Purpose: This study investigated the efficacy of bactericidal concentrations of three GRAS-status phytochemicals, namely trans-cinnamaldehyde (5 mM), carvacrol (6 mM) and eugenol (18 mM) in decreasing Vph in oysters during depuration. Moreover, the efficacy of these phytochemicals in reducing Vph in shucked oysters was determined.
Methods: A two-isolate cocktail of Vph (~8 log CFU/ml) was added to artificial seawater tanks to facilitate pathogen accumulation in oysters. Infected oysters were transferred to depuration tanks containing water with or without the phytochemicals. Oysters collected at 0, 6, 12, 24 h of depuration were homogenized in neutralizing broth and enumerated on Thiosulfate Citrate Bile Salt Sucrose agar following serial dilutions. Additionally, shucked oysters were surface-inoculated with ~6 log CFU of Vph and subjected to air-drying for 30 min. The oyster meat was treated with the phytochemicals for 2 min, and surviving Vph was enumerated as before. Both experiments had duplicate samples and repeated three times.
Results: In the depuration experiment, the average accumulation of Vph was ~6 log CFU/oyster. Approximately 4.5 to 5.0 log CFU of Vph/oyster was recovered from control samples. However, the presence of phytochemicals in the depuration water decreased Vph by ~3.5 log CFU/oyster (P < 0.05). Additionally, trans-cinnamaldehyde and eugenol reduced Vph on shucked oyster meat to undetectable levels, whereas carvacrol decreased the pathogen by ~5.0 log CFU/oyster (P < 0.05).
Significance: The results suggest that trans-cinnamaldehyde, carvacrol and eugenol could potentially be used to reduce Vph in oysters. However, the effect of these phytochemicals on the sensory characteristics of oysters needs to determined. Additionally, follow up studies under commercial settings are necessary to validate these results.