Thermal inactivation of Salmonella spp. in pate made from chicken livers

Authors: Porto-Fett, Anna; Shoyer, Brad; Shane, Laura; Osorio, Manuela; Henry, Elizabeth; Jung, Yang Jin; Luchansky, John

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/28/2019
Publication Date: 5/21/2019
Citation: Porto Fett, A.C., Shoyer, B.A., Shane, L.E., Osoria, M., Henry, E.D., Jung, Y.N., Luchansky, J.B. 2019. Thermal inactivation of Salmonella spp. in pate made from chicken livers. Journal of Food Protection. 82(6):980-987.

Interpretive Summary: Pate is specialty meat product made with finely- or coarsely-minced meats and fat, along with a variety of seasonings and spices. Pate may be served warm, refrigerated, or at room temperature as an entree or as a component of other dishes. The most traditional pates are made with liver from poultry, such as chicken, and are prepared by either sautéing the livers prior to blending with other ingredients or by immersing the raw liver mixture in a water bath. Poultry meat, including giblets such as livers and gizzards, is a major source of pathogenic bacteria, such as Salmonella. Although consumption of undercooked pate prepared from chicken livers is a well-established vehicle for transmission of Salmonella spp., there is a culinary trend toward consumption of undercooked pate for taste and texture preferences. Thus, given that poultry livers may harbor Salmonella, undercooked chicken liver and/or chicken liver products may pose an appreciable threat to consumer safety. Our goal was validated cooking practices to reduce the potential risk of salmonellosis associated with chicken livers and pate made therefrom. Pate was prepared with raw chicken liver and hard boiled eggs plus a mixture of sautéed onions, salt, black pepper, and butter. The pate batter was then heated in a water bath to internal temperatures ranging from 60 to 73.9 degreeC or by cooking chicken livers in a frying pan for 3 to 8 min with a mixture of sautéed onions, salt, black pepper, and butter. Regardless of the cooking practice used to prepare chicken liver pate, levels of Salmonella decreased by 10 to 1 million cells per gram. These findings may be useful for establishing cooking guidelines for pate and, thus, for lowering the risk of illness if chicken livers are contaminated with Salmonella and the attendant batter is not handle/cooked properly.

Technical Abstract: The effect of heating times and temperatures on inactivation of Salmonella spp. in chicken liver pate was evaluated. Raw chicken liver (1 kg) was blended in a mixer with two hard boiled eggs plus a mixture of sautéed onions (10%), salt (0.5%), black pepper (0.25%), and butter (11.2%). The tempered pate batter was inoculated with a nine-strain cocktail (ca. 6.5 log CFU/g) of Salmonella spp. and ca. 25 g portions of the raw pate batter were aseptically transferred into sterile 50-mL polypropylene conical tubes. The tubes were completely submerged in a thermostatically-controlled, circulating water bath. One set of pate was cooked via bain-marie (i.e., water bath) to target instantaneous internal temperatures ranging from 60 to 73.9 degreeC in a water bath set at 74.9 degreeC, whereas an otherwise similar set of pate was cooked at 60 to 73.9 degreeC, with subsequent holding times of 3 to 30 min, in a water bath set at 1 degreeC above of each target end point cooking temperature. After cooking, the tubes containing pate were removed from the heated water and immediately cooled in an ice-water bath for 30 min. In related experiments, pate was prepared as above but with inoculated chicken livers (500 g; ca. 5.8 log CFU/g) that were previously cooked in a frying pan for 3, 4, 5, 6, 7, or 8 min with a mixture of sautéed onions (10%), salt (0.5%), black pepper (0.25%), and butter (11.2%). The cooked mixture was then blended with a hard-boiled egg. Regardless of the cooking process, when pate was heated to a target instantaneous internal temperature of 60 to 73.9 degreeC, pathogen numbers decreased by ca. 1.9 to at least 6.4 log CFU/g; additional reductions of ca. 0.8 to 1.3 log CFU/g were observed when pate was cooked to 60 to 68 degreeC and then held at the end point temperature for 3 to 30 min. For pate prepared using livers inoculated with Salmonella that were cooked in a frying pan for 3 to 8 min prior to blending, pathogen numbers decreased by ca. 1.0 to 4.9 log CFU/g. These findings may be useful for establishing cooking guidelines for pate and, thus, for lowering the risk of illness if chicken livers are contaminated with Salmonella and the attendant batter is not handle/cooked properly.