Effect of high-pressure processing on strains of Enterobacter sakazakii.

Four strains of Enterobacter sakazakii were inoculated into tryptic soy broth and reconstituted powdered infant formula and exposed to high-pressure processing. Pressures of 200, 400, and 600 MPa were used for each medium for 1 min. E. sakazakii was reduced by more than 6 log (strains A and B) in both media at 600 MPa. Strain B was significantly (P < or = 0.05) more pressure resistant than the other strains, with just more than a 3-log reduction at 600 MPa in both media. The reconstituted infant formula has a significant (P < or = 0.05) protective effect for certain strains and pressures (strain B at 400 MPa and strain D at 400 and 600 MPa). Differences in log reductions between media (milk and broth) were also observed for certain strains and specific pressures (strain B at 400 MPa and strain D at 400 and 600 MPa; P < or = 0.05). This research showed that E. sakazakii, when present in reconstituted powdered infant formula, can be submitted to high-pressure processing (600 MPa for 1 min) and achieve log reductions ranging from 3 to 6.84, depending on the strain.

KCN inhibition of lipoxygenase in purple, green, and white eggplants.

Lipoxygenase activity in three cultivars (purple, green, and white) of eggplant, Solanum melongena, were compared. Activity was greatest in the purple and lowest in the white variety. In contrast to reports that NaCN did not inhibit eggplant lipoxygenase, in these studies cyanide completely inhibited the enzyme in all three varieties.

Role of organic acids during processing to improve quality of channel catfish fillets.

A microbial preparation derived from aquacultured channel catfish fillets (Ictalurus punctatus) was acidified with 0, 1, 2 and 4% (vol/vol) weak organic and held in an ice bath at 0 degree C to simulate the chilling process. Additionally, catfish fillets were sprayed under varying pressures at 15 degrees C with organic acids to evaluate the efficacy of concentrations of organic acids and spray pressures to ameliorate the microbiological quality. To determine plate counts, the dilution fluid was neutralized to pH 7.2 with 1.0 M NaOH. The aerobic plates counts of microorganisms in the chilling water were monitored over a 20-min interval. Aerobic plate counts were found on the channel catfish fillets before and after spray washing with organic acids. Plates were incubated at 35 degrees C for 48 h. The addition of organic acids tot he microbial preparation used in simulating the chilling process significantly (P < 0.05) reduced the number of bacterial surviving. The number of surviving bacteria in the chilled water decreased with increasing concentration and time of exposure to organic acids. Propionic acid had the most detrimental effect on organisms present in the microfloral preparation followed by acetic and lactic acids. Spray washing of catfish fillets with water did not significantly (P < 0.05) affect the microbial quality of fillets. However, catfish fillets sprayed with organic (lactic and propionic) acids significantly (P < 0.05) reduced the microbial counts by 10-fold. Lactic and propionic acids were not significantly (P > 0.05) different in influencing the aerobic counts of the catfish fillets.

Growth of inoculated psychrotrophic pathogens on refrigerated fillets of aquacultured rainbow trout and channel catfish.

Aquacultured rainbow trout (Oncorhynchus mykiss) and channel catfish (Ictalurus punctatus) fillets were inoculated with the psychrotrophic pathogens Listeria monocytogenes and Aeromonas hydrophila: cell populations were monitored during refrigerated storage at 2 to 4 degrees C. Fillets of both species were placed individually in sterile plastic bags and inoculated with cell suspensions (10(4.7) CFU/100 g of fish) of either A. hydrophila or L monocytogenes or of both A. hydrophila and L. monocytogenes, for a total of three treatments for each species of fish. Each inoculum and fillet were mixed to ensure uniform distribution and then stored at 2 to 4 degrees C. A. hydrophila, L. monocytogenes, and aerobic cell populations were determined on days 1, 3, 6, 8, 10, 13, and 15. Individually inoculated A. hydrophila and L. monocytogenes grew on catfish and trout fillets during the 15-day study. There was no inhibition of either pathogen by the natural flora on the fillets. Both psychrotrophic pathogens grew equally well in catfish and trout fillets inoculated with a combination of A. hydrophila and L. monocytogenes. In all three treatments, the counts of the psychrotrophic pathogens were lower than the aerobic plate counts. The growth of the psychrotrophic pathogens L. monocytogenes and/or A. hydrophila during refrigerated storage on aquacultured fish fillets could increase the food hazard risk, particularly where there is a possibility of cross-contamination with ready-to-eat food products.

Influence of processing schemes on indicative bacteria and quality of fresh aquacultured catfish fillets.

