varieties (P = 0.0001). Lower counts were associated with varieties exhibiting higher Brix values and higher titratable acidity. Differences in APC for stored and fresh apples used for cider production were not significant (P > 0.05). Yeast and mold counts revealed relationships similar to those for APCs. The relationship between initial microbial load found on incoming fruit and final cider microbial population was curvilinear, with the weakest correlations for the lowest apple microflora concentrations. The lack of linearity suggests that processing equipment contributed to cider contamination. Tree-picked quality fruit should be used for unpasteurized cider production, and careful manufacturing practices at cider plants can impact both safety and quality of the final product.