Inactivation kinetics of Vibrio parahaemolyticus on sand shrimp (Metapenaeus ensis) by cinnamaldehyde at 4°C

Sand shrimp (Metapenaeus ensis), shrimp shell, and shrimp meat were inoculated with a three-strain cocktail of Vibrio parahaemolyticus with or without the natural antimicrobial cinnamaldehyde (2.5 mg/ml) and were, then, stored at 4°C for up to 25 days and 18 inactivation curves were obtained. V. parahaemolyticus were inactivated down to the minimum level of detection (2.48 log CFU/g) on thiosulfate citrate bile salts sucrose agar (TCBS) plates within 7 and 10 days with low and high densities of V. parahaemolyticus inoculation, 4.5 log CFU/g and 8.2 log CFU/g, respectively. With adding cinnamaldehyde, the inactivation process of V. parahaemolyticus with low populations, 4.5 log CFU/g, lasted for only 4 days. Therefore, cinnamaldehyde inactivated cells faster as expected. However, unexpectedly, in shrimp meat cases, cells have much more persistence of over even 25 days before entering the minimum level of detection both with and without cinnamaldehyde treatment. Therefore, a hypothesis was formed that when cells kept in cold environments (4°C) after several days recovered to up to 10³–10⁴ CFU/g towards the end of the experiments and with starvation (shell and shrimp studies), cells might render a viable but nonculturable (VBNC) state.