Fresh aquacultured catfish fillets were obtained from three processors using different processing protocols in summer, autumn, winter, and spring and evaluated for microbial quality. Twenty freshly processed fillets were randomly selected and each fillet was placed in a sterile polyethylene bag. The fillets were transported on ice-pack overnight by air immediately after processing. Five fillets were randomly selected for microbial assays. Each fillet was weighed and an equal volume of sterile 0.1% peptone water at 0 to 1 degrees C was added aseptically. The fillet was massaged (or rinsed) for 120 s and the rinse was used to determine microbial quality. Aerobes (incubation at 35 degrees C for 48 h) and psychrotrophs (incubation at 20 degrees C for 96 h) were enumerated using 3M Petrifilm Aerobic Count plates. Escherichia coli (incubation at 35 degrees C for 24 to 48 h) and total coliforms (incubation at 35 degrees C for 24 to 48 h) were enumerated on 3M Petrifilm E. coli Count plates. Staphylococcus aureus counts were determined on Baird-Parker agar (incubation at 35 degrees C for 48 h). Significant differences (P < or = 0.05) in aerobic, psychrotrophic, total coliform, E. coli, and S. aureus counts due to temperature effects during production and variations in processing protocols were observed. E. coli and S. aureus counts were significantly different during the four seasons. E. coli and S. aureus counts were high during summer and low during winter weather. There was a significant difference (P < or = 0.05) in aerobic, psychrotrophic, and total coliform counts among the three processors during warm weather; however, these differences were significantly (P < or = 0.05) reduced in cold weather.

Microbiological quality and safety of quahog clams, Mercenaria mercenaria, during refrigeration and at elevated storage temperatures.

The effects of storage temperatures and times on the microbiological quality and safety of hard-shelled quahog clams (Mercenaria mercenaria) were examined. Samples were stored at four different incubation temperatures (3.3, 7.2, 10.0, and 12.8 degrees C) for a period of 3 weeks, following their harvest from summer growing waters (> or = 27 degrees C) and winter waters (< or = 4 degrees C). Clams were analyzed for two naturally occurring pathogens, Vibrio parahaemolyticus and Vibrio vulnificus. During the summer, V. parahaemolyticus was isolated from 56% of the stored samples, with the highest concentration, 6,100/g, occurring on day 12 at 12.8 degrees C. Also, during the summer, V. vulnificus was isolated from 11% of the stored samples, with the highest concentration of 1,500/g occurring on day 15 at 7.2 degrees C. No Vibrio spp. were detected during the winter. During summer storage, aerobic mesophilic counts on plate count agar (PCA) containing 2% NaCl ranged from 10(4) to 10(8) CFU/g, and during storage of the winter samples, aerobic mesophilic PCA (with added NaCl) counts ranged from <100 to 10(4) CFU/g. Comparatively, summer storage mesophilic counts on PCA containing no added NaCl ranged from <100 to 10(5) CFU/g, and for the winter samples the range was <100 to 10(2) CFU/g. Coliform and fecal coliform counts ranged from <0.3 to 61.1/g and <0.3 to 24.4/g, respectively. There was no statistical correlation between the length of storage or the temperature of incubation and the presence of V. parahaemolyticus, V. vulnificus, coliforms, or fecal coliforms. However, storage time and incubation temperature affected the PCA counts (P < or = 0.05) in quahog clams.

Levels of Vibrio vulnificus and organoleptic quality of raw shellstock oysters (Crassostrea virginica) maintained at different storage temperatures.

Temperature abuse during raw oyster harvesting and storage may allow for the multiplication of natural spoilage flora as well as microbial pathogens, thus posing a potential health threat to susceptible consumers and compromising product quality. The objective of this study was to provide a scientific basis for determining whether different refrigeration and abuse temperatures for raw oysters would result in a spoiled product before it became unsafe. Raw shellstock oysters (Crassostrea virginica) purchased from a commercial Virginia processor were subjected to different temperature abuse conditions (7, 13, and 21 degrees C) over a 10-day storage period. Salinity, pH, halophilic plate count (HPC), total culturable Vibrio counts, and culturable Vibrio vulnificus counts were determined at each abuse condition. V. vulnificus isolates were confirmed by a specific enzyme-linked immunosorbent assay. Olfactory analysis was performed to determine consumer acceptability of the oysters at each abuse stage. The pH of the oysters decreased over time in each storage condition. The HPC increased 2 to 4 logs for all storage conditions, while olfactory acceptance decreased over time. V. vulnificus levels increased over time, reaching 10(5) to 10(6) CFU/g by day 6. The length of storage had a greater effect on the bacterial counts and olfactory acceptance of the oysters (P < 0.05) over time than did the storage temperature (P < 0.05).

