The effectiveness of a typical production process for eliminating Escherichia coli O157:H7 in directly acidified snack sticks made with beef or a venison/beef fat blend was evaluated for formulations of different fat content (10% and 25%) and type of direct acidulant (encapsulated citric or lactic acid). Raw batter inoculated with E. coli O157:H7 to an initial level of approximately 7.1 log CFU/g was stuffed into 21‐mm casings and processed according to a thermal‐processing schedule typical of those used commercially for directly acidified sausage products (maximum internal product temperature of 68.3 °C, followed by drying and cooling). For both beef and venison/beef fat blend snack sticks, log reductions ranged from 6.2 to > 6.6 CFU/g at the end of processing. Although moderate reductions (1.5 to 2.0 log CFU/g) were achieved as a result of processing to internal product temperatures of 68.3 °C, latter stages of the process (during which products were dried and cooled) factored prominently in the overall lethality of the process, and were essential in achieving the 5‐log reduction required by the U.S. Dept. of Agriculture, Food Safety and Inspection Service. The efficacy of the process was not affected (P≤ 0.05) by fat content (10% or 25%) or by the type of direct acidulant used (encapsulated citric or lactic acid). Phenol red sorbitol agar was more effective for recovering heat‐ and acid‐injured E. coli O157 than MacConkey sorbitol agar was and, therefore, provided a more conservative estimate of process lethality.
USDA/FSIS guidelines require sausage manufacturers to validate their processes to assure that they can achieve a five-log (99.999%) reduction of E. coli O157:H7. Some small meat processors use encapsulated acids instead of lactic acid starter cultures to produce directly acidified sausages. The objectives of this study were to determine 1) the effects of typical thermal processing temperatures and times on reducing E. coli O157:H7 in directly acidified all-beef and venison-containing beef snack sticks, 2) the effect of fat content (10 and 25%) on lethality, and 3) the effect of acid type (citric versus lactic) on lethality. For both all-beef and venison-containing beef snack sticks, E. coli O157:H7 reductions of approximately 3 log cycles (99.9%) were observed when product internal temperature reached 148 and 155ºF. Reductions increased to more than 5 log cycles after 2 hours of slow drying in which the smokehouse temperature was sequentially decreased to 70°F. Encapsulated citric acid was slightly more effective at lowering product pH, compared with the encapsulated lactic acid. Similar pathogen reductions were observed with 10 and 25% fat content. This study demonstrates that the defined processing schedule used to manufacture beef and venison-containing beef snack sticks is adequate to provide microbiologically safe products and to meet USDA guidelines for pathogen reduction. The processing schedule must include an extended drying phase, in addition to the thermal step, to meet these requirements.
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