George J. Flick

Inactivation of a Norovirus by High-Pressure Processing

ABSTRACT Murine norovirus (strain MNV-1), a propagable norovirus, was evaluated for susceptibility to high-pressure processing. Experiments with virus stocks in Dulbeccos modified Eagle medium demonstrated that at room temperature (20°C) the virus was inactivated over a pressure range of 350 to 450 MPa, with a 5-min, 450-MPa treatment being sufficient to inactivate 6.85 log10 PFU of MNV-1. The inactivation of MNV-1 was enhanced when pressure was applied at an initial temperature of 5°C; a 5-min pressure treatment of 350 MPa at 30°C inactivated 1.15 log10 PFU of virus, while the same treatment at 5°C resulted in a reduction of 5.56 log10 PFU. Evaluation of virus inactivation as a function of treatment times ranging from 0 to 150 s and 0 to 900 s at 5°C and 20°C, respectively, indicated that a decreasing rate of inactivation with time was consistent with Weibull or log-logistic inactivation kinetics. The inactivation of MNV-1 directly within oyster tissues was demonstrated; a 5-min, 400-MPa treatment at 5°C was sufficient to inactivate 4.05 log10 PFU. This work is the first demonstration that norovirus can be inactivated by high pressure and suggests good prospects for inactivation of nonpropagable human norovirus strains in foods.

Biogenic Amines in Fish and Shellfish

Publisher Summary This chapter focuses on biogenic amines in fish and shellfish. The term “biogenic amines” refers to the nonvolatile amines, such as cadaverine, putrescine, spermidine, spermine, tyramine, tryptamine, and histamine, produced post mortem in fish and shellfish products. The compounds are reported to originate from the decarboxylation of specific free amino acids in fish or shellfish tissue. Chemically, the biogenic amines are defined as low-molecular-weight aliphatic, alicyclic, or heterocyclic organic bases. The use of chemical compounds as objective product standards or the indices of quality has long been suggested because these tests are rapid when compared to traditional microbiological analyses and less subject to individual interpretation than sensory analyses. Moreover, clinical studies have considered the activity of diamine oxidases to be a useful parameter, thus, many different assays to determine the activity of diamine oxidases have been proposed. Procedures using radioactive substrate achieve high sensitivity and most recently the use of high-performance liquid chromatography has been described.

SURVIVAL OF TOXOPLASMA GONDII OOCYSTS IN EASTERN OYSTERS (CRASSOSTREA VIRGINICA)

Toxoplasma gondii has recently been recognized to be widely prevalent in the marine environment. It has previously been determined that Eastern oysters (Crassostrea virginica) can remove sporulated T. gondii oocysts from seawater and that oocysts retain their infectivity for mice. This study examined the long-term survival of T. gondii oocysts in oysters and examined how efficient oysters were at removing oocysts from seawater. Oysters in 76-L aquaria (15 oysters per aquarium) were exposed to 1 × 106 oocysts for 24 hr and examined at intervals up to 85 days postexposure (PE). Ninety percent (9 of 10) of these oysters were positive on day 1 PE using mouse bioassay. Tissue cysts were observed in 1 of 2 mice fed tissue from oysters exposed 21 days previously. Toxoplasma gondii antibodies were found in 2 of 3 mice fed oysters that had been exposed 85 days previously. In another study, groups of 10 oysters in 76-L aquaria were exposed to 1 × 105, 5 × 104, or 1 × 104 sporulated T. gondii oocysts for 24 hr and then processed for bioassay in mice. All oysters exposed to 1 × 105 oocysts were infected, and 60% of oysters exposed to 5 × 104 oocysts were positive when fed to mice. The studies with exposure to 1 × 104 oocysts were repeated twice, and 10 and 25% of oysters were positive when fed to mice. These studies indicate that T. gondii can survive for several months in oysters and that oysters can readily remove T. gondii oocysts from seawater. Infected filter feeders may serve as a source of T. gondii for marine mammals and possibly humans.