Biogenic amine survey and organoleptic changes in fresh, stored, and temperature-abused bluefish (Pomatomus saltatrix).

Changes in histamine, putrescine, and cadaverine concentrations in bluefish filets (Pomatomus saltatrix) stored at 5, 10, and 15 degrees C were determined using high-performance liquid chromatography. An organoleptic assessment was conducted simultaneously with the biogenic amine analyses. The histamine levels found in fresh bluefish obtained from wholesale seafood distributors ranged between <1 ppm and 99 with an average of 39 ppm. Putrescine and cadaverine were not found in fresh bluefish. Fish fillets stored at each of the three temperatures developed histamine. The greatest accumulation of histamine was observed in fish stored at 15 degrees C, which developed histamine levels as high as 2,200 ppm. Putrescine levels increased at each temperature during storage. Cadaverine was present only in uninoculated bluefish stored at 15 degrees C. Histamine achieved higher levels in bluefish pieces inoculated with Morganella morganii, which demonstrates that bluefish support bacterial histamine formation. Histamine levels at each temperature exceeded the 50-ppm advisory level established by the Food and Drug Administration before 100% sensory rejection. Standard plate counts increased during storage of fish at all temperatures, but the correlation between histamine levels and standard plate count was not significant.

Growth and histamine formation of Morganella morganii in determining the safety and quality of inoculated and uninoculated bluefish (Pomatomus saltatrix).

The objective of this study was to determine the effect of normal microflora and Morganella morganii on histamine formation and olfactory acceptability in raw bluefish under controlled storage conditions. Fillets inoculated with and without M. morganii were stored at 5, 10, and 15 degrees C for 7 days. Microbial isolates from surface swabs were identified and screened for histidine decarboxylase activity. Olfactory acceptance was performed by an informal sensory panel. Histamine levels were quantified using high-performance liquid chromatography and fluorescence detection. While olfactory acceptance decreased, histamine concentration and bacterial counts increased. Storage temperature had a significant effect on histamine levels, bacterial counts, and olfactory acceptance of the bluefish. Inoculation with M. morganii had a positive significant effect on histamine formation for bluefish held at 10 and 15 degrees C (P < 0.0001). The results of the study will serve in supporting U.S. Food and Drug Administration (FDA) regulations regarding guidance and hazard levels of histamine in fresh bluefish.

Indicative and pathogenic microbiological quality of aquacultured finfish grown in different production systems.

The nature and number of indicator and pathogenic microbes in fish reared using recirculating and nonrecirculating water systems were compared. For each system, 20 samples of rainbow trout (Oncorhynchus mykiss), tilapia (Oreochromis spp.), hybrid striped bass (Morone saxatilis x M. chrysops), and pacu (Piaractus mesopotamicus) were randomly selected and gutted, and microbial analyses were performed using AOAC procedures. Five fish were subsampled and analyzed for indicative microbial quality with 3M Petrifilm (). The general microbial quality differed significantly (P < 0.05) among the production systems, except for total coliform counts. Rainbow trout cultured in recirculating and nonrecirculating water systems had lower counts for aerobes (2.00 to 3.11 log CFU/g) (p < 0.05), than other species, whereas trout reared in a recirculating water system had significantly lower psychrotrophic numbers (0.86 to 1.85 log CFU/g). Pacu had the highest fecal coliform counts (2.74 to 3.70 log CFU/g), whereas hybrid striped bass and rainbow trout grown in nonrecirculating systems had lower fecal coliform counts (0.00 to 1.39 log CFU/g). Rainbow trout grown in a nonrecirculating system had significantly higher Escherichia coli counts (0.00 to 2.11 log CFU/g). The human bacterial pathogens Listeria monocytogenes, Yersinia enterocolitica, Escherichia coli O157:H7 and Salmonella spp. were not isolated form the fish sampled. However, Clostridium botulinum botulinum was isolated from all the aquacultured fish sampled except pacu and tilapia grown in a recirculating aquaculture system. However, the counts were very low, ranging from 0.0 to 2.3 MPN/g.

Effects of high pressure processing on hatching of eggs of the zoonotic rat tapeworm Hymenolepis diminuta.

