The efficacy of ultrasound on the inactivation of Shiga toxin-producing Escherichia coli in raw beef trim

Authors: JACKSON-DAVIS, ARMITRA - Alabama A & M University; DANIEL, MARCIAUNA - Alabama A & M University; Luchansky, John; Porto-Fett, Anna; KASSAMA, LAMIN - Alabama A & M University

Submitted to: Foods
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/14/2019
Publication Date: 10/14/2019
Citation: Jackson-Davis, A., Daniel, M., Luchansky, J.B., Porto Fett, A.C., Kassama, L. 2019. The efficacy of ultrasound on the inactivation of Shiga toxin-producing Escherichia coli in raw beef trim. Foods. 2(5). https://www.doi.org/10.29016/2475-2366/1000120.

Interpretive Summary: We monitored the levels of Shiga toxin-producing cells of Escherichia coli (STEC) in raw beef trim and uncooked meatballs containing beef, pork, and/or veal following treatment with ultrasound or high pressure. Beef trim or ground veal or a blend of ground veal-beef-pork for meatballs were inoculated with about 7 million cells of STEC. The ground products were then mixed with liquid whole eggs and seasonings before being shaped by hand into 40-g balls. Meatballs were stored at -20 deg C (i.e., frozen) or at 4 deg C (i.e., fresh) for up to 18 h before being treated by the application of 87,000 pounds per square inch (psi) of pressure for up to 6 min or before being subjected to ultrasound treatment of 20 kilohertz (kHz) at 23 deg C for 15 min. As expected, the longer the time of ultrasound or HPP treatment, the greater the reduction of STEC levels within beef trim or meatballs. This work provides new information on the effect of ultrasound and HPP on inactivation of STEC in beef trim and meatballs. These results will help establish guidelines and best practices for pre-treating meatballs by food manufacturers to enhance public health.

Technical Abstract: We investigated the efficacy of ultrasound and high-pressure processing (HPP) to inactivate Shiga-toxin producing cells of Escherichia coli (STEC) in raw meat products containing beef. Beef trim or ground meat mixtures (1/3 veal + 1/3 beef + 1/3 pork) were inoculated (ca. 7.0 log CFU/g) with a single strain of STEC O157:H7 or an 8-strain rifampicin-resistant cocktail of STEC (O111:H, O45:H2, O103:H2, O104:H4, O121:H19, O145:NM, O26:H11 and O157:H7), respectively. Twenty-five gram portions of inoculated beef trim were stored at 4ºC for 24 h and then were or were not treated with organic acids (2.4% lactic/citric acid), or a surfactant (0.5% sodium lauryl sulfate, or a blend of the organic acid mixture plus surfactant before being subjected to ultrasound (20 kHz) treatment at 23 deg C with resident times of 0, 10, and 15 min. Inoculated ground veal and a ground beef + ground pork + ground veal meatball formulation were mixed with liquid whole eggs and seasonings, shaped by hand into 40 g meatballs, and stored at -20 deg C (frozen) or at 4 deg C (fresh) for 18 h. The meatball samples were vacuum-sealed in double-bagged plastic pouches and processed at 600 MPa for 45, 90, 180, and 360 sec. Samples were plated onto sorbitol MacConkey agar plates (SMAC) with rifampicin (100 µg/mL) and incubated for 24 h. Up to three trials were conducted for each experimental treatment, with three samples tested at each sampling interval. The effect of the ultrasound, with or without pre-treatment with organic acids and/or or a surfactant, showed that STEC were not significantly (p>0.05) inactivated on beef trim (<1.0 log reduction). Regarding HPP, in general, the longer the time that meat containing STEC was subjected to pressure, the great the inactivation of the pathogen. Moreover, greater reductions were observed for meatballs that were fresh (ca. 3.2 to 6.0 log CFU/g) compared to otherwise similar meatballs that were stored frozen (ca. 0.7 to 1.7 log CFU/g) prior to HPP treatment. This work provides new information on the effect of ultrasound and HPP on inactivation of STEC in beef trim and meatballs.