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Front. Microbiol. | doi: 10.3389/fmicb.2018.02802

Improved microbial safety of direct ozone-depurated shellstock Eastern oysters (Crassostrea virginica) by superchilled storage

 Violeta T. Pardío Sedas1*,  Karla M. López Hernández1, Sóstenes R. Rodríguez Dehaibes1,  Víctor d. Suárez Valencia2, David I. Martínez Herrera1,  Argel Flores Primo1, Isaura R. Mozo1 and  Roxana Uscanga Serrano1
  • 1Facultad de Medicina Veterinaria y Zootecnia, Universidad Veracruzana, Mexico
  • 2Universidad Autónoma de Coahuila, Mexico

The effect of superchilled storage at -1°C on the microbial safety of oyster depurated with 0.2, 0.4, and 0.6 mg/L ozone was studied for 14 days. Fecal coliforms (4,100-16,000 MPN/100g), E. coli (1,500-3,650 MPN/100g), V. cholerae non-O1/non-O139 (13.0-102.0 MPN/g), and Salmonella spp. (2.270-3.035x103 CFU/g) were initially present in raw oysters. After 6 h depuration, fecal coliform counts decreased (P<0.05) to 300, 20 and 20 MPN/100g for 0.2, 0.4 and 0.6 mg/L treatments, while a 0.3 log decrease in control oysters was observed. Initial E. coli counts decreased (P<0.05) in oysters to 50, 20 and 20 MPN/100g for 0.2, 0.4 and 0.6 mg/L treatments, respectively. A 1 log reduction in Vibrio cholerae non-O1/non-139 levels were observed in 0.4 and 0.6 mg/L-treatments after 2 and 4 h depuration. Salmonella spp. was not detected in oyster samples after 6 h depuration in 0.4 and 0.6 mg/L-ozone treatments. Considering the bacterial loads after depuration, at the end of superchilled storage the 0.4 mg/L-ozonated oysters attained lower (P<0.05) fecal coliform levels (280 MPN/100 g) and E. coli counts in 0.4 and 0.6 mg/L-ozonated oysters (20 and 95 MPN/100 g, respectively). A 2-log decrease in V. cholerae non-O1/non-O139 levels on day 5 in 0.4 and 0.6 mg/L-ozonated oysters (<0.3 MPN/g) was attained. V. cholerae non-O1/non-O139 counts in control oysters decreased 1 log on day 9 of superchilled storage. Salmonella spp. was not detected in ozonated and superchilled stored oysters. Levels of fecal coliforms, E. coli, Salmonella spp., and V. cholerae non-O1/non-O139 in nonozone-depurated oyster samples were higher than in control, 0.4 and 0.6 mg/L ozonated oyster samples during superchilled storage. The cumulative mortality ratesafter 14 days of storage for superchilled oysters (22.2%) was higher (P<0.05) than 0.6 mg/L O3 (7.2%) and 0.4 mg/L O3 (5.8%) treatments, and control oysters (5.6%). pH values in control oysters decreased significantly (P<0.05) throughout the storage period but not in oysters of both ozone treatments, indicating no detrimental effects on oyster survival. The results of this study suggest that superchilled storage enables ozonated shellstock oysters (0.4 mg/L-6 h) stored for 9 days to be safe human consumption.

Keywords: American oyster (Crassostrea virginica), direct- ozone depuration, Superchilled storage, Vibrio cholera, Salmonella, Escherichia coli, Fecal coliform

Received: 11 Sep 2018; Accepted: 31 Oct 2018.

Edited by:

Eugenia Bezirtzoglou, Democritus University of Thrace, Greece

Reviewed by:

Mariana C. Chifiriuc, University of Bucharest, Romania
Athanasios Alexopoulos, Democritus University of Thrace, Greece  

Copyright: © 2018 Pardío Sedas, López Hernández, Rodríguez Dehaibes, Suárez Valencia, Martínez Herrera, Flores Primo, Mozo and Uscanga Serrano. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Dr. Violeta T. Pardío Sedas, Facultad de Medicina Veterinaria y Zootecnia, Universidad Veracruzana, Veracruz, Mexico,