High hydrostatic pressure processing (HPP) is an effective non-thermal treatment to remove pathogens from a variety of food and food products. It has been extensively examined using prokaryotic organisms but has had limited study on eukaryotic organisms. Treatment using HPP has been shown to be effective in inactivating nematode larvae in food and Ascaris suum eggs. Nothing is known on the efficacy of HPP on tapeworm cysts or eggs. Eggs of important zoonotic tapeworms including Echinococcus and Taenia spp. can potentially contaminate water and food intended for human consumption. The present study examined the efficacy of HPP on the viability of Hymenolepis diminuta eggs. Efficacy of HPP treatment was measured using an egg hatch assay in two experiments. One thousand unhatched H. diminuta eggs in Hanks balanced salt solution were packaged in sealable bags and exposed to 100-600megapascals (MPa; 1MPa=10atm=147psi) for 60s in a commercial HPP unit. Positive (no HPP) and negative (No HPP but frozen/thawed) controls were examined in each experiment. None of the HPP untreated and frozen eggs (negative controls) were able to hatch or exclude trypan blue when placed in the hatching solution in experiment 1 or 2. HPP untreated and nonfrozen eggs (positive controls) hatched and excluded trypan blue; 75% were positive in experiment 1 and 80% were positive in experiment 2. No hatched eggs were observed when they were exposed to 300-600MPa for 60s. Treatment at 400MPa and above caused rupturing of the oncosphere. Results from this study indicate that HPP is a possible method to inactivate tapeworm eggs and that the susceptibility of tapeworm eggs to HPP is similar to or greater than that of nematode eggs or tissue larvae.

High hydrostatic pressure processing of murine norovirus 1-contaminated oysters inhibits oral infection in STAT-1(-/-)-deficient female mice.

We have previously demonstrated that high pressure processing (HPP) is effective in preventing in vitro replication of murine norovirus strain 1 (MNV-1), a human norovirus surrogate, in a monocyte cell line following extraction from MNV-1-contaminated oysters. In the present study, the efficacy of HPP to prevent in vivo replication within mice fed HPP-treated MNV-1-seeded oyster extracts was evaluated. Oyster homogenate extracts seeded with MNV-1 were given 5-min, 400-MPa (58,016-psi) treatments and orally gavaged into immunodeficient (STAT-1(-/-)) female mice. Mice orally gavaged with HPP-treated MNV-1 showed significant (P ≤ 0.05) weight loss leading to enhanced morbidity, whereas those given 100 and 200 PFU of HPP-treated MNV-1 were comparable to uninfected controls. MNV-1 was detected, via real-time PCR, within the liver, spleen, and brain of all mice fed non-HPP-treated homogenate but was not detected in the tissues of mice fed HPP-treated homogenates or in uninfected control mice. Hepatocellular necrosis and lymphoid depletion in the spleen were observed in non-HPP-treated MNV-1 mice only. These results clearly show that HPP prevents MNV-1 infection in vivo and validates that viral inactivation by HPP in vitro is essentially equivalent to that in vivo. Further, the data suggest that HPP may be an effective food processing intervention for norovirus-contaminated shellfish and thus may decrease risk to both immunocompromised and immunocompetent individuals who consume shellfish.

Microbial contamination of shellfish: prevalence, risk to human health, and control strategies.

There has been significant concern in recent times about the safety of molluscan shellfish for human consumption. Despite extensive efforts to assure a safe supply of molluscan shellfish, the number of cases of disease and death are still great enough to cause concern among the public. The number of cases of illness and death associated with the ingestion of shellfish falls in the lower end of the range of other similar microbial pathogen-related foodborne disease. Disease and deaths due to viruses and naturally occurring bacteria are now of greatest concern because they are the most often cited causative agents. The greatest risk of disease or death due to shellfish consumption is among the population with underlying health conditions who choose to consume raw shellfish. Control strategies to limit shellfish-borne disease should focus upon disease and death caused by viruses and naturally occurring bacteria among at-risk populations.

Composition and Pesticide and Herbicide Residue Analysis of Fresh and 40-Year-Old Pasteurized Blue Crab ( Callinectes sapidus ) Meat.

Fresh and 40-year-old pasteurized blue crab ( Callinectes sapidus ) meat was analyzed for proximate composition, mineral, heavy metal, and amino acid content and volatiles concentration and possible pesticide and herbicide residue levels. Both fresh and 40-year-old meat had similar proximate compositions. The 40-year-old crab meat contained high levels of iron, manganese, copper, and heavy metals compared to the fresh. Recovery of total amino acids was lower from the 40-year-old meat. Aspartic acid, glutamic acid, leucine, lysine, and arginine were the major protein amino acids of fresh and 40-year-old crab meat. The 40-year-old meat contained high concentrations of ethanol and trimethylamine compared to the fresh. No herbicide residues were detected in either of the products. Decomposition products of pesticide DDT were detected at very low levels only in the 40-year-old crab meat.