Master of Science (MS)
School of Nutrition and Food Sciences
"Vibrio parahaemolyticus" (Vp) and "Vibrio vulnificus" (Vv) are halophilic bacteria naturally occurring in estuarine environments that may concentrate in filter feeding shellfish. Consumption of raw or under-cooked seafood contaminated with Vp or Vv may lead to the development of acute gastroenteritis or fatal septicemia in at-risk individuals, respectively. This research encompassed two separate but related projects: evaluation of a low temperature pasteurization (LTP) technique for the reduction of Vp and Vv in commercial quantities of shucked oysters (SO) and the investigation of the efficacy of a citrus fruit extract, BIOSECUR® F440D in reducing/eliminating Vv in vitro. Commercially available SO ("Crassostrea virginica"), artificially contaminated with pure Vibrio pathogens (3 ml) were used for evaluation of a LTP technique. Pure Vv cultures were used to test citrus extract. Vibrio vulnificus agar (VVA) with either 2% or 3% (mg/l) NaCl was used for plating Vv and Vp, respectively. The heat treatments of 40°C and 45° C reduced bacterial counts, however cultures survived even after 24 and 48 h of refrigeration (temperatures above freezing). Vv was more heat sensitive than Vp at 40°C and 45°C, with average bacterial counts of 4.9 and 6.0 log CFU/g without refrigeration, respectively. Unheated samples indicated that simple refrigeration is not adequate to reduce Vv and Vp in SO, as then was only a 0.79 and 0.61-log reduction, respectively. Both Vibrio species were reduced to non-detectable (ND) levels with and without refrigeration at treatments of 50°C and 55°C, making them the most effective treatments at 0, 24, and 48 h. BIOSECUR® F440D at 0.5%, 1.0%, 1.5%, and 2.0% concentrations were used to determine the lowest effective concentration needed to achieve a significant log reduction of Vv. The 2.0%, 1.5% and 1.0% concentrations reduced Vv levels significantly (ND, 5.45, and 3.85 log-reduction, respectively). The 0.5% concentration resulted in a 2.39-log reduction. LTP of SO meat at 50°C for 12 minutes is an effective PHP for control of Vibrio species. BIOSECUR® F440D might contribute to the development of a value added PHP technique for reduction of Vv in oysters.
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Scott, Ronson Renard, "Treatments to reduce the risk of Vibrio species in vitro and in shucked oysters" (2013). LSU Master's Theses. 587.
Janes, Marlene E.