A SANITARY AUDIT OF THE HEAT SHOCK PROCESS FOR SHELL OYSTERS. 1 North Carolina State University Seafood Laboratory

Transcription

1 A SANITARY AUDIT OF THE HEAT SHOCK PROCESS FOR SHELL OYSTERS Greg Bolton 1, Wayne Mobly 2 & David Green 1 1 North Carolina State University Seafood Laboratory 2 North Carolina Department of Environmental Health & Natural Resources Shellfish Sanitation The process whereby live oysters (shellstock) are exposed to heat (water) to facilitate shucking of meats was audited to determine proper sanitary and good manufacturing practices. Two North Carolina certified shellfish shucking plants participated. Oysters were obtained from Galveston Bay, Texas. Sixteen batches of oysters were heat shocked in two tanks over 7 hours at plant one. Individual baskets of oysters were heat shocked at plant two over 10 hours of operations. Temperature profiles, water samples and meat samples were collected during processing operations. Process water samples were analyzed for ph, total solids (mg/l), aerobic plate counts (APC, cfu/ml), thermophilic aerobic plate counts (TAPC, cfu/ml) and fecal coliforms (FC, MPN/ml). Oyster meats were analyzed for APC (cfu/g), and E. coli (E.C, MPN/g) according to NSSP procedures. No evidence was found that not completely draining and flushing the tanks at 3-hour intervals or less poses a significant public health hazard. Implications for industry/public health personnel are discussed in relation to GMPs, sanitation SOPs and HACCP requirements.

2 Objective : To determine the health significance of the process water used in heat shocking of oysters to prepare them for shucking. This study was conducted in order to determine the health significance of not changing the process water at three-hour intervals in heat shock tanks used in commercial oyster shucking operations. Materials & Methods: Two North Carolina certified shellfish shucking plants were observed Oysters were harvested from Galveston Bay, Texas Study #1 from Area 2 on November 5, 2000 Study #2 from Area 1 on March 16, 2001 Study #1 and study #2 were conducted at North Carolina certified shellfish plants with cooperation of the state shellfish authority. Study 1: Oysters were removed from bushel sacks and placed in stainless steel mesh baskets (900lbs) Baskets were immersed in heat shock tanks (1 liters) Exposure time varied depending on oyster attributes (e.g., size & shell thickness) as determined by the tank operator A total of 17 batches of oysters were heat shocked in the two tanks over a 7 hour time period. General observations were made including tank design, oyster loading rates, time in/out of process water and time of sample collection. Process water temperatures were monitored during operations using a Yokogawa Model DR130 portable hybrid recording potentiometer equipped with 10 type-t thermocouples.

3 Study 2: Oysters were removed from bushel sacks and placed into a stainless steel hopper Individual baskets were filled with oysters Baskets were placed in heat shock tanks for minutes Oysters were removed and rinsed with potable water before shucking Methods: Process water temperatures were monitored using a hybrid recorder with type T thermocouples Process water samples were taken at 1 hour intervals Oysters samples were taken prior to heat shock, after heat shock and after shucking Water and shellfish samples were iced immediately and transferred to the NC DENR Shellfish Laboratory. Microbiological testing was performed within 12 hours. Duplicate water samples were transported on ice to the NC State University Seafood Laboratory for physicochemical analysis. Methods: Process water samples were analyzed for ph, total solids, aerobic plate counts, thermophilic aerobic plate counts and fecal coliforms Oysters meats were analyzed for aerobic plate counts and E. coli according to standard NSSP procedures

4 Temperature (F) Temperature* of Process Water During Study 2, Tank 1 Baskets remained in heat shock tank 6 to 8 minutes For purposes of time and because there was more data collected during study 2, only those results are shown. Temperatures in tank 1did not remain at or above 140F according to NSSP regulations. 7:20 8:12 9:04 9:56 10:48 11:39 12:31 1:23 2:15 3:07 3:59 4:50 Time *Temperatures are an average value of 5 probes per observation. Each batch consisted of 10 to 12 baskets of oysters (ca. 600 lbs). Temperature (F) Temperature* of Process Water During Study 2, Tank 2 Baskets remained in heat shock tank 6 to 8 minutes The temperature in tank 2 did not remain at or above 140F during operation. The spike in temperature occurred during the lunch break while there were no oysters in the tank. 7:20 8:12 9:04 9:56 10:48 11:39 12:31 1:23 2:15 3:07 3:59 4:50 Time *Temperatures are an average value of 5 probes per observation. Each batch consisted of 10 to 12 baskets of oysters (ca. 600 lbs). Process Water Aerobic and Thermophilic Aerobic Plate Counts in Study 2, Tank APC Thermophilic APC 3,000 cfu/ml All process water samples (Tank 1) analyzed for aerobic plate count (APC) and thermophilic aerobic plate count (TAPC) were less than,000 cfu/ml. The proportion of TAPC to standard APC increased with time. 0 Hours 1 Hour 2 Hours 3 Hours 4 Hours 5 Hours 6 Hours 7 Hours 8 Hours 9 Hours 10 Hours Detection limit for APC and Thermophilic APC

