Viability of cells of shiga-toxin producing Escherichia coli and Listeria monocytogenes within plant-sourced versus beef-sourced protein samples in response to high pressure

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

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/15/2020
Publication Date: 4/24/2020
Citation: Porto Fett, A.C., Shane, L.E., Shoyer, B.A., Osoria, M., Jung, Y.N., Luchansky, J.B. 2020. Viability of cells of shiga-toxin producing Escherichia coli and Listeria monocytogenes within plant-sourced versus beef-sourced protein samples in response to high pressure. Journal of Food Protection. https://doi.org/10.4315/JFP-19-558.
DOI: https://doi.org/10.4315/JFP-19-558

Interpretive Summary: For consumers following a high-protein, low carbohydrate/fat diet, there is considerable interest in consumption of alternatives to “farm-grown meats”, namely plant-based meat/proteins. However, as a raw product, pathogenic bacteria could potentially be associated with plant-based proteins, and if the resulting plant-based burgers were consumed as undercooked (i.e., cooked to less than 165degF), then it may present a greater potential public health risk than beef-based burgers, especially since we have shown that it supports survival of Shiga toxin-producing Escherichia coli (STEC) and/or outgrowth of Listeria monocytogenes (Lm) at refrigeration temperatures. Thus, we evaluated high pressure processing (HPP), a clean label technology for controlling pathogenic bacteria in foods that is commonly used by industry to treat a variety of raw and ready-to-eat foods, to lower the levels of undesirable bacteria associated with commercially-prepared plant burgers. Depending on the pressure used, high pressure processing effectively inactivated all pathogens tested by up to 99.999% on both plant-based and conventional beef-based burgers, whether stored fresh or frozen prior to treatment. The higher the pressure used, the greater the inactivation of pathogens. Pressurization had little effect on the quality of plant-based burgers, whereas it noticeably affected the color of beef burgers. Thus, in addition to lowering the levels of pathogenic bacteria via HPP without adversely affecting product quality, the attendant reduction in either the types or levels of bacteria naturally present on/in plant burgers should also result in an extension of shelf life.

Technical Abstract: We evaluated high pressure processing to lower levels of Shiga toxin-producing Escherichia coli (STEC) and Listeria monocytogenes inoculated into plant-sourced and beef-sourced proteins. In brief, multi-strain cocktails of STEC and L. monocytogenes were separately inoculated (ca. 7.0 log CFU/g) into 25-g portions of plant-based or beef-based protein samples. Refrigerated (i.e., 4degC) or frozen (i.e., -20degC) samples were exposed to 350 MPa for up to 18 min or 600 MPa for up to 12 min. When refrigerated plant- and beef-based samples were treated at 350 MPa for up to 9 min, levels of STEC were reduced by ca. 0.7 to 1.3 log CFU/g. However, levels of L. monocytogenes remained relatively unchanged (ca. less than or equal to 0.3 log CFU/g decrease) in plant-based, but were reduced by ca. 0.3 to 2.0 log CFU/g in beef-based samples. For refrigerated plant- and beef-based samples treated at 600 MPa for up 4.5 min, levels of STEC and L. monocytogenes were reduced by ca. 0.7 to 4.1 and ca. 0.3 to 5.6 log CFU/g, respectively. Similarly, when frozen plant- and beef-based samples were treated at 350 MPa up to 18 min, reductions of ca. 1.7 to 3.6 and ca. 0.6 to 3.6 log CFU/g in STEC and L. monocytogenes numbers, respectively, were observed. For frozen plant- or beef-based protein samples, exposed to 600 MPa for up to 12 min, resulted in reductions of ca. 2.4 to 4.4 log and ca. 1.8 to 3.4 log CFU/g in levels of STEC and L. monocytogenes, respectively. Via empirical observation pressurization did not affect the quality of the plant-sourced protein, whereas appreciable changes in color were observed in pressurized ground beef. These data confirm that time and pressure levels already validated for control of STEC and L. monocytogenes in ground beef will likely be equally effective towards these same pathogens in plant-sourced protein