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Abstracts
Workgroup: Public Health and Processing
Development of Processing Procedures for Oyster Products to Inactive Vibrio vulnificus and Vibrio parahaemolyticus in Raw Oysters
Principal Investigator(s):
P. Mallikarjunan, Virginia Polytechnic Institute and State University, kumar@vt.edu
Co-Investigator(s):
Dr. Michael Jahncke, Virginia Seafood Agricultural Research and Extension Center
Dr. Susan Duncan, Dept. of Food Science and Technology, VPI and SU
Dr. Daniel E. Farkas, Dept. of Food Science and Technology, Oregon Sate University
Dr. Robert Grodner, Professor Emeritus, Dept. of Food Science, Louisiana State University
Dr. Linda Andrews, Dept. of food Science, Mississippi State University
Dr. Susan Duncan, Dept. of Food Science and Technology, VPI and SU
Dr. Daniel E. Farkas, Dept. of Food Science and Technology, Oregon Sate University
Dr. Robert Grodner, Professor Emeritus, Dept. of Food Science, Louisiana State University
Dr. Linda Andrews, Dept. of food Science, Mississippi State University
Funding Period: 9/1/99-3/31/03
Although there are many studies carried on the thermal properties of various meat and seafood products, there were limited data available on thermal properties for oysters, especially related to the temperature. The thermal properties including thermal conductivity, specific heat, and thermal diffusivity of shucked oysters over the temperature range of 0 ƒC and 55 ƒC were determined. In addition mathematical models to describe the microwave heating of oysters were developed so that suitable microwave treatment procedures can be identified.
Pure cultures of Vibrio parahaemolyticus (clinical strains 03:K6) and Vibrio vulnificus cultures were incubated overnight in phosphate buffered saline (PBS) to obtain initial concentrations of approximately 108 CFU/ml. Viable plate counts of Vibrio parahaemolyticus and Vibrio vulnificus in pure culture were determined on tryptic soy agar plates after HHP treatments of 30, 35, 45, 50, 55 and 85 k psi for 0 to 20 min. Whole eastern oysters (Crassostrea virginica) were cultured in an aquarium by feeding high concentration Vibrios culture overnight to obtain the initial microbial count of 106 CFU/ml inside the oyster tissues. They were also treated with high pressure of 40, 45, 50, 55 and 85 k psi. The results indicated that pure cultures of Vibrio parahaemolyticus were more resistant compared with Vibrio vulnificus at all pressure levels and at all times. . Oyster tissues provided a good shelter for bacteria survival as a five log reduction of Vibrio parahaemolyticus was observed at 45 k psi after 3 min high pressure treatment.
Live oysters, with naturally incurred and artificially inoculated Vibrios, were exposed to 0 to3 kGy dose Cobalt-60 gamma radiation. One kGy dose reduced the Vibrios to nondetectable levels and at the same time maintained good sensory quality, a normal shelf life of 15 days, and minimum mortality. Higher irradiation doses increased the mortality rate and reduced shelf life.
IMPACTS and/or BENEFITS:
Measurement of thermal and electric properties of oysters has filled the void in the basic physical properties related to oysters. They can be used in modeling temperature distribution inside the oyster tissues during thermal processing including microwave pasteurization. Modeling of heating profile of oyster samples provided a key to control the non-uniform temperature distribution within the sample and microwave oven for seeking optimum heating procedures. High pressure trials on Vibrios pure culture as well as inoculated oyster tissues have found the basic knowledge on the effectiveness of high hydrostatic pressure on oysters in shell, in addition, it made us understand more about the high pressure inactivation kinetics. Upon approval by the USFDA, irradiation processing of live oysters will provide an effective post harvest treatment for reducing the risk of Vibrio illnesses.
PROJECT PUBLICATIONS:
X. Hu and P. Mallikarjunan, 2001. Thermal and dielectric properties of shucked oysters. In Seventh Conference of Food Engineering (P. Mallikarjunan and G. V. Barbosa-Canovas, Editors). A proceedings of 7th Conference of Food Engineering held at Reno, NV Nov 5-9. American Institute of Chemical Engineers, New York, NY. p 356-362.
X. Hu, J. Koo, P. Mallikarjunan and M. L. Jahncke, 2002. High pressure inactivation kinetics of Vibrio vulnificus and Vibrio parahaemolytics in buffer solution and whole oysters. To be presented at the annual meeting of Institute of Food Technologists. June 15-19, Anaheim, CA.
J. Koo, X. Hu, M. L. Jahncke, and P. Mallikarjunan. 2002. Effect of High Hydrostatic Pressure on Vibrio parahaemolyticus and Vibrio vulnificus in Pure Cultures and Whole Eastern Oysters (Crassostrea virginica). To be presented at the annual meeting of Institute of Food Technologists. June 15-19, Anaheim, CA.
X. Hu and P. Mallikarjunan. 2002. Heat Transfer During Microwave Processing of Fish Gel. To be presented at the annual meeting of Institute of Food Technologists. June 15-19, Anaheim, CA.
L. S. Andrews, M. L. Jahncke, P. Mallikarjunan, and C. D. Veal, 2002. Gamma Irradiation Processing to Reduce the Risk of Vibrio Infections from Raw Oysters. To be presented at the annual meeting of Institute of Food Technologists. June 15-19, Anaheim, CA.
X. Hu and P. Mallikarjunan. 2002. Mathematical Modeling of Microwave Heating of Fish Gel using Finite Element Method. To be presented at the annual meeting of American Society of Agricultural Engineers. July 28-31, Chicago, IL.
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