51A-17 |
High Hydrostatic Pressure Effect on Vibrio parahaemolyticus in Oysters |
H. CALIK and H. An. Food Science and Technology / OSU Seafood Lab, Oregon State University, OSU Seafood Lab 2001 Marine Drive, Rm 253, Astoria, OR 97103-3427
Many cases of Vibrio parahaemolyticus (Vp)-induced gastroenteritis occurred in the Pacific Northwest due to consumption of raw oysters. High Hydrostatic Pressure (HHP) Technology has shown good potential in reducing pathogens. HHP can reduce the bacterial loads to desired levels without losing the flavor and appearance of raw oysters since it is a heatless treatment. The objective was to determine effect of HHP treatment on Vp in oysters and establish optimum HHP conditions (time/pressure) for processing oysters. Oysters were obtained from commercial sources in Washington. Different strains of Vp were isolated from oysters following the FDA Bacteriological Analytical Manual and were confirmed by using Vitek and API 20E system. Clinically confirmed virulent Vp strains were obtained from FDA, Seattle, WA. Both clinical and environmental Vp strains were treated with HHP at different settings (1-11 min at 35K psi; 1-5 min at 40K psi; 30-120 s at 45K psi; 10-60 s at 50K psi). Total Vp were enumerated before and after HHP treatment to determine survival of Vp. Plate counts showed that Vp strains are susceptible to HHP. The optimum conditions for reducing Vp counts from 109 cfu/ml to 101 cfu/ml was achieved at 50K psi in 30 seconds. It requires longer time to achieve similar reduction of Vp at lower pressures. At 35K psi, it took 14.5 minute to reduce the count to 101 cfu/ml Vp survival. Clinical Vp strains did not show higher resistance to HHP over environmental strains. Both clinical and environmental Vp strains responded similarly to HHP treatments. HHP treatment appears to be a satisfactory means to reduce Vp counts. However, Vp occurring in oysters could respond to HHP treatment differently from the pure culture due to the protective environment in the oyster. Future work will concentrate on HHP effects on Vp in artificially inoculated oysters.
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