Effect of cooling rates and temperatures on quality and safety of quahog clams (Mercenaria mercenaria).
The model ordinance in the National Shellfish Sanitation Program's Guide for the Control of Molluscan Shellfish was initially established for oysters; however, the clam industry also follows the protocol. Rapid cooling during periods when the growing waters exceed 80 °F (26.7 °C) results in cold shock, which causes unacceptable mortalities in clams. The clam industry was looking for a procedure to lower the clams to the standard temperature while minimizing shell shock mortalities during the warm summer months. Three tempering treatments were examined, and total aerobic plate counts (APCs) and most-probable-number (MPN) counts of Vibrio, V. parahaemolyticus, and fecal coliforms were enumerated. In treatment 1 (control), clams were harvested, held for 5 h at 90 °F (32.2 °C), and then moved to 45 °F (7.2 °C) for storage. In treatment 2, clams were harvested and held for 5 h at 90 °F (32.2 °C), followed by 12 h at 65 °F (18.3 °C) and 12 h at 55 °F (12.8 °C), and then were moved to 45 °F (7.2 °C) for long-term storage. In treatment 3, clams were harvested and held for 5 h at 90 °F (32.2 °C), followed by 24 h at 55 °F (12.8 °C) before being moved to 45 °F (7.2 °C) for long-term storage. Three replicate trials were performed with triplicate analyses during late June through early to mid-August. The current National Shellfish Sanitation Program standard is treatment 1; it contained statistically (P ≤ 0.05) higher total APCs than treatments 2 and 3 throughout the 21-day storage period. APCs ranged from 2.3 × 10(4) immediately after harvest to 2.7 × 10(6), 1.6 × 10(5), and 4.8 × 10(5) for treatments 1, 2, and 3, respectively, after 14 days of storage. A statistical analysis showed that treatments 2 and 3 had significantly lower total MPN per gram Vibrio than treatment 1 on day 7 but were equal to treatment 1 on days 1 and 14. MPN per gram for V. parahaemolyticus was statistically lower in treatments 2 and 3 than in treatment 1 on storage days 1 and 7. However, on day 14, treatment 3 was significantly lower than treatments 1 and 2. There was no statistical difference for fecal coliforms. The greatest mortality occurred in treatment 1 (87.4%), followed by treatment 2 (83.3%) and treatment 3 (66.0%). The outcome of this research clearly shows that treatments 2 and 3 can cool clams to a temperature of 45 °F (7.2 °C) without compromising quality or safety and can reduce the number of dead clams introduced into the marketplace.
Department of Food Science and Technology, Virginia Polytechnic Institute and State University, 360 Duck Pond Drive, Blacksburg, Virginia 24061, USA. lgranata@vt.edu.
Linda Ankenman
LA
Granata
Department of Food Science and Technology, Virginia Polytechnic Institute and State University, 360 Duck Pond Drive, Blacksburg, Virginia 24061, USA.
Dianne Wall
DW
Bourne
Department of Food Science and Technology, Virginia Polytechnic Institute and State University, 360 Duck Pond Drive, Blacksburg, Virginia 24061, USA.
George J
GJ
Flick
Cherrystone Aqua Farms, P. O. Box 222, 15026 Harbor Lane, Eastville, Virginia 23347, USA.
Michael
M
Peirson
Cherrystone Aqua Farms, P. O. Box 222, 15026 Harbor Lane, Eastville, Virginia 23347, USA.
Tara
T
Riley
Division of Shellfish Sanitation, Virginia Department of Health, 109 Governor Street, Room 614, Richmond, Virginia 23219, USA.
Robert E
RE
Croonenberghs
LISA (Laboratory for Interdisciplinary Statistical Analysis), Virginia Polytechnic Institute and State University, 405 Hutcheson Hall, Blacksburg, Virginia 24061, USA; Scientific Test and Analysis Techniques Test and Evaluation Center of Excellence (STAT T&E COE), Air Force Institute of Technology, 2950 Hobson Way, Building 646, Room 201, Wright-Patterson AFB, Ohio 45433, USA.
Jennifer
J
Kensler
D000818:Animals; D003080:Cold Temperature; D005506:Food Contamination / Q000032:analysis; D005519:Food Preservation / Q000295:instrumentation / Q000379:methods*; D059022:Food Safety; D049891:Mercenaria / Q000737:chemistry*; D012621:Seasons; D012758:Shellfish / Q000032:analysis* / Q000382:microbiology; D014733:Vibrio / Q000254:growth & development / Q000302:isolation & purification