5 Process Water Aerobic and Thermophilic Aerobic Plate Counts in Study 2, Tank APC Thermophilic APC All process water samples (Tank 2) analyzed for APC and TAPC were less than,000 cfu/ml. The proportion of TAPC to standard APC increased with time ,000 cfu/ml Hours 1 Hour 2 Hours 3 Hours 4 Hours 5 Hours 6 Hours 7 Hours 8 Hours 9 Hours 10 Hours Detection limit for APC and Thermophilic APC Process Water ph and Total Solids (mg/l) During Study 2 Time Tank 1 Tank 2 (hr) ph TS ph TS Process water ph ranged from 7.77 to 7.09 during operation generally decreasing over time. There was an increase in total solids from 2.14 to 5.72 mg/l. during the 10 hours of production. Oyster Meats Aerobic Plate Counts and E. coli in Study 2, Tank ,000 cfu/g ,000 cfu/g MPN/g 18 MPN/g 10 No significant increase in APC was found in meat samples (Tank 1) when comparing initial shellstock samples to hourly process samples or packing room samples (far right). APC meat samples remained below 10,000 cfu/g and no samples produced an E. coli (EC) MPN/ g above Shellstock 4 hour 6 hour 8 hour 10 hour APC (cfu( cfu/g) E. coli (MPN/g) APC Action Level for Oysters APC Detection limit E. coli Action Level Oysters E. coli Detection limit

6 Oyster Meats Aerobic Plate Counts and E. coli in Study 2, Tank ,000 cfu/g ,000 cfu/g MPN/g MPN/g No significant increase in APC was found in meat samples (Tank 2) when comparing initial shellstock samples to hourly process samples or packing room samples (far right). APC meat samples remained below 10,000 cfu/g and only 1 sample produced an E. coli (EC) MPN/ g above Shellstock 4 hour 6 hour 8 hour 10 hour APC (cfu( cfu/g) E. coli (MPN/g) APC Action Level for Oysters APC Detection limit E. coli Action Level Oysters E. coli Detection limit Discussion: Improvements are needed in GMPs Pre-wash shellstock A major concern was that shellstock should be cleaned to remove excess dirt and mud prior to placement in heat shock process water. Discussion: Improvements are needed in GMPs Process water temperature Obvious improvements need to be made in GMP s. Heat shock process water needs to be maintained at or above 140F.

7 Discussion: Reduced Health Risks Previous studies (Hesselman et al., 1999) have shown a 2 to 4 log reduction in Vibrio vulnificus in the American oyster after heat shocking. There seems to be potential to improve the current heat shock process in order to both aid in shucking and significantly reduce the risk of illnesses caused by naturally occurring bacteria in oysters. Conclusion: No evidence that heat shock process water poses a significant public health hazard Although process water temperatures in these studies did not meet NSSP standards, there were no high bacteria levels in the oyster meats. Outcome: NSSP rule change made in July, 2001 Based on this and other information filed in an ISSC petition, a rule change was made at the 2001 ISSC meeting. The rule was put into effect in July 2001 stating that heat shock process water need only be change once per production day.

8 References Hesselman, D.M., Motes, M.L. and Lewis, J.P Effects of Commercial heat-shock process on Vibrio vulnificus in the American oyster, Crassostrea virginica, harvested from the Gulf coast. J. Food Protection: 6(11): NC Shellfish, Sanitation Section, A NCAC 18A, SECTION Sanitation of Shellfish. NC DENR Shellfish Sanitation Program. U.S. Food and Drug Administration Code of Federal Regulations. 21 CFR Parts 123 and 1240, Procedures for the Safer and Sanitary Processing and Importing of Fish and Fishery Products. DHHS/PHS/FDA/Office of Seafood, Washington, D.C. U. S. Food and Drug Administration National Shellfish Sanitation Program Model Ordinance. DHHS/PHS/FDA/ Office of Seafood, Washington, D.C.