Electrolyzed oxidizing water treatment for reducing Vibrio contamination in oysters

Graduation date: 2006Oysters can be easily contaminated with spoilage and pathogenic bacteria through contaminated waster. The United States produces more than 27 million pounds of oysters each year and most of them are sold and consumed raw without further processing. Growth of naturally contaminating bacteria in oysters during storage results in loss of quality and product value. Contamination of pathogenic bacteria such as Vibrio parahaemolyticus and Vibrio vulnificus in oysters is also a safety concern of the industry and consumers. The traditional depuration process for reducing bacterial contamination in oysters using clean seawater has been reported to be ineffective in reducing Vibrio contamination in oysters. This study investigated effects of electrolyzed oxidizing (EO) water treatment on reducing both V. parahaemolyticus and V. vulnificus contamination in oysters. Freshly harvested Pacific oysters were inoculated with 5-strain cocktail of V. parahaemolyticus or V. vulnificus at levels of 10⁴ and 10⁶ MPN/g. Inoculated oysters were held in EO water (chlorine: 30 ppm, pH: 2.82, ORP: 1131 mV) containing 1% NaCl at room temperature. Reductions of V. parahaemolyticus and V. vulnificus in oysters during the treatment were determined at 0, 2, 4, 6, and 8 h. EO water containing 30 ppm of chlorine was found to exhibit strong bactericidal effects against pure cultures of V. parahaemolyticus and V. vulnificus (>6.6-log reductions in 15s). Holding oysters inoculated with V. parahaemolyticus or V. vulnificus in EO water (30 pin chlorine) containing 1% NaCl for 4-6 h resulted in significant reductions of V. parahaemolyticus and V. vulnificus by 1.13 and 1.05 log MPN/g, respectively. However, extended exposure (>12 h) of oysters in EO water containing high levels of chlorine (>30 ppm) was found to be detrimental to oysters. EO water could be used as a post-harvest treatment to reduce Vibrio contamination in oysters. However, treatment should be limited to 4-6 h to avoid death of oysters. Further studies are needed to determine effects of EO water treatments on sensory characteristics of treated oysters