Consumer method to control Salmonella and Listeria species in shrimp.

The purpose of this study was to determine whether the current consumer method of boiling shrimp until floating and pink in color is adequate for destroying Listeria and Salmonella. Shrimp samples were submerged in bacterial suspensions of Listeria and Salmonella for 30 min and allowed to air dry for 1 h under a biosafety cabinet. Color parameters were then measured with a spectrophotometer programmed with the CIELAB system. Twenty-four shrimp samples were divided into groups (days 0, 1, or 2) and stored at 4°C. The samples were treated by placing them in boiling water (100°C) on days 0, 1, and 2. The shrimp were immediately removed from the boiling water once they floated to the surface, and color parameters were measured. Bacterial counts were determined, and the log CFU per gram was calculated. The effect of sodium tripolyphosphate on the color change of cooked shrimp also was determined. Initial bacterial counts on shrimp after air drying were 5.31 ± 0.14 log CFU/g for Salmonella Enteritidis, 5.24 ± 0.31 log CFU/g for Salmonella Infantis, 5.40 ± 0.16 log CFU/g for Salmonella Typhimurium, 3.91 + 0.11 log CFU/g for Listeria innocua, 4.45 ± 0.11 log CFU/g for Listeria monocytogenes (1/2a), and 3.70 ± 0.22 log CFU/g for Listeria welshimeri. On days 0, 1, and 2, all bacterial counts were reduced to nondetectable levels for shrimp samples that floated. The average time for shrimp to float was 96 ± 8 s. The bacterial counts remained at nondetectable levels (<10 log CFU/g) during refrigerated (4°C) storage of cooked shrimp for 2 days. The redness, yellowness, and lightness were significantly higher (P < 0.0001) for the cooked shrimp than for the uncooked shrimp on all days tested. The standard deviation for redness in the cooked shrimp was large, indicating a wide range of pink coloration on all days tested. The results suggest that boiling shrimp until they float will significantly reduce Listeria and Salmonella contamination, but color change is not a good indication of reduction of these pathogens because of the wide natural color variation.