| Summary: | A common method used by consumers to determine if shrimp are thoroughly cooked when boiling, is to wait until the shrimp float to the top of the water and are pink in color. The purpose of this study was to determine whether the current floating and color cooking method is adequate to ensure the elimination of Listeria and Salmonella species. Furthermore, to determine if processing and storage methods reduce the effectiveness of this method. Shrimp samples were submerged into bacterial suspensions for 30 min then allowed to air dry for 1 hr and color parameters were measured using a colorimeter. Shrimp samples were separated into three groups; day 0, 1, or 2, and stored at 4ºC. The shrimp samples were then treated by placing into boiling water (100°C) on days 0 (inoculation day), 1 and 2. The shrimp were immediately removed from the boiling water once they started floating and color parameters were measured. Bacterial counts were determined by making serial dilutions, spread plating, incubating plates at 37°C for 24 h and calculating Log CFU/g. Typical storage conditions, the use of the additive sodium tripolyphosphate and freezing methods were then tested for their effect on the control of these pathogens in boiled shrimp. Initial bacterial counts ranged from 3.0 to 5.4 Log CFU/g of shrimp. On day 0, 1, and 2 all bacterial counts were reduced to non-detectable levels for shrimp samples that floated in the boiling water. The bacterial counts remained at non-detectable levels during refrigerated (4°C) storage. The redness (a*), yellowness (b*) and lightness (L*) were significantly higher (p<0.0001) in the cooked shrimp compared to uncooked for all days tested. However, the standard deviation for the redness (a*) in the cooked shrimp was large indicating a wide range of pink coloration for all days tested. The flash freezing method led to development of heat resistance in Listeria monocytogenes. Brine freezing was determined to be a better method for microbial reduction. Our results suggest that boiling shrimp until they float will significantly reduce Listeria species and Salmonella species but color change will not and color variation can occur.
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