Removal of Toxoplasma gondii Oocysts from Sea Water by Eastern Oysters (Crassostrea virginica)

SUMMARY. Toxoplasma gondii infections have been reported in a number of marine mammals. Presently it is not known how these animals acquire T. gondii from their aquatic environment. The eastern oyster, Crassostrea virginica, has been shown to remove Cryptosporidium oocysts from seawater and a similar phenomenon may be occurring with T. gondii oocysts and marine invertebrates. The present study was done to determine if eastern oysters could remove and retain T. gondii oocysts from seawater. Oocysts of the VEG strain of T. gondii (1 × 106 oocysts) were placed in seawater (32 ppt NaCl) containing live eastern oysters. The infected seawater was removed one day postinoculation (PI) and replaced with fresh seawater. Selected oysters were removed at 1, 3 and 6 days PL Hemolymph, gill washes, and oyster tissue were collected separately at each observation time. The oyster tissue was homogenized and all 3 samples fed separately to mice. Toxoplasma gondii positive mice were observed at each time period. The results indicate that T. gondii oocysts can be removed from seawater by eastern oysters and retain their infectivity. Contaminated raw oysters may serve as a source of T. gondii infection for marine mammals and humans.

Sporulation and survival of Toxoplasma gondii oocysts in seawater

ABSTRACT. We have been collaborating since 1992 in studies on southern sea otters (Enhdyra lutris nereis) as part of a program to define factors, which may be responsible for limiting the growth of the southern sea otter population. We previously demonstrated Toxoplasma gondii in sea otiers. We postulated that cat feces containing oocysts could be entering the marine environment through storm run‐off or through municipal sewage since cat feces are often disposed down toilets by cat owners. The present study examined the sporulation of T. gondii oocysts in seawater and the survival of sporulated oocysts in seawater. Unsporulated oocysts were placed in 1.5 ppt artificial seawater, 32 ppt artificial seawater or 2% sulfuric acid (positive control) at 24 C in an incubator. Samples were examined daily for 3 days and development monitored by counting 100 oocysts from each sample. From 75 to 80% of the oocysts were sporulated by 3 days post‐inoculation under all treatment conditions. Groups of 2 mice were fed 10,000 oocysts each from each of the 3 treatment groups. All inoculated mice developed toxoplasmosis indicating that oocysts were capable of sporulating in seawater. Survival of sporulated oocysts was examined by placing sporulated T. gondii oocysts in 15 ppt seawater at room temperature 22–24 C (RT) or in a refrigerator kept at 4 C. Mice fed oocysts that had been stored at 4C or RT for 6 months became infected. These results indicate that T. gondii oocysts can sporulate and remain viable in seawater for several months.

Effect of ascorbyl palmitate on the quality of frying fats for deep frying operations

The addition of 0.02% ascorbyl palmitate (AP) reduced color development of frying fat (animal fat/vegetable oil [A-V] shortening) and vegetable oil (partially hydrogenated soybean [V-S] oil) in simulation studies. It also reduced peroxide values, development of conjugated diene hydroperoxides (CDHP) and their subsequent degradation to volatile compounds, such as decanal and 2,-4 decadienal, indicating that AP has the ability to inhibit thermal oxidation/degradation of frying fats and oils. A commercial french fry fat had lower CDHP values compared to A-V fat in simulated studies, and fried chicken oil had lower CDHP values than the V-S oil. Peanut oil had higher thermal stability than the other fats and oils.

Effects of High-Pressure Processing on Toxoplasma gondii Tissue Cysts in Ground Pork

Ingestion of Toxoplasma gondii tissue cysts can result in severe disease in immunocompromised individuals and pregnant women. Treatment of meat and meat products to eliminate viable T. gondii tissue cysts would provide a means to protect consumers. In this study, we examined the effects of high-pressure processing (HPP) on ground pork containing viable tissue cysts of the VEG strain of T. gondii. Ground pork containing tissue cysts was exposed to 400, 300, 200, 100, or 0 MPa treatment for 30, 60, or 90 sec in a commercial HPP unit. The HPP-treated ground pork was subjected to acid–pepsin digestion and bioassayed in mice. The results of the mouse bioassay revealed that none of the mice inoculated with tissue cysts exposed to 400 or 300 MPa became infected, whereas all mice inoculated with tissue cysts exposed to 200, 100, or 0 MPa became infected with T. gondii regardless of exposure time. Results indicate that HPP treatment of ground pork with 300 MPa of pressure will render tissue cysts of T. gondii nonviable and make pork safe for human consumption.

Direct sampling capillary gas chromatography of volatiles in vegetable oils

Direct sampling gas chromatography used for determining volatiles and, indirectly, the flavor of vegetable oils, has been improved by a capillary column in place of the usual packed columns. Data on two good vegetable oils from a supermarket, and on one of these samples after intentional deterioration, are presented. Use of the capillary column provides a more efficient technique to differentiate between the better oils than did the previously used packed columns.

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